787 Carb Problems

[Jnz]

I am having what I believe to be carb problems on my 98 speedster. I rebuilt both carbs using kits from shopsbt and prior to this I used a kit on my 787 gsx and had no problem. I've been reading that most places don't sell genuine Mikuni and the aftermarket causes problems. I have one motor that fires right up the other takes a little more work to get it initially started. Restarts don't seem to be a problem. One engine will hit the rev limiter and the other falls on it self at about 3k. The first few times it died trying to go past and after a 2 more attempts it just would sit at 3k, not strong like its hitting the neutral safety but stumbling. I have pulled the carbs apart and they are clean, nothing in the filters and have two external Mikuni fuel pumps. Compression is 150 across the board both motors. Prior to taking them apart this time I pressure tested them and the seats held pressure no bubbling and I switched the springs out to black ones to get pop off set right. The only issue I was having a hard time with was getting the covers to seal it seemed to want to leak down until I tightened the screws with a vice grip to get them tighter than with a screw driver. Now my question is, are the aftermarket kits really causing me all this trouble ? If so, do they need complete kits again or are there separate parts I can order genuine of to take care of the issue ?

 

[ryffish]

I've had that problem also with mikuni carbs I do believe it was needle valve . I was told that the oem replacements were not exact which if you used the knockoffs it would make your engine run dangerously lean . I ended up finding a carb on ebay with low hours worked awesome . But I know there has to be someone who could sell the true oem needle valve for them.

 

[Jnz]

Needle and seat are still original. I replaced the oring and there were no leaks when testing. Are you talking about the diaphragm ?

 

[Jnz]

I was just going to find new diaphragms, but then I also had leaks on the cover with the filter under and the oring didn't seem to seal. I actually ordered a factory oring for one and I dont remember that making a difference. The screws still needed me to clamp on the outside of them with a vice grips to give another turn to seal. Otherwise they wouldn't pass the pressure holding test.

 

[Rmcrabb]

Any resolution here? I have a carb I can't seem to get sealed. I got it to seal once but after running a bit it leaking from the cover opposite the diaphragm

 

[Jnz]

Solution for me was genuine Mikuni kits and seals. Had it on the water yesterday. Runs great !

 

[Rmcrabb]

Did you physically see the difference with the genuine parts. Like the diaphragm material or the oring thickness?

 

[racerxxx]

One of the biggest issues is the stud length on the diaphragms. They will hold the metering arm open and allow fuel to seep. No bueno. If you scrol back over the last few pages of fuel related issues one of the first questions asked is did you use genuine mikuni rebuild kits. Thru years of experience on the forum from guys pulling their hair out and then replacing the parts with genuine parts and the carbs work is the proof. There are guys on here that do this stuff for a living, they swear by the genuine parts fun their own experiences.

See the post above yours.