Newbie, 1971 super beetle with a backfire

[jbake18]

A few years ago I bought a 71 super beetle with a wunderbug front and domas flatbed rear. I was eager to get it on the road, but was in a little over my head at the time. It had stripped spark plug threads, so I pulled the engine and brought it to an aircooled mechanic 2 hours away. He fixed the threads and went through the 1600, making sure it was tuned and ready to go. I put the motor back in and it seemed to run well, but never really got to drive it. Life got in the way, and the car has sat for 2-3 years since. I finally have the chance to work on it again, but am not sure where to begin, as this is way different than anything I am used to. I drained the gas and put fresh gas in, now it starts but has a backfire. When cold, it idles fine, revs up okay with a slight backfire, but when warm it backfires pretty bad and struggles to idle. What could cause this after sitting? I tried adjusting the screws on the carb, at best it backfires, at worst it struggles to run at all. The motor appears to be mostly stock, aftermarket pulley, valve covers, header, etc. I am leery of adjusting too much more of what was set by somebody more knowledgeable than me, so am looking for advice on what to do next.

[67rustavenger]

Back firing through the carb?
Or out the exhaust?
Rob & Daves pages are full easy to understand fixes.
http://www.vw-resource.com/backfiring.html
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[jbake18]

Thanks for the link. It backfires through the exhuast. My engine sounds similar to the example in the article. Where I get a little confused though is how he suggests fixing it. It sounds like I am probably running a little lean? I have tried adjusting the screws on the carb to no avail. He goes into rejetting the carb, but I think the engine ran well ~2.5 years ago with the jets in it, so I'm not sure how that could be my problem.

Is it possible that these jets are slightly clogged from sitting? Something else I was wondering, is that it has been running on an open header, with no muffler. I also haven't ran it much with the air cleaner on since it's kinda dirty. Could these be enough together to cause it to lean out?

I also read through the article about air leaking into the intake manifold. How likely is it that a leak would develop from sitting/where would it likely be? I'm hoping to check this too in the next few days.

[PDX_VW_Erik]

[jbake18]

It has j tubes on it. Basically complete exhaust minus the muffler. Just been test running it right now definitely not driving it, not much in the air around here and the carb gets covered back up when not running

[mukluk]