Genuine Mikuni VM22-133 initial jetting for Tecumseh H50 motorsports engine.

M

MikeHoncho

Member
Hi, quick backstory, I purchased a single seat Manco kart with a never ran Tecumseh H50 motorsports engine for my 7 year old. I have quickly found out that his driving style and the factory tillotson 365b are not a match.

I’m looking for a ballpark starting point on jetting the Mikuni VM22 carb, I’m at 450 feet above sea level with average temps in the 50’s and 60’s. I do not know the compression ratio or cam specs other than the parts in it are the ones supplied by Tecumseh for this engine.
Exhaust is 1 foot of 1” header pipe into a factory KTM 125 2 stroke silencer. No porting has been performed or any other machine work.

Any help is greatly appreciated.
 
Put it on see what happens. Another option would be jet it similar to a briggs Lo 206 .
Does it have the air filter they are needed for numorous reasons jetting being one .
 
flattop1 said:
Put it on see what happens. Another option would be jet it similar to a briggs Lo 206 .
Does it have the air filter they are needed for numorous reasons jetting being one .
Click to expand...
Yes it does have an air filter, I know it will need fine tuning, I’m just looking at trying not to spend a fortune on jets to get started. Thank you for you input.
 
I think id start with a richer idle jet . Then a Lo206. Maybe . 020
What jets are in it
 
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flattop1 said:
I think id start with a richer idle jet . Then a Lo206. Maybe . 020
What jets are in it
Click to expand...
I couldn’t tell you for sure, as the carb and filter and the like are in the mail. I believe it’s a 12.5 pilot and 100 main that comes preinstalled on the VM22
 
Mm vs decimal . Flatheads are pretty forgiving . As far as jetting.
If it bogs off idle richen the pilot.
There's probably a post in here you just have to go through them . It' d be for a briggs but close enough. Probably within the last 20 pages.
 
MikeHoncho said:
I couldn’t tell you for sure, as the carb and filter and the like are in the mail. I believe it’s a 12.5 pilot and 100 main that comes preinstalled on the VM22
Click to expand...
Just a heads up but if it comes with an adapter for a flathead...it's most likely a Briggs adapter, not a H50 adapter. The bolt spacing from a Briggs to a H50 is not the same. You'll probably have to ream out the mount holes on the carb. The exhaust bolt spacing is also not the same as the Briggs which is what most pipes are for. You'll need to get a H50 spec pipe with the right side flange chopped flush in order to get the carb to sit correctly. It can be done, but if you're looking at "briggs" pieces and adapters just be aware they don't work perfect on those H50's.
 
I have it fairly dialed now that I was able to take some time with it today, Mikuni jet #20 for the pilot with air screw 1.5 turns out, needle down one clip from the middle and a #140 main. There is a very slight stumble if I quickly whack the throttle, so I’m considering going to a #22.5 pilot to see if I can’t tune that transition out.

The carb itself bolted up perfectly to the supplied H50 motorsports intake adapter, which I’m very thankful for.

Overall the Kart is much more friendly for my boy to drive, it also starts easier and idles much nicer compared to the Tilly. I’m happy not fouling plugs every couple of hours and contaminating the oil with fuel.
 
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