Troubleshooting advice

D

Dewshan

Member
Hello! Working on getting a 1931 Victoria back on the road. Engine was rebuilt but i dont know much about who did it etc. It does start but runs weak and sputters when you try to rev it. Spark is good, timing is good- have done it many times with nurex wrench. Known working carb was swapped over - did not fix problem. After pulling spark plugs i believe 4th cylinder is not firing- it was perfectly clean. What does everyone think the next thing to check would be? Timing gear to make sure it is indexed correctly. Or valve clearances? I have removed valve cover but have not checked anything yet. Third choice would be take the head off to investigate i guess? I only want to do this as a last resort. I have compression on all cylinders.
 
Sat for a long time maybe 12years or so. Has new sparkplugs. Moved spark plugs around . #4 always perfectly clean. Has spark
 
did you do a compression test on # 4? If no compression I would pull side cover and see if valves are opening and closing.
 
Is the distributor body new? Its rare, but the arm maybe cracked. If you are getting air and fuel, it has to be spark.
 
Its old ...i am getting spark to #4 when i gap the copper strip. I also have a cut away cap that lets you see spark going to the 4 leads in distributor looks to be working ok. I guess i could pull it and check it out. I have the puller for that.
 
I bet your problem is an intake air leak. Do the trick with starting fluid before you start taking things apart. Goo luck.
 
Sticking valves is a high probability. Recommend dripping Marvel Mystery Oil directly into the carb intake at elevated rpm and also puting MMO in the fuel tank (4 oz. for full tank).
 
You've said you have compression on all 4 cylinders but have you done an actual compression test? If so what are the numbers?
 
I would do the easy things first. Change the condenser. Short each plug in turn with the engine running and confirm it is the only cylinder that is missing. Change the distributer body, it could be cracked. Run the car in the garage in the dark and see if there is any, sparking where it shouldn't (distributer body, coil, down the spark plug to ground). Set points at 0.020) Good luck, Ed
 
I second what Ed said.

It is really hard to diagnose issues over the internet. But it has to be either fuel or ignition. The plugs can be firing during idle but fail when the throttle is opened because of increased pressure. The spark has to overcome the increased pressure. If the compression numbers are good and no vacuum leaks, I would concentrate on the ignition first.

Try to borrow a known good distributor and coil. The symptoms sound like a bad condenser.

You can check the valve timing by bringing the engine to top dead center by using the timing pin then check to see if the valves in number 4 cylinder are off their seats by an equal amount. If they are then the cam timing is good. If not then the cam timing is bad. A fiber optic scope can be used to view the valves or a dental mirror and flash light. But do the ignition swap first.
 
I agree with post #13 and would also dribble SEAFOAM into the carburetor when running at an increased throttle. Do this ONLY in open area as you will be getting a lot of smoke out the exhaust!
 
nkaminar said:
I second what Ed said.


You can check the valve timing by bringing the engine to top dead center by using the timing pin then check to see if the valves in number 4 cylinder are off their seats by an equal amount. If they are then the cam timing is good. If not then the cam timing is bad. A fiber optic scope can be used to view the valves or a dental mirror and flash light. But do the ignition swap first.
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Ok i have it in what the timing gear thinks is tdc. Both valves have no gap for a feeler gauge on cyl 4. In tdc these valves have space for the guage. From front to back. 1,2,4,and 6. Valves 3,5,7,8 no room for feeler gauge.
 
Dewshan said:
Ok i have it in what the timing gear thinks is tdc. Both valves have no gap for a feeler gauge on cyl 4. In tdc these valves have space for the guage. From front to back. 1,2,4,and 6. Valves 3,5,7,8 no room for feeler gauge.
Click to expand...

So it sounds like you have the valve cover off and all valves are moving? What are the numbers on your compression test?

Have you checked for carbon arcing as suggested in post #13.
 
Your cam is timed correctly. If not, one of the valves on cylinder 4 would have a gap where you could stick a feeler gauge. I had initially intended to peek into the spark plug hole, but your method is also correct.
 
Yes all valves are moving... compression test had it in 50s all cylinders but it wasnt super accurate my tester not the best for large spark plug holes. Was just checking for compression. I dont think this engine was broken in much after rebuild. New coil, changed condenser, have looked at it running in the dark and did not see arcing. In tdc on the timing gear i can not get a feeler gauge in either valve on cyl 4. Is this the problem?
 
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