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Old 07/20/10, 12:56 AM
HermitJohn's Avatar  
Join Date: May 2002
Posts: 8,056
Mikuni slide type carburetors

Replacement carbs for small engines are getting amazingly expensive. I have an old Tecumseh HH70 that I was thinking of putting back into use after its 20 year nap. It was one I used on a snowblower when I was in Michigan and brought with me when I moved here. Ok condition, just never used it again. Carb was adjustable as I remember it was a PITA, required one jet setting to start and run good cold, then as it warmed up, had to lean it out a bit with jet screw. Not absolutely horrible, but not something I ever relished messing with everytime I used it. But anyway somewhere along the line while it was doing its impression of Rip Van Winkle, its carburetor went AWOL.

Believe it or not a new OEM carb for it is still available.... for $100.... A used one on ebay sold for $44. Thats nuts, I'd be amazed if I could get $44 for the whole engine if it was tuned and running good.

But got to reading about the gokart and minibike folk that hotrod small engines. They like the MIkuni slide carbs or the Chinese clones of those carbs. But they also remove the governors. Well you do get quite a bang for your buck, the China clone Mikuni is all metal, has a real choke, and you can buy new jets in various sizes for it. Completely tunable. And get this, $20 shipped price for a 22mm version which is about right size for my engine. Come close to bolting right up too. BUT, and there is always a BUT, I need to keep the governor. Yep, going to use it on an old 24 inch Yazoo push mower. Well the Mikuni requires use of a throttle cable out of top of the sidedraft carb. By looks of it, has a internal spring to keep sliding throttle plate closed.

So has anybody seen one of these set up to work with a governor? Google is no help, just keep finding instructions on how to remove the governor when using a Mikuni... I am doubtful the governor would like that mandatory return spring, plus pushing a cable doesnt seem way to go either. Maybe with a real light return spring??? Governors I've seen on small engines always use rod from governor arm to throttle plate with no spring on throttle, the governor opens and closes throttle freely as it sees fit to maintain set rpm.

Probably help if I saw one of these carbs up close and personal and could play with it. I've just never been into motor scooters and such so never worked with Mikuni type carb.
"What would you do with a brain if you had one?" -Dorothy

"Well, then ignore what I have to say and go with what works for you." -Eliot Coleman
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Old 07/20/10, 08:39 AM
Ray Ray is offline
Join Date: Dec 2002
Location: MO
Posts: 974

sometimes Scribd has alot of this type info free just go there and type in the search you want. they have images in the books too. best wishes, ray
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Old 07/20/10, 08:59 AM
Cabin Fever's Avatar
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Join Date: May 2002
Location: Between Crosslake and Emily Minnesota
Posts: 14,591
I'm not going to be much help. All I can tell you is that both of my Polaris snowmobiles use Mikuni carbs. One sled is a 3-cylinder and the other is a 2-cylinder. Each cylinder has its own carb....consequently I own five Mikuni carburetors. Desired speed (rpm) is set by the cable to the trottle lever. No governor is involved.

Last edited by Cabin Fever; 07/20/10 at 09:09 AM.
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Old 07/20/10, 03:00 PM
HermitJohn's Avatar  
Join Date: May 2002
Posts: 8,056
Yep, like I said these Mikuni carbs were designed for scooters and other small vehicles that dont need a governor. I just thought maybe somebody had adapted one for use with a governor. Shame, look like nice little carbs considering modern OEM small engine carbs have become plastic throw aways.

Oh well, not super big deal, not like I need the mower running tomorrow or anything. Perhaps I'll run across the original carb for this engine. I have vague recollection that I took it off to clean and rebuild it, and somehow that just never got done. I rarely go to auctions anymore or probably find whole engine pretty cheap that could at least donate its carburetor.

Suppose thats why the old adjustable Tecumseh engine carbs bring some money on ebay, cause they are adjustable. Back in that era, I never considered them particularly wonderful carb.
"What would you do with a brain if you had one?" -Dorothy

"Well, then ignore what I have to say and go with what works for you." -Eliot Coleman
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Old 07/21/10, 10:51 AM
Join Date: Dec 2003
Posts: 3,693
I've not adapted one to a governor, but it would be simple enough. The spring that pushes down the slide piston is very light, it's not going to cause the governor any troubles. Almost all are cable actuated, with the cable going down into the slide and pulling it up. You could use some bicycle cable to work it and adapt it to the linkage. They would also work with a solid rod instead of the cable, if that was easier for you.
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