It seems to be as the weather is getting colder, but today my car started backfiring like crazy when driving. At first it only happened while the engine was cold, but now even when the choke if fully opened it still does it. Engine is 1600DP with 34 pict 3 and a single vacuum distributor. There are no holes in the preheat tubes as manifold has just been replaced.

Any ideas guys?

Thanks,
Simon

ahhhhhhhhh just been replaced and when did this start to happen before or after the manafold fixup

Not really sure. Car has been away for around 7 months being painted and when I got it back the manifold, carby and distributor were changed. The old manifold had holes in the preheat so stumbled. The old distributor was a 009 so was changed to a single vacuum and the carby was changed from a 31 pict 4 to a 34 pict 3. Has an aftermarket chrome airfilter and a single quiet pack exhaust. Could this be causing it to run lean?

back fireing is usually caused by a leak in the inlet or outlet i would have a good look around or have a friend give it a little rev while you listern for a leak
good luck

check the points gap n make sure its 0.016 inch

what dave said !

points gap closing up sounds like your issue.

Thanks for all your suggestions guys . Setup a tacho so we could try and adjust timing and idle to see if that did anything. After setting the timing and trying to adjust the idle we found that the idle is sitting on bout 900rpm for a bit and then for no reason at all goes up to around 2000rpm for a few seconds before returning. Revving it makes it backfire with flames out the exhaust. Still think its air leak or points? Why would it only become this bad all of a sudden?

Thanks,
Simon

its an air leak, probably from the inlet gasket or from the rubber boots on the manifolds.

were new metal gaskets used ?

new boots put on ?

all nuts and clamps done up ?

Yep, new gaskets, new boots dont know how tight the nuts are. Mechanic changed over the manifold and everything so I think my best bet would be to take it back to him. Could it also be worn out throttle shaft bushings? Been reading Rob and Dave's site.
Thanks,
Simon

get a length of 1/8 tubing and start the engine

stick one end onf the tube in yr ear hole and use the other end around all the inlet joints to see in you can hear any sucking noises tighten as necessary

spray some hydrocarbons aerosol with a tube attached(degreaser/wd40) near the inlet to the head. If the revs pick up you are sucking air.

And the winning answer is......2 dead spark plugs...or so we were told.

Simon