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Old 02-20-2013, 04:05 AM   #1 (permalink)
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small engine surging/backfiring/runs hot

Have a 7hp tecumseh or so snowblower that finally had to start up not long ago, it starts fine but once warmed up it starts backfiring then surging. Under load it smooths out noticibly but once i'm not plowing 26 inch high drifts it's back to sputter and backfire. It ran so hot that the exhaust manifold was glowing ORANGE when I was done at night which is probably not good... (and maybe I even damaged it but didn't notice while running it or I would have stopped, coulnd't see til it was in the dark)

I'm pretty sure it's bad-gas related, it ran flawless in october when I put some gas in, didn't start it til december/never seen gas go bad that quick before but thats the first time it ran poorly like this. Ended up not even able to keep it running until later on a warmer day in january and using new gas to dilute the old let it start finally but then it did this surge/backfire routine when warm. I just had it serviced/cleaned the previous year so it's not years of built up varnish/it's all from just one recent crappy tank. :-/ Is this something that some off the shelf additive could maybe help dissolve and get out of the carb? After burning $170 to get it running last season I can't even afford to do it again this year with other bills, and though I can turn wrenches on some car stuff i'm not comfortable with disassembling things with lots of tiny loseable parts and such to DIY though if there were some simple/easy instructions on how to disassemble a few key parts, things that wont explode 50 tiny springs gears and levers across my dirty garage floor, to spray some cleaner in some places then put back on I can do.

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Old 02-20-2013, 09:09 AM   #2 (permalink)
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Drain all of the bad fuel out and replace with fresh fuel. Small engines are sensitive to varnish... Do not use additives to try to clean out the carb. It is a waste of money.

If you store small engines put sta-bil in the last tank then run it through. That is the only product I have found that does what it says.

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Old 02-20-2013, 10:22 AM   #3 (permalink)
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Partially plugged main jet causing lean condition

It appears the main jet is partially plugged. It's a pretty simple repair. Shut off or drain the fuel tank. Note if the fuel bowl has a step in the bottom and remember the orientation of it. Looking at the diagram, there is a screw at the very bottom - this is the main mixture adjustment. Gently screw it in, counting the turns required until it seats. Now remove the entire bowl by backing out the brass fitting directly under washer #44. Gently rock the bowl and remove it. Gently turn #20 (idle mix) screw in counting the turns until it seats. Now remove screw #20. Using a straw on a can of carb cleaner, spray through the opening screw #20 came out of. This will generally remove debris from the main jet port. Clean the bowl and main jet assembly with carb cleaner. Reinstall the bowl and the mixture screws. Refill the gas, and start it up running about 3/4 throttle. After it has warmed up, slowly screw the main jet inward until it begins to run rough. Back the main mixture screw out slowly until it runs smoothly and add 1/8 turn in the same direction. Return the throttle to idle speed and adjust the idle mixture screw by slowly turning it inward until the governor begins to surge and then slowly back it out until it smooths out again. Return the throttle to 3/4 and engage the auger. If it runs rough, back the main mixture screw out slowly until it runs smooth. Disengage the auger, and adjust the idle mix screw until it runs without surging. That should just about do it.

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