Yamaha YTM200 / Mikuni VM22 / Float Height / Idle / Fuel Mixture

[Hutch08]

Currently going through a complete service on my YTM200K, adjusting valves, cam chain, clutch, carb, brakes, etc...



I pulled the carb off the bike, gave it a thorough cleaning and am checking to make sure everything is in proper spec's.

According to the manual, the float height should be 21.5mm and the fuel level in the bowl should be 3mm from the carb body.

When I checked my float level, it seemed to be on the higher side... but due to the the angle of the carb, the fuel level is higher on the front than back.
So should I be checking it in the middle? front? back?

Here's a picture of the level initially:



I pulled the bowl and tried to see the point at which the needle was fully seated, looked to be around 19mm from the float to carb body.

I adjusted the tab on the float to close the needle around 21mm. Here's how it looks now:



I'm wondering if that's going to be too low now? When I got the bike it started and ran fine, but I did feel that it was a little sluggish down low. Sometimes if you quickly gave it full throttle off the start it would hesitate, which I've heard can be a symptom of running lean or rich...

On the topic of jetting, once I get the floats dialed I'll have to set the idle and fuel mixture screw.

Manual states that the idle be set to 1400rpm and the Mixture screw set to 2 1/4 turns out. Anyone have any tips on dialing in the idle and mixture screws?
Also, to confirm the Mikuni VM's mixture screw is an "air screw", clockwise will make mixture more rich, counter clockwise will lean the mixture?

Thanks guys!

[Jmoozy27]

That's one of the sweetest looking tri motos I've ever seen!!!

[Hutch08]

That's one of the sweetest looking tri motos I've ever seen!!!

Thanks man!

Here it is last summer when I bought it off a buddy, he got it from his uncle which was the original owner.



The bike was 100% original, just had a burned out high beam and missing the tail light. I put the pro taper handlbars on it because the stockers were bent slightly on the one side.
I've also got an air filter adapter for a Raptor 350 along with a clamp-on UNI filter on the way to replace the deteriorated foam factory air filter.
The rubber carb boot was showing it's age, had some dry-rot cracking so I replaced it with a 1.25" ID fuel hose that fit perfectly.



The valves were actually still in factory spec and on the tighter side of tolerance. The motor pulled just over 145psi on the compression test, I think factory spec is like 129 to 149psi with a minimum of 114psi.

It's never been "restored" either... she's just been hiding in a barn for many years.

[Hutch08]

So I did some reading outside the manual... Mikuni states that float height is set from the gasket surface on the carb body, not the actual carb body "lip" like I used.
I decided to pull the carb again and see where I was at... I tested the fuel level in the bowl on the bench sitting dead level in vice.

Sure enough, it was now a little on the low side. Yamaha recommended 3mm, and I was sitting about 6mm.
I pulled the bowl and re-adjusted the float tab so the moment before the needle spring compresses was 21.5mm, as per the manual.


Buttoned the carb back together and checked the fuel level with the tube, and voila... 3mm from the carb body all the way around.


Mounted the carb and for curiosity I checked the fuel level with the carb as it sits leaned forward, so for anyone looking to adjust on the bike it should look like this:


So I was a little high to begin with, but not as bad as I suspected.

[Jmoozy27]

Glad you got it. Fire it up yet?

[Yamawheeler]

Thanks for the info and pics. Very nice ytm.