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Discussion Starter · #1 ·
Hi All

I'm cleaning a set of carbs from a 1980 CM400. I'm not new to cleaningcarbs, but do have a question about the pilot passage route. The jetappears to be pressed in. I believe the center of the jet is clear, but whenI squirt carb cleaner and chase with air, I can not verify where or if itscoming out. Can someone explain to methe passage after the pilot jet and what I should be looking for to verify allthe passages are clear? I know it gets fuelfrom the jet next to it, but after it goes through the pilot jet I cannot traceit – it appears to go to the cut off valve on the side, but I don’t think I’mgetting air/cleaner to show there. Isthis pilot jet smaller than what a torch tip cleaner can do? I do have a micro drill bit set, but they areonly about an inch long. The rest of thecarb was in reasonable shape. The ownerof the said it ran, but horribly and only on choke. As a side note, I wasn’t real thrilled whenhe dropped them off…Seems like every old set of Keihins I work on they use thisplug system and are way more complicated than Mikunis, but they are real smoothwhen operating properly. They’ve allbeen consistent with the pilot circuit – after the jet, the fuel goes to sometransition holes,
situated right on the edge of the butterflyand then the fuel continues to the screw, which meters the one pilot passagebetween the engine and butterfly.

 

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The simple explanation: The primary main jet limits the total amount of fuel that is delivered to the engine by the idle jet, slow jet (what you are calling the pilot jet), and the primary main jet combined. Another way to put it, the idle jet gets it's fuel from the slow jet which in turn gets it's fuel from the primary main jet. Carb cleaner sprayed through the slow jet should come out the second orifice in the carb throat, the one just behind the throttle butterfly.

https://www.hondatwins.net/forums/63-fuel-supply-carburation/16943-vbulletin-carb-circuits.html

Cleaning those non-removable slow jets can be a problem. High pressure air and guitar strings (sorry, don't remember which note) following ultrasonic cleaner can help.

https://www.hondatwins.net/forums/63-fuel-supply-carburation/24191-rebuilding-vbulletin-carbs.html
 

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The slow press in jet is removable on the CX carbs, I'm not sure if that is also the case for your CM400. The slow jet has holes in the sides that also can get clogged and you can only clean those if you remove the slow jet(ultrasonic may do it if you leave it in).
 

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Discussion Starter · #4 ·
Thanks guys. I poked around more here an found that photo of the cutaway of by Larry. Holy hell that was awesome. I have a set of micro drill bits and the smallest one is an 80. Its so fine its like a hair. I got that to go through the jet and now its passing cleaner to the air cutout, the screw and the holes in throat. I'm not about to pull the pressed in jet out - these are a friends carbs, and I spent the better part of 90 min last night extracting the main jet nozzle in the other carb. The thing was stuck tight...I tried heat, ultrasonic, cleaner, soaking etc. Ended up using a variety of left hand bits, extraction kit and some cussing. Thank goodness I got it out and the carb body is ok - I was careful to test how far I could go with my bits on the other one before drilling. Found out its now discontinued so had to snag one on ebay...
 

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I am in desperate need of a primary nozzle as well. My eBay searches have found nothing. Any other ideas?
 

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You can google the part number:

16166-447-671

But they seem to be pretty much NLA.

If you can pick up a used 3 jet VB carb from any of the SOHC 2 cyl bikes it should be the same.
 

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You can google the part number:

16166-447-671

But they seem to be pretty much NLA.

If you can pick up a used 3 jet VB carb from any of the SOHC 2 cyl bikes it should be the same.
Found exactly one on the internet, eBay, NOS even! $22 shipped. Hopefully this will fix my issue of not really running. Thanks a million!
 
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