Fuel flow problems with Mikuni pump. a/f ratio is Never balanced.

xBrent92

xBrent92

New Member
#21
#21
I'm not sure about going eBay for a carburetor. I didn't really want to say but.. i'll admit... i got this 390 carb off of ebay :/ for $15

And the jet size.. It is either the size of the predator stock jet or smaller.
So i jetted it up. Maybe too big But i figured bigger carb= bigger allowable jet size. I'll let you guys know sometime ( .078 ) Either way, i have race fuel and 2 other jets to play with when i decide to mess around with the system and use it.
The Emulsion tube was noticeably bigger. I don't know the precise measurement but it is noticeable.


Twid said:
275
Click to expand...
.290 for the win :p @104LSA 246duration

added: i have a post before this.
 
Last edited:
xBrent92

xBrent92

New Member
#23
#23
Update:
So i cleared all debris from the tank hose inlet and the outlet, attached a slightly longer fuel line to reach the carb with ease and at first it ran real nice. i mean it ran MEAN lol.Like full speed in half a second mean especially with the .078 main jet.
But then it started running lean. i blew through the carburetor fuel inlet and hardly any pressure was going through. hmm..

So i opened it up and ran a wire through both ends of the fuel inlet and the other end of that,(what's it called? high speed jet?) to clean any debris and then i was able to blow through it. No trash came out but it allowed pressure through .

With it back to normal i test ran it with no load for a minute and it did the same thing..ran lean and couldn't even blow through the carburetor fuel inlet and now i have to repeat the cleaning process.

So the problem has been narrowed down to the carburetor. I tried removing above the fuel lever to see if i could see anything but it's like it was glued then screwed in there really tight.

I've learned the importance of a fuel filter now :thumbsup: . My carb gaskets are now custom Felpro as well.
 
Last edited:
xBrent92

xBrent92

New Member
#25
#25
Alrighhhtt. Drilled pilot jet.
Purrs like a kitty at idle and roars like a lion on acceleration. Needs a slighhhtly bigger main jet though just like CarPlayLB said.
and possibly 32pound springs.
 
L

Latent

Active Member
#26
#26
I run the 390 carb on a 196cc clone and its perfect for my application, but my engine build is black mamba cam, flat top piston, dual valve springs, champion rockers, milled .003, 28.5 intake 25mm exhaust, jetting is 28/42 and its PERFECT. I read through your thread and I came to the conclusion that either the carb was too big for your engine if you have stock valves on a 6.5hp clone, an air leak or a fuel pump problem. Personally I ran the mikuni fuel pump and it doesn't compare to other high flow fuel pumps you can get for cheaper on ebay. I don't currently run a fuel pump and had no problems. Maybe try running it without the fuel pump and see how that goes. Just my .02$ :thumbsup:
 
You must log in or register to reply here.
Top