mikuni issues on mud motor

[aksmj]

I've been lurking around here a lot in the last few months. I've learned tons while putting together this predator 212 that I am using on a duck hunting boat. What I thought was going to be the last part of the puzzle is driving me insane...the mikuni 22mm knock off.

mods on the motor are arc flywheel, arc rod, black mamba jr, 26lb springs, straight exhaust, and a uni on the mikuni.

I have a fair amount of experience with carburetion on harleys and dirt bikes but maybe I'm missing something with these little motors. I'm losing it, it's duck season out here in Utah!

I've spent the last 3 days trying to get this mikuni right. I got the 130 and 12.5 jets with it since, after reading a ton, that seemed to be a fairly safe bet. Put the jets in and put the carb on and it fired right up but goes straight to 5-6000 rpms and stays there.
I've spent a ton of time going through the mikuni manual, the agk post and saw a good post on diygokarts.
I've thoroughly gone through the whole tuning process with the mixture screw and idle adjust multiple times. Idle adjust on the side of the carb is functional, moves the slide up or down easily. Turning the mixture screw either way does nothing. Which makes me think air leak.
I've checked for leaks around the manifold. Got no change in revs spraying carb cleaner all around it.
new gaskets and I used some high temp on the connections as well.
Tried the 15 pilot jet. no change at all.
Tried different clip positions on the needle with all of the previous combinations.
I've cleaned the carb and jets, re cleaned, and cleaned again.
The throttle cable isn't keeping the slide up either-thoroughly dealt with that.
Does a insulator need to be run with the manifold in this situation?


Could it be that I need to go all the way to 17.5? I would think that if that's the case, the 15 would at least show some sort of change from the 12.5

Through all of this, now I need a new float bowl gasket and a new mixture screw. Seems like there is fuel coming through the threads of the mixture screw. Didn't think that was possible.

Anyone know where to get a mixture screw for the 22mm (that's not on ebay shipping from China)

I really appreciate any insight.

and thanks for everything I've already learned from you guys' previous posts.

 

[ole4]

if you are running that fast on startup then either the slide adjuster is in too much or the cable is holding the slide up. Pilot jet can't do that. Are you using one of the Chinese clone mikunis with the oval slide area? then your jetting is close. If the slide is down then you must have a air leak Can you post of picture of the carb and manifold?

 

[aksmj]

Yeah, I can't help but think it is a leak. Ive gone back through and disassembled and reassembled the manifold to the motor and carb to the manifold.
I've tried it with the throttle cable off and the slide seems all the way down.
I can get a picture when it's light out tomorrow. It's the short manifold from nr

Yeah, it is the clone round slide small body.

 

[durandbagwell86]

Run a 15 pilot jet. I think you are running with the enricher open. Set idle screw with it closed (lever down).

 

[aksmj]

Run a 15 pilot jet. I think you are running with the enricher open. Set idle screw with it closed (lever down).

Seems like there is a lot of confusion with these Chinese mikunis and and the enricher. With the the carb off I looked in there and pushing the lever down closes the little piece over the small hole. Which would be "choking" it no?

 

[ole4]

No that is the run position lifting the rubber piston lets extra fuel and air in.

 

[aksmj]

man, I've seen so many threads on the enricher lever position. Half say up, half say down haha.
This is a case where I seriously hope you just made me feel like an idiot!

 

[aksmj]

You are definitely right! wow haha... Getting closer with it, but still a bit finicky. Throttle response is real nice but when it's coming back down to idle it takes an extra second to get down to around 3,000 rpm and then kind of jumps around. I'm going to take it out to the water now and try to get it dialed. I feel like tuning it with the resistance of the water against the prop will be more accurate than in my driveway.

 

[ole4]

3000 is still high should be around 1200-1500 according to my mini tach's You can lower slide screw a bit then readjust air bleed for best idle. Should not have to go more than two turns out on air bleed screw

 

[durandbagwell86]

You are definitely right! wow haha... Getting closer with it, but still a bit finicky. Throttle response is real nice but when it's coming back down to idle it takes an extra second to get down to around 3,000 rpm and then kind of jumps around. I'm going to take it out to the water now and try to get it dialed. I feel like tuning it with the resistance of the water against the prop will be more accurate than in my driveway.

I knew that was the problem. Now you need a 15-17.5 pilot jet and needle clip in center position. I had a similar build but with a black mamba sr. Cam and fully ported head, I have hit 32 mph with it on my 1232 Jon boat with a 5.5" prop. Hope you get it flying.

 

[aksmj]

I seriously feel like a jerk with this whole enricher thing.
Whatever, glad it was something so simple. Got the boat in the water today and that made a world of a difference being able to tune it out there. I have it idling nicely around 2500-2800 in the water. Doesn't want to go much lower than that and I'm fine with it. With the prop out, it jumps to about 4-5000. I ran the 12.5 pilot, needle one down from middle position and 2.5 turns out on the mixture. Plug was reading rich. Put needle up to the middle position and tried the 15 pilot jet and the spark plug read much better. Over all I'm happy with where it's at for now. gps says top speed was 13.5. I was out on the great salt lake and it was super windy. Fun in a little flat bottom boat.
I really built it for torque though as that's what these mud motors need to get through the shallow muck.

durand...that is seriously impressive. And in a 1232!?! slightly terrifying. I think I'm going to get a bigger prop, I feel like the motor will push it.

 

[aksmj]

I knew that was the problem. Now you need a 15-17.5 pilot jet and needle clip in center position. I had a similar build but with a black mamba sr. Cam and fully ported head, I have hit 32 mph with it on my 1232 Jon boat with a 5.5" prop. Hope you get it flying.

Did you ever have an issue with a bit of fuel slowly dripping from the carb drain while running? I'm thinking since this little thing shakes so dang much a bit of fuel is constantly splashing into the bowl overflow tube? The drain screw is good.

 

[durandbagwell86]

Did you ever have an issue with a bit of fuel slowly dripping from the carb drain while running? I'm thinking since this little thing shakes so dang much a bit of fuel is constantly splashing into the bowl overflow tube? The drain screw is good.

Mine might've leaked very slowly, but not much at all. It might be the float height. Yeah, 32+ on a 1232 is awesome. The small 5.5" prop turning over 8000 RPMs and an awesome holeshot. I was running a Robertson torque loop header on it.

 

[aksmj]

Yeah, I'll check the float height again, maybe lower it a hair. Been out hunting with it the past two days and it's been running really nice. Did almost lose my pipe from the nuts trying to rattle off the studs. Even after torquing them and lock tight. I think I'm going to order the robertson loop. Not convinced this tiny straight pipe is doing all that much.