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09-23-2021, 07:50 PM | #1 |
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Model A dies with throttle open
Hey guys, my Model A recently started - seemingly without rhyme or reason - getting into a "mood" where it will idle forever just fine, but if you even touch the throttle it immediately dies. Eventually it starts acting right again, like a switch was flipped, but nothing specific seems to cause it.
I recently had to replace the head gasket. I am currently running without a muffler (the exhaust manifold is about to be replaced with a custom unit and I didn't feel like putting the muffler back on just to immediately have to remove it a couple weeks later). Here is some video. https://www.youtube.com/watch?v=f00E_w28000 Shortly after this video, I was able to tease the RPM up by gently pumping the throttle. It backfired through the carburetor and then began acting normally again: https://www.youtube.com/watch?v=6oo9soVn1SU Any input is appreciated. |
09-23-2021, 08:01 PM | #2 |
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Re: Model A dies with throttle open
Sounds like a manifold leak. Take an LP torch, unlit, and direct the gas around the manifold gasket area while idling the engine. You'll hear the RPM increase if you have a leak.
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09-23-2021, 08:10 PM | #3 | |
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Re: Model A dies with throttle open
Quote:
when it backfired through the carb it must have cleaned some some crap from a jet inside the carb. pull the carb off and make sure it is clean and assembled correctly. backfire through the carb could be too lean. flames out your exhaust could be retarded timing. ou |
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09-23-2021, 08:14 PM | #4 | ||
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Re: Model A dies with throttle open
Quote:
Quote:
As for the flames, it breathes fire seemingly no matter what I do with the timing. I was concerned about it at first but have been told it's pretty normal. |
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09-23-2021, 08:30 PM | #5 |
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Re: Model A dies with throttle open
the second video doesn't sound too bad can you put the pipe back on and drive it?
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09-23-2021, 08:36 PM | #6 |
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Re: Model A dies with throttle open
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09-23-2021, 08:37 PM | #7 | ||
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Re: Model A dies with throttle open
Quote:
The popping and cackling when revving down gets lots of mixed reactions from neighbors haha. Quote:
I should note it wasn't doing this before the head gasket replacement, but I did a lot of other little stuff to the engine while that was ongoing - I had the manifolds completely off, rebuilt the distributor, rewired the ignition, replaced the ignition coil, etc... so it's hard to point at any specific thing as a possible culprit. Manifold gasket leak makes sense to me though. It is hard to troubleshoot since this is pretty intermittent and I still don't know what's causing it or making it stop. I thought I had fixed it for good a couple days ago but it just decided to do it again. I was fortunate that this time it did it in the garage and not on the road since I was able to get video. Last edited by trevorsworth; 09-23-2021 at 09:04 PM. |
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09-23-2021, 09:29 PM | #8 |
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Re: Model A dies with throttle open
Two things.
Have you taken the carburettor apart? If so, make sure the venturi is in there and not somewhere on your workbench. You mentioned you were able to get the revs up by pumping the accelerator. Pumping the Model A accelerator does nothing - there is no pump on it. You would probably have done better by easing it open.
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09-23-2021, 09:43 PM | #9 | |
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Re: Model A dies with throttle open
Quote:
Yes, I do know there's not a pump in the A carburetor. Using the hand throttle to slowly open it would certainly have worked better but that's not what I did. |
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09-24-2021, 07:33 AM | #10 |
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Re: Model A dies with throttle open
Next time it happens try loosening the gas cap. Sometimes the vents can get plugged or the wrong cap can get put on and suction will build up in the gas tank and restrict gas flow.
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A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past. |
09-24-2021, 07:36 AM | #11 |
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Re: Model A dies with throttle open
I WOULD SWAP CARBS JUST FOR THE..............
was having a similar problem yesterday, swapped out carb and running terrific. |
09-24-2021, 09:50 AM | #12 |
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Re: Model A dies with throttle open
Yep. Seems lean. Either vacuum leak or lean carburetor condition.
These carburetors are as simple as they get, easy to fix. |
09-24-2021, 09:53 AM | #13 |
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Re: Model A dies with throttle open
It runs on the idle system but dies on the transition to high speed. I'm thinking the cap or main jets are clogged. Take apart carb and clean the jets and passages.
http://modelabasics.com/carb%20basics%202.htm |
09-24-2021, 10:34 AM | #14 |
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Re: Model A dies with throttle open
I have exactly the same problem as trevorsworth, except that it's continous on my car.
The engine idles nicely after warming up (choke off and GAV completely closed), but as soon as I push the accelerator, the revs drop and you can hear it sucking in air without igniting the mixture. The engine has almost no power, while it ran just fine two years ago. (when it was last driven) If I slowly increase the gas through the hand lever, I can get the revs up, but only to about 1.5 - 2k rpm (estimated), after that the same as above happens. Now, if I clog up 1/2 to 3/4 of the air intake of the carb with my hand, the revs climb fast and the motor seems to have more power. Am I right in assuming that it's running WAY too lean and I either have a) dirt / gummed up fuel in my carb or b) a partially clogged up jet ? Can the float cause problems like that too? EDIT: I forgot, there is a steady fuel stream through the gas line and I had the fuel cap removed for testing, so it's not most likely not a problem with not getting enough fuel to the carb. Last edited by bavArian; 09-24-2021 at 11:04 AM. |
09-24-2021, 11:32 AM | #15 | |
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Re: Model A dies with throttle open
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09-24-2021, 11:58 AM | #16 |
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Re: Model A dies with throttle open
Turning the GAV open 1 turn seems to not change much. I'll try tomorrow with more than 1 revolution, maybe that will fix it? (I doubt it though)
If that doesn't help, I'll check for vacuum leaks and in case I don't find any will probably disassemble the carb and check the GAV valve seat and the passageways. Using brake cleaner is probably not the recommended method with the exhaust manifold being on the same side as the intake? Clean Water with a pump sprayer or culinary torch? |
09-24-2021, 06:43 PM | #17 | |
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Re: Model A dies with throttle open
Quote:
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09-25-2021, 01:02 PM | #18 |
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Re: Model A dies with throttle open
Update:
Chuck was right! Found a vacuum leak today, the throttle shaft has some play. Spraying brake cleaner onto the shaft helped, the engine ran better but still not at all nice. After taking the carb apart I found that the float chamber was surprisingly clean, but the entire intake area was quite dirty. Also the main jet was completely clogged from what seemed to be gummed up gas, the cap jet was basically the same. So I took the carb off and disassembled it. To my surprise, it even came apart without much of a fight. I cleaned everything up, polished the venturi because the inner surface was quite rough (it's a die cast venturi), changed the gaskets for new ones and put the carb back into the car. What a change! The engine runs a lot better now, not perfect yet, but certainly way better than yesterday! It can even move on it's own now! Over the winter I'll install new throttle shaft bushings along with a new shaft and check the idle circuit (which runs fine atm) and the seat of the GAV-valve. Thanks a lot everyone! |
09-25-2021, 01:26 PM | #19 |
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Re: Model A dies with throttle open
Try lubing the throttle shaft with dialectic grease until you can fit a replacement shaft, or rebush the casting.
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09-25-2021, 02:34 PM | #20 |
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Re: Model A dies with throttle open
I already thought about using grease, but I'd guessed that it would liquify as soon as the engine is warmed up the first time?
The intake manifold becomes quite hot when the engine is running after all. Maybe high temperature grease will work? Anyone tried it? |
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