H50 with Mikuni carb setup

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paulsblocks

New Member
#1
#1
Hello! This is (I think) a Tecumseh H50 off of a snowblower (if I'm wrong please correct me). I'm working on getting a throttle linkage set up on it and after doing a little bit of thinking and testing I want to do something different with the throttle setup. Has anyone put a Mikuni carb on one of these or done something differently? I just want to get away from the stock setup because it likes to hold the throttle halfway open. doesn't have to necessarily have to be a Mikuni, I'd just like o find some sort of round slide carb or some other easy way of hooking up a minibike throttle cable to it.

atec.jpg atec2.jpg atec3.jpg
 
delray

delray

Well-Known Member
#3
#3
you can't put a mikuni on a flathead tecumseh without a billet rod. my opinion tecumseh engines are very weak when it comes to stock rods and with a mikuni on it. the motor will rev way above the stock governor rpm's (3600) and you will have no way of controlling rpm's with that style carb on it.
 
C

cfh

Well-Known Member
#9
#9
I put slide carbs on Tecumseh's all the time without issue, and without (or with) a billet rod. But then again, i don't run them at high rpm for extended time. It's not like 3700 is going to lose a rod (versus 3600.) What happens is the rod journals get starved for oil at extended high rpm, and seizes the journal, and THAT breaks the rod. If you only leave it WFO for a few seconds, you're fine. Or if you run a Torque converter, that really helps too, as it hold the rpms down.

Look at it this way... Rupp sold H50 and HS40 engines with Dellorto slide carbs and the governor defeated from 1968 to 1973. They sold *a lot* of them. Did they all burn up? heck no. Did some burn up. Heck yes. But it's all in your right hand. If you only know off and WFO, yea, you're gonna wreck things.

Also a H50 billet rod is pretty impossible to find (i haven't seen one for sale for *years*.) You can still get a billet rod for a HS40/HS50, but i don't anyone is gonna find a billet rod for an H50. So if you want to run a slide carb on that engine, best to have a sensible right hand.
 
delray

delray

Well-Known Member
#10
#10
cfh said:
I put slide carbs on Tecumseh's all the time without issue, and without (or with) a billet rod. But then again, i don't run them at high rpm for extended time. It's not like 3700 is going to lose a rod (versus 3600.) What happens is the rod journals get starved for oil at extended high rpm, and seizes the journal, and THAT breaks the rod. If you only leave it WFO for a few seconds, you're fine. Or if you run a Torque converter, that really helps too, as it hold the rpms down.

Look at it this way... Rupp sold H50 and HS40 engines with Dellorto slide carbs and the governor defeated from 1968 to 1973. They sold *a lot* of them. Did they all burn up? heck no. Did some burn up. Heck yes. But it's all in your right hand. If you only know off and WFO, yea, you're gonna wreck things.

Also a H50 billet rod is pretty impossible to find (i haven't seen one for sale for *years*.) You can still get a billet rod for a HS40/HS50, but i don't anyone is gonna find a billet rod for an H50. So if you want to run a slide carb on that engine, best to have a sensible right hand.
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yep i'm with you with a burst of throttle. high rpm's that differnent story. two most damage rod motors i have seen are the H blocks's and hs-40's kind of a believer on using 5w-30 oil when it comes oiling tight clearance areas and staying away from straight 30w. this is a common use in the gokart world of racing.
 
mustangfrank

mustangfrank

Well-Known Member
#11
#11
paulsblocks said:
Hello! This is (I think) a Tecumseh H50 off of a snowblower (if I'm wrong please correct me). I'm working on getting a throttle linkage set up on it and after doing a little bit of thinking and testing I want to do something different with the throttle setup. Has anyone put a Mikuni carb on one of these or done something differently? I just want to get away from the stock setup because it likes to hold the throttle halfway open. doesn't have to necessarily have to be a Mikuni, I'd just like o find some sort of round slide carb or some other easy way of hooking up a minibike throttle cable to it.

View attachment 271532 View attachment 271533 View attachment 271534
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Slide carb setup has it's benefits and the downside mentioned of no governor especially if the mini will be in other less careful hands. If you want to keep the stock carb you'll have better control if you switch to a minibike throttle with the heavier return spring. That control assy on it is the throttle lever type that wasn't designed with a return spring.

A couple pics of my H50 shroud with a factory minibike throttle assy and a new one (same part), the new ones don't come with a cable stay included for some dumb reason so save yours or they have them at good hardware stores.

20201122_165641.jpg 20201122_165554.jpg

Pics are a little blurry, my tablet was fogging up...that part number will yield better pics with a search.
 
P

paulsblocks

New Member
#13
#13
delray said:
you can't put a mikuni on a flathead tecumseh without a billet rod. my opinion tecumseh engines are very weak when it comes to stock rods and with a mikuni on it. the motor will rev way above the stock governor rpm's (3600) and you will have no way of controlling rpm's with that style carb on it.
Click to expand...
Is there any other carb i could put on it that wouldn't be as powerful as a mikuni? Trying to avoid doing engine internals
 
P

paulsblocks

New Member
#14
#14
cfh said:
I put slide carbs on Tecumseh's all the time without issue, and without (or with) a billet rod. But then again, i don't run them at high rpm for extended time. It's not like 3700 is going to lose a rod (versus 3600.) What happens is the rod journals get starved for oil at extended high rpm, and seizes the journal, and THAT breaks the rod. If you only leave it WFO for a few seconds, you're fine. Or if you run a Torque converter, that really helps too, as it hold the rpms down.

Look at it this way... Rupp sold H50 and HS40 engines with Dellorto slide carbs and the governor defeated from 1968 to 1973. They sold *a lot* of them. Did they all burn up? heck no. Did some burn up. Heck yes. But it's all in your right hand. If you only know off and WFO, yea, you're gonna wreck things.

Also a H50 billet rod is pretty impossible to find (i haven't seen one for sale for *years*.) You can still get a billet rod for a HS40/HS50, but i don't anyone is gonna find a billet rod for an H50. So if you want to run a slide carb on that engine, best to have a sensible right hand.
Click to expand...
Alright good to know. What slide carbs have you ran with these? I'm familiar with mikunis so thats my first insight, but im not picky as long as I can bolt it up and its tunable
 
mustangfrank

mustangfrank

Well-Known Member
#15
#15
paulsblocks said:
Is there any other carb i could put on it that wouldn't be as powerful as a mikuni? Trying to avoid doing engine internals
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You can't run the factory governor with any carb other than factory type, the lack of a governor to keep the RPM below 4k and a weak factory connecting rod is the issue.
 
delray

delray

Well-Known Member
#16
#16
paulsblocks said:
Is there any other carb i could put on it that wouldn't be as powerful as a mikuni? Trying to avoid doing engine internals
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as you can see this can be a very hot topic when someone wants to run a mikuni on a stock tecumseh. even i have done it. i don't endorse and saying it's just ok run and all. i personally had very good luck with a ohh-motor with a stock rod thats been clean up and the rod beam been polish. of course this rod is little different then yours and the hs-stuff. engine pulls hard up to 4700+ all day and has been holding every summer i take it out for a spin....:scooter:
for you if you do put a mikuni on it. run 5w-30 and a tach and make sure it stays under 5000 rpm's. better yet make it 4500+ i'm sure your stock cam won't build any power after that anyway.
goodluck.
 
C

cfh

Well-Known Member
#17
#17
I've run quite a few different slide carbs on Tecumseh motors. My favorite are the Dellorto (not necessarily the ua19), but they are pricey. The cheap Honda style slide carbs work great on the Tecumseh. i have a pretty extensive write up about them here: http://www.pinrepair.com/minibikes/tecumsehmb.htm#carb2
Personally i don't like stock Tecumseh carbs, unless you are running the bike in the winter. They are awesome and start easy in cold weather. but they just suck, they are basically lawnmower carbs designed for a fixed rpm. the slide carb stuff is a lot nicer and tunable. it's nearly free performance for a tecumseh. but you will be running without a governor, so you need to have a proper right hand...
 
delray

delray

Well-Known Member
#18
#18
cfh said:
I've run quite a few different slide carbs on Tecumseh motors. My favorite are the Dellorto (not necessarily the ua19), but they are pricey. The cheap Honda style slide carbs work great on the Tecumseh. i have a pretty extensive write up about them here: http://www.pinrepair.com/minibikes/tecumsehmb.htm#carb2
Personally i don't like stock Tecumseh carbs, unless you are running the bike in the winter. They are awesome and start easy in cold weather. but they just suck, they are basically lawnmower carbs designed for a fixed rpm. the slide carb stuff is a lot nicer and tunable. it's nearly free performance for a tecumseh. but you will be running without a governor, so you need to have a proper right hand...
Click to expand...
just remember he is running big block engine. so stock or mod it will need at least 22mm carb...:scooter:
 
P

paulsblocks

New Member
#19
#19
cfh said:
I've run quite a few different slide carbs on Tecumseh motors. My favorite are the Dellorto (not necessarily the ua19), but they are pricey. The cheap Honda style slide carbs work great on the Tecumseh. i have a pretty extensive write up about them here: http://www.pinrepair.com/minibikes/tecumsehmb.htm#carb2
Personally i don't like stock Tecumseh carbs, unless you are running the bike in the winter. They are awesome and start easy in cold weather. but they just suck, they are basically lawnmower carbs designed for a fixed rpm. the slide carb stuff is a lot nicer and tunable. it's nearly free performance for a tecumseh. but you will be running without a governor, so you need to have a proper right hand...
Click to expand...
That was the first thing that came up on Google when I searched this topic. Awesome guide! I saw you recommended for an 80cc honda engine on there. Do you know if that'll bolt right up to this engine or am I going to need a custom fabbed intake? The stock intake manifold on it right now has a little under 46mm between the bolts to the carb
 
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