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Old 02-09-2011, 11:10 PM   #1
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Default Are cherry hot mufflers normal?

Newbie here, but not new to blowing snow. I recently obtained 20 some year old Noma powered by an Tecumseh HMSK80. I have run it a few times and have noticed that within minutes the muffler becomes cherry red, and occassionally backfires. Flame can be seen coming out of the muffler. I have never seen the red hot muffler like that. Some claim that it is normal. Is it normal to be red hot like that?

I did some research on the internet and was pointed in two directions, a dirty carb and stuck valve. I cleaned the carb, but did not rebuild it, except the bowl gasket because I could see gas leaking out from around it. This did not seem to solve the red hot muffler problem. I should mention that the machine was not performing properly when I experienced this it would surge and hunt. The machine does seem to run somewhat better after the cleaning. I should also mention that I can hear a squishing noise in the carb when the primer is pushed and fuel comes out of the choke plate area when the primer is pushed. Is this normal?

Next I sprayed seafoam in the spark plug hole onto the valves. I can observe the valves moving up and down. I still am getting the red hot muffler.

I am to the point where I am ready to buy a new carb if this will resolve the issue. Will it?
Thanks,
Hillbilly
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Old 02-09-2011, 11:18 PM   #2
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I should add that I have been running the machin without the cover over the carb, the one with the emergency stop key. Would the wire from the cover not being on the ground, cause this condition.
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Hillbilly
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Old 02-10-2011, 04:23 AM   #3
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All the wire does is kill the engine by shorting out the spark plug. It should have no effect on running.

Sounds like you are either running lean or you have a valve that isn't closing fully. I have been reading a lot of reports lately of Tecumseh engines needing to have the exhaust valve ground down slightly because the clearance becomes 0. It is usually associated with the smaller 5 HP engines though. The lean condition can be dirty carb or just not properly adjusted carb. If it is surging and hunting I would lean towards carb as well.

The other thing I have heard is it was kind of normal with old L-Head engines. When you add to that the fact that most people snowblow in the dark it makes it stand out even more.
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Old 02-10-2011, 12:59 PM   #4
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Mufflers running red are NOT the norm. Your engine is running extremely lean. Needs a total carb rebuild including a thorough soaking cleaning. Also, a blown head gasket could cause a lean condition. I have an 8hp tecumseh on my 1995 MTD snowblower and it takes me 2.5 -3.5 hours to clear my drive way. My muffler never gets red hot.

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Old 02-11-2011, 12:50 PM   #5
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Improper exhaust valve clearance could be causing the exhaust valve not to fully seat. This will not only burn the exhaust valve it will cause the muffler to get very hot. As stated above it could also be a very lean carb,blown head gasket or even a loose carburetor or a bad carb intake gasket. I would check the carburetor related issues first and it you don't find anything pull the lifter cover and check out the valve clearance both valves.
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Old 02-11-2011, 07:30 PM   #6
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Another common cause is that the speed governor has been messed with and the engine rpms are too high. Neighbors machine had this same characteristic after he rebuilt his carb and accidentally changed the angle of the governor arm/throttle link. Engine over revved at wide open throttle and the muffler would get red hot and eventually sparks would start to be seen (not a good sign!).

We readjusted his governor and the machine is running fine now.
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Old 02-19-2011, 09:00 AM   #7
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Go through the whole carb and intake system to eliminate that side of the problem. Then do a compression check to see if your exhuast valve is leaking. If it is try lapping the valve and that will possably fix it.
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Old 02-19-2011, 10:40 AM   #8
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Quote:
Originally Posted by BOSMECH View Post
Go through the whole carb and intake system to eliminate that side of the problem. Then do a compression check to see if your exhuast valve is leaking. If it is try lapping the valve and that will possably fix it.
Before lapping the valve check the lash on the valve. If the lash is too tight or even non existent (i have seen 0 lash on some exhaust valves ) correct that first before lapping the valve.
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