# WHAT can cause Backfiring??? (pierburg 1b3 solex carb)



## broken dipstick (Mar 8, 2007)

ok so i rebuilt the carb.. pierburg 1b3
replaced all the vacuum lines.
still trying to figure out why the choke was disconnected and also the choke pull diaphragm
i tried to connect the diaphragm but it made the engine die out and was also unable to accelerate at all.... but also the needle valve i had put in incorrectly so it wouldnt close all the way but that is solved now
http://forums.vwvortex.com/zerothread?id=3666177
now i have it running fine at idle. but it backfires and pops (sometimes dies out) when i press the accelerator.. ??








wtf is happening? it seems like the timing is off but how could this be?
could the distributor have gotten turned a little bit?? thus advancing or retarding the spark?
we had the plugs out and cleaned them before this and had the cap off as well.
it ran ok before.. i even drove it back from kc (5 hrs) on the interstate etc and it was fine.. would only die occaisionally at idle speeds. it would chug and miss when cold but when warmed up ran absolutely fine.
but the carb leaked gas bad so i rebuilt it and now the problems arise.
the carb:
























these pics are with the waterchoke off
i have a spare carb on its way from Germany but that will probably take 3-4 weeks so i need to at least get it running ok... i'm not so worried about the choke or the pulldown diaphragm because the choke is disconnected and i accidentally broke one of the nipples on the diaphragm







(black thing with two vacuum ports)
these IMO should only affect startup? they both were disconnected before when i drove it home if that helps.. (it ran fine with them disconnected before.. accelerated fine, only chugged on startup until warm)
so:
what all can cause backfiring?? i know timing but what else? richness can too? but i don't see how it can still be rich because it idles stable and not rich but pops and sometimes dies on acceleration? anyways this has me stumped i guess i'll check the timing??


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## frechem (Oct 19, 2002)

*Re: WHAT can cause Backfiring??? (broken dipstick)*

Backfiring is caused by the motor running too lean.


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## broken dipstick (Mar 8, 2007)

*Re: WHAT can cause Backfiring??? (frechem)*

hmm maybe i'll mess with that before the timing? although it seems to miss really badly?


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## epjetta (Sep 19, 2006)

*Re: WHAT can cause Backfiring??? (broken dipstick)*

misses happen from a lean condition too http://****************.com/smile/emthup.gif


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## broken dipstick (Mar 8, 2007)

*Re: WHAT can cause Backfiring??? (epjetta)*

well found out it was flooding because on the new needle valve i got the spring to hold it closed was too weak and allowing an unlimited flow of gas.
i put back in the original needle valve, now it will run fine but at the same time it still pops (a little) when i accelerate.
we did mess with the timing by turning the distributor so i know we need to fix that.. and it's probly why it pops now. althought it's behaving much more normally now. so the popping is probably a combo of timing off by a little bit and either too lean or too rich now. but at least the freakin thing will run.
it was getting so much gas with the "new" needle valve it was squirting out the top vent of the bowl



_Modified by broken dipstick at 1:24 PM 2-17-2008_


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## chameleon78 (Oct 31, 2006)

*Re: WHAT can cause Backfiring??? (broken dipstick)*

so what ended up happening with this carb? fed up with it? i know you got a new one just last week...


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## broken dipstick (Mar 8, 2007)

*Re: WHAT can cause Backfiring??? (chameleon78)*

the pierburg no matter what i did to it would not choke properly on startup..
so fux it, i bought a weber.
anyone want a pierburg carb?








if you fitted it with manual choke it would run fine, i just figured i've sunk enough time/money into it already
oh and all the backfiring that was happening.... i had two plugwires switched around


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