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Mikuni VM22 Choke Pickup Tubes Questions

D

DaleGribble

Forum Newbie
Hey all,

I'm working on a rack of VM22s that came off a 1977 GS550. In the process of disassembling, I noticed all of the choke pickup tubes vary in length and the tube on carb #4 seems a little bent.

I'm assuming they vary in length because they aren't all seated fully, but I haven't been able to verify because they don't want to come out and I don't want to accidentally damage them.

Are these tubes pressed in or are they threaded in?
 

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The tubes are lightly pressed in and only go into the body around 5mm if that .
The short ones are clearly shorter than that so it's almost certain that they have been snapped off at some point and re fitted once the broken pieces in the body has been removed.
It's not uncommon for them to fracture at the base as the brass tube get brittle with age.
It possible to fabricate new ones from brass tube bought from a model shop if you can't get any from some donor carbs.
The VM22,VM24, VM26 and VM28 4 banks all share the same pick up tubes.
 
zed1015 said:
The tubes are lightly pressed in and only go into the body around 5mm if that .
The short ones are clearly shorter than that so it's almost certain that they have been snapped off at some point and re fitted once the broken pieces in the body has been removed.
It's not uncommon for them to fracture at the base as the brass tube get brittle with age.
It possible to fabricate new ones from brass tube bought from a model shop if you can't get any from some donor carbs.
The VM22,VM24, VM26 and VM28 4 banks all share the same pick up tubes.
Click to expand...
Do you think that shorter one would still pull fuel? If I can get away with it, I'd run it until winter when I plan to do a top end rebuild.
 
If I remember correctly, it's 3 mm od tubing.
I'm fortunate to have a crazed* machinist as a friend. We cut tubing to length, put one end in a dab of molten solder, let it cool and drilled the appropriate size hole.

Warming up the carb body aided in pressing the tube into the carb body.

* he loves a new challenge. He works on 60-70s British cars as a hobby
 
DaleGribble said:
Do you think that shorter one would still pull fuel? If I can get away with it, I'd run it until winter when I plan to do a top end rebuild.
Click to expand...
Providing it is sitting below the fuel level in the bowl is should still pull fuel but possible not as strong as the ones at the correct depth.
Saying that they are only active when the choke/enrichener is applied for cold starts so shouldn't cause a problem once running and off choke.
As long as at least a couple of cylinders get a sufficient rich mix to fire from cold the others will catch up once the motor is warm.
 
My thought is yes they should suck fuel as long are they stick into it. But how much is the question. Some have a tiny pinhole restrictor to meter fuel intake.
 
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