Renault Caravelle Backfires Raising RPM

RENAULT
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CAPNDAVY
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  • 1 POST
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?
May 26, 2006 at 12:07 AM
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JACOBANDNICKOLAS
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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.
Mar 20, 2009 at 4:46 PM
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Suggested Repair

Confirm the ignition points are the correct size for this engine and adjust dwell so the points stay open longer. Incorrect dwell can fire the spark at the wrong time as RPM rises and cause exhaust backfire. A sticking valve is less likely if the engine idles smoothly.

Conversation Summary

The owner of a 1960s Renault Caravelle with an 800cc Gordini engine reports popping and backfiring through the exhaust when RPM is raised slightly. The car sat for about two years, but it starts quickly and idles smoothly. Points, condenser, plugs, and timing were addressed, yet dwell only reaches about 51 instead of the specified 57. The expert says the dwell and possibly undersized points are the likely cause, not an internal valve problem, because an internal fault would also appear at idle.

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