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Author Topic: Running Hot?  (Read 1997 times)
Vince
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« on: July 19, 2014, 06:10:04 PM »

I wanted to post this info to get some helpful feedback and perhaps new ideas, and just to put my mind at ease.  My 1969 Z/28 seems to me anyway to be running hot even though the temp gauge shows well within the standards, reading barely over the first quarter of the gauge when driving and only going to the halfway point after shutting the engine off when I am guessing heat soak comes into play.  Sometimes when I pull away from a stop after driving for a half hour the car bucks, backfires, and then stalls.  I can't get it restarted for about 15 minutes until it cools down.  When I open the hood it is like I can feel a blast of hot air.  Previously the heat riser valve was stuck closed, but I had the flapper taken out.  Wouldn't this mean that no more hot exhaust gases are being circulated up to the intake manifold anymore to warm the carb at start-up?  When starting the car cold it does take longer to warm up now. 
Is it correct that the sensor for the temp gauge is in the engine block?  Is it possible the heads and intake manifold are getting hot for some reason even though the gauge reads fine?  Could there be gunk blocking a coolant passage in the engine, fan clutch not working,  smog pump or AIR system not working properly, etc.? 
About 2 weeks ago I drove it only about 2 miles at no more than 35-40 mph.  When I got to my driveway and turned the engine off and opened the hood I could see heat waves coming up from the passenger side exhaust manifold.  It was a hot day, in the low to mid 90's.  None of my other cars, or truck, put out anywhere near the heat that my '69 Z does.  And yet the temp gauge still reads fine; could the temp gauge be inaccurate?  My own thought is that I am boiling the fuel in the carburetor even with a heat shield, and that is why it wants to stall or kill and is so hard to restart until it cools down.  Am I overreacting or misinterpreting something?  Thanks guys for any and all help and ideas. 
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z28z11
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« Reply #1 on: July 19, 2014, 08:40:43 PM »

Temp gauge is in the head. I always ran an aftermarket Stewart Warner in the intake close to the water outlet, mechanical gauge. 180 thermostat would always give me 180, no more.

Check your fan clutch, run a dose of cleaner through the whole system, dump and refill with 50-50 Prestone or equivalent. Older radiators over time will build up an incredible amount of scale in the lower tubes: if you haven't rebuilt the core, you might do so if all of the other remedies don't affect it. Drop in a new thermostat when you clean the system, and always run a thermostat - the restriction it offers to water flow slows down the flow enough to let it pick up more heat for transfer at the radiator. After you have checked all of the above, get yourself an inexpensive infrared handheld thermometer and check the radiator, engine block and heads for hot spots. Rebuild your water pump if you're unsure of it - sometimes the impeller can wear down and lose efficiency over time. You can also use "water wetter" additives, that allow the water to pick up more heat as it flows through the system.

Did you use block off plates for the heat riser ports on the manifold gasket ? I always do to keep the temp away from the carb and gas. Check your mixture, especially if you are running a working A.I.R. pump - too lean on today's gas can make 'em run hotter, too.

One thing I hate is an engine to run warm - I don't like to think of what heat does to an engine for life expectancy -

Regards -

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« Reply #2 on: July 19, 2014, 10:16:15 PM »

Temp gauge is in the head. I always ran an aftermarket Stewart Warner in the intake close to the water outlet, mechanical gauge. 180 thermostat would always give me 180, no more.

Check your fan clutch, run a dose of cleaner through the whole system, dump and refill with 50-50 Prestone or equivalent. Older radiators over time will build up an incredible amount of scale in the lower tubes: if you haven't rebuilt the core, you might do so if all of the other remedies don't affect it. Drop in a new thermostat when you clean the system, and always run a thermostat - the restriction it offers to water flow slows down the flow enough to let it pick up more heat for transfer at the radiator. After you have checked all of the above, get yourself an inexpensive infrared handheld thermometer and check the radiator, engine block and heads for hot spots. Rebuild your water pump if you're unsure of it - sometimes the impeller can wear down and lose efficiency over time. You can also use "water wetter" additives, that allow the water to pick up more heat as it flows through the system.

Did you use block off plates for the heat riser ports on the manifold gasket ? I always do to keep the temp away from the carb and gas. Check your mixture, especially if you are running a working A.I.R. pump - too lean on today's gas can make 'em run hotter, too.

One thing I hate is an engine to run warm - I don't like to think of what heat does to an engine for life expectancy -

Regards -



Ditto.

John Z has a good article on cooling systems in this site.
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JohnZ
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« Reply #3 on: July 20, 2014, 10:31:18 AM »

John Z has a good article on cooling systems in this site.


http://www.camaros.org/pdf/corv_cooling2.pdf
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« Reply #4 on: July 21, 2014, 12:25:55 AM »

If it isn't puking any water, I'd change the coil. This sounds like a classic case of the ignition coil overheating, then working once cooled down. Just a thought and good luck.
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« Reply #5 on: July 21, 2014, 08:44:41 AM »

If it isn't puking any water, I'd change the coil. This sounds like a classic case of the ignition coil overheating, then working once cooled down. Just a thought and good luck.
 I have seen that happen with my fathers '66 Mustang. It was easy to narrow down because when the car was hot and no longer would start, the spark was weak and yellow in color instead of a strong 'snap' and blue in color. Changing the coil fixed it.

Mike
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Stingr69
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« Reply #6 on: July 21, 2014, 09:18:45 AM »

Timimg retarded? 

I would use a stainless steel shim to block the heat passage in the intake manifold/head on the drivers side only.

Do you have an Infra red heat gun to verify the actual temperature?  Nice to have or borrow.

-Mark.
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JohnZ
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« Reply #7 on: July 21, 2014, 09:26:30 AM »

smog pump or AIR system not working properly, etc.?   It was a hot day, in the low to mid 90's.  None of my other cars, or truck, put out anywhere near the heat that my '69 Z does.  And yet the temp gauge still reads fine; could the temp gauge be inaccurate?

If your A.I.R. system is still functional and the rubber diaphragm in the diverter valve has failed (and almost all have failed), the valve defaults to the open position, which blows air into the exhaust manifolds all the time, under all conditions. That will cause hotter exhaust manifolds, without any affect on coolant temperature.

Rule #1 when diagnosing a potential cooling issue is to make sure you really have a problem before you start throwing parts and money at it; verify your temp gauge accuracy with an I.R. gun before you do anything else, as noted in the cooling article I posted a link to earlier.
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Vince
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« Reply #8 on: July 21, 2014, 12:24:26 PM »

Thanks guys for all your ideas and responses.  I do have an infrared gun so will start from there trying to narrow things down as I go.  You guys have given me some things to look at that I never thought of.  Thanks JohnZ for the article; it was very informative.  It might take awhile for me to check everything but will let you guys know what I find out. 

I did want to ask one more question.  Will blocking off the heat passages in the intake manifold still make a difference even with my car not having a flapper anymore in the heat riser valve? 

I guess what got me the most perplexed was that with all this (in my opinion anyway) excessive heat build-up and hard starting if the engine stalled, the temp gauge still showed well within the normal range. 
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« Reply #9 on: July 21, 2014, 02:26:07 PM »

You want a manual gauge or IR ( or both!) to verify temp first. After readings are obtained, trouble shooting can begin to narrow down problems. If in fact your coolant is normal but under hood temps are increased due to hotter exhaust manifolds (as John stated)....for starters...take off your air cleaner and give the accelerator pump a few gentle pumps with your finger to see if anything is coming out of the primary squirter. (vapor lock, boiling off fuel ?


Coil can be bench tested--heat increases resistance in electronics. It does mimic a bad coil, but what's increasing the heat, and how much?

To sum it up...hot, dense air is bad news for these quasi race 302's...any engine for that matter (those scoops are not just decoration) Todays engine management systems(computer) re tunes for conditions as needed.

Post some temperature readings ,everyone will figure it out pretty quick.
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« Reply #10 on: July 21, 2014, 10:23:06 PM »

  Blocking off the manifold heat ports will stop the choke from working right if you have the spring/lever choke. That heat is what acts upon the spring and moves the choke flap open as the car warms up.
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« Reply #11 on: July 22, 2014, 08:46:30 AM »

Harbor Freight sells the IR tool for usually $29.00. One of the best tools I have bought lately. It is as accurate as the $600.00 one we have at work, just does not record or do thermal images. They have many uses.
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« Reply #12 on: July 22, 2014, 11:48:01 AM »

The intake manifold ehaust heat passage will still flow some exhaust even if the flapper is removed.  You can block the non-choke stove side of the intake at the passage and the choke will still work from the heat migration in the aluminum but it might be a little slower to pull off.  Not a big deal.  If the passage is blocked on one side, no exhaust gas will travel through inside the intake manifold.

-Mark.
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Vince
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« Reply #13 on: July 29, 2014, 03:45:47 PM »

Well I was finally able to do some checking on the underhood temps.  I drove the Z for between 2-3 miles to get the engine up to temp.  The outside air temp was in the mid 80's.  While driving the temp gauge stayed right around the first quarter marking, maybe one mark up toward the half marking.  While idling in my driveway the gauge read right at the one half marking.  The engine would not hold a steady idle but slowly had the idle decrease until the engine died.  This happened 3-4 times.  While the engine was not running the temp gauge would increase until it was between the one half marking and the three quarter marking.  This I take to be normal due to heat soak. 
Here are the temps I recorded with an infrared gun: 

radiator hose at thermostat- 183, bottom radiator hose- 164
exhaust manifold left hand side (driver's) from front to back- 364, 455, 417
exhaust manifold right hand (passenger) side again from front to back- 433, 570, 562
intake manifold at the high rise part on driver's side- 227
radiator across top- 145
radiator across bottom- 99
valve cover driver's side- 164
valve cover passenger side- 194
driver's side head-194, right at the temp sensor was 179
passenger side head- 253

I wasn't able to get accurate readings anywhere else or didn't think of trying anywhere else.  Definitely the right hand side (passenger) of the engine is a lot hotter than the driver's side.  I wasn't able to check other things while taking these temp readings as the engine was too hot to touch.  Any ideas out there?  Thanks again guys for all your help and opinions.  Just to add a side note:  the engine used to be able to idle for extended periods right at 900-1,000 rpm, with the temp gauge reading not much higher than the one quarter marking and without dying.  It also would restart while warm or hot with no problem. 
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z28z11
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« Reply #14 on: July 29, 2014, 05:26:47 PM »

Really does begin to sound more like a flow problem. Flush the system with the best product you can find, change the water pump and the thermostat. Check and/or change the cap - you need to run about 12-15 psi in the system to make it work properly. If no big improvement, I'd take the radiator out and replace with another known used clear radiator, or a cheap repop just to isolate the problem. Or, just core the old one like most of us are having to experience.

What does the coolant look like ? Dark colored, any foam in it ? Leaking head gaskets can cause hot spots/steam pockets like this. Oil clean ? Any coolant contamination ? Hoses collapsing ?

Bad flow across the radiator could also be a culprit, as we conjectured before. Bet the lower half is plugged - that's why the temp is so low in the bottom half.

One other thing - I witnessed a big block Chevelle do this once upon a time - turns out it was spun bearing (main), causing the engine to not only run hot, but choke down and die when it warmed up enough to start galling on the crank. Check your oil pressure with a mechanical gauge, and a mechanical temp gauge if you can. Just to make sure -

Regards, and good luck -
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« Reply #15 on: July 30, 2014, 10:00:35 AM »

<< Well I was finally able to do some checking on the underhood temps.  I drove the Z for between 2-3 miles to get the engine up to temp.  The outside air temp was in the mid 80's.  While driving the temp gauge stayed right around the first quarter marking, maybe one mark up toward the half marking.  While idling in my driveway the gauge read right at the one half marking.  The engine would not hold a steady idle but slowly had the idle decrease until the engine died.  This happened 3-4 times.  While the engine was not running the temp gauge would increase until it was between the one half marking and the three quarter marking.  This I take to be normal due to heat soak.  
Here are the temps I recorded with an infrared gun:  

radiator hose at thermostat- 183, bottom radiator hose- 164  >>

The last line above are the only temps that mean anything, and they're normal - don't agonize over all the other external temps - they are what they are, and you can't change them. You don't have a cooling problem, you have a typical fuel percolation problem, aggravated by low E10 fuel boiling points. Insulating your fuel line from the frame to the carb will help, as will an aluminum heat shield that extends under both fuel bowls. E10 fuel boils at 150*F, and at extended idle, the fuel bowls get hotter than that.

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« Reply #16 on: July 30, 2014, 11:28:54 AM »

Yep - the only thing else to do is slide a stainless steel shim in between the intake and the head on the drivers side right in the middle of the manifold to block that passage.  It will help to reduce the cooking of the carburetor and fuel percolation. Only do this if you have eliminated the heat riser function.

Just go to the kitchen when your wife is not around and find a flat bottomed stanless bowl.  Cut out a flat piece of material with tin snips just wide enough to fit between the manifold bolts in the center of the drivers side. Bend a small tab over to help you push it in.  Loosten the manifold bolts just a little and see if you can slide that metal down in there between the gasket and the intake. Try not to disturb the gasket too much.  Tighten the bolts back up and see if that helps.  It worked for me when I had the percolation issue.

PS - if you go snatch the bowl when the wife is watching, you are a BOSS!  Cheesy

Good luck!

-Mark.
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z28z11
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« Reply #17 on: July 30, 2014, 09:57:55 PM »


You don't have a cooling problem, you have a typical fuel percolation problem, aggravated by low E10 fuel boiling points.


Since John brought it up, let's discuss fuel for a second - any local station carry straight (non-ethanol) gas, and/or what are you running through the motor ? I would not recommend any E10 gas for any early engine, especially one that uses neoprene tipped needles in the carb, or rubber fuel lines. Like John indicates, the percolation is a problem, plus the stuff eats everything else, and has an affinity for moisture build up in the tank. Nothing draws a vacuum worse than ethanol in my opinion. Find a race gas distributor and run 100+ octane unleaded, or blend it with non-ethanol regular to stretch it.

I would, regardless, clean the cooling system completely, especially if the motor sits for a decent while without running up to operation temps regularly. Buildups are inevitable internally to the block, heads and radiator - keep them clean and they'll function accordingly.

2 cents -
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Vince
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« Reply #18 on: July 31, 2014, 12:46:41 PM »

Really does begin to sound more like a flow problem. Flush the system with the best product you can find, change the water pump and the thermostat. Check and/or change the cap - you need to run about 12-15 psi in the system to make it work properly. If no big improvement, I'd take the radiator out and replace with another known used clear radiator, or a cheap repop just to isolate the problem. Or, just core the old one like most of us are having to experience.

What does the coolant look like ? Dark colored, any foam in it ? Leaking head gaskets can cause hot spots/steam pockets like this. Oil clean ? Any coolant contamination ? Hoses collapsing ?

Bad flow across the radiator could also be a culprit, as we conjectured before. Bet the lower half is plugged - that's why the temp is so low in the bottom half.

One other thing - I witnessed a big block Chevelle do this once upon a time - turns out it was spun bearing (main), causing the engine to not only run hot, but choke down and die when it warmed up enough to start galling on the crank. Check your oil pressure with a mechanical gauge, and a mechanical temp gauge if you can. Just to make sure -

Regards, and good luck -

Thank you for your response.  I had the current radiator recored and a new thermostat put in 14 years ago.  The coolant looks fine, the correct color green and no foam.  The oil is very clean.  I have noticed no hose collapsing.  I have the coolant replaced every 2 years.  I'll have the shop were I usually take my Z check the radiator functioning, etc.  Sure hope it is no spun bearing or any internal engine problem. 
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Vince
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« Reply #19 on: July 31, 2014, 12:52:50 PM »

<< Well I was finally able to do some checking on the underhood temps.  I drove the Z for between 2-3 miles to get the engine up to temp.  The outside air temp was in the mid 80's.  While driving the temp gauge stayed right around the first quarter marking, maybe one mark up toward the half marking.  While idling in my driveway the gauge read right at the one half marking.  The engine would not hold a steady idle but slowly had the idle decrease until the engine died.  This happened 3-4 times.  While the engine was not running the temp gauge would increase until it was between the one half marking and the three quarter marking.  This I take to be normal due to heat soak. 
Here are the temps I recorded with an infrared gun: 

radiator hose at thermostat- 183, bottom radiator hose- 164  >>

The last line above are the only temps that mean anything, and they're normal - don't agonize over all the other external temps - they are what they are, and you can't change them. You don't have a cooling problem, you have a typical fuel percolation problem, aggravated by low E10 fuel boiling points. Insulating your fuel line from the frame to the carb will help, as will an aluminum heat shield that extends under both fuel bowls. E10 fuel boils at 150*F, and at extended idle, the fuel bowls get hotter than that.



Thanks JohnZ for your insight.  My car already had the aluminum heat shield installed when I bought it from the previous owner 18 yrs. ago.  I'll try insulating the fuel line as you suggested. 
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Vince
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« Reply #20 on: July 31, 2014, 01:00:54 PM »

Yep - the only thing else to do is slide a stainless steel shim in between the intake and the head on the drivers side right in the middle of the manifold to block that passage.  It will help to reduce the cooking of the carburetor and fuel percolation. Only do this if you have eliminated the heat riser function.

Just go to the kitchen when your wife is not around and find a flat bottomed stanless bowl.  Cut out a flat piece of material with tin snips just wide enough to fit between the manifold bolts in the center of the drivers side. Bend a small tab over to help you push it in.  Loosten the manifold bolts just a little and see if you can slide that metal down in there between the gasket and the intake. Try not to disturb the gasket too much.  Tighten the bolts back up and see if that helps.  It worked for me when I had the percolation issue.

PS - if you go snatch the bowl when the wife is watching, you are a BOSS!  Cheesy

Good luck!

-Mark.

I definitely will install the blocking shims on the driver's side intake manifold.  I know that my heat riser function has been disabled.  I am not going to take the chance of cutting the shim as you described whether the wife is around or not. She would miss the bowl even if she didn't actually see me take it.  Smiley
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Vince
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« Reply #21 on: July 31, 2014, 01:10:31 PM »


You don't have a cooling problem, you have a typical fuel percolation problem, aggravated by low E10 fuel boiling points.


Since John brought it up, let's discuss fuel for a second - any local station carry straight (non-ethanol) gas, and/or what are you running through the motor ? I would not recommend any E10 gas for any early engine, especially one that uses neoprene tipped needles in the carb, or rubber fuel lines. Like John indicates, the percolation is a problem, plus the stuff eats everything else, and has an affinity for moisture build up in the tank. Nothing draws a vacuum worse than ethanol in my opinion. Find a race gas distributor and run 100+ octane unleaded, or blend it with non-ethanol regular to stretch it.

I would, regardless, clean the cooling system completely, especially if the motor sits for a decent while without running up to operation temps regularly. Buildups are inevitable internally to the block, heads and radiator - keep them clean and they'll function accordingly.

2 cents -

I live in a small town in the Sierra Foothills in California.  There are no stations around here that I am aware of that sell non-ethanol gas.  I use premium Chevron, Shell, or 76 in it.  I'll do some research to see if I can obtain unleaded racing gas in my local area.  My car does sit every so often, sometimes up to 2 months between my taking it out for a spin.  I plan on having the radiator and engine gone completely over to check for gunk build-up.  Thanks for your info. 
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« Reply #22 on: August 06, 2014, 12:51:10 PM »

I plan to have my smog pump deveined and the screws put into the exhaust manifolds in place of the extension tubes.  I have 2 questions:

What is the easiest or best way to completely degut the smog pump?  What do I take out and what do I leave?  I am guessing when done it will just have a rotating pulley on the outside, but what is left on the inside if anything; is there still something rotating on the inside? 

What screws exactly do I need for the exhaust manifolds?  I have read on other posts here on CRG that they should be stainless (I am guessing steel), #10 x 1/2 in., flat top.  Where is the best place to get them, hardware store or auto parts place? 

Thank you.  I really appreciate all the help from all you guys on this website.  I wish I knew more about first gen Camaros, especially mechanical wise. 
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« Reply #23 on: August 06, 2014, 09:49:03 PM »

De-vane the pump - the rotor spins, but doesn't pump air, obviously. Block the vacuum tube for the divertor valve.

You can use roofing nails (galvanized) in the extension tubes - seals off the extension tubes, flat surface to seal on. Drop them in, tighten the tube fitting and you're all set.

My opinion - others ?

Regards -

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« Reply #24 on: August 07, 2014, 09:35:40 AM »

You can use roofing nails (galvanized) in the extension tubes - seals off the extension tubes, flat surface to seal on. Drop them in, tighten the tube fitting and you're all set.

My opinion - others ?

Regards -



That leaves both the extension tubes AND the roofing nails in the exhaust stream - I prefer to knock out the extension tubes and use the #10 x 1/2" flat head machine screws to plug the holes; leaves nothing at all in the exhaust stream.
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« Reply #25 on: August 07, 2014, 09:54:51 AM »

My only reason for leaving the tubes in place is the 30 degree countersink under the tube - the tube seat seals that, then the flat nail head seals the top of the tube. You could always cut the tubes/nail short if you don't want to obstruct exhaust gas flow. On the other hand, as fragile as the manifold is to work with, I would not alter the tube hole itself for the risk of either damaging the manifold or not being able to reverse the alteration (like I experienced with my originals when trying to extract tapered pipe plugs from the A.I.R ports). I have worked out a lot of pipe plugs from these things, up to and including drilling out the old plugs/fittings, and lifting leftover materials out 1 thread at a time. Nothing like spending 4-5 hours doing that on an expensive, unobtanium exhaust manifold- great for relaxation and stress relief (LOL !).

Regards -
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« Reply #26 on: August 07, 2014, 02:33:55 PM »

Vince I also live in California, and as far as gasoline goes, I have learned a few things concerning the oxygenated/ethanol gasoline formula used only for California. 1) it has a  very short shelf life. If you don't go through a tank longer than a few months it starts to turn green, and lose its potency. 2) keeping this in mind you also have to observe the station you purchase gasoline from, if it is a slow station and they are not getting tankers dropping off gasoline fairly often, same result gas gets stagnate. 3) Now I cannot prove this, but I have had issues 3 times now with Chevron gasoline in older cars. I just rebuilt my carb on my mustang only to find out the fuel we just got from Chevron starting to separate, and there is like an orange jelly in the gasoline. I knew about Chevron gasoline being inferior already, but my wife thought gas is gas, filled it up there by accident. I know this may cause some people to laugh, but it has happened more than once both previous ties from Chevron in California. I fill up about a half tank at a time from a real busy Shel station here in SoCal, with 91 octane and have never had a problem.
Just my 2 cents from what I have learned the hard way pertaining to California gas. I do miss the midwest's gasoline, both Speedway and Citgo sold 93 and 94 at some stations out there, and for cheaper!
Hope this helps some Smiley
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« Reply #27 on: August 07, 2014, 11:01:15 PM »

I would fill the tank with leaded race gas before I spent money anywhere else. Also make sure the race gas doesn't have Ethanol. I know Tognotti's in Sacramento has race gas.
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« Reply #28 on: August 08, 2014, 07:51:49 AM »

I run Marine Sta-bil in the boat to combat effects of ethanol in the fuel. SBC is a SBC. On mine it's fed by a low pressure pick up pump and high pressure feed for the fuel injection. These do not like alcohol. Alcohol also acts as a sponge for moisture.  Seafoam appears another popular product with the boaters.

Also is anybody rejecting their carbs? One could assume a lean condition is being created requiring an increase in jet size.
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janobyte
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« Reply #29 on: August 08, 2014, 09:07:11 AM »

Let me add ,of course having the option I'd run race fuel in the car. Always have. Total agreement.
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JohnZ
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« Reply #30 on: August 08, 2014, 10:20:58 AM »

My only reason for leaving the tubes in place is the 30 degree countersink under the tube - the tube seat seals that, then the flat nail head seals the top of the tube.

That's why I use the #10 x 1/2" flat head machine screws - they have a flat top, and a 30-degree taper on the bottom that matches the countersink in the manifold that would normally be sealed by the tube nut.
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'69 Z/28
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« Reply #31 on: August 10, 2014, 05:34:56 PM »

I wanted to thank all you guys once again for your responses and help.  I am taking things one step at a time.  I think it has been narrowed down to a fuel percolation problem with excessive heat being produced from the exhaust manifolds due to the AIR pump pumping air all the time, due to a broken diaphragm in the diverter valve, plus a vacuum leak from the same cause.  The cooling system checks out fine.  The timing checks out fine.  I'm still looking for a racing gas distributor in my local area. 
What do you guys think about Joe Gibbs Driven Carb Defender Fuel Additive, for counteracting the ethanol in gas, possible help or waste of money?
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Vince
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« Reply #32 on: October 03, 2014, 06:32:25 PM »

I finally got the AIR system inactivated.  Checked for a vacuum leak around the carb and couldn't find any.  Car seems to hold an idle now without slowly going down and dying.  One thing I have noticed since I have been doing a lot of work with the air cleaner off is that after the car has idled awhile, though still not anywhere near hot, after I shut the engine off a vapor or mist almost as thick as smoke comes out of the carb throat.  The carb is still cold to the touch when this occurs.  What is causing this? 
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JohnZ
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« Reply #33 on: October 04, 2014, 09:15:56 AM »

I finally got the AIR system inactivated.  Checked for a vacuum leak around the carb and couldn't find any.  Car seems to hold an idle now without slowly going down and dying.  One thing I have noticed since I have been doing a lot of work with the air cleaner off is that after the car has idled awhile, though still not anywhere near hot, after I shut the engine off a vapor or mist almost as thick as smoke comes out of the carb throat.  The carb is still cold to the touch when this occurs.  What is causing this? 

Crankcase vapors - if you had the air cleaner and PCV hoses connected, you wouldn't see it.
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'69 Z/28
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« Reply #34 on: October 04, 2014, 12:57:03 PM »

Thank you John.  Glad to hear it is something as simple as you described.   
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BULLITT65
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« Reply #35 on: October 04, 2014, 03:56:08 PM »

I finally got the AIR system inactivated.  Checked for a vacuum leak around the carb and couldn't find any.  Car seems to hold an idle now without slowly going down and dying.  One thing I have noticed since I have been doing a lot of work with the air cleaner off is that after the car has idled awhile, though still not anywhere near hot, after I shut the engine off a vapor or mist almost as thick as smoke comes out of the carb throat.  The carb is still cold to the touch when this occurs.  What is causing this? 

Crankcase vapors - if you had the air cleaner and PCV hoses connected, you wouldn't see it.
shoot, you close the hood and you won't see it.... Cheesy
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1969 garnet red Z/28 46k mile unrestored X77
Looking for 3192477 (front) spiral shocks 3192851 (rear) please
Looking for an original LOF soft ray windshield
Looking for original Delco side post negative battery cable part # 6297651AV
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