# Hmsk80 r&r carb still blows white smoke after full throttle



## brianmilw (Oct 23, 2013)

The motor is a 1995 tecumseh HMSK80 8 HP SNOWKING ON A MTD 826
OK I have no idea and am stumped. i bought a carb rebuilding kit after having a surging problem. cleaning it didn't fix my problem.

AFTER REBUILTING I SET THE CARB AT 1 TURN ON THE IDLE JET......1 1/2 TURNS FROM SEAT ON BOTTOM MAIN JET AND THE ENGINE IS ONLY SURGING ON FULL THROTTLE AND ACTING IRRATICALLY LIKE FUEL IS BUILDING UP FROM A RICH RUN CONDITOIN.

IT WILL IDLE FOR AWHILE WITH NO SMOKE BUT NO MATTER HOW MANY DIFFERENT WAYS I WENT ADJUSTED A LITTLE LEAN OR RICH OF BOTH JETS I GET A WHITE CLOUD OF SMOKE WHEN GOING FROM IDLE JET TO MAIN FROM LOW SPEED TO HIGH,..

I DID A ....OPPS SORRY ABOUT CAPS.
i did a compression test on the motor and it is @ 140psi

on full throttle when it is surging if i lean out the bottom main jet a little bit i start to get back fires and small sparks inside of the muffler.

if i richen it up about 1/2 making it a whole 2 turns out from factory starting point the rpm's stabilizes and keeps running at fulll throttle but engine kills when i drop to low idle and runs irratically.

Ive rebuilt and adjusted carbs on a few old h70 and had no problems... im stuck. i think it is a govenor problem. I can see pliers marks on the little tab and watched a video where the guy said the govenor wont cause a surging or flooding rich condition it just opens the buttefly on carb and kind of understand where when a engine bogs down under load the airflow or weights on shaft would move lever to add more throttle than the set high run condition. might be off????.

when i turns the motor over without the spark plug in the govenor arm is rocking back and forth and i hear a noise coming from the area which could be a normal noise not sure.

someone help me before i cut this thing in half with my rose tip wrench!!!!!

also, I got the hole on the body of the carb by stamp cleaned. all 3 small holes under small welsh plug.on body of carb. blew out everything on carb. all passages. had both choke and thottle butterflys and shafts out. everything is like new.

one more thing, no smoke on constant full throttle.
no smoke on idle but no matter what my needle jet adjusts are I get big white poofs of smoke when switching from idle to full with black smoke following after the white sometimes depending on if i have the needles adjusted funky.

dropping from full rpm to idle. the engine usually dies but will start back up and idle....
at idle it runs irratic sometimes.

new plug had thick carbon black coating and looked rich.

could this be the exhaust valve? crank case venelaltion or something odd? I have no idea and have thrown the rag in for right now... just poked around for a few idea's. Tech's, engineers and the knowledgeable please help...


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## Rentahusband (Aug 25, 2008)

Are the gaskets between the carb and elbow/elbow and engine in good shape? As Geo says, spray some carb cleaner around the mating surfaces, if the engine tempo changes, then there is an air leak. If that checks ok, then look at the flywheel key to see if it is sheared at all. Remove flywheel to verify the condition of the key. Outdoorpowerinfo.com has really good info on the breakdown of carbs. Valve clearences are .008-.012 for both.


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## usmcgrunt (Sep 16, 2007)

After checking the suggestions by Rentahusband, try adjusting your carb again starting from the initial settings. Start the engine and allow it to warm up a few minutes. At idle, turn the side air screw in until the engine stumbles, then turn in out until it stumbles again. Screw the needle back in a 1/4 turn at a time and pausing while the engine reacts until you find the spot it runs best at and leave it. . Raise the throttle to full speed and use the same procedure as the low speed adjustment on the high speed needle on the bottom.

It sounds like you may need a valve adjustment. Check the clearance when engine is cold.Have you checked the oil level? To high a level will cause smoking. Also, smell the oil for a gasoline odor which could be caused by a leaking needle and seat in the carb.


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## brianmilw (Oct 23, 2013)

Governor was way out of wack, carb was rebuilt and adjusted before post. might have a dirty filter in tank limiting fuel,.


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## brianmilw (Oct 23, 2013)

does anyone know what the rpm specifications are at idle and full throttle?


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## Rentahusband (Aug 25, 2008)

Around 1,500 for idle and around 3,500 for full throttle. To my knowledge these do not have an in-tank filter.


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## paulr44 (Oct 14, 2008)

Tough one. First you've had good responses so far, but I want to add a couple things.

One, compression at 140 PSI sounds high - this isn't a factor for the smoke condition, but with Tec. engines normally I'd expect to see 60 to 80 as they have a compression release.

White smoke is usually oil. There are several ways obviously for that oil to migrate into the intake / combustion chamber, which I will discuss.

1. Bad breather. On older snow-blowers (all engines years ago) the breather hose usually is vented to the atmosphere, but a bad breather can't control the CC (crank case) partial-vacuum that it's supposed to. Breathers let air out, are not supposed to let air in. 12 water-column inches of CC vacuum at full throttle would not be unreasonable.

2. Related to #1, I saw many Tecumseh engines pump oil from the breather from a CC leak, as dipstick tubes were often loose. I'd always tighten them when doing a service. Also, I had one that I had to put a gasket under the tube flange to stop it from leaking air.

3. Overspeeding / overfilled / too light an oil weight can cause oil to foam and make an engine smoke.

4. Worn rings or valve guides. Oil migration from the bottom end obviously.

5. Glazed cylinder walls. Rare but have seen it first-hand.

The surging can be a number of things, such as an intake (gasket) vacuum leak, worn throttle shaft, improperly set-up governor, worn (groove in spool) governor gear, worn governor shaft boss in block, restricted carburetor, worn linkage...these are the common culprits. I WILL ADD THAT MANY TECUMSEH snowblower and similar engines SURGE as part of their nature WHEN NOT UNDER LOAD. If it doesn't surge under load when fully warmed up, tell the owner it's normal.

AND LASTLY, IF YOU'RE TESTING THIS UNIT WITH THE HEATER BOX OVER THE CARB. AREA and it's ABOVE like 35 - 45 degrees outside, the engine is probably overheating WHICH CAN over-expand the cylinder and make it smoke and surge, have a hard time re-starting or not want to re-start at all. The heater box should be removed for testing in warmer weather, and you'd have to set it up on the rich side to account for an engine needing more fuel when the air density is higher as it is when cold outside (ask a race car driver or test one yourself). We always set 'em up rich when servicing them in warmer weather.

Good luck.


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