Backfire and flames from exhaust - Snowblower Forum : Snow Blower Forums
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post #1 of 14 Old 12-23-2016, 11:55 AM Thread Starter
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Backfire and flames from exhaust

I have an Ariens ST8 24. I just replaced the carburetor with a new non adjustable one that I purchased on ebay. It fired up and ran good. Then when after a bit I would try to move the throttle lever and nothing would happen to the snowblower. I just replaced the throttle lever assembly. ( i think that's what it is called) Now the snowblower started to backfire and have blue flames coming out from the exhaust. Any ideas on what is causing this problem. thanks
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post #2 of 14 Old 12-23-2016, 12:09 PM
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exhaust valve stem needs to be ground down and shortened, the stem is more then likely stretched from heat
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post #3 of 14 Old 12-23-2016, 12:23 PM
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Yup, you have zero lash at the exhaust valve. Spec varies around .006" the exhaust valve cannot close because of it is always in contact with the lifter. So during the combustion stroke the expanding gasses leak out the exhaust valve at ignition causing your popping and flames.

I'm assuming it's a Tecumseh, you can remove the valve cover and file the valve stem down for a quick fix but the valve to seat seal may have suffered from the leakage. The best way is to remove the head and lap the valves into the seat for a perfect seal.
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post #4 of 14 Old 12-23-2016, 12:39 PM Thread Starter
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I was hoping that I didn't have to dig into the engine. I'm not confident with dealing with that kind of stuff.
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post #5 of 14 Old 12-23-2016, 01:14 PM
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It's really very easy as a repair. The hardest part is removing all the shrouding, and carb again to access the breather area. "Most" head bolts come right out, but every once in a while you get one that wants to play games. Best advice I can offer is to not try and "ease" them out. Try setting the socket in a short extension and then rapping the end sharply with a hammer on each head bolt first, then spray with PB Blaster, let it sit for a half hour. I usually try tightening them somewhat even if they don't budge, then with the socket set very well and straight up and down bump the ratchet with your hand to loosen, hoping for a snap release. Only ones I've ever broken off in the head I had tried applying slow constant pressure with a socket/ratchet and as I increased pressure "bam" the **** thing broke off. Almost always the last one, never the first one The valve stem doesn't really "elongate" the seat wears away/gets beat down and the decrease in the dimension of the stem to tappet is effectively shortened. Doesn't matter though, the fix is very slightly shortening the stem. Very slight chance you have a sheared or partially sheared flywheel key also. Rare on snow blowers unless previous to this problem you ingested, hit something or had service involving the flywheel (coil/points replacement, replaced starter cup). This situation almost always is caused by improper torque of the flywheel nut upon reassembly.
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post #6 of 14 Old 12-23-2016, 01:51 PM
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It's tougher job, but I think there are YouTube videos on doing it. Maybe even that donyboy guy. He has very well done informative videos on a lot of repairs.
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post #7 of 14 Old 12-23-2016, 02:02 PM
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Honestly, gaining access to the valve stem is as easy as replacing the carb. You can simply use a file to file the stem till you have proper clearance Without removing everything. Obviously it's a Jerry rigging way to do it, but when you're stuck in a hard spot in the middle of snow season...
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post #8 of 14 Old 12-23-2016, 03:03 PM
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Quote:
Originally Posted by jtclays View Post
It's really very easy as a repair. The hardest part is removing all the shrouding, and carb again to access the breather area. "Most" head bolts come right out, but every once in a while you get one that wants to play games. Best advice I can offer is to not try and "ease" them out. Try setting the socket in a short extension and then rapping the end sharply with a hammer on each head bolt first, then spray with PB Blaster, let it sit for a half hour. I usually try tightening them somewhat even if they don't budge, then with the socket set very well and straight up and down bump the ratchet with your hand to loosen, hoping for a snap release. Only ones I've ever broken off in the head I had tried applying slow constant pressure with a socket/ratchet and as I increased pressure "bam" the **** thing broke off. Almost always the last one, never the first one The valve stem doesn't really "elongate" the seat wears away/gets beat down and the decrease in the dimension of the stem to tappet is effectively shortened. Doesn't matter though, the fix is very slightly shortening the stem. Very slight chance you have a sheared or partially sheared flywheel key also. Rare on snow blowers unless previous to this problem you ingested, hit something or had service involving the flywheel (coil/points replacement, replaced starter cup). This situation almost always is caused by improper torque of the flywheel nut upon reassembly.
You are absolutely correct on getting the head bolts out, JT. I used to get exhaust manifold bolts out with a 3/8" impact wrench. These were car/truck engines. Never broke any. Other guys would be snappng them off all the time when they tried the gentle method.

Joe
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post #9 of 14 Old 12-23-2016, 03:40 PM
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I want flames coming out of my exhaust too!!!!

Toro 824QXE SNOWMASTER

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post #10 of 14 Old 12-23-2016, 09:36 PM
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Quote:
Originally Posted by pearlfinish View Post
I want flames coming out of my exhaust too!!!!
lol
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