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fishnwiz

Fire breathing dragon

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fishnwiz

I had a call from my buddy and he asked me about an issue he has been having with a blower that he owns. I have NOT had a chance to look the blower over myself but this is his story.

He purchased a used 8 hp blower from a neighbor of his that repairs blowers and small engines. The engine ran rough when he purchased it so the neighbor replaced the carb with a brand new carb. The blower starts but runs rough and spits fire out of the muffler at idle but under load runs excellent. Neighbor thought it might be the coil and replaced it but motor and tried to readjust the carb..still spits fire at idle and runs poor.

Any ideas on this one before I take a ride to check it out?

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arnoldir

Hello Fishnwiz,

I agree with Ray, sounds like the exhaust valve has stretched or the seat has sunken into the block.

I've been through this before.

Pop the lifter cover / breather and check clearance between valve and lifter.

If to tight, I pop the valve and dremel the end.

Good luck getting it sorted.

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ZippoVarga

I would agree with a worn/cracked exhaust valve seat possibility, but with good power when throttled up, it sorta goes against the bad exhaust valve notion. It wouldn't have good power at any throttle position with the bad valve seat to valve clearance.

With the symptom being present after a carb and coil change, I would suspect a condenser and/or points issue. Pull the plug and check for a continuous hot spark. If it is sporadic or intermittent or the spark appears weak then you need to check the points and condenser and replace if necessary. Also, it may be as simple as an incorrect spark plug that runs too cool at idle but is hot enough above idle to fire well enough. Just my two cents worth, for what they're worth.

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HubbardRA

Usually when there is too much clearance in a valve, due to the stem getting longer as it gets hotter, the engine will start missing and most times will stop running when it gets hot. Letting it cool down will allow the engine to re-start. Your problem does not sound like the seat has been worn farther into the block and caused the extra clearance.

There is a possibility you may have a burned valve which lowers the compression at low speeds, but becomes insignificant at higher speeds.

It also sounds like it could be a poor idle adjustment on the carb.

A leaky carb or intake manifold gasket can also cause an engine to act like yours is. A small leak can lower the vacuum at idle and cause the engine to run lean at idle. The flame out the muffler is an indication of an engine running lean. When the engine is speeded up the leak is much less significant, and may be compensated for by the main jet adjustment.

So my main choices in order of my opinion are from most likely to least likely:

1. leaking carb gasket

2. leaky head gasket

3. idle mixture not adjusted properly

4. burned valve.

You can check for a leaky manifold gasket by starting the engine, then spraying carb cleaner or starting fluid around each of the gaskets. Some people just spray water. If it hits a leak the engine will either speed up or slow down significantly enough to see a difference. Sometimes this test will also work with a leaky head gasket. Many times the head gasket will leak underneath the sheetmetal and you will not be able to see the gasoline deposits from the leak.

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fishnwiz

Thanks Zipp and Hubbard! I mentioned the plug switch to my Buddie..have not heard back. I was wondering about the valve issues and how that would effect WOT performance but you seemed to have answered that for me.I have had no hands on time with this blower yet so I am just looking for a starting point to save a little time. Thanks to all for helping me narrow my search for a starting point!

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ZippoVarga

I concur with Rods diagnosis as well, I hadn't considered leaky intake/head gaskets or idle set screw issues with your symptoms. All sounds like very possible culprits.

Please keep us posted!

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