Author Topic: 396 L34 hard to start when hot  (Read 10101 times)

RAS68

  • Member
  • ***
  • Posts: 98
    • View Profile
396 L34 hard to start when hot
« on: October 05, 2020, 06:33:35 PM »
HELP!!! I have a long standing problem - my 68 L34 has a starting issue when engine is hot. I have tried so many things: New battery cable, new battery with high CCA, double checked and rebuilt alternator + replaced voltage regulator to make sure battery is being charged, Checked voltage at coil (12 v at start ~ 9 -10 v at run), adjusted timing and finally a reduction gear starter. So now it will turn over when it is hot ( not real fast but fast enough) but it does not want to start when hot. I can get a jump box or a jump off another car and it will start right away within one or two cranks. By itself it will not start until I wait about 30 minutes. What is going on here? I don't know what else to try. By the way this 396 has been rebuilt and compression is 10:1. I love CRG and the discussion forum and the experts here have helped me out many times. I am hoping CRG can help me get this bug out so I can fully enjoy my car. Any ideas are welcome.
Thanks,
Allen
'68 SS L34 07C NOR

169INDY

  • Hero Member
  • *****
  • Posts: 1786
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #1 on: October 05, 2020, 06:47:47 PM »
Any ideas are welcome.

Triple Check the Grounding at the Engine. (ie Neg side of your circuit)

You Say it Starts when Jumped,,,, "Wondering out loud",,,, When another 12VDC Source is added via a jumper cable or box lead they create another Path & source of Amps around your existing Neg Circuit.

Just a Random Thought,,,,,,

I am understanding your frustration.

Jim
Jim
68 SS/RS L35 Th-400 LOS
69 Pace Car L48 Th-350 LOS
68 Z28 M21 LOS

RAS68

  • Member
  • ***
  • Posts: 98
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #2 on: October 05, 2020, 07:17:52 PM »
Thanks Jim for the prompt reply. I will try that and triple check the ground side tonight.
Allen
'68 SS L34 07C NOR

WorkinProgress

  • Member
  • ***
  • Posts: 319
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #3 on: October 05, 2020, 09:13:42 PM »
I have around here a Chevrolet Service Letter for a solenoid problem. Engines after they sat that were brought up to full temp, were hard to start shortly after. Not sure if that is your problem, but GM solved it with a different solenoid.

                                     - Warren

WorkinProgress

  • Member
  • ***
  • Posts: 319
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #4 on: October 05, 2020, 09:57:03 PM »
I found a couple of sheets on hot start cranking. Doesn't say anything about the solenoid but that could be something I read on a different sheet, whereabouts unknown at this time. Discusses starter replacement.

I cannot post the sheets as file too large.

Anyone that wants copies, put in subject "Service Bulletins" and email me at keepitallgm@yahoo.com 

                                              - Warren

william

  • CRG Member
  • *****
  • Posts: 3119
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #5 on: October 06, 2020, 12:34:20 AM »
Are you using the solenoid heat shield [#5]?
Learning more and more about less and less...

Kelley W King

  • Hero Member
  • *****
  • Posts: 1410
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #6 on: October 06, 2020, 11:43:31 AM »
I had a 396 that did pretty much the same thing. I backed off the timing a little and turned over better and started. I cannot remember the timing numbers but big blocks like a lot of timing to run the best but it is not the best for starting. The main ground issue stated above should also be checked.
69 Z28 RS Scuncio Hi Performance
69 SS L78
67 SS Chevelle
64 Corvette
66 GTO Tiger Gold
77 Trans Am Special Edition

RAS68

  • Member
  • ***
  • Posts: 98
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #7 on: October 06, 2020, 05:23:01 PM »
Thanks for all the replies and suggestions. I will try the heat shield as well. But the motor does over. I used to have the issue where when it was hot the Starter would barely turn over. Now that I have the reduction gear starter from 1980's GM truck it turns over pretty well even when hot. But the engine does not seem to want to start. Just turns over. After it cools down again it will start. But like I said - if I add a jumper cable from another car it turns over quicker and starts right up. Its a mystery but I am determined to solve this once and for all.

Allen
'68 SS L34 07C NOR

RAS68

  • Member
  • ***
  • Posts: 98
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #8 on: October 06, 2020, 05:38:17 PM »
One more thing - I have the Pertronics ignition conversion but I use the stock distributor and high performance coil. Could this set up be part of the problem?
Allen
'68 SS L34 07C NOR

usa1ti

  • Member
  • ***
  • Posts: 91
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #9 on: October 06, 2020, 06:56:34 PM »
Just a couple of observations on this. Your voltage really should be checking 12.8v to 13.8v most all of the time. As far as the timing the higher the compression the more total timing you need to get the flame travel over the dome so you fire the cylinder early with bigger piston domes. On my 14 to 1 598 alcohol motor I run 42 degrees total. My 12 to 1 427 engines I run about 38 degrees total. On a 10 to 1 396 motor 34-36 degrees is prob good. It will take a fresh starter to do this but I run good GM starters up to 38 degrees with no problem. Another IF... If the float levels are too high a hot fuel line / under hood temp will push a little fuel over the needle and seats causing some minor flooding after shutoff. hard to start until it clears the fuel out. Have had this happen before.
Todd, East TN

RAS68

  • Member
  • ***
  • Posts: 98
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #10 on: October 06, 2020, 09:30:31 PM »
Todd - Thanks for the idea about the flooding. I have original Quadrajet carb on it. How can I tell if it is flooding? Will I be able to see a trickle of fuel if I take the air cleaner off? If that is happening, what do you adjust to correct it? Can you adjust float level while the carb is still on the car?
'68 SS L34 07C NOR

TODD

  • Member
  • ***
  • Posts: 139
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #11 on: October 07, 2020, 12:04:04 PM »
Allen so the resistance wire to the Petronix is in place? The hot 12V wire from the starter to coil is intact? If I remember correctly Petronix units caused stock tach issues but starting issues would only be if its not wired correctly for cranking voltage to coil. I would recheck the Petronix set-up requirements for your unit.
Todd

Henry Cloutier

  • Member
  • ***
  • Posts: 81
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #12 on: October 08, 2020, 01:39:35 AM »
Hello, I had the same experience with my 327 in a 1968 Camaro. For sure it was not stock; had angle plug heads, Offenhauser 360 manifold, Holley 950 three barrel, 11-1 pistons and dual point ignition. The engine liked a lot of initial timing. I don't remember the settings from back then. But one way I knew to much timing was set was hard starting when hot. My friend at the time was driving a 1967 tri-power 400ci GTO. His did the same thing when to much initial was set. GM products at least the old ones anyway like lots of timing to run, just not in the start sequence. At the time it was explained to me that to much initial is firing the fuel mixture to soon impeding the start process. Once the engine is running no issues. Good luck in your troubleshooting!

Henry   

Kelley W King

  • Hero Member
  • *****
  • Posts: 1410
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #13 on: October 08, 2020, 11:50:19 AM »
I agree with Henry. Turning the dizzy vac can a little towards the firewall is free and takes only a couple minuits to try.
69 Z28 RS Scuncio Hi Performance
69 SS L78
67 SS Chevelle
64 Corvette
66 GTO Tiger Gold
77 Trans Am Special Edition

RAS68

  • Member
  • ***
  • Posts: 98
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #14 on: October 10, 2020, 06:03:02 PM »
Ill try the adjusting the timing and let you know. Im also going to try an Odyessey battery with 880 CCA.
Thanks to every one for ideas and advice.
Allen
'68 SS L34 07C NOR

Henry Cloutier

  • Member
  • ***
  • Posts: 81
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #15 on: October 11, 2020, 12:29:28 AM »

  Just curious, What is your timing at now?

Henry

PHAT69AMX

  • Member
  • ***
  • Posts: 89
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #16 on: October 27, 2020, 04:50:14 AM »
What might be the numbers stamped on the Distributor, or really what's needed, is what are the numbers stamped on the bottom of the Pole Piece in your Distributor and is the Sleeve still in place on the mechanical advance travel limiter pin?  The Initial Timing Advance should not be changed without first knowing how much potential total mechanical advance is in the distributor.  This must be considered to avoid over advance.  Agree, more advance at idle helps many things, but also agree too much initial advance can cause difficult hot starting.  So one must first know how much Total Mechanical Advance the Distributor is capable of in order to determine how much advance at idle is enough and not too much.  But this is complicated by if the mechanical Advance may already be working some even at idle, which it sometimes does, depending on weights and springs and center cam.  So the 'right way' to set the timing advance is at 'high' rpm using a dial back timing light and adjusting the distributor to set Total Advance with the Mechanical Advance all-in and NO Vacuum advance at all, vacuum advance disconnected and plugged.  Then whatever the timing advance is at idle is whatever it is.  What matters is total advance and all-in by when.

  Also, was the top distributor bushing grease well re-packed with grease?  Has the distributor been checked for sideplay?  Sideplay can reap intermittent havoc with distributor ignitions.  That top bushing is not motor oil lubricated, it is only lubricated by the grease well in the distributor housing, and if original 50 years is a long time.  Distributor grease well pictured is filled with wheel bearing grease.  The correct original GM Grease that should be used in the Distributor top bushing grease well is red and a jar of it is pictured.

RAS68

  • Member
  • ***
  • Posts: 98
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #17 on: November 13, 2020, 05:56:03 PM »
Thanks again to everyone for the ideas and suggestions. The last post about mechanical advance is very interesting - Im going to look into that as well. I backed off the timing some and it does start better when hot. I also found that it will start pretty easy when hot if I floor the gas pedal during start or just before I turn I key. What does that mean?
Allen
'68 SS L34 07C NOR

Leon in Mn.

  • Member
  • ***
  • Posts: 65
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #18 on: November 13, 2020, 10:37:15 PM »
I thought I would chime in here as well as back in the day I  went to school on these vehicles (old school but not THAT old) and worked on them as well.  All of these comments are great, but another issue is fuel percolating/and evaporating in the float bowl at high temps.  This can cause vapor lock and like one poster stated to check the float level.  It can "blubber over" into the manifold and cause a temporary flooding.  Do you know for sure that you have the heat shield plate under your Quadrajet? I'm assuming you have the Quadrajet? If that is not in place and in the right position along with the gasket in the right position, it can cause many problems.  It can also burn out the plugs in the bottom of the carb which can leak fuel out of the bowl and into the hot manifold below, not only draining the fuel bowl, but causing flooding.  Sometimes hooking up another vehicle just gives the car that extra spin and voltage to overcome the hard start which normally it wouldn't need.  Try searching for "manifold hot slot problem" on these cars and you will find a lot of info, and what you can do if you didn't yet find the remedy.   Something else that would cause a flooding like scenario is to make sure your heat riser isn't stuck in the closed position .......Just something to think about if you are still looking for the problem.   :)
 Leon

Henry Cloutier

  • Member
  • ***
  • Posts: 81
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #19 on: November 18, 2020, 01:57:49 AM »

Hi there,
I'm certainly no engineer, and there is most likely a better explanation for easier starting with the gas pedal held to the floor. I always equated it to unloading the engine since the throttle blades are open allowing the engine the best opportunity to spin freely when hot. Near as I can figure the engine when hot is at its optimum with the piston rings fully seated and friction at it's highest. When the timing is to far advanced the engine is trying to fire with no inertia to sustain the motion. The engine kicks back because the starter has limited ability to overcome this kick back and struggles to turn over. Lessening the initial timing allows the engine to fire closer to TDC which helps the engine sustain the inertia generated buy the starter during the start sequence. Once running the engine can handle more timing which is better for overall performance.
Fuel boiling and vapor lock are common with these old cars. Back in the day us back yard guys clipped close pins to the fuel lines to act as heat sinks; not very attractive but worked really well.

Best regards,

Henry 

Kelley W King

  • Hero Member
  • *****
  • Posts: 1410
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #20 on: November 18, 2020, 12:39:59 PM »
Since you are a "back in the day" guy Henry, try aluminum foil around the lines. Adds a little shine to the engine also. On a serious note then heat sink plate kits with the 1/2 spacer is only about $35 bucks if you have room. Worth a try maybe.
69 Z28 RS Scuncio Hi Performance
69 SS L78
67 SS Chevelle
64 Corvette
66 GTO Tiger Gold
77 Trans Am Special Edition

Henry Cloutier

  • Member
  • ***
  • Posts: 81
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #21 on: November 18, 2020, 10:03:00 PM »

Dang,
 I wish I had thought of the foil-"back in the day," perhaps it would have helped with the radio reception as well!
Henry

Stingr69

  • Hero Member
  • *****
  • Posts: 901
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #22 on: November 20, 2020, 02:05:12 PM »
I agree with the heat boiling the current crappy gas in the carb is a concern.  The hot slot has been an issue forever.  If you have the hot slot intake it needs to be addressed as they are carb cookers.  A heat insulator under the carb is an easy fix.

169INDY

  • Hero Member
  • *****
  • Posts: 1786
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #23 on: November 20, 2020, 05:12:59 PM »
I think there are a few threads about Drill & Tap and "set" pipe plugs in the hot slot end passage hole and block it off for good, esp nice since what 99% do NOT daily drive these old buckets of bolts.
Jim
68 SS/RS L35 Th-400 LOS
69 Pace Car L48 Th-350 LOS
68 Z28 M21 LOS

z28z11

  • Hero Member
  • *****
  • Posts: 1853
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #24 on: November 20, 2020, 10:48:15 PM »
I think there are a few threads about Drill & Tap and "set" pipe plugs in the hot slot end passage hole and block it off for good, esp nice since what 99% do NOT daily drive these old buckets of bolts.

You dont have to drill and tap it to block it - takes a 7/16 freeze plug, just drive it in securely (it won't back out), gasket it with the stainless shim under the gasket, and forget it. It's actually a safety precaution as well - you don't need hot exhaust crossover temps under the Quad bowls -

Regards,
Steve
1968 Z28 M21/U17 BRG/W 1967 Chevy ll Nova SS 
1969 Z28 X77/M20/VE3 LeMans/W
1969 L78 X66/N66 Cortez/BVT
1969 Z11 L48/M35/C60/C06  1949 3100 5wd 235/6

RAS68

  • Member
  • ***
  • Posts: 98
    • View Profile
Re: 396 L34 hard to start when hot
« Reply #25 on: January 18, 2021, 09:56:12 PM »
Here is an update to this thread - I backed off the timing a little which did help, and I did some diagnostic on the voltage regulator + alternator circuit. I found that the regulator ground wire was not making a good connection and corrected that. I also purchased the biggest CCA battery I could find that fits in the stock battery tray. My car now starts much better even when it is hot. Wow, talk about going around the world just to get next door. But it seems that I needed all those adjustments and corrections together to completely solve the issue. Thanks to those that responded with helpful suggestions.
Allen
'68 SS L34 07C NOR

 

anything