VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 Rough running 30 motor after sitting 5 min.

My 30 motor is running great. Quiet, extremely smooth and very strong.
Original carb. points at 18, timing at about 15-18 and plugs at 25.
When the engine is at operating temp, after a 10-15 mile run at 45-55mph, I stop for 5-10 minutes. Fire up the car, and she starts bogging and missing and has no power. Have to play with the gas peddle and it will eventually will pick up and run perfectly again.

Stop for 2-3 minutes and no problem.
Stop for 20 minutes or more. No problem.

Checked fuel line temp from the pump to the carb and it is warm but I can hold my hand on it.
Carb, on the other hand is too hot to touch for more than a couple of seconds.

Partial vapor lock?
Fuel boiling in float bowl?

Is there supposed to be an insulator spacer between the carb base and the intake manifold?

Any ideas?

Thanks
Dale

I am thinking that the heat is boiling the fuel in the carburetor bowl and over fueling on start up. Never had the problem with an updraft but guess it is possible. Don't know of a fix other than a thicker gasket between manifold and carburetor. Essentially the carburetor is attached to a tube through the exhaust manifold so the residual exhaust heat can be transferred to the carburetor.

What type of gasoline are you using? I have a car that does the exact same thing when I am running gas with Ethanol.

Also, you might want to run AC C-86 or C87 spark plugs, gap them to .040" and increase your timing to 18 degrees.

What kind of gas are you using? I like ethanol gas but it does have a lower boiling point than regular gas and I have an older tractor that I have had trouble with similar to your problem when we used ethanol in it. The gas tank is mounted directly above the engine and the ethanol would actually boil in the gas tank and the engine acted like it was having vapor lock. It didn't hurt the tractor but the problem went away with straight regular. It also had an updraft carburetor...............Sorry Charlie, I like ethanol but it can cause some problems in older carbureted vehicles.

Hey Uncle Ed! You have been a supporter of that garbage gas Ethanol in the past so I am a little surprised that you have admitted that Ethanol does cause problems in older vehicles. Unlike Charlie, at least you are willing to admit Ethanol's short comings and I'm glad to see that you are being direct with your experiences on using Ethanol in older vehicles.

I have a friend of mine that has a beautifully restored 1944 John Deere tractor and he absolutely refuses to use Ethanol in his tractor because of the continued vapor locking problems as we are discussing here. Other guys that I know in the Antique Tractor Club do the same as well because of the vapor locking issues with their vintage tractors.

Many of us have had problems with that junk gas, especially vapor locking in the older rigs with carburetors, so it sounds like we can now add you to the list as one that has had some issues with Ethanol also.

Yep JYD, I will agree that it is not perfect and it can vapor lock more easily, is hard on old rubber parts not designed for it and it also can loosen up varnish in a dirty old system. That being said I think it is a great fuel for fuel injected vehicles which most cars on the road are these days. The only rubber part on my vintage Chevys is the fuel pump diaphragm so I'm not too worried about using it in them but prefer to use regular in them if it is available. I did have a Chrysler Lebaron 4 cyl. that would get to running rough on regular and a tank of ethanol and it would smooth right out, that is when I switched to ethanol in my modern vehicles.

Thanks for the replies.
The only gas available to me is unfortunately ethanol.
I was thinking vapor lock, but had not thought about the lower boiling point of alcohol.

My plugs are set at 40, not what I stated above.
Timing is set at 18 btdc, points are at 18 but the motor likes it when I run with the spark retarded a bit. I am guessing it is retarded about half way. Maybe to about 14-15 degrees BTDC?
May have to try a 3/8" thick phenolic spacer between the carb base and the manifold. Any thoughts about this?
Thanks,
Dale

Hello akdale,
When the engine acts up next time, see if the choke will have any effect to get it running smoothly again. That should verify that there is indeed a fuel starvation issue. A spacer sounds like a good idea. Maybe a piece of reflective insulation between block and carb could be tried for a test also. Let us know how it works out for you.

Will do. Thanks.