Backfire? Need help
 

After 1½ years not driving my P-car (rust repair etc.) I've now done about 700 miles in it. I haven't changed anything in the engine (1976 3.2SS CIS) except new plugs, oil filter, fuel filter, oil, a straight (test) pipe and added a pop off valve.

Two times I've experienced:

The engine is cold. I turn the key to start the engine. Without starting the engine there is a BIG BANG from the engine room and blue smoke coming up through the air filter cover. If I try to turn the key again, the engine starts and runs just fine.

My car has never done this before. Is it backfire? What shall I do about it?

Thanks.

I forgot to mention that my mechanic adjusted the valves, when the engine was out.

Can't really say why you have a backfire other than you just may need to drive it more. 700 miles in 1 1/2 years is not enough. No car runs very well if it just sits idle.

X2. Get her out and get her up to temp. Run some good gas through, a couple of tanks. all should be well.

If you search you will see this is very common behavior for CIS cars. You or your mech should check your cold control pressure. This is a function of the WUR (warmup regulator) which can be easily adjusted if required. Your ccp may be too high, causing a lean mixture at start.

Hi Paul. I've now searched to find out how to adjust the WUR to lower the cold control pressure, but I can't find the answer.....

Try "WUR adjustment "via the top right hand corner search button. Poster Tripster and others have done writeups on this. There may be something in Wayne's book, and in the tech articles of this site.