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post #1 of 10 Old 11-12-2015, 05:12 PM Thread Starter
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Can't get it to run right

Hi all-

I have an 8 HP tecumseh in a snow king. Couldn't get it to run off choke, so I figured the previous owner let the carb gum up. I replaced the carb and cleaned (as best I could) the spark plug.

It will run off choke now, but it never gets to a sweet spot. It will surge up and down and pop (lean). SO I give it more gas little by little, reallllly slowly and wait for idle to improve (by adjusting the jet on the bottom of the bowl). As soon as it get smooth, it dies and I can feel gas spitting on my hand (way too rich). Seems there's no sweet spot.

Idle is ok, and I have the idle mixture about 1 and 1/4 turn out. Seems to like it there and idles good.

Bring the thottle up and it complains, coughs out black smoke and runs crappy again, so I lean it out, rinse and repeat.

Any ideas?

Thanks all
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post #2 of 10 Old 11-12-2015, 05:42 PM
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killerfomula.
Your problem may be the adjustment procedure your using. With the motor at idle, you adjust the low speed screw on the "side" of the carb until it idles smoothly and responds to the throttle being moved to fast.. The high speed screw is in the bottom of the carb and is adjusted at full throttle until the engine runs at peak performance.

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post #3 of 10 Old 11-12-2015, 06:36 PM
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Brother GRUNT is the man to seek the answers for those engines. anyhoo ALOHA from the paradise city.

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post #4 of 10 Old 11-12-2015, 07:15 PM Thread Starter
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Quote:
Originally Posted by Grunt View Post
killerfomula.
Your problem may be the adjustment procedure your using. With the motor at idle, you adjust the low speed screw on the "side" of the carb until it idles smoothly and responds to the throttle being moved to fast.. The high speed screw is in the bottom of the carb and is adjusted at full throttle until the engine runs at peak performance.
Thanks grunt.

I have gotten the idle mixture screw and idle speed pretty sweet, I think. It's the jet screw I'm having issues with. When I move off idle it grunts and belches and groans its way up to full throttle with smoke and flames and popping. ANy less idle mixture and it dies. Done it several times, and the motor is nice and warm. Just can't get it to run well at full throttle.
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post #5 of 10 Old 11-12-2015, 07:17 PM
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Quote:
Originally Posted by killerfomula View Post
Hi all-


Any ideas?

Thanks all
Yes. I would also advise you to check out your governor spring and governor setting. I found, at least on mine I needed to replace the spring and adjust the governor setting. I would second Brother Powershift93 in following Brother Grunt's advise on the carb adjusting. Oh, I almost forgot, that these are tiny carbs and even slight adjustments can lead to big changes in performance. I had to relearn the way I was thinking because I was so use to tuning automotive carbs.

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post #6 of 10 Old 11-12-2015, 10:45 PM
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You said you cleaned the spark plug the best you could. I would get a new plug and see what happens.

Are you using fresh gas recently purchased?

Did you use a new gasket between the carb and intake manifold?

Surging can be caused by a governor problem, but it is usually a caused by a restriction in the carb passages or jets. A new carb doesn't necessarily mean a good or clean carb. Another possibility, since the engine seems to be "coughing", have you ever checked your valve clearances? Older Tecumseh engines are notorious for needing the valves adjusted to get a good running motor.

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post #7 of 10 Old 11-14-2015, 06:09 AM
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Yeah, I was thinking about valve clearances, too, especially since you mentioned "flames." Let's hope not though, as that is easy to check but a lot harder to actually fix.....

How old is the 8 hp? Does it have breaker points or a module/coil mounted outside the flywheel? If it has points (ignition mounted under the flywheel) the rubbing block on the points could be worn and you might be barely getting any point opening. This has the effect of retarding the ignition timing. I just went through this on one of my old H60s.

Does it have low oil shut down? If so, you might try disconnecting that wire as an easy check. That was a running issue once, on my 8 Tec generator engine.....
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post #8 of 10 Old 11-14-2015, 08:57 AM
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Welcome killler!

+1 on the idle circuit & possible valve condition.

Alot of folks don't realize that even at the "fast" position, most of the fuel is still being supplied by the idle circuit...throttle butterfly should be barely open.

At "fast" speed, the governor is engaged...so if the idle circuit is restricted (blocked vent, fuel passages, etc.), the engine senses a slow cam shaft (thinks it's under load), opens the throttle butterfly creating a rich condition...dumps a bunch of fuel in the chamber that it doesn't need, revs-up and the extra fuel pops-off in your hot muffler/exhaust. You'll often notice alot of those no-load problems vanish when there is a real load...the idle circuit is being bypassed.


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post #9 of 10 Old 11-14-2015, 05:51 PM
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Take the carb bowl off. and look at the brass bolt that holds the bowl on, it has a lot of threads, and there, are two holes on the side, through the threads, they must be clear. If not, clear them with a wire from a wire brush, or the wire from a twist tie. Good luck.
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post #10 of 10 Old 11-14-2015, 10:04 PM
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also make sure the bowl is positioned right and the needle is still attached to the float and goes in the hole good, and that there is a white little o-ring/gasket at the bottom of that hole that the needle goes in. If you have a bowl where half of the bottom of it is raised up a little higher than the rest of the bowl, make sure that the raised up part is aligned so that it faces the hinge of the float. You want the float to be able to move up and down freely and not hit any part of the raised up portion of the bowl. I worked on a blower where the carb float bowl had been put on incorrectly and it acted a lot like you are describing. Snap some photos of the carb too if you can. The more the better.
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