Classic/Antique Car Repair/backfire

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Question
My 1929 Model A lost water, started to backfire and wouldn't run.  After we took the head off, We found a cracked valve.  Replaced all valves, springs and guides. Sent head to machine shop. Installed leakless water pump.  Engine now idles ok but is rough under load and backfires.  Can't drive as it has no power. Changed condenser, timed, did compression test, rebuilt carb, etc.  AM wondering if this could be a case where one or two of the rings have failed and I need to install new rings.  Or if their are other problems.  I don't want a new engine unless there is no choice. My mechanic owns his own Model A and is no stranger to this but can't get it to run.

Answer
The only thing that comes to mind are the points, but I'm sure you checked those out.  If it has good compression, is timed properly, clean plugs, gas, good carb., idles good, ????? That's a tough one.  I recently ran into a car where the point arm spring broke and there was very little force against the cam.  The point arm would float above idle.  Pull it back with your finger and make sure it is not weak or broken.  If that does not do it, then put new points in. I don't think the coil is the prob.  There is a higher probability that a new condenser is bad, than a good condenser going bad.  I put in a new one once, then tried to fix everything else, until an old timer flipped the points and said the cond. was bad.  The A can cook the cond. from the manifold heat, but not very often. Try it with new points and the old condenser, after you know that the arm spring is good.  Let me know what you find out.  jack

I thought of two more things you might check.  If you put on a new gas line, make sure you did not place the ferrule too far from the end going into the carb.  If the tube extends too far into the carb, it will hit the screen and block flow into the bowl.  It will idle, but there will not be enough gas under load.
The other thing is to open up your mixture at the choke rod and see if that clears things up.  If it does, then you need to take another look at the carb.  jack

Classic/Antique Car Repair

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jack bahm

Expertise

Only repair type questions on the 1928-1931 Ford Model A.

Experience

Owned one when I was 15 yrs old, and now have owned 5. Still own and play with 2 of them.

Organizations
Oakleaf region of MARC. Model A Restorers Club. I have put several Model A videos on the Oakleaf site that may be of help. Things like how to start the A, how to Time it, how to troubleshoot it.. Go to oakleafregion.org and you will find them. Also, go to youtube.com and search for "jackbahm" and you will find over a hundred videos. Many about the Model A and our outings. jack

Publications
"More than you need to know about cars." Just a small book for Car Nuts. Blurb.com "Model A Ford Tips and Hints" Blurb.com "Get A Horse" (What to do when Henry's Lady quits on you.) Blurb.com or Snyder's Antique Parts. "Engineering Stuff" (For the Kid who likes to take things apart and get them back together). Kids book for ages 10-16. Blurb.com 2012 Many Model A movies that can be found on youtube.com/jackbahm

Education/Credentials
BSME LSU, 1958, Masters of automotive engineering from the Chrysler Institute of engineering, 1960, MBA Mich State, 1976. Worked as an engineer at Chrysler from 1958 to the end of 1991.

Awards and Honors
Two patents while working in auto industry. Go to this site for my Model A videos. http://www.youtube.com/playlist?list=PLhL36Rc6o5MI4aqHM-yfhqcze8Qq6aS9s

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