free website stats program mikuni carb | Harley Davidson Forums

mikuni carb

M

Midnight Reign

Active Member
my GF just bought an 89 XL, came into the garage the other day to a huge puddle of gas on the floor. After some investigation found that thetank had drained through the over flow on the carb, (petcock in the on position). First thought was carb float set too high, so I removed the carb and reset float to where the valve closed with the float in the up position, cleaned the bowl and sprayed carb cleaner through every port and jet, all passages appear to be uncloged and flowing freely. After reassembly put gas in the tank and fired it up with no issues, bike runs great. But after shutting it off and leaving the petcock open it is still leaking fuel through the overflow on the carb. I am not very familiar with the Mikuni carbs and was wondering if anyone else is familiar with this issue? With the bike running the is an occassional drip from the overflow tube.
 
Part of the shuting down procedure is to turn the gas off. So whenever you shut the bike off she has to turn the gas off. Now that will help with a big protion of the issues but there still may be an additional problem. Mikuni has a fair website.
 
When you set the float level, did you remove the float needle from it's seat and make sure there was no debris in there? Or, the float needle or seat could have a nick in it preventing total seal. Make sure the float does not have a pin hole in it and gas got into it, preventing it from seating the needle completely.
 
I know about shutting the petcock off, but in my opinion that is only a back up in case there is some other issue. I did remove the needle and inspect for tears or a wear ring in the rubber tip, and sparyed all passages with carb cleaner. float is dry and inspected well, no sign of fuel intrusion into the float. guess it will come apart again and set the float to shut off in a lower position still. Was hoping someone else had specific experience with this issue before I tear into it again. just have to keep after it till I figure it out.
 
My HS 40 manual lists the following for overflow conditions.
Worn needle valve or dirty valve seat. Improper fuel level in float bowl. Damaged float bowl O-ring gasket. Loose float bowl screws. Pressurized fuel tank. Broken needle valve O-ring.
 
The only time I have had this issue is when the needle valve was bad. The standard is to shut off the petcock on non-vaccuum operated systems.

I've had it happen on my 77 FXE a couple of times. It usually involved me forgetting to turn the gas when it happened. That's about the only way you'll see it. Unless it's a total failure. I've had that happen also. I spent a ride home from Daytona one year turn the petcock off and on unti I got to the house.
 
The soft rubberised tip of the float needle will harden after a number of years use and will start to leak simple just replace the float needle however it comes as part of a kit that includes the needle seat
is i have mikuni hsr carbs on both my big twins i carry a spare needle kit it my tool roll
modern fuels are not kind to rubber parts in carbs and i seem to be rebuilding a carb every couple of years

Brian
 
Thanx for all the replies. So now I am a bit more familar with this mikuni carb, having had it apart 3 times today. All of my diagnoises have pointed me to the needle valve as most of you also mentioned. I was able to get it set to a point where it does not leak any longer, however I had to move the tab on the float much further than what I would have expected. So my current opinion is that the rubber tip on the needle valves is old dried out and in need of replacement, which is what I will do. In the meantime the bike rides fine, and should be OK untill the rebuild kit comes in. And of course we will need to be vigilant in making sure the petcock is turned off everytime the bike is shut down. Thanx again to all that took time out of thier day to help.
 
You must log in or register to reply here.
Back
Top