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Engine backfires when increasing RPM - sticky valve?

Tiny
CAPNDAVY
  • MEMBER
  • RENAULT
It's a little 800cc Renault watercooled engine from the 1960's - a "Gordini" powered Caravelle. It has sat on the blocks for about 2 years with rare startups.
The engine starts quickly and idles pretty smoothly but increasing just a few hundred rpms and the engine starts popping and backfiring, I think thru the exhaust. I've changed the points, condenser and plugs, set timing. The dwell is supposed to be 57 but I can only set about 51 before I reach the end of the adjustment cam.
I was wondering if a valve is sticking and hoping there is a simple solution -- something about Marvel Mystery Oil or a similar product -- I can use before opening things up?
I understand there is a diagnostic involving removing the valve cover and observing the valve operation?
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Friday, May 26th, 2006 AT 7:07 AM

1 Reply

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,269 POSTS
Hi:
First, I thought this was a chrysler product. However, the dwell is the problem. The points need to stay open longer. If they are sending spark at the wrong time (at a higher RPM) you will get a backfire. If there was internal engine problems, I think you would notice it at an idle too.

Make sure the points are the right ones for the car. They may be too small.

Let me know what you find.
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Friday, March 20th, 2009 AT 11:46 PM

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