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Bizarre, funky issue when rolling up to a stoplight

  • Thread starter Thread starter Catbus
  • Start date Start date
Carbs are 1-4 from left to right as you sit on the bike

#3 has a port on the left side, that's the vacuum port.

The other "ports" are vents. They're between 1-2 and 3-4
 
Big T said:
Carbs are 1-4 from left to right as you sit on the bike

#3 has a port on the left side, that's the vacuum port.

The other "ports" are vents. They're between 1-2 and 3-4
Click to expand...

Thanks,

they're Mikuni VM22SS I believe.
 
Big T said:
Carbs are 1-4 from left to right as you sit on the bike

#3 has a port on the left side, that's the vacuum port.

The other "ports" are vents. They're between 1-2 and 3-4
Click to expand...

So if #3 is the one that goes into the petcock, and #2 is a vent hose... I've had the vent hose hooked up to the Petcock this whole time since I adjusted the floats in the carbs several weeks ago... and I guess thats why it doesn't pull a vacuum to work on the other modes than PRI.
Counter-intuitive since the #2 vent hose is closer to the petcock, and the actual vacuum hose goes across the leftside 2 carbs.
 
I believe they needed the space between 2-3 to get the vacuum port in there. Next time you have the carbs off, look into the intake side of #3 and you'll see the hole that creates the vacuum

Hooking up the hoses correctly may solve your problem
 
Okay I went and took a picture of my setup, the top hose closest to the petcock is the one attached. I started the bike and felt no suction coming from the far right hose pictured. Carbs numbered left from right.




dual.jpg
 
That dangling hose is a vent line originally over the air box from carburetor 4. There is a corresponding vent line from carburetor 2. The vacuum port is blocked from view by your fuel line from the petcock and the fin on the back of carburetor 3 in the picture of 3 and 4. It comes off carburetor number 3 in a similar position as the vents on 2 and 4. Is that just the picture angle or is the fuel line damaged where it curves into the fuel T?
 
Last edited:
Okay so I took another photo, if the vacuum hose is on the same carb as the one with the fuel line, than I do have vent hose on Carb 2 hooked into my petcock. Carb 4 has a dangling hose, carb 3 has a dangling hose. The fuel line is not kinked but is slightly wet where it enters the petcock so I will replace it most likely.
As seen in the 2nd part of this photo,
20626195_10155159910897415_1795787851153142577_o.jpg

OldVet66 said:
That dangling hose is a vent line originally over the air box from carburetor 4. There is a corresponding vent line from carburetor 2. The vacuum port is blocked from view by your fuel line from the petcock and the fin on the back of carburetor 3 in the picture of 3 and 4. It comes off carburetor number 3 in a similar position as the vents on 2 and 4. Is that just the picture angle or is the fuel line damaged where it curves into the fuel T?
Click to expand...
 
It appears that you have the vacuum line in your hand in the first photo looking at carburetor 3. Put that on the petcock vacuum line. Get rid of that junk setup with the fuel filter. It's just restricting fuel flow. Your petcock has a more than adequate filter screen in the fuel tank. That line should go directly from petcock to fuel T. That may solve your problems in that respect, but proper jetting may be your next concern.
 
Ok
You have the vent hose connected to the petcock
Connect the hose from #3 to the petcock and see what happens
 
Also, get rid of the fuel filter
And, take pictures before, during and after you take something apart. Digital photos are a godsend for a beginner (and, us old guys)
 
Thank you so much. I took the petcock off and disassembled it and soaked it all in gas and gave it a scrub. It was very dirty and gritty. It looks like the previous owner put the diaphram on wrong and one of the edge holes where it loops around the screw was been folded over. I put it all back together and tested the air flow with my mouth and it still feels not right but alas I have no reference, so tomorrow I'll put everything back together, and put the right vacuum hose on the petcock. When I replace the fuel line (upon further inspection is cracked slightly) I'll omit the cone fuel thingy.


OldVet66 said:
It appears that you have the vacuum line in your hand in the first photo looking at carburetor 3. Put that on the petcock vacuum line. Get rid of that junk setup with the fuel filter. It's just restricting fuel flow. Your petcock has a more than adequate filter screen in the fuel tank. That line should go directly from petcock to fuel T. That may solve your problems in that respect, but proper jetting may be your next concern.
Click to expand...
 
Well hot damn! I followed those steps and the bike fired right up as usual, but the problem is gone! And now, when I coast with the clutch in in any gear, the RPM actually dip down to 1K, which it never previously did. Thanks for the tip about the vacuum hose, no one else could solve that.

Except now, since reconnecting the petcock, there's a very bad drip coming out of I believe the 2 screws holding the petcock to the tank. The O-Ring gasket inside seems perfectly fine, perhaps all the grit and metal particles were causing a sort of seal, but I was cursing up a storm as I really do not like draining my gas tank twice in 24 hours. So I got a little morsel of properly running bike, but alas, it's back into pieces as I try and figure out what the hell to do now.

ALSO, I noticed when the petcock was re-assembled that there were two notches filed/scratched into the petcock at 45 degree angles from RES and ON, and ON and PRI. When I set the petcock there, it blew air through fine. I think these are the ACTUAL spots where there's flow. I am really wondering what the previous owners did to this bike, as I' discovering more and more as I go. Maybe they replaced a part from a different bike, but who knows.

Big T said:
Ok
You have the vent hose connected to the petcock
Connect the hose from #3 to the petcock and see what happens
Click to expand...
 
The petcock requires washers on the bolts that have a seal. You can still order them from OEM sources. Be careful with them because the seal is directly against the threads.
 
Post up some pictures of what you have there.
You have now discovered the joy of working on old bikes. Previous Owner Syndrome
 
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