Sputter at high RPMs

DJ S

DJ S

Well-known member
My car is sputtering, or occasionally missing at high RPMs and under load. When it's sputtering, I've tried richening the mixture and pulling the choke but it doesn't help. I've cleaned the plugs, cleaned the points, readjusted point gap, readjusted timing, change the distributor body, change the rotor, changed the cap, and chased all the wires, checked all the wiring for 6 volts, and nothing. I tried all of these, one at a time, and absolutely nothing has helped. Could it be a weak valve spring as I just tore the engine down, cleaned it, put all new gaskets, lapped the valves and this problem didn't exist prior to this? Suggestions are greatly appreciated!!
 
Did you check valve clearance ? after doing valve job. ? Seen weak points spring, what revs is it missing at , ??
 
Model A's, you need to understand and use the spark lever. The spark needs to be adjusted for speed and load. Also sounds like a fuel issue maybe too, not enough flow. Do you have an added filter between the sediment bowl and carb?
 
Valve clearances were all over the place. Non-adjustable tappets, so I couldn't do anything about it. The block is no good, long story, so I didn't want to sink too much money into it. I just need to get it to last me this year. No added filtee, good fuel flow, this doesn't appeae to be a fuel flow or carb problem, we also tried a different carb. I couldn't give you a number but the revs are quite high, nearing the end I would say.
 
Do you know about what RPM your in? I do Mfg a better distributor cam for the Model A-B It will give you more dwell time about 9 more degrees, that is if it is an ignition problem.
 
I read your post a little closer I see you had the engine apart do you have split valve guides or the one piece guides, just thinking if there the split ones you could have a valve sticking the split ones can be a problem with a little miss alignment and if you had them out and reinstalled a valve could be sticking? just a thought.
 
yes judging by what you said a few posts up on the valves and adjustment I would say you have a valve problem. If you don't want to make that right than you may as well just run it and deal with the problem. just my 2 cent worth.
Have fun with it this summer and rebuild in winter.
 
So let me just make some clarifications on the situation concerning the valves. This engine has split valve guides and non-adjustable tappets. I removed the entire valve train for inspection. I noticed that #1 exhaust was severly pitted and worn, so I replaced it. I ensured to achieve proper valve clearance by grinding down the valve stem (.013"). This valve, however was tight in the valve guide but with some oil and movement, it began move easier, still not overly easy but it could be moved my hand. The other valves had far more clearance than they needed, which is why I couldn't make any adjustments. I reinstalled all the valves lapped them and reinstalled all the old valve springs. The reason I didn't overhaul the entire valve train is because this motor has several cracks on the exterior water jacket that can't be repaired because the remaining metal is too thin. So I used high-temp JB Weld to patch them for now just to get through this year, while rebuildig a motor over the summer, to be installed this coming winter.
 
With the car parked rev up the motor and short out the plugs to see if you can find the clylinder thats missing. It's probably #1 with the tight vavle, remove the tight valve spring and with some polishing cloth polish the stem. Use some mmo or penetrating oil and spin the valve stem in place, I had a tight valve stem and was able to free it up some. I think I use a heavy rubber band wrapped around the stem twice spinning it like trying to start a fire caveman style. The more it run the better it got, any way might be worth a try. Don't tell anyone what I did when I didn't have much green stuff:-)
You might be able to slip a lengh of rubber fuel hose over the stem and spin the valve with a drill, with the spring off
 
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DJ S said:
So let me just make some clarifications on the situation concerning the valves. This engine has split valve guides and non-adjustable tappets. I removed the entire valve train for inspection. I noticed that #1 exhaust was severly pitted and worn, so I replaced it. I ensured to achieve proper valve clearance by grinding down the valve stem (.013"). This valve, however was tight in the valve guide but with some oil and movement, it began move easier, still not overly easy but it could be moved my hand. The other valves had far more clearance than they needed, which is why I couldn't make any adjustments. I reinstalled all the valves lapped them and reinstalled all the old valve springs. The reason I didn't overhaul the entire valve train is because this motor has several cracks on the exterior water jacket that can't be repaired because the remaining metal is too thin. So I used high-temp JB Weld to patch them for now just to get through this year, while rebuildig a motor over the summer, to be installed this coming winter.
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Hey DJ,
'and reinstalled the old valve springs'....
If you did not make sure that the OLD valve springs were/are all good (i.e.- via testing for equal seat pressure), there is your problem, IMO, especially at high speed, as you describe !

BTW...I think that you confuse, when you say that 'they have tooo much clearance and you cannot adjust that'. Why not ?
You can and maybe should have ground the seats while measuring clearance reduction. Especially , if you do not intend long time use of this engine due to other problems.

Excessive clearances plus any weak springs will not be good at high rpms, IMO.
 
Bill Stipe said:
yes judging by what you said a few posts up on the valves and adjustment I would say you have a valve problem. If you don't want to make that right than you may as well just run it and deal with the problem. just my 2 cent worth.
Have fun with it this summer and rebuild in winter.
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As with most threads after getting more of the story i agree.
 
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