backfire through carbs

I just picked up my new(to me) 71 911 targa. It has weber carbs on the 2.2 engine.

It backfires like crazy through the #2 cylinder. This has even deformed the airbox(excess heat). This problem comes and goes while accelerating. It seems to idle relatively smooth. The car has hardly been moved in the past 4 years. after driving it it smoothes out a little.

I suspect that its just crap from the engine sitting for a while. I assume the valves need to be adjusted which I will do this weekend. any other suggestions?

Thanks in advance for all comments.

I will post picts of the new car when they are developed.

Jamie
71 911T Targa

Jamie,

The backfire thru #2 may be caused by a lean air/gas mixture on the #2 cylinder. Webers are very tempermental and a slight error in adjustment can cause poor running.

Timing is imperative but I would start with a simple fix before getting into timing adjustments(even though they may be to blame). I'd adjust the mixture on #2 first. Good luck with it.

Rich Boylan

See the other posts on Webers throughout this BBS.
I'd remove the idle jet carriers one by one and blow out the passages and inspect and clean the jets. I once had one that was deformed by either overtightening of the carrier or an obstruction in the passage. If these units get the slightest blockage, they cause misfires.
Also think about removing the mains and doing the same with them. Have fun with the Webers, they're interesting....and the sound of those six throats opening up on acceleration is memorable.

The carbs are an easy item to check. The next item I would look at is the valve adjustment for that cylinder because if an intake valve looses some of it's clearance (gets to tight) then the valve will stay open just a little too long and backfiring will result. See if you can find out when the last valve adjustment was done as it might be due or overdue? Good luck.

Thanks for your replies. I suspected it was the carbs. I ran a can of carb cleaner through them last night. It ran much smoother after doing this. I then sprayed som more and let them sit to soak. I will fire them up tonight after work.

I checked some previous post and found a suggestion to remove the carbs completely, and soak them in carb cleaner. then pull the jets and blow them out. I might have to try that. CAn the gaskets be reused or do I need new ones?

Looks like I get to do a good tuneup this weekend. I already pulled the dist and rotor for a good cleaning. that took care of the other missing I heard. I noticed that the rotor and cooresponding contact points on the dist cap are looking a little worn. ARe there replacements for a Marelli system? I did not see them at Perf Prod.(the only catalog that has come in the mail so far). I hope that I do not have to do the whole Bosch upgrade( I do not have the money now).

I have to say I am excited about being a Porsche owner. This has been a dream for a long time.

Jamie
71 911T targa