Powersport engine - no adjustment carbs

Ding Ding

Well-Known Member
#1
A bike recently purchased came with the newer style Tecumseh "Powersport" engine, of the 3.5 HP variety. The carb was very very sticky so I took it off the engine and tore it apart for cleaning. I immediately realized there is no low or high speed adjustment on the carb.......which seems kind of dumb. Between the lack of adjustment and it being completely gummed up with old fuel, I thought this would be a great opportunity to replace the carb with a brand new one that allows for fuel adjustments.

Question: Will a 4 HP adjustable carb work on the 3.5 HP engine?

Please chime in with insight on this debacle.

Mike
 

Ding Ding

Well-Known Member
#3
Thanks, Dave! That is exactly what I wanted to hear.

And I suppose there is no need to get/try a 4HP carb when I can get the more appropriate 3.5 HP one.
 
#4
Mike, you got it right. Those carbs suck for mini bikes or variable throttle requirements. You can indeed use the older style Tecumseh carburetors on these and several of us have gone that route. You can also use the Tecumseh Clone carbs (China) which cost a fraction of the Tec carbs.

Here's a Chinese version.
This is correct. Those stock carbs suck. You can also replace it with a Walbro intended for a Clinton engine, something like this:
Walbro Carb Carburetor Clinton Tecumseh Go Kart LMB 202 | eBay

I have one of those Powersports 3.5 on my MTD and that's the route I went. ( I didn't buy it from thjat guy, I have my own secret stash) It was a direct bolt on but I had to fab up some linkage. The air cleaner even fit, in the right location. I also had to source the correct slant intake for the 3.5 'cause it's differeent than the HS40. Works really good, always starts first pull. Those are tourquey lil motors, really surprising amount of power for the HP rating.


Hard to see in this pic but that's a Clinton carb on there:

 

markus

Well-Known Member
#5
This is correct. Those stock carbs suck. You can also replace it with a Walbro intended for a Clinton engine, something like this:
Walbro Carb Carburetor Clinton Tecumseh Go Kart LMB 202 | eBay

I have one of those Powersports 3.5 on my MTD and that's the route I went. ( I didn't buy it from thjat guy, I have my own secret stash) It was a direct bolt on but I had to fab up some linkage. The air cleaner even fit, in the right location. I also had to source the correct slant intake for the 3.5 'cause it's differeent than the HS40. Works really good, always starts first pull. Those are tourquey lil motors, really surprising amount of power for the HP rating.


Hard to see in this pic but that's a Clinton carb on there:



You know if you cross reference the H35 powersport to the H40 powersport, the only thing you will find different is the sticker :laugh: They are cool little engines, The bottom ends are the larger HS parts, but they do have dinky little exhaust valves. I just picked up a recreational 1994 h35 (same larger bottom end but has the larger exhaust valve :thumbsup: ) for a build, will be using a mid 80's external coil shroud with the 4 bolt recoil on it and a few other things, should make for a good strong engine, I did a 2000 H35 small valve version last year and it ran well.
 

Ding Ding

Well-Known Member
#6
You know if you cross reference the H35 powersport to the H40 powersport, the only thing you will find different is the sticker :laugh: They are cool little engines, The bottom ends are the larger HS parts, but they do have dinky little exhaust valves. I just picked up a recreational 1994 h35 (same larger bottom end but has the larger exhaust valve :thumbsup: ) for a build, will be using a mid 80's external coil shroud with the 4 bolt recoil on it and a few other things, should make for a good strong engine, I did a 2000 H35 small valve version last year and it ran well.
Interesting to hear about the lack of parts variances from a H35 to H40. Did you swap to an adjustable carb on your powersport engine?
 

markus

Well-Known Member
#7
Interesting to hear about the lack of parts variances from a H35 to H40. Did you swap to an adjustable carb on your powersport engine?
I actually didn't, It ran pretty good when I got it, I just flushed it out when I cleaned up the engine. I would have gone to an adjustable though if it would have required anything more than a quick flush out and fresh bowl gaskets as I would have preferred it.
 

Ding Ding

Well-Known Member
#10
Update:

I spent $15 on a new fully adjustable carb for this H35 engine and finally installed it in a bike. I am very impressed by this engine. Smooth, quiet, and makes much more power than I ever thought it would. I earned a new respect for these new-old powersport engines!



 

markus

Well-Known Member
#12
Yea those really are great engines, They updated to a mechanical compression release in those years, something they very briefly used on the HS40 in the first couple years of production. The H engines never got them though, they always either had a pass through hole on on the outside of the valve seat or an added bump on the cam lobe, so they got a bit of a power boost when they came up with that cam for them :thumbsup:

I just wish there were more late 1980's donor engines floating around to scrounge the shrouds with 4 post recoils for them as I never dug that fan type recoil they went to.

Looks great :thumbsup:
 

Fisher1983

Active Member
#13
My Dads Manco Streaker has a Power Sport 3.5.....It startled me with the power output. Im turning a side exhaust 3.5 edger engine into a wannabe Power Sport for my Doodle Bug. It runs really good as is and has little use.
 
#14
I agree I have quite a few 3.5hp ones mostly side poopers a couple 4hp but they make really good power for 3.5hp will keep up next to my daughter with a Honda gc160 both stock engines
 
#15
I agree I have quite a few 3.5hp ones mostly side poopers a couple 4hp but they make really good power for 3.5hp will keep up next to my daughter with a Honda gc160 both stock engines
So the side poopers are worth building? Like I said I'm building one right now. Already did the exhaust. Buying parts for the front mount tank and the shorter Powersport intake with mini bike throttle control. It ran good with the edger stuff on there...I bet it'll scream with the Powersport package on it.
 
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