VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1912-1928 carb

after tearing into my 1927 carb,cleaning and putting back together i still have the same problem. will not run unless the choke is used. runs fine if i use 3-4ths choke. any ideas? thanks in advance

Could be that you are loseing vacuum at the intake or around it the choke allows the engine to develope more vacuum in the venturi. Of course one of the jets could be stopped up nd restricting the fuel flow. Then who really knows till you do a systematic trouble shooting routine? Do you have full fuel flow into the carb, does the carb have a strainer on the input line?

Do you have that hot air tube hooked to the carburetor? If not you may not be vaporizing the gas completely. What that means is particulate gas is carried into the cylinders. Particles do not burn fast enough to help provide useable power, just carbon to foul spark plugs and coat the muffler and tail pipe. So additional gas is required thereby the use of the choke is needed to get enough gas vapor to make a fast enough burn.

Another factor is deterioration of the gasoline. As the lower boiling or higher vapor pressure components are eliminated from the tank the remaining gas does not vaporize enough. Or the gasoline oxidizes to form low volatile compounds again affecting the burn rate.

Then some of the higher non-volatile compounds coat parts in the carburetor reducing the metering orifices size producing a lean condition in the cylinders. Most carburetor cleaners have little to no affect on these gums and varnishes. Those that do may take multiple applications to clean out the contamination.

Which of the above is the problem will only be determined when the engine runs right.

Oh, almost forgot (not really but makes for better reading), some carburetor repairs in the past resulted in incorrect parts being installed or alteration of parts (I have run into both many times). Of course the solution is putting in the correct parts.

...It has to be something to do with chemistry, don't it?.....

Yup, nearly everything has something to do with chemistry. Even you Mr. Mack are a chemistry factory! If not, your not!

I had a similar problem with my RX-O and it turned out to be a plugged idle circuit. I had to get that tiny little screw out the top and clean out that passage. Worked great after that.

Jerry27, I had the same problem and changed the carb 3 times before I opened up the vacuum tank and found everything full of rust. I cleaned it all out and never had a problem again.

thanks to all who have helped to solve my idle problems. i will again be into my carb this week. after reading all suggestions i think my problem is with the idle circut. will let you know what i find