Title says it all. I go to start it up and the rpms immediately go out of control, extremely high, and I have to immediately turn it off otherwise she will blow. I have tried several times on different days with the same results. I assume this is internal to the carb because it does not appear to have any throttle cable or linkage sticking issues. This is a manual choke also and no visual issues there either. It is fitted with an old style 2 barrel Holley. My plan is to remove the carb and clean it. Can anyone suggest some troubleshooting for me or suggest things to check? Maybe I am barking up the wrong tree thinking it is a fuel issue?
I’ve had a vacuum leak at the carb base that would make it idle crazy high. Finally figured it out and it was one carb to manifold bolt lose. Cranked it down and it fixed it all
Thanks! I’ll investigate that. Sure would be an easy fix. These aren’t just high rpms, it is screaming high. I don’t have the chance to even look at the gauge because I need to shut her down before it blows. They climb very fast and extremely high. Surprised it hasn’t blown yet. Any other ideas or suggestions guys?
Well it has to be getting air from somewhere to do this. Is your carb closed? Did you at least remove the aircleaner and look? Otherwise it would have to be a hell of a vacume leak and the air would be coming from below the fuel dump tubes.
Carb isn’t closed. Nothing visually seems wrong. Yes air cleaner is off while I am inspecting. I’m not near it now, so maybe it is loose on the intake or air coming in from the gasket. I’ll be checking that soon. It does sound like the consensus for you guys is that it is a carb issue and more than likely too much air. That is helpful for sure. I was thinking too much fuel.
Your throttle plates should be closed. It sounds as though they are hanging open for some reason. You need to understand the foot feed controls the air intake. Not fuel. The air passing the fuel dumps pull in gas To much fuel would flood the motor and it would not start.
How did you adapt the Holley? Throttle plates might be hanging up on whatever adapter you used. I'd be looking into a two single setup as apposed to the single two barrel.
I had a few minutes to look today and the carb is tight on the manifold and I didn’t see any cracks in the carb or manifold where air could be coming in. I think it might be the throttle plates being stuck open. It’s real dark in the shed and I need to investigate this further with better lighting.
Maybe do a compression test of the engine. An engine with really low compression (worn out piston rings) will idle very high.
Are you pulling the choke cable all the way out? Have you tried pushing it back in as soon as it starts to get it off the fast idle cam? May be as simple as adjusting the fast idle screw on the right side of carb. If you aren't using the choke to start it.... Yeah, you have throttle open too far or a big vacuum leak.
Probably a vacuum leak somewhere, spray carb cleaner while running around mating surfaces like where the carb meets the manifold, manifold meets the head. If the engine changes when you spray, you've found your leak.
I am in agreement that something is preventing the throttle plates from closing. Either the throttle plate itself is catching on something and preventing full closure or your pedal linkage is incorrectly adjusted/just plain too short and isn't allowing full closure. Remove air breather, hold the choke open, and look straight down into the carb. You will be able to see the throttle plate deep in the hole. It should appear to be completely closed/horizontal. Grab the linkage and open/close the throttle and watch stuff move so you are absolutely sure you are looking at the correct part of the carb. Use a flashlight not an open flame/cigarette lighter to see into the carb You could also remove the carb from the engine completely and verify your carb is able to close fully on its own (post pics if unsure) without the manifold or the linkage attached. Once you are positive it is able to close fully, hold the choke open and look inside to see the position of the throttle plate (it will appear to be completely closed). Bolt it back on the engine, manually move the throttle linkage while looking into the carb with the choke plate open ... is it still appearing to fully close or is it partially open? If not able to close fully, determine why it won't close/what it is hitting and remove/file away the obstruction while keeping the filings out of the engine. It could be a vacuum leak but based on your description of instant full throttle, I am guessing it is more likely a throttle linkage/carb issue. I would not start the engine again until you are positive the throttle plates are closing.
For some reason unknown to me, Chrysler specified many carbs in the '30's, '40's, and '50's to be designed with the throttle plate(s) about half open if sitting on a workbench (or on an engine). Just one of the questions I wish I had asked my mentor at Carter 40 years ago. Chrysler depended on the throttle return spring to close the throttle. How is your spring? If I had one of those earlier Chryslers, I would be running TWO throttle return springs. EDIT: This post is not entirely applicable to the thread (I just read that you are using a Holley), but I would still check the condition of your throttle return spring. Jon.
Very embarrassing for me to say this but I thought I owed the solution to you guys. This was user error. Nothing mechanically wrong. Long story short, this engine is in a tractor that i pull with, and the throttle is a hand lever. Well, after sitting for 8 months I guess I forgot forward lever meant full throttle. This year when I took it out of storage, I tried starting it with the throttle wide open, when I thought forward was for closed, or close to it (idle).
Now that’s owning up to the problem. I’d been following along. Thanks for coming back and filling us in.
It takes a real man to own up to his mistakes even though all of us make hem at times! Edit: I made a mistake in the spelling of "them"! LOL
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