Author Topic: Getting a skip / hesitation during cruise speeds  (Read 1923 times)

DonSTP

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Getting a skip / hesitation during cruise speeds
« on: July 02, 2010, 05:09:54 PM »
I just installed a new MSD Pro-billet distibutor, new plugs, new wires, timed the engine, etc...and just about all of my problems went away, except I'm getting a skip or hesitation during cruise speeds.  I doubled checked my plug wire connections to my distributor cap and they're all in the correct order on the cap. 

Its almost like the engine is mis-firing, but I get no back fire.  I smell heavy gas like I'm not igniting all the fuel in one or more cylinders. 

Any suggestions?

Thanks,
Don

daytho1

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Re: Getting a skip / hesitation during cruise speeds
« Reply #1 on: July 03, 2010, 12:05:40 PM »
What types of problems were you having that made you replace the distributor?  Is the hesitation severe?  What does it do at idle speeds?
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Sauron327

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Re: Getting a skip / hesitation during cruise speeds
« Reply #2 on: July 03, 2010, 12:53:06 PM »
What carb? Is it a lean surge? I run stock ignition systems with no difficulties. Did you eliminate the resistor wire feeding that billet distributor? What model is it? They call for full 12 volts don't they?

Stingr69

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Re: Getting a skip / hesitation during cruise speeds
« Reply #3 on: July 29, 2010, 02:50:36 PM »
Don,
What is the curve like on the new distributor? What is the total sum of your initial advance plus all the centrifugal advance plus all the vacuum advance?

-Mark.

JohnZ

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Re: Getting a skip / hesitation during cruise speeds
« Reply #4 on: July 29, 2010, 05:27:40 PM »
Don,
What is the curve like on the new distributor? What is the total sum of your initial advance plus all the centrifugal advance plus all the vacuum advance?

-Mark.

Total timing is only initial plus centrifugal; vacuum advance isn't part of that equation. Vacuum advance is disconnected and plugged when setting initial timing and checking total timing. What matters is how much advance the VAC adds; if it's more than 15*, it's excessive (common problem with HEI distributors).
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Stingr69

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Re: Getting a skip / hesitation during cruise speeds
« Reply #5 on: July 30, 2010, 03:52:07 PM »
John,
OP is at cruise where it is likely ALL of the advance will be fully deployed. I am concerned that he might be somewhere over 52 degrees or so. He might be firing too early at cruise conditions. High cylinder pressure well before the piston gets to TDC might not be the cause here but if we ask, we might learn more about what we are looking at.

-Mark.
 

JohnZ

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Re: Getting a skip / hesitation during cruise speeds
« Reply #6 on: July 30, 2010, 04:22:40 PM »
John,
OP is at cruise where it is likely ALL of the advance will be fully deployed. I am concerned that he might be somewhere over 52 degrees or so. He might be firing too early at cruise conditions. High cylinder pressure well before the piston gets to TDC might not be the cause here but if we ask, we might learn more about what we are looking at.

-Mark.
 


I understand that, but it won't be fully-deployed at cruise, as there's still a load on the engine at cruise; peak vacuum only occurs under two conditions - at idle in neutral, or at cruise when you take your foot off the gas. Best way to determine what the VAC is doing is to connect a vacuum pump to it (MityVac) with a timing light hooked up and see how the timing changes as varyng levels of vacuum are applied. To properly spec a VAC, you need to know four things:

1. At what vacuum level does it start to deploy.

2. At what vacuum level is it fully deployed.

3. How much advance does it add when fully deployed.

4. Engine manifold vacuum level at normal idle.

Stingr69

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Re: Getting a skip / hesitation during cruise speeds
« Reply #7 on: July 30, 2010, 07:04:17 PM »
John,
You have mail.

-Mark.