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Help adjusting Weber ICH34

16K views 10 replies 4 participants last post by  east high 
#1 ·
Yesterday I reinstalled my carburetor after rebuilding it. Trying to get it dialed in, looking at tech articles from various different websites and can’t quite get it running at its best. Drove it to work but still having issues with hesitation when giving it gas on starting from a complete stop in gear and some slight popping every now and then from the exhaust. Seems a little underpowered possibly as well. Also some rough/uneven idling. The Weber parts diagram I have is a little confusing as it lists all these parts/screws but doesn’t say exactly which one is which. I’m pretty familiar with the idle speed screw and it’s function. I’ve attached photos of the other two screws, could someone give me some advise on what the adjustments should be on these?
 

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#2 ·
From my experience with a variety of carbs over the years, the image on the left is the mixture screw, the image on the right looks like it could possibly be the main jet. Popping and lack of power makes me think you're running lean. That could mean a rejet or your timing is off.
 
#3 ·
That looks like a 2.25.
That screw with the spring is only for the idle mixture and think it is an air screw.
You say you rebuilt the carb, what does that mean?
Did you check the float level height?
You have that crummy PCV diaphragm that can suck in loads of air and lean out the mixture.
Have you checked the distributor, set the timing, checked the spark plugs?
All the ignotion and air flow has to be spot on before any carb tuning can take place.
 
#7 ·
Replied to your questions within your quote.

That looks like a 2.25.
Yes it is a 5mb petrol 2.25.
That screw with the spring is only for the idle mixture and think it is an air screw.
You say you rebuilt the carb, what does that mean?
I disassembled, soaked carb body, screws and all metal ancillaries overnight in chemdip, removed next day, dried off, installed new gasket and new main jet that the float connects to in the fuel bowl, reinstalled same jets that had soaked. Installed new fuel filter in carb body. Calibrated float level as per Weber specs for the plastic float.
Did you check the float level height?
Yes
You have that crummy PCV diaphragm that can suck in loads of air and lean out the mixture.
Have you checked the distributor, set the timing, checked the spark plugs?
Yes
All the ignotion and air flow has to be spot on before any carb tuning can take place.
 
#4 ·
34ich

If the issue is dying at idle - or will only run with the choke - the idle jet (right picture) is clogged. To unclog it remove and blow through it - a tiny strand of copper wire can also be useful.

If that's not the issue, I'd check the float to ensure the bowl is filling. When it comes to setting the high speed mixture (left picture) - screw the mixture screw to closed (tighten by hand) and back out 1.5 revolutions. That is the starting place for tuning.

Hope this helps.
 
#5 ·
If the issue is dying at idle - or will only run with the choke - the idle jet (right picture) is clogged. To unclog it remove and blow through it - a tiny strand of copper wire can also be useful.

If that's not the issue, I'd check the float to ensure the bowl is filling. When it comes to setting the high speed mixture (left picture) - screw the mixture screw to closed (tighten by hand) and back out 1.5 revolutions. That is the starting place for tuning.

Hope this helps.
Thanks. My question though is if the idle jet screw is adjustable or if it just has one setting (I.e. screwed all the way finger tight)?
 
#10 ·
Thank you all for all of your suggestions! I think I finally have my carb dialed in, may need to make some slight tweaks to the idle mixture screw or check my timing again as the engine wants a little throttle when starting from a complete stop but otherwise has no more hesitation. I screwed the idle jet screw in completely as recommended, backed the idle speed screw completely off and turned it in about 1.5 turns, then adjusted the idle mixture screw in and out and found a midway point where the idle seemed fairly strong and smooth then further adjusted the idle speed to get it to around 750 rpm. I am getting more power now too that the carb is properly adjusted. Thanks!
 
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