Recently replaced head gasket and appreciated the Forum's advice. Putting everything back in place, I noticed points were pitted/spiked pretty bad and off center between point block and arm. Replaced points with spare set and set the gap at 0.018. Set timing with Nu-Rex Timing Wrench with #1 cylinder at TDC by timing pin. Cleaned up the plugs and reset gaps to 0.035. Car starts easily when cold and idles smooth. Retorqued head gasket once cool to the touch. Took out for a spin but immediately started bucking with acceleration. Thought maybe it had not warmed up enough, tried again and the same bucking approximately 2 times per second when accelerating. What did I miss here?
Model A Bucking with Acceleration
- Thread starter TMB
- Start date
The Master Cylinder
Well-known member
Marshall V. Daut
Well-known member
Which carburetor do you have? A photo would help.
Marshall
Marshall
• Timing set fully retarded (lever up). My rotor is in the same position at TDC
• I have a Zenith-2 carburetor. Did not touch any settings on the carburetor. What would cause a carburetor problem?
• I don't have a timing light.
• I did try increasing gas via the GAV but did not make a difference
• I have a Zenith-2 carburetor. Did not touch any settings on the carburetor. What would cause a carburetor problem?
• I don't have a timing light.
• I did try increasing gas via the GAV but did not make a difference
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Big hammer
Well-known member
New points will wear the follower down very quickly ! When new I set the points at .022 , when my A starts to buck idling in low gear easing down the driveway, I clean the points by running rough cardboard from parts boxes through the points and set at .022 . Your new points may have oils on them ?!
Jim Brierley
Well-known member
Guy's, some advice from an olde phart. Timing won't cause an intermittent miss. Too retarded will cause low power and maybe over heating. Too advanced will cause detonation which will ruin the Babbitt in the rods. Turn on your brain when tinkering with your Model, and maybe have it on when driving too?
nkaminar
Well-known member
Could be ignition. If there is an intermittent connection or intermittent short somewhere. The condensor may be starting to fail. Go through the ignition system looking for problems using your multimeter while wiggling the wires and connections. Check the wire under the top plate in the distributor. Make sure the arm for the movable point is not close to the cam. (Some new points are defective and the arm will be close to the cam because the rubbing block is not correct.) Important: replace the high tension wire from the coil to the distributor top.
When idling or when the plugs are sitting in the air there is less voltage needed to jump the gap. When accelerating there is high pressure in the cylinders and more voltage is needed to jump the gap. So if there is some part of the ignition that is limiting the voltage, like the high tension wire, then the engine will idle well but miss when accelerating.
When idling or when the plugs are sitting in the air there is less voltage needed to jump the gap. When accelerating there is high pressure in the cylinders and more voltage is needed to jump the gap. So if there is some part of the ignition that is limiting the voltage, like the high tension wire, then the engine will idle well but miss when accelerating.
Bucking on acceleration update:
Finally got a chance to readjust timing according to Les Andrew's red book. Much better but still bucks in first gear unless I rev up the engine. Does not buck in 2nd or 3rd now so I am making progress. Later I will test going up a hill and see if that makes a difference. Thanks to all for all the guidance.
Finally got a chance to readjust timing according to Les Andrew's red book. Much better but still bucks in first gear unless I rev up the engine. Does not buck in 2nd or 3rd now so I am making progress. Later I will test going up a hill and see if that makes a difference. Thanks to all for all the guidance.
nkaminar - I did inspect the high tension wire. It is the braided type with the brass crimp ends. Looks relatively new however, it was not set up according to the instructions from Snyder's. Insulation was not cut back 1/4" and center wire soldered to the end. I did solder both ends then replaced the high tension wire. Not sure if that was a factor because I adjusted the timing at the same time. Thanks for all your advice.
Marshall V. Daut
Well-known member
If your starter switch has a fuse holder on it, by-pass it and see if that makes any difference. Some of the repo fuse holder blocks are poorly soldered and break down under power and high RPM demands. This affects the ignition and causes misfiring and bucking.
M.
M.
Will give this a try. Thanks
Ernie Vitucci
Well-known member
Good afternoon...Might also take a hold of the rotor and see if it is nice and solid or if it will move a bit as you try to wiggle it. if it wiggles...the bushings are warn and that means your ignition spark is not jumping 25 thousands at each of the four points...could be your problem....Could also be a crack in the Distributor Body...start the car in the garage at night and you might see a spark coming out of the distributor...Ernie in Arizona
I woiuld go back to Troubleshooting 101: if you have a new problem, what was the last thing you screwed around with before the problem occurred? From TMB's description there wasn't anything fuel-related, so I'd concentrate on the points replacement, adjustment and subsequent timing. 0.018" is on the tight side of adjustment, especially with a new set of points. As someone stated, the rub blocks on new points wears quickly, so you may now be down at say 0.016" or less.
But there's a clue: the initial statement was that the points were pitted and "off center between point block and arm" and that you replaced them with "spare set". There were some sets of replacement points that had the incorrect arm length (in fact, Snyders sells a replacement point block to compensate for this). These "bad" points sets were sold between 2017 and late 2023, according to the Snyder's website. If you bought the replacement points during that time then you may very well have a set of the bad points. There is really no workaround other than the replacement point block or a new set of proper points. Also, on your new points, recommend setting them around 0.022" and watching them as they wear.
But check your point gap first, I'd bet it's closed down from when you installed them even in that short of time running.
But there's a clue: the initial statement was that the points were pitted and "off center between point block and arm" and that you replaced them with "spare set". There were some sets of replacement points that had the incorrect arm length (in fact, Snyders sells a replacement point block to compensate for this). These "bad" points sets were sold between 2017 and late 2023, according to the Snyder's website. If you bought the replacement points during that time then you may very well have a set of the bad points. There is really no workaround other than the replacement point block or a new set of proper points. Also, on your new points, recommend setting them around 0.022" and watching them as they wear.
But check your point gap first, I'd bet it's closed down from when you installed them even in that short of time running.
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