Noticable momentary hesitation at highway speed???

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This has been really vexing me...

I have a 66 16 200, MSD-6A ignition, Pertronix ignitir and a new Pony Carb 1100 with clear fuel filter. 3-speed manual tranny.

I installed a fuel pressure gage before the filter to the carb and was getting 5.5 psi at idle. New fuel tank 2 yrs ago.

The car seems to have a slight blip or miss at highway speeds of about 50 mph or more. It will drive along great and then you can feel it sort of chug for a split second.

I checked all the plugs and they all look great...a nice even tan color.

I cleaned out some rust in the fuel filter and have done a check of the fuel pump by making sure it could pump a pint of fuel into a jar in about 10 or 15 seconds with the motor just started. So pretty sure the fuel pump is okay.

So I'm getting air, fuel and spark...hmmm.

Anyone have any suggestions?

Thanks,
Steve-O
 
Okefenokee Comet":2jw4r8s1 said:
I vote spark, which Petronix is it?

The original pertronix without any spark advance capability...so it would be Pertonix 1, I guess.

Sorry about posting this in drivetrain...not sure hwere my brian was...meant to post in small block inline 6 forum.

Cheers,
Steve
 
No replies :cry: Could you bypass the MSD to rule it out or reinstall the points to rule out the petronix? How long have you been running this setup? Did you bypass the resister wire?
 
I'm thinking carb issue. Not often I blame this part of a motor. Main reason to say so, is the lack of a plausible reason for the problem to lie with ignition.

My surmise is that fuel bowl level is fluctuating due to a blockage in its vent, or a vacuum "seep". What could then happen is the main jet is either sucking air momentarily, or swamped and not passing fuel at all. Not sure how you could exactly diagnose it, other than trial carb substitution.

Regards, Adam.
 
I had this problem, but at about 60 mph and it would not let me go any faster than that. Fuel regulator! The mister gasket kind (cheap-oo) would only at first run 3 psi fully open. Great gas mileage, though. Still do not have the regulator reinstalled, I am waiting to buy one better quality and also with a by-pass. And on the Pertronix, make sure you have a full 12 volts to the coil. Check float level, also. Good luck.

Kirk ' 73 bronco
 
Things I'll try...checking 12 v at the coil under load (idle should be okay) and separating the wires as best I can and more dielectric grease inside the rotor cap.

As far as the carb...damn it, I just put on the new Pony Carb 1100 and sold the old carb. Maybe I can take it off and blow out all the passages with some low pressure air. Not enough psi to do damage but maybe to remove any dirt, etc.
Will keep you posted.
Cheers,
Steve-O
 
You could also try an isolator and an auxiliary fuel pressure gauge inside the cab. That would reveal any fluctuations in pressure delivered.

Ignition problems tend to manifest steadily at whatever threshold they appear. Ie; when a certain operating temperature is reached, or RPM. You then get a consistent misfire or chug, not a now-and-then.
 
Intermittent problems are the worst :evil: Can you reproduce the symptoms on demand? I.E; anytime you take it above 50 mph it cuts out? Does it get worse at higher speed? If so, I have to agree with Addo, it is in the fuel system. You mentioned a new fuel tank two years ago. Does it have a filter inside the tank? They can get gummed up and really give you fits.
Joe
 
addo":1ulrie8v said:
You could also try an isolator and an auxiliary fuel pressure gauge inside the cab. That would reveal any fluctuations in pressure delivered.

Ignition problems tend to manifest steadily at whatever threshold they appear. Ie; when a certain operating temperature is reached, or RPM. You then get a consistent misfire or chug, not a now-and-then.

I had a fuel gage in line and got 5.5 psi at idle, I may try to run it via fuel hose to a spot where I can see it when I'm driving the car, like temporarily on my cowl vent.

Could be fuel. I will keep you in the loop.

Steve-O
 
One thing I would try: different spark plugs.

I just ran thru 3 sets of Autolites in a row that exhibited something like this symptom. Shortly after the symptom (200+ miles or so), one or more would suddenly foul, like it was burned out and unable to keep itself clean. Otherwise, everything looked fine.

I just switched to Champions (not my favorites), and the whole issue went away! (Hmmm...)
 
MarkP":1qrj26nk said:
One thing I would try: different spark plugs.

I just ran thru 3 sets of Autolites in a row that exhibited something like this symptom. Shortly after the symptom (200+ miles or so), one or more would suddenly foul, like it was burned out and unable to keep itself clean. Otherwise, everything looked fine.

I just switched to Champions (not my favorites), and the whole issue went away! (Hmmm...)

All the plugs look good and Ihave a nice 12.5 V to the coil at idle.

Si I have to agree it may be fuel related. I will righ the gage and let you know what I find.

What is a "isolator" ?? wrt the fuel pressure gage set up?
 
An isolator decouples the gauge from the actual fluid providing the pressure, by use of an intermediate section with a different fluid. It means you can have a fuel pressure gauge inside the cab, or oil pressure, or whatever, with no worries about leakage or fire risk.
 
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