Carb adjust failure...valve adjustment next??

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Laldog

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Ok, so I've spent the past week or so trying to get my Weber carbs adjusted to eliminate popping and backfire from the rear exhaust. Absolute failure. No amount of adjustment eliminates the popping and backfire. Car accelerates and runs great until I take my foot off the gas.
Very minimal exhaust leaks from new Fitz Bitz exhaust.

Timing was adjusted with the help of a couple of local mechanics who swear timing is accurate.

So my question is this: Should I tackle the valve adjustment next with the assumption that this may be preventing an accurate carb adjustment.

Any other suggestions as to recommended next steps would be greatly appreciated.

Thanks.
 
Stevehose said:
When did the backfire start happening?
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I would say this spring.
I figured it was the hoe in my muffler, so I replaced muffler with S.S. exhaust system (from behind the headers back) about 3 months ago. Initially it was quiet and all seemed well, but the past month or so things have gotten increasingly ugly
 
I will volunteer John to help. You drive your coupe to Sudbury and we all work on it together. John really knows Webers and has that great toy that senses the air-fuel mixture while driving with a probe in the exhaust.
 
Have you checked for vacuum leaks? Need to determine if the popping is from being lean or rich. I suspect the former. To test this theory, after checking for obvious leaks around the carbs with carb cleaner or similar, i would back out the idle mixture screws a couple turns to see if that has any affect on the backfire. Unless your valves are way out of adjustment I would think this is not your problem but can’t hurt to check.
 
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Stevehose said:
Have you checked for vacuum leaks? Need to determine if the popping is from being lean or rich. I suspect the former. To test this theory, after checking for obvious leaks around the carbs with carb cleaner or similar, i would back out the idle mixture screws a couple turns to see if that has any affect on the backfire. Unless your valves are way out of adjustment I would think this is not your problem but can’t hurt to check.
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No sign of vacuum leak. I'll check again.

I pretty much went both ways with the idle mixture screws (both lean and rich). I was inclined to go towards a lean mixture, since the smell and what I have read indicated that my backfire is caused by a rich condition. I'll check how things with a lean condition tomorrow.
Thanks.
 
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