I have a 32-36 weber on my 1641cc vw engine.it has a big lift cam,so it has low vuccum on idle.i can not get it to idle.can you help me. i have tried to weaken the power valve spring to compensait for the low vuccum.i have also drilled a small hole in the primery butterfly so that i could have the butterfly in the right position with the transfer slot.i am useing 130-130 fuel jets.the car doesn't drive to bad.just has an inconsistant idle ,sometimes high,sometimes low and stalls.

Question edited for clarity.
Question moved from Motorcycles.

If it didn't backfire before the rebuild, then it wouldn't be the carburetor jets.

Check the ignition timing and for inlet manifold leaks, and exhaust leaks.

https://www.google.com/search?q=VW+1641+backfires

,,

this is caused by mixture getting past the idle and being sucked into the combustion chambers and being ignited by the hot spots and combustion pressures
Very common on early english cars and some american cars
The japanese carbies had a solenoid valve that fitted into the idle circuit so that when the ignition was turned off , the solenoid closed off that idle circuit and prevented the problem
you may have to "play " with the idle mixture screws to get a better mix so that the mixture is too rich to run on or change the weber to a model that has the solenoid shut off

not sure what you mean, idle? High idle usualy bend a rod to position the cam in the right place when engine is cold or with the choke plate held about 1/8" open and low idle is turn the idle screw with the engine warm. The screw rests high on the cam when cold and low on the cam when engine has warmed. you may find an index marking on the cam.

the high lift cam has no compensation and so the valve retainer bottomed out causing the rocker to slip sideways and bend the push rod
you would have been better fitting a prolonged duration cam rather that a high lift for the following reasons
1 --- you can used standard rocker gear
2 ---there is no valve bounce at high rpm
3 --- smoother air flow in the inlet manifold so there is not such a stop/ start action when rpm is low
4--- less wear on cam followers and cam lobes
cam shafts are all about open duration so longer open with smaller lift is better than the same duration with a fast up and down action

VW what car?
what year>?
no model, no year,
no joy.
are these custom carbs? if yes, NO ONE CAN answer that.
because.
Jets are tuned for YOUR engine alone.
if all this is true,then get the weber book, huh? and read it.
it tells you how to tune any weber, and its not simple. not at all
the webers are the most difficult to tune but on the other hand they are the best. (less compromise , makes great racing carbs).
there are on line weber tunning pages, why not google that.

in the old days, we'd use spark plug readings for full week end (wasted ) to tune any custom carb,,

fast forward, 21st century, we have nice wide bad 0xy sensor tool.
its about, $150 now.
we put a 02 exhaust bug on the exhaust headers, (both if v8)
and we tune the carb. using this tool , in about 1hour.
way less for only idle , idle is very simple NO ENGINE LOAD.
I set it to stoich and drive.
end story, unless , issues driving or up hills.

on stock carbs the idle has a mixture screw.
we set it to max RPM and the unscrew 1/2 turn (rich)
not all carbs some use an air screw. (backwards)
contrats, the most complex question ever asked on fixya.
ever.
join a car forum for your car, then find custom carb section
then ask there. bingo,, must maybe 1 other person did this.
but i can tell you if the engine is different , with custom exhaust
all the tuning must be done over.
eg: custom cam, milled heads, exhaust, bored cylinders. or ported inakes. all change DEMAND for fuel and must be tuned to match it.
same is true with EFI. (speed density) but not air density EFI.
see.... ?

1983, a very old car. and worse a carb. (will need cleaning kit)
E80 or E90 (83' is both as option)???????
what country, lots of variance by , COUNTRY!
is compression good. check that.
which engine,? (skip diesel)
1.3 L 2A I4
1.3 L 2E I4
1.5 L 3A I4
1.6 L 4A I4
1.8 L 1C diesel I4

e90 had
Gasoline: 1.3 L I4
1.5 L I4
1.6 L I4 after posting engine, and Weber model part number.
we can answer with alacrity.

my guess is that white smoke is from engine back fire to the carb.
this caused by 2 things , bad spark or cam timiing.
or a very lean carb.

check compression 150psi or more.
check spark timing,
check cam timing if compression is low.
check for Vacuum leaks at this will cause the engine to go lean
at idle. on all carbs.

Assuming that the engine does start;
does the starter motor turn for some time before the engine fires up or does the engine start easily?
does the engine idle smoothly or is it shaking?

You might want to check your injection timing - the pump timing in relation to the crank- and cam timing as well as the injection timing device on the pump itself.
Then there is the needle lift sensor on the number 3 injector that can play up as well.
These things usually play up on high milage...

If you have a 5.4L V8, this is most likley a vuccum leak. If you have a check engine light on, and the code tells you that the mixture is lean in rail one and two, it's bad news. There is a vaccum hose under the manafold that goes to the power brake system. Unless you are a mechanic, the manafold must be removed by a professional to replace the hose as the original EGR valve connections no longer exists. Varriable valve timing on the cam shafts has eliminated the connection above the manafold. About $600.

check the idle circuit for restrictons remove jets and clean

replace your fuel filter first. If that does not do it, then try an air-flow meter. (if the check engine light is on it may be an airflow meter.