Mikuni Carb/fuel delivery issue

Mini Bike & Go-Kart Parts

#1
Hi, I have a mikuni 22 that I'm having some problems with. When I try to feed it fuel, fuel doesn't even go down the line into the carb. But the weird thing is, that when the carb is attached to the manifold it does this, but when it's off, it flows perfectly fine. I tried cleaning it twice, changing idle, and even swapping fuel lines. But to no success. Any help would be much appreciated.
 

mustangfrank

Well-Known Member
#2
Hi, I have a mikuni 22 that I'm having some problems with. When I try to feed it fuel, fuel doesn't even go down the line into the carb. But the weird thing is, that when the carb is attached to the manifold it does this, but when it's off, it flows perfectly fine. I tried cleaning it twice, changing idle, and even swapping fuel lines. But to no success. Any help would be much appreciated.
Not sure exactly what you are trying to describe but it sounds like maybe a float/float level/fuel inlet issue? What was the original problem, not running? Tank high enough above carb? Pictures can usually help and get better answers.
 
#3
My first thought is the carb is at an angle when it's on the manifold and this is causing the float to bind by touching somewhere inside the bowl. When it's off I imagine you are holding it level and the float is not binding. Also, the needle could be sticking in the seat or the float height is not set properly.
 
#5
Not sure exactly what you are trying to describe but it sounds like maybe a float/float level/fuel inlet issue? What was the original problem, not running? Tank high enough above carb? Pictures can usually help and get better answers.
The original problem is that fuel won't go to the carb when it's attached to the manifold. I also checked the bowls and it appeared to be level. tank level isn't an issue because I have a fuel pump (and that works as intended when it's not connected to the carb. I don't know if it helps, but when it starts, it runs high idle on choke, but when it's off of it, it will start bogging out and then die. I provide whatever pics you need later on today.
 
#7
My first thought is the carb is at an angle when it's on the manifold and this is causing the float to bind by touching somewhere inside the bowl. When it's off I imagine you are holding it level and the float is not binding. Also, the needle could be sticking in the seat or the float height is not set properly.
I don't think its the needle because i'll take the whole needle, spring, and slider system out and it still does it
 

mustangfrank

Well-Known Member
#8
The original problem is that fuel won't go to the carb when it's attached to the manifold. I also checked the bowls and it appeared to be level. tank level isn't an issue because I have a fuel pump (and that works as intended when it's not connected to the carb. I don't know if it helps, but when it starts, it runs high idle on choke, but when it's off of it, it will start bogging out and then die. I provide whatever pics you need later on today.
The point of the question is to determine if the carb & fuel delivery system ever worked or if you're putting new parts on an engine and it's never ran as a combo, we're typing words over the internet blindly and we get a ton of these issues.

So assuming it used to run fine as is with this carb and you haven't changed anything then it started to stall off the choke...

Stalling out, bogging off the choke does indicate going lean or a fuel delivery issue. I'd clean every tiny orifice with a carb tool or wire, I'm guessing a bowl vent/line and/or jet is plugged, which could cause the running issue and possibly the fuel "flow" issue.
 
#9
The point of the question is to determine if the carb & fuel delivery system ever worked or if you're putting new parts on an engine and it's never ran as a combo, we're typing words over the internet blindly and we get a ton of these issues.

So assuming it used to run fine as is with this carb and you haven't changed anything then it started to stall off the choke...

Stalling out, bogging off the choke does indicate going lean or a fuel delivery issue. I'd clean every tiny orifice with a carb tool or wire, I'm guessing a bowl vent/line and/or jet is plugged, which could cause the running issue and possibly the fuel "flow" issue.
Ok, Ill try and clean the whole thing out again and see if that fixes it. I also forgot to mention this. I dont know if this is of any use, When I finished it originally, I swapped the fuel lines out, noticed it doing that problem, then switched back to the original lines im currently using, and no the problem is happening (It started to do this when I switched to the new lines)
 

mustangfrank

Well-Known Member
#10
Ok, Ill try and clean the whole thing out again and see if that fixes it. I also forgot to mention this. I dont know if this is of any use, When I finished it originally, I swapped the fuel lines out, noticed it doing that problem, then switched back to the original lines im currently using, and no the problem is happening (It started to do this when I switched to the new lines)
Gotta ask...are you sure the fuel lines are on the pump correctly and the pump works? First question I always ask myself..."what did I touch last?"
 
#11
Gotta ask...are you sure the fuel lines are on the pump correctly and the pump works? First question I always ask myself..."what did I touch last?"
yes they are on correctly. I made sure of it. I know this because when I take the fuel line off the carb and suck and blow into the compression inlit. Fuel flows as it should, but when I re-attach it to my carb, it stops flowing.
 
#12
yes they are on correctly. I made sure of it. I know this because when I take the fuel line off the carb and suck and blow into the compression inlit. Fuel flows as it should, but when I re-attach it to my carb, it stops flowing.
Just a guess but maybe the fuel pump is weak or not able to keep up. I know it's not a car but when you have a fuel issue in a vehicle the line pressure is one of the things that they check.
 
#14
Just a guess but maybe the fuel pump is weak or not able to keep up. I know it's not a car but when you have a fuel issue in a vehicle the line pressure is one of the things that they check.
I don't think it is. When it originally did work, it was able to keep up very well and never was starved until the tank ran out.
 

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