Help adjusting Weber ICH34 - Defender Source
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  #1  
Old December 11th, 2017, 12:47 PM
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Baird M. Gehring
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Help adjusting Weber ICH34

Yesterday I reinstalled my carburetor after rebuilding it. Trying to get it dialed in, looking at tech articles from various different websites and canít 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 doesnít say exactly which one is which. Iím pretty familiar with the idle speed screw and itís function. Iíve 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  
Old December 11th, 2017, 01:52 PM
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Gerad Davis
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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.
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Old December 11th, 2017, 02:31 PM
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Robert Davis
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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.
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  #4  
Old December 11th, 2017, 03:25 PM
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David Murrell
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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.
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  #5  
Old December 11th, 2017, 04:55 PM
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Baird M. Gehring
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Quote:
Originally Posted by dmurrell View Post
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)?
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Old December 11th, 2017, 05:00 PM
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David Murrell
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Idle Jet

The idle jet is not adjustable.
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  #7  
Old December 11th, 2017, 05:02 PM
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Baird M. Gehring
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Replied to your questions within your quote.

Quote:
Originally Posted by rdavisinva View Post
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.
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Old December 11th, 2017, 05:05 PM
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Gerad Davis
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Weber 34 ich user manual

Idle jet needs to tight. Use the mixture screw (left image) to adjust the mixture. Page two of the PDF should clear things up.
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  #9  
Old December 11th, 2017, 06:25 PM
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Robert Davis
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Quote:
Originally Posted by BMGmotors View Post
Replied to your questions within your quote.
If that crummy PCV diaphragm thing is sucking in air, it will lean out the mixture so bad that you'll never get the engine to run properly, much less idle.
If the carb body is warped, it will cause poor running.
If the gas is old, it will cause poor running.
If there are any buna O-rings, the current fuel available will dissolve them.

There are only 2 adjustments on the carb, the idle speed screw on the arm where the linkage connects and the idle mixture screw with the spring (to hold it in position).

When we worked on lots of 2.25 series vehicles, got to a point where we would not rebuild carbs.
The engine would run badly and then it would run fine after a new carb was installed.
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Uncle "Richard" Douglas has a Land Rover with big wheels that never gets stuck... until he breaks something so it won't go. Uncle Douglas always breaks something. - Anna Crowther at the Conclave 2012 (AKA Carburetor Neck)

"What's with this death wobble, Uncle Douglas, I can't keep it in 1 lane?"
UD: "Just Power through it man!"
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  #10  
Old December 12th, 2017, 10:27 PM
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Baird M. Gehring
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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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  #11  
Old December 13th, 2017, 12:50 PM
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Gerad Davis
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When it doubt, set the mixture screw 1 1/2 turns out!
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