Model A is "bucking." Why dat?

700rpm

700rpm

Well-known member
I recently put a rebuilt engine in my 29 Tudor. The engine was balanced and the flywheel was lightened (I think by 20#, but I can't remember for sure). Now, however, when decelerating on a downhill slope, the car wants to buck, like my 55 Chevy use to do when the four-barrel would load up. But I don't have a four-barrel on my sedan. It's all stock, except for the lightening and balancing. It's timed to a gnat's eyebrow, so I don't think that's it. It runs fine as long as it's got a load on it. It's only on the deceleration.

Any idees?
 
:confused:Carb maybe not functioning properly,Jets need cleaning. Tight manifold bolts,carb tight to manifold,air leaks. Proper rotor/cap gap all four?
 
Last edited:
How is your choke rod setting? Try turning the choke rod closed when this bucking occurs. It sounds like a too rich mixture or the points are set too close. Points should be .018-.022 inch gap.
 
:rolleyes: Does all of the above 'advice' REALLY apply to a Model A that is "decelerating on a downhill slope"?? :eek:

I am truly baffled as to how incorrect coil polarity, faulty point setting, or a plugged carburetor jets would affect an engine that is coasting on a downhill slope to the point where it would cause the whole car to buck! Could y'all please explain this further to me??:confused:

(Remember he said it runs great under a load.)


.
 
Like HE SAID!!!! its acting like his 55 chevy carb loading up! Bucking must mean different things to different people! He didn't say the whole car was bucking! All the above is tring to help this person out with ideas..
 
Had a simular problem with my Dakota. Turned out a new clutch was the answer. With the replacement engine and new clutch all is well now. Rod
 
The hole for fuel pickup is in rear side of the float bowel chamber.

If the float level is set to low the fuel may be running away from the port thus causing a lean fuel problem and causing "bucking", or missing.

I bet you have a stalling at stop signs problem too.

Just my W.A.G. at the problem
 
:confused:does "bucking" mean misfiring? or back popple via exhaust? or spitting back via carb? or is the whole car skittering and jumping about on its suspension? or whaat? pleeease?
 
Gary WA said:
Like HE SAID!!!! its acting like his 55 chevy carb loading up! Bucking must mean different things to different people! He didn't say the whole car was bucking! All the above is tring to help this person out with ideas..
Click to expand...

Yes Gary, I will agree with you that he did NOT say the "whole car" however he DID say the car. Here is his quote: "Now, however, when decelerating on a downhill slope, the car wants to buck, like my 55 Chevy use to do when the four-barrel would load up." The "car" is more than just the engine, ....and if you don't mind, please explain to us how when the engine is not under power, an improper rotor gap, or loose manifold, or plugged carburetor jet could cause this. I am not necessarily saying you are wrong, --however I would like to understand your theory on how these items could cause this problem.
 
700rpm said:
I recently put a rebuilt engine in my 29 Tudor. The engine was balanced and the flywheel was lightened (I think by 20#, but I can't remember for sure). Now, however, when decelerating on a downhill slope, the car wants to buck, like my 55 Chevy use to do when the four-barrel would load up. But I don't have a four-barrel on my sedan. It's all stock, except for the lightening and balancing. It's timed to a gnat's eyebrow, so I don't think that's it. It runs fine as long as it's got a load on it. It's only on the deceleration.

Any idees?
Click to expand...
IMO, Jerry in Shasta has come closest to defining your problem. "Bucking" (whatever you want to call it) occurs with intermittant fuel or spark delivery. Since you state that problem occurs "WHEN DECELERATING DOWNHILL"...this somewhat narrows your problem to FUEL delivery being intermittant..ergo..Jerry's evaluation(and mine):rolleyes:.
 
hardtimes said:
IMO, Jerry in Shasta has come closest to defining your problem. "Bucking" (whatever you want to call it) occurs with intermittant fuel or spark delivery. Since you state that problem occurs "WHEN DECELERATING DOWNHILL"...this somewhat narrows your problem to FUEL delivery being intermittant..ergo..Jerry's evaluation(and mine):rolleyes:.
Click to expand...

I could understand your reasoning if it weren't for the fact that 700rpm says that the problem only occurs during deceleration and does not occur when the engine is under a load. Under a load would cause the engine to use more fuel (than during deceleration) so if there was a fuel/spark delivery problem, why wouldn't this problem be happening during the "under load" driving?

.
 
Re: Model A is "bucking." Why dat? My theory!!!

:rolleyes:The automobile feeds on a liquid diet of gasoline.If it overeats-operates on an over-rich mixture--it becomes sluggish in its performance and is feverish.Isn't that most human? Starve your motor-operate it on a lean mixture- and it becomes feeble and faltering in its delivery of power. It must be properly fed-it's diet must be pure and correctly balanced,otherwise,like living folk, it looses its pep and its punch and its dependability.Perhaps you never have realized that the motor has a highly developed nervous system. The ignition distributor is the brain of the engine- it signals its various commands to the different cylinders even as the human brain signals our muscles for action. The network of ignition wiring corresponds to the tingling nerves which play such an important part in controlling human endeavor.If the delicate tissues composing the human brain are seriously disturbed,complete lapse of activity is the result. Less serious disturbances at the center of control or derangements effecting the nervous system may cause partial paralysis or irregular functioning. SO with the engines nervous system . Some serious derangement of the distributor may cause a "DEAD" motor.Less serious maladies such as dirty points,plugs,bad wiring,loose connections,chafed insulation and like disorders cause the Engine to MISS AND LAG;to act much as a person beset with some nervous ailment. And that is my theory and reasoning for my answer to the questions. Keep On "A'ing. Gary www.whidbeymodelaclub.com..
 
Gentlemen, thank you for all your theories. I wish I could be more descriptive of the problem. I can add that when it is bucking, if I give it some gas so as to accelerate the bucking stops. Or if I disengage the clutch and just coast it seems to idle OK. It idles fine when coming to a stop (I've had the condition of it quitting when coming to a stop, where I had to operate the hand throttle to keep it from stalling. I reset my float and checked my jets and that is no longer a problem.) We were careful to align the flywheel when we reassembled the engine, though we did put in a new pressure plate. Again, though, the clutch works very smoothly when shifting, shifts gears cleanly, and doesn't chatter. I should say that I have been playing with these cars for almost 50 years, so I have some experience with A's, but have never encountered this condition before. I too suspect a fuel problem, and I have another good carb I could try in it. Maybe I can get to that tomorrow. I'll let y'all know if that changes anything. In the meantime, though, I'm still open to suggestions.
 
I had a similar problem in the woody. After changing the entire engine, carb, dist, manifold with a set up that was previously proven to run well in my sedan, the problem persisted. The station wagon had a BW overdrive, which I suspected was contributing to the problem. Later on, during a ground up restoration, I found the splines in the drive shaft collar to the BW were worn. I theorized that with the excessive wear, even the slightest hickup in the engine from either a too lean cough when cold or a too rich loping effect from loading up on a long down grade was ricocheting back and forth through the excess drive shaft slop. Having the splines and collars rebuilt solved most of the bucking. There is still some occasional light bucking on long down hill grades. I suspect there is wear inside the BW as a result of the bucking from the worn splines. It could be your U joint and the drive shaft splines are worn too much.
 
:confused:Have you looked your zenith over for cracks, and sized all the jets?proper gaskets on the jets>none on idle.downhill slope>rust in the tank moving ! Just some more thinking!!!with the years of experience you have ! same here @ 60 we had a car the same type scenerio did all the basic things and it was spark plugs!
 
Last edited:
You must log in or register to reply here.
Back
Top