On my 73 RD350, my left carb will not stop dripping gas out of the overflow when I park it overnight, or sometimes just for a couple hours.
I put in the rubber tipped float needles and new seats, new bowl gaskets and new plug gaskets, new petcock, and even raised the float level on the left side. This all helped but didnt fix it.
Am I missing something???
If the brass overflow tube in the bowl is cracked the carb will leak. After you shut the petcock off it will leak until the bowl empties out and then stop, if the petcock is working ok.
If you confirm that the overflow tube is OK then you need to start eliminating potential sources.
1) Check the petcock. Disconnect the fuel hoses and run them into a cup overnight to see if fuel builds up. If no fuel is present after the test, move on to the next step.
2) Disassemble the carb and make sure the float valve is clean and seals properly. Check for debris or corrosion in the seat & needle tip.
3) Re-check your float height. When set at the correct level fuel will not run out of the overflow unless there is a continuous fuel source upstream that is getting by the float valve. Float height spec is 15mm (+/-1mm), measured from gasket surface to float arm (see bottom of this page: https://www.vintagebikebuilder.com/setting-mikuni-float-levels.html)
Is that bowl is from Left Carb ?
Should there be a hole at marked area
(https://i.postimg.cc/PPh6m3X8/VM28.jpg) (https://postimg.cc/PPh6m3X8)
Quote from: KANDY on May 24, 2025, 02:34:32 PMIs that bowl is from Left Carb ?
Should there should be a hole at marked area
(https://i.postimg.cc/PPh6m3X8/VM28.jpg) (https://postimg.cc/PPh6m3X8)
That's a right one. Left one does have a hole.
So I have checked the petcock, and I put about 50psi to tge overflow with my finger over it and the bowl filled with gas, and no bubbles. The tank has been cleaned, I run fuel filters, and the valve seats are brand new. I looked it all over before installing.
I have the float set at 17mm measured with no gasket.
I will get some pics of everything tomorrow.
float should be set to 15.
take needle out, make sure there isn't some crap behind the seat. blow air thru it backwards from seat to feed pipe common issue. :twocents:
Well I went through and cleaned it again, and now I am more confused. Just to try it, I sealed up around the overflow tube some more, double checked float heights(left is at 16mm) and let the left float bowl sit with some gas in it to see if it would leak.
Later I went for a ride, turned off the fuel, then shut it off. I was back in an hour and the bike was dripping gas around the jet plug/overflow on that left carb.
(https://i.postimg.cc/QHBv0Lrg/20250525-163934.jpg) (https://postimg.cc/QHBv0Lrg)
Right carb
(https://i.postimg.cc/gLL4qW6n/20250525-170236.jpg) (https://postimg.cc/gLL4qW6n)
Left carb
(https://i.postimg.cc/KRytsL69/20250525-164904.jpg) (https://postimg.cc/KRytsL69)
Left float height
I may try that left needle seat again, but it looked spotless every time. And it doesn't seem to matter uf I run the fuel down some before shutting off the bike.
it's dripping around the jet plug? ie the 17mm cab on rhe bottom of the bowl? if so, us the red fiber seal in there?
Quote from: m in sc on May 28, 2025, 08:56:28 PMit's dripping around the jet plug? ie the 17mm cab on rhe bottom of the bowl? if so, us the red fiber seal in there?
Yes, I replaced it along with the float bowl gaskets. These have a hair big inner dai., but the problem has not changed.
i know this may sound odd, but how far over does the bike lean on the side stand?? it could have a bent or shorter side stand. i have seen several older bikes lean really at a precipitous angle almost falling over. set up straight and see if it stops
Quote from: 747drvr on May 28, 2025, 10:32:11 PMi know this may sound odd, but how far over does the bike lean on the side stand?? it could have a bent or shorter side stand. i have seen several older bikes lean really at a precipitous angle almost falling over. set up straight and see if it stops
I really don't think it leans too far, but its worth a shot. I'll put the side stand on some blocks of wood next time and see how it goes
It is possible that the floats themselves are the culprits, for lack of a better description, saturated. The post that the floats are located on and the floats could also be an area to look at, possibly binding just enough to be a problem, and causing the float not to move freely. I personally have had floats be the problem on carbs over the years.
^ true
My RD does the same 'side stand' thing occasionally; with an increased lean angle on the sidestand, independent floats sit at different levels, and only the 'low side' float pushes on the needle bracket, effectively raising the fuel level.
Carbs with floats mounted on the needle arm instead of bowl pins do not seem to have this issue so much.