Carb issue hs40

Bbqman

Active Member
#1
Well, I bought the service carb put my choke shaft on it. Still runs like crap Pops and backfires when I try and go full throttle. Once it gets going and it's warm full throttle does not open the butterfly the whole way. So full throttle I am going about 5 mph of that. Plus it idles to high and the idle screw not touching the butterfly. I give up. It's the same part number as original carb. Governor is set correctly. I don't get it. I have tried eBay carbs and other brands. This latest is a Tecumseh service carb with the same part number as the original. I would appreciate any help. I can't figure out out. Thanks
 

joshua. c.

Well-Known Member
#2
Sounds like it's out of tune and running rich, adjust the jet needles. These carbs like a lean idle adjustment and a perfect high speed adjustment. Stock Tecumseh 3-5hp carbs only allow the butterfly to open 3/4 of the way at when opened fully. this can be fixed by grinding at the spot that stops the throttle plate from moving until it opens fully. I don't know if this is true with aftermarket carbs.

The throttle not opening enough may be the control spring location. There are multiple holes the throttle Controle spring can attach to on the governor arm, move it up to go faster down to go slower but with the bike popping its more likely the tuning issue making you go slow.
 

old shed finds

Well-Known Member
#4
I'm about to challenge this subject too as I'm doing a rebuild on a Rupp Sprint HS40 I'm thinking of trying the diagram carburetor? I am missing the 130 dollar slant intake so a bowl carburetor may not tune in on the Rupp angle. Anyhow I'm scared to get a Tecumseh carburetor to work right.
 

mustangfrank

Well-Known Member
#5
I'm about to challenge this subject too as I'm doing a rebuild on a Rupp Sprint HS40 I'm thinking of trying the diagram carburetor? I am missing the 130 dollar slant intake so a bowl carburetor may not tune in on the Rupp angle. Anyhow I'm scared to get a Tecumseh carburetor to work right.
I'm not a fan of the diaphragm carbs unless they were on the engine originally. There's always the slant adapter for 20 bucks + postage...#33301A SLANTED INTAKE ADAPTER for Tecumseh engine (blackwidowmotorsports.net)

I've read a couple posts of guys running a bowl carb at 20 degrees without a slant intake, just have to set the float level accordingly.
 

Triley41395

Well-Known Member
#6
I'm not a fan of the diaphragm carbs unless they were on the engine originally. There's always the slant adapter for 20 bucks + postage...#33301A SLANTED INTAKE ADAPTER for Tecumseh engine (blackwidowmotorsports.net)

I've read a couple posts of guys running a bowl carb at 20 degrees without a slant intake, just have to set the float level accordingly.
My brother has a regular (Straight) intake on his rupp and he did have the float set higher than normal. The only problem he had was you HAD to have a gas shut off at the tank and HAD to use it when you were not riding. His bike runs pretty good.
 

mustangfrank

Well-Known Member
#7
My brother has a regular (Straight) intake on his rupp and he did have the float set higher than normal. The only problem he had was you HAD to have a gas shut off at the tank and HAD to use it when you were not riding. His bike runs pretty good.
Yeah, I don't advocate running them like that plus it just hurts the eyes. You'll want to set your bro's float/float level LOWER than stock/level operation and check the bowl gasket to keep gas from leaking out, (if he's still running it like that).
 
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