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ss74nova

High speed adjustment problem

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ss74nova

High speed adjustment problem

I have a 1982 Sears LT 8 36 lawn tractor with a 8HP Tecumseh engine. I replaced the carb with a new aftermarket one (oregon 50-6425) because the old one wasn't correct, didn't have any adjustment screws & didn't run worth a crap. I got the low speed adjustment on the carb working OK. The high speed adjustment I just can't get right. I run it at full throttle & turn the high speed adjustment screw located on the bottom of the bowl of the carb. I get it close , but then it runs rough & won't smooth out. It seems to keep changing or searching. I see the govenor rod move back & forth a lot when it acts up.

Could this be the carb, govenor, worn flyweel key, points & condensor, coil, ect.

I had run it out of gas in early fall, but still had the issue back then. I tried to start it recently & it would just crank. I sprayed some gumcutter down the carb & it would back fire out the muffler. I'd also see some vapor come back up the carb. Without the gumcutter & with the choke on I would see a spray of unburnt fuel out the muffler. After a while it started to run really rough & then smoothed out & ran ok until I tried to adjust the high speed jet.

Any other engine when I would spray gumcutter down the carb would fire right up & run. This one had a hard time.

Could this be a timing issue? Where should I start before I tear into this too deep?

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fishnwiz

Could be a broken/cracked breather tube or fuel line. Your carb may be getting too much air.Using carb cleaner or starting fluid, spray a little around the sides and bottom and back of the carb (with the air cleaner on ) while the engine is running and see if that effects the engine performance. Could also be bad gaskets.

Regarding flywheel key...usally the symptoms of partial shear to keyway results in hard starting as well as backfire issues.If the engine did backfire it may have partially sheared your key.

Are you sure the fuel line and filter is clear and unobstructed? You also may want to try running a little Seafoam in the gas and see if this helps with clearing your issue.

Best of luck.

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ss74nova

I also had replaced with brand new, the rubber crankcase breather tube hose to the air cleaner & the breather valve on the engine. All the carb, air cleaner & intake to block gaskets are new. The foem gasket that seals the air cleaner to the engine shroud is broken. I wonder if I can seal it with rtv? or get a new gasket?

I dumped some (mechanic in a bottle) in the fuel tank & ran it for 20 min, but still the issues.

I'll try running it & spraying carb cleaner around the intake & carb areas & see what happens.

Once it was running & warm it restarted ok.

Maybe it's the foem air cleaner gasket letting too much air in.

Thanks Mark, I'll give that a try first then look into the keyway.:)

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fishnwiz

You seem to have everything covered for the most part. With the new carb you should not be having issues with high speed. You are sure that you have the correct replacement carb?

I have seen issues with some of the cheap china knockoff carbs straight out of the box.

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ss74nova

Well, I was hoping the new carb wasn't the problem. It was half the cost of the oem carb which was $80. The oregon brand name kind of sold it for me, but I'm almost sure it was probaly made in China. Everything is these days. It's not a direct replacement, but I was told by a carb rebuilder, that the only thing different would be the choke & throttle linkage would have to be changed & the fuel hose was on the opposite side. I had a piece of preformed fuel hose with a very sharp bend that cleared between the block & carb & it didn't kink at all. Most of the carb replacements I looked at didn't even have any adjustment screws, but this one did.

Trying to save money, but hope it didn't hurt me in the long run. That's why I'm looking for alternative fixes.

Someone had put the wrong carb on this engine when I got it & the fuel hose was kinked right off & there were no adjustment screws on the carb at all.

You've been a great help Mark. If there's anything else critism or not let me know, I'm still learning.

Thanks for all your help.

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ss74nova

Seems like the high speed was a problem from the day I got it with the origonal carb. Didn't have much power mowing tall grass. Kind of ran rough & not efficient on full throttle. Hopefully the carb isn't the problem, but I'll keep it in the back of my mind.

Here's a funny thing:

When I first got it I was running it to see what was wrong with it & after it got hot it was spewing oil out the breather on the exhaust. It was smoking so bad I thought it was going to catch on fire. Shut it down. Checked the oil & seemed a little overfull but not enough to cause alarm. Ordered new breather hose & breather valve & installed. Ran engine did same thing as before. Blew oil all over exhaust when hot. I drained a lot of oil out of the engine to get it down to the full mark. Seemed fine after that with the breather/overfull problem, which wasn't a breather problem after all.sm00

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ss74nova

Put a film of RTV on the intake to block & intake to carb gaskets. Still same problem. Pulled flywheel & key is fine. Ordered points & condenser. Gonna try that next. Anybody know the correct point gap for a Tecumseh 8hp model # 143-296032 Serial # 8284C. I believe it's a 1982 year. Not much info on the internet for these. I found a gap of .020 , not sure if that is correct because it's for a HH80 Tecumseh engine. Thanks.

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EDS

Two ideas for you.

1. The idle jet actually provides some fuel across the full RPM range. The next time it does this, open the Idle jet about 1/8 turn and see if your main jet issue is improved.

2. If the wrong carb is a LME-34,for a HH120, there is an issue with the main fuel nozzle. Once it is removed, the air passage will never line up again. If this might be your problem, I have a picture I can send off list.

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ss74nova

Thanks Ed !

1. I'll try the low speed adjustment after I get the points & condenser installed.

2. Not sure what you mean. The engine is a Tecumseh 8 hp model # 143-296032 & serial # 8284C. I think it's a 1982 engine accoding to the serial #. The new carb I installed was a Oregon 50-6425 carb.

Thanks,

Tim

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BLT
quote:Originally posted by ss74nova

Thanks Ed ! 1. I'll try the low speed adjustment after I get the points & condenser installed.2. Not sure what you mean. The engine is a Tecumseh 8 hp model # 143-296032 & serial # 8284C. I think it's a 1982 engine accoding to the serial #. The new carb I installed was a Oregon 50-6425 carb.Thanks,Tim


id="quote">
id="quote">143-296032 is TEC VM80 150126F

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ss74nova

I still have the exact same problem as before. Unable to get the high speed adjusted correctly. :( Low speed is ok. It surges at high speed & after running a while when it's hot it starts backfiring out the muffler. I just can't get it adjusted correctly. Frustrating. :(! I replaced the points & condenser & gapped to .020. I replaced the whole fuel hose. I even tried running it without the fuel filter & same problem. I replaced all the intake gaskets & put a film of RTV on each side. I replaced the carb as in the previos posts. Seems like the same problem when I had the first carb, but that was not the correct carb. I replaced the spark plug with new & gapped it to .030.

It seems on cold start it runs fine no surging. Then 30 seconds to a minute it starts surging. When it gets hot it also starts surging & backfiring out the muffler. sm00 I also tried adjusting the low speed a bit to see if the high speed would smooth out but to no avail.

Could this be electrical or fuel related? Is there anything else to do before I drop $80 on a new OEM carb? Any ideas?

Thanks,

Tim

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ss74nova

Being it acts up as it gets hot would the coil make more sense. Under full load would a weak coil break up the spark & have my symptoms? I can get a coil off amazon for $19.95.

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ss74nova

Well I pulled the flywheel off again to replace the coil. I pulled the points cover & noticed the points soaked with oil. When I pulled the flywheel the first time and saw oil I just thought I used too much rust penetrant to get the flywheel off. So I cleaned it real good with brakeclean & blew it dry. Now for the second time I think I need a crank seal. I wonder if that's my problem, oil on the points making it not run right. The previos owner had overfilled the crankcase with oil at least a quart or two. I wonder if that's what blew the seal out. I'll try replacing the crank seal. Any thoughts or other ideas are welcome. Thanks.

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