Tuning/popping issues

[sparky232]

Hey all, I'm pulling my hair out here. Finally got my 61 356 running pretty decent after 3 years of headaches but can't seem to figure out what is going on with some backfiring through carbs mainly when just cruising down the road around 2,000 rpm. Im certain this is being caused by number 1 cylinder mixture screw not having barely any effect when tuning. I've cleaned idle jets on that carb, synced with snail, replaced all the usual stuff (cap rotor plugs wires), checked points and timing, checked floats, and still can't seem to figure out whats up. Have also given it the quick once over with carb cleaner looking for vacuum leaks and come up with nothing. So essentially, lean condition on 1/2 carb but cant figure out why. Any advice would be greatly appreciated.
Btw, i'm running weber 40s, carter electric pump, 12v alt conversion.
Thanks in advance for any insight

[badsix]

sounds like a lean condition, I would think at 2000 rpms you would be coming off the idle jets. have you done a valve adjustment check exhaust valve not opening properly due to a bad cam.
Jay D.

[MMW]

Exhaust leak? Sometimes that will make it pop especially on deceleration.

Have you done a compression test? Could be a burnt/leaky valve?

Edit - Just re-read the post and I see it is popping back through the carbs. Most likely nothing to di with exhaust but still could be a valve not sealing correctly.
_________________
Mic
1959 356 coupe
Missing the original engine 72488
Update - third pc. found!
Now just need the case halves.
1965 fenderless beetle

[roy mawbey]

If the carbs were Zeniths and not Weber then I would still suspect dirt in the internals. It sounds like a partially blocked passage? to me especially as one of the mixture screws does not have any effect.

I know little about Weber carbs but in principle provided as you say the electrics are all first class then it sounds like the carb to me.

Did you check every single jet, air and petrol?

Hope you find it, I can imagine its most annoying.

Roy
_________________
Roy
RHD356A super75 106954

[PD41]

Try spraying some quick start at idle around the carb and manifold.
Maybe a leak ? Check for a idle jump when doing this.

[sraucher]

Possible warped carb manifold?