Technical help during problem determination

[Harry S.]

I went for a 70 mile ride this morning in my 63. It's a 250hp car. The temp outside was 84 and my thermostat never got over 180. It ran fine at the beginning then I noticed when I hit the gas there was a shudder/stumble in the engine. It did it in all gears after I got rolling. As soon as I got home and the car cooled a bit it was fine. It happened last year on a similar length ride.

Anyway this is a question as to where to start the problem analysis. To me I think it's a result of the engine bay heat having an affect on one or more spark plug wires, a plug or the coil. I just don't think it's gas related.

Any thoughts?

Happy the 4th
Cheers

[Rick A.]

Re: Technical help during problem determination

Harry - would agree and believe it would be called a "heat sink" problem

[Joe L.]

Re: Technical help during problem determination

I went for a 70 mile ride this morning in my 63. It's a 250hp car. The temp outside was 84 and my thermostat never got over 180. It ran fine at the beginning then I noticed when I hit the gas there was a shudder/stumble in the engine. It did it in all gears after I got rolling. As soon as I got home and the car cooled a bit it was fine. It happened last year on a similar length ride.

Anyway this is a question as to where to start the problem analysis. To me I think it's a result of the engine bay heat having an affect on one or more spark plug wires, a plug or the coil. I just don't think it's gas related.

Any thoughts?

Happy the 4th
Cheers

Harry------


One thing you could try is to install a thick insulating type gasket between the carb and manifold. Of course, this won't be correct but it might improve driveability.

[Gene M.]

Re: Technical help during problem determination

Do the easy stuff first to find the issue. Do all the spark plugs look the same? Any vacuum hose cracks? Plug wire resistance look ok? Loose intake manifold bolts or carb nuts? Any crack or carbon track in distributor cap? Ignition point condenser?

Do you have the long tip rotor in distributor? The short one can tax the ignition with the wider gap to the cap contacts.

[Harry S.]

Re: Technical help during problem determination

Harry------


One thing you could try is to install a thick insulating type gasket between the carb and manifold. Of course, this won't be correct but it might improve driveability.

Joe, I'm looking for one as I type.

Thanks

[Harry S.]

Re: Technical help during problem determination

Do the easy stuff first to find the issue. Do all the spark plugs look the same? Any vacuum hose cracks? Plug wire resistance look ok? Loose intake manifold bolts or carb nuts? Any crack or carbon track in distributor cap? Ignition point condenser?

Do you have the long tip rotor in distributor? The short one can tax the ignition with the wider gap to the cap contacts.

Gene, Just added a few of your items to the list to check

[David H.]

Re: Technical help during problem determination

I went for a 70 mile ride this morning in my 63. It's a 250hp car. The temp outside was 84 and my thermostat never got over 180. It ran fine at the beginning then I noticed when I hit the gas there was a shudder/stumble in the engine. It did it in all gears after I got rolling. As soon as I got home and the car cooled a bit it was fine. It happened last year on a similar length ride.

Anyway this is a question as to where to start the problem analysis. To me I think it's a result of the engine bay heat having an affect on one or more spark plug wires, a plug or the coil. I just don't think it's gas related.

Any thoughts?

Happy the 4th
Cheers

Harry,

Any chance exhaust manifold heat riser valve stuck closed? See link below.

https://www.forums.ncrs.org/showthre...r-stuck-closed

Dave

[Harry S.]

Re: Technical help during problem determination

Harry------


One thing you could try is to install a thick insulating type gasket between the carb and manifold. Of course, this won't be correct but it might improve driveability.

Joe, 1/4 inch or 1/2 inch gasket? I found both.

[Harry S.]

Re: Technical help during problem determination

Harry,

Any chance exhaust manifold heat riser valve stuck closed? See link below.

https://www.forums.ncrs.org/showthre...r-stuck-closed


Dave

I'll check again but I think its ok

[Bruce W.]

Re: Technical help during problem determination

Harry, I had a similar problem on one of my vettes. Car ran fine when cold but whent it got hot i had mis firing problems. It was the coil. when it cooled down it ran fine. I would check your coil with an om meter or pick up a replacement coil.
Bruce

[Joe L.]

Re: Technical help during problem determination

Joe, 1/4 inch or 1/2 inch gasket? I found both.

Harry-----

If it were me and I was trying to solve this problem, I think I'd go with the 1/4" gasket. You do want a little heat to get to the carb to improve fuel atomization. If it's made of a good insulating material, 1/4" ought to be enough. When GM was using this type gasket, they were usually 1/4" or less in thickness and they worked well.

[Frank D.]

Re: Technical help during problem determination

You could buy a not-too-expensive Echlin IC-12 ignition coil from NAPA and swap it on as a troubleshooting tool....otherwise its hard to diagnose an intermittent ignition problem with the coil.. If it doesn't solve the problem it'll still make a nice "hot spare" part...

I had the same problem (63 bone stock 250hp car) last summer, you can try this carb spacer and it comes with the taller carb mounting studs and extra gaskets you'll need - any more than 1/4" and you will have hood clearance problems:

https://www.dashman.net/product.html?id=203



If you just want to try a WCFB pheonlic 1/4" spacer for free PM me your address and you can stick my extra one on the car as a loaner but I can't mail it out until after the holiday.

I use aluminum foil to check hood clearance (some prefer modeling clay). The thickness of the compressed foil with the hood closed tells you what you have to play with.

I also drilled and tapped the intake manifold and put plugs in the "hot slot" openings along with F/I gaskets that blocked off the intake heat runners and wired open the exhaust heat riser.


Vapor lock is the fuel pump trying to push vapor through the line and the voodoo fix used to be clothespins on the fuel line (never worked). But, first make sure your pump-to-carb fuel hardline is at least 1/4" away from the passenger side head and possibly consider insulating it. Fuel atomization isn't a problem in the temps we operate in IMO.

These insanely hot Florida days exacerbate the problem. Strangely when I rebuilt my numbers matching WCFB I haven't encountered the problem since. In only use the Daytona Parts WCFB rebuild kits now with the "thumbtack" needle valves:

http://www.daytonaparts.com/daytona-carburetor-float-valve.html

The needle valves seem to allow the float settings to be somewhat less critical than other kits...

[Loren L.]

Re: Technical help during problem determination

More help with "shudder"/"stumble" - does it continue to run but somehow "roughens" up or does it actually stop for a split second and relight it self? If it occurs when you ask for a "little more", I'd look at the spark advance.

[Joe L.]

Re: Technical help during problem determination

You could buy a not-too-expensive Echlin IC-12 ignition coil from NAPA and swap it on as a troubleshooting tool....otherwise its hard to diagnose an intermittent ignition problem with the coil.. If it doesn't solve the problem it'll still make a nice "hot spare" part...

I had the same problem (63 bone stock 250hp car) last summer, you can try this carb spacer and it comes with the taller carb mounting studs and extra gaskets you'll need - any more than 1/4" and you will have hood clearance problems:

https://www.dashman.net/product.html?id=203



If you just want to try a WCFB pheonlic 1/4" spacer for free PM me your address and you can stick my extra one on the car as a loaner but I can't mail it out until after the holiday.

I use aluminum foil to check hood clearance (some prefer modeling clay). The thickness of the compressed foil with the hood closed tells you what you have to play with.

I also drilled and tapped the intake manifold and put plugs in the "hot slot" openings along with F/I gaskets that blocked off the intake heat runners and wired open the exhaust heat riser.


Vapor lock is the fuel pump trying to push vapor through the line and the voodoo fix used to be clothespins on the fuel line (never worked). But, first make sure your pump-to-carb fuel hardline is at least 1/4" away from the passenger side head and possibly consider insulating it. Fuel atomization isn't a problem in the temps we operate in IMO.

These insanely hot Florida days exacerbate the problem. Strangely when I rebuilt my numbers matching WCFB I haven't encountered the problem since. In only use the Daytona Parts WCFB rebuild kits now with the "thumbtack" needle valves:

http://www.daytonaparts.com/daytona-carburetor-float-valve.html

The needle valves seem to allow the float settings to be somewhat less critical than other kits...

Frank------

Hood clearance should be no problem with just adding the thicker insulating gasket. The same hood was used with applications using a high rise aluminum manifold which was more than 1/4" higher than the 250 HP manifold.

The 1963 250 HP manifold did not have a heat slot.

[Harry S.]

Re: Technical help during problem determination

Frank,

Thanks for the pictures. I'll try that as a last resort. This may be a common problem with 250hp 63's with a WCFB.