Mikuni SBN fuel dribble

302much

302much

Location
Highland Village, TX
Ok, I tracked down a set locally.. I also ordered some 66E-24412-00-00 so I will see if that is the same part or not.

Good news is this definitely works. No dribbles with heavy spring and 1.5, 1.8, and 2.0 NS. I did pick up some dribbling (still less than before and kinda intermittent) when I dropped to a softer spring. But I will lower pop off by using heavy spring and larger NS.

I think I'm lean in the mid-range (under 1/4 throttle bog) now, makes sense because of the extra fuel it was getting. But I couldn't fix it with what I had.

Right now I'm at 135 low jet and 32 psi popoff. I got some bigger Lows coming in the mail now.
 
302much

302much

Location
Highland Village, TX
Here is the Yamaha PN referenced above. It has a pocket milled around the check valve. I think that actually may help even more..

Will try to do some tuning tomorrow with these new ones instled.
 

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Robb235

Location
Chattanooga, TN
I found this forum doing a Google search, trying to figure my issue with valve bodies.

I'm rebuilding a set of Mikuni 44 I-Series carburetors that go on Yamaha's 66v motor (1200cc power valve), that powers the GP1200R jetski. The screw that holds on the BN34/107 check valve was corroded, and my screw extractor ripped the head off of the screw, leaving the body of the screw stuck inside the valve body. The Mikuni manual identified the valve body as part number BN44/165, so I ordered a new one online. To my surprise, the new one that showed up at my door had the hole directly over top of the BN34/107 check valve, instead of being offset like the OEM one.

I'm not sure I understand the reasoning behind the offset hole in the valve body? How does that help with dribble? What are the effects using the straight thru hole design (6R7-24412-01-00) versus using my OEM style with the hole offset (66E-24412-00-00)? How critical is it that I stick with the offset design?
 
veedubs

veedubs

Location
Dallas, GA
chadly

chadly

Location
minnesota
glad this popped up.

last year i was having the same issue with my dasa 48s. they would dribble at idle, upped the pop off from like 20 to 30 same issue. going to check mine tonight while i set them up for my new motor and compare my valves to the above ones.

maybe mine are completely different than the above posts, but for the 5 min of work could solve a lot of headaches for me or others if it is the case.
 
fastgtfairlane

fastgtfairlane

Location
Charlotte, NC
The dribble problem is coming from too high of fuel pressure especially with dual carbs that have 2 fuel pumps. Also being that the engine is bored, higher compression, pipe etc all which cause a much stronger pulse to the fuel pumps. This causes fuel to dribble past the needle and seat uncontrollably. Adding extra diaphragms don't always help either. This causes an almost impossible condition to tune out. The solution is to remove the fuel pumps and drill out the internal restrictor to the .125 Id that the fuel hose is. Then use a mikuni main jet in the outlet of the return. #60 is like stock size.. this equalizes the fuel pressure between both carbs and makes it much easier to tune. From there, get a fuel pressure gauge, connect between the carb and return tee on either carb, increase the jet in the return until the idle psi is around 2psi and 5-6 psi at wot. This will make your engine idle like stock and make the carbs much easier to tune. I have a built 735 with dual 44s and am running a 80 main jet. Larger engine might be up to 90-95 jet in the return. Definitely recommend using gauge to tune your setup to take the guesswork out.
 
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