The Stovebolt Site Forums The Shop Area Engine Shop Carburetor Ghostie.......

I have just rebuilt my Carter W-1 and it runs beautifully - until I run the truck for an extended period at highway speed. Then the engine idles rather high at stop signs and so forth. I had a Rochester that used to do the same thing. I put a second Rochester on the truck and never had a problem with it. I decided to put the old original Carter back on for nostalgia and here we go again! Runs perfectly until I drive it in the above mentioned way. Might this be a sticking throttle valve? Very curious...........
I appreciate any suggestions on this little problem.

Thanks,
littlebuddie

Is your throttle linkage returning all the way to the stop when this happens? If not check for obstructions or a weak return spring. I had a similar problem that turned out to be an improperly adjusted hand throttle that was keeping it from returning to idle.

Do you still have the phenolic spacer in between the intake manifold and the carb? You might be experiencing heat soak. How does it start if you shut it off hot and try to start it right back up?

I have seen old carburetors that had worn throttle shafts and worn throttle plates that would do this same thing. After being open for some time, the shaft/throttle plate would wiggle to one side in the casting, and when the accelerator was released, it would hang open slightly.

Stuart

Thanks for all of your replies. Good thought Tiny however I have not had the hand throttle connected for many years. The return spring seems fine and looking down the venturi when the engine is cool, I don't see that the throttle plate is stuck open, though it does have a little 1mm or less gap when shut. 4ontheFloor , I still have the phenolic spacer. I have not tried to shut it off and start it up again when it is hot so I will have to try that. It's just fine on a cold start though. atomarc , I have thought about the throttle plate hanging and the throttle shaft is undoubtedly worn to some degree from age but I have gently stomped the gas pedal to see if that would kick it down but no it doesn't. Thanks for the ideas and I'll keep checking these things.

littlebuddie

I would suggest that you hook up the hand throttle and adjust the idle with the engine warm and use the hand throttle to increase the cold idle; works for me.

Hmmmmm, very interesting idea Baldy ..............
I've got to get a new throttle inner wire, old one is broken off too short. Can that wire be replaced so I can keep the original knob? Kinda looks like not :confused:

littlebuddie

If your 48 is like my 38 the wire is stuck inside a metal shaft that is connected to the knob. The end of the metal shaft is smashed onto the wire to hold it. It's possible to tap around the end of the shaft to open it enough to get the wire out. Be patient and there's no guarantee that this will work without breaking the knob shaft. FYI the end of the wire that's stuck in the shaft will have the end smashed to spread it a bit so it doesn't pull out easily. If a repop would suit you I believe The Filling Station and Chevs of the 40s both sell repop knobs. I believe The Filling Station has a better selection covering more years. I may be full of do-do but I think that's right.

Just asking, but is it possible if the carb is not the problem. Could it be a small vacuum leak opening up somewhere with the thermal expansion of a hot engine?

Thanks for the anatomy of the hand throttle Tiny , I wasn't quite ready to do an autopsy on it because it looked like a transplant could be tricky. I may try to get it apart and look. At his point, I can't make it more nonfunctional than it already is. That's another good point beltfed , tomorrow I'll go over the area with a can of bump spray and see if I can get it to hiccup.
Thank You All!
littlebuddie

I would concur with Baldy.

I cannot think of a single manual choke carburetor that is supposed to have the idle adjusted on a cold engine (although someone will probably find one just to prove me wrong ). This is also generally true with auto choke carburetors.

When adjusting the idle on a carburetor, start the engine and run at a fast idle until the engine is warmed to NORMAL OPERATING TEMPERATURE; then adjust the curb idle speed.

Fuel is not vaporised as efficiently in a cold engine; REQUIRING additional mixture to be present to maintain a "cold" idle. The idle circuit does not change from cold to hot; thus the extra mixture when hot (if set cold) would cause a higher engine RPM when hot.

Typically, 2 methods are employed to maintain a good idle when cold: (A) increasing the throttle opening (thus adding some fuel though the idle transition circuit) as suggested by Baldy; and (B), adding additional fuel through the use of the hand choke.

Since the atomization of fuel will increase on a cold engine with an increase in the ambient temperature, it may sometimes be difficult to obtain a "perfect" setting in temperatures of 70 degrees F or more. But a good rule of thumb would be that if an engine equiped with a manual choke carb IDLES WELL ON A COLD ENGINE WITH THE AMBIENT BELOW 50 DEGREES F. AND NO CHOKE OR HAND THROTTLE, then the idle is adjusted TOO RICH or too high.

Jon.

Carb passed the vacuum leak test. Carbking and Baldy, I will reorganize and try your suggestion next. Makes a great deal of sense. Thank's everyone for your great help!

littlebuddie