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I have a Yard machines snowblower with an 8h Tecumseh

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engine. I know a...
I have a Yard machines snowblower with an 8h Tecumseh engine. I know a little bit about fixing small engines, I've repaired a few things but my problem is that I lack knowledge in the theory portion. I have some books....
Anyway, for this machine, I only got about 60psi on a compression test. Carburetor looks good, but I'm cleaning it out and bought a carb kit. I removed the cylinder head and need to replace the gasket (although it was still in one continuous piece, it ripped apart when I removed the head).
I have cleaned up the top of the piston and around the valves. I removed the side crankcase breather. I think I will replace that too as there seemed to be some oil residue inside of the tube meant for air (excess pressure).
My next step is the valve themselves....could this be the problem with my low compression, is what I'm wondering, but firstly before I go the route of removing the valves and performing my first ever valve lapping job, I noticed something as I turned the flywheel to watch the movements of the piston and valves.
It seems that during the compression phase (when the piston is coming back up and the intake valve has closed) that the exhaust valve is opening slightly but closes once the piston has reached the top. Is this ok or could it be contributing to the lack of compression and the snowblower not starting??
Submitted: 8 months ago.Category: Small Engine
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Answered in 16 minutes by:
11/11/2017
Technician: JohnF2015, Technician replied 8 months ago
JohnF2015
JohnF2015, Technician
Category: Small Engine
Satisfied Customers: 1,241
Experience: Owner/Service Technician at S & J Small Engines
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Hi, my name is***** will be assisting you.

With 60psi I doubt that you have any compression issues. This engine will only have around 60psi even when brand new.

The valves are designed to operate that way, it is an internal compression release built into the camshaft that causes the valve to bump open a little bit when coming up on compression stroke for easier starting. Once the engine is running there is a flyweight on the compression release that causes it to flip out of the way and no longer release compression once the engine reaches around 800 rpm and above.

I would take a more serious look at the carburetor, more especially the bolt/nut that holds the carburetor bowl on. Make certain that all of the holes (3 - 4) are thoroughly clean and have no blockage in them. There are two parrallel to each other near the bottom of the bolt/nut, there is one more smaller hole down the the top center of the bolt/nut and then one more possible hole just near the top edge of the threads on the bolt/nut. If these all are not thoroughly clean with no blockage it will cause the engine to not start at all or if you can get it started it will not run correctly.

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Technician: JohnF2015, Technician replied 8 months ago

Have you checked spark at the plug? I didn't see a mention of this. You may want to check to make certain that you have good spark at the plug if you haven't already.

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Customer reply replied 8 months ago
Oh yes, I have a brand new spark plug in place and I had also checked the ignition wire, I do have spark!
Really? With only 60psi I should be able to start a ANY small engine?? I know this for a Honda (incidently, that was the first engine I opened up and repaired, first a connecting rod, then a camshaft on another Honda engine)
Alright, I've got a Tecumseh engine book, I'll follow it for cleaning out the carb. There are three holes in the bolt that holds the bowl in place (two of themat the base are right across from each other so you can see right through, the other is closer to the top so I'll stick a thin wire into that one). There is something else fitted into the bottom of the bowl, it has a spring on it so if you push on it the fuel inside will come out.
Getting back to the valves, because I want to make sure that the problem is not them before I put everything back together, I looked at the intake valve, and it appears to be seated at a slight angle (when looking at it from the side, across the plane of the piston and valves) I would think it should be sitting flat?
Then again, perhaps with my lack of knowledge/experience, I'm fearing the worst!!
I'll go and get the carb ready, when the new head gasket comes in I'll put everything back together and see what happens!!
Technician: JohnF2015, Technician replied 8 months ago

As for cleaning the holes in the bolt that holds the carburetor bowl on, don't forget to clean the small hole that is down through the top center of the bolt. This small hole actually serves as the main fuel jet for the carburetor, if it is blocked then the engine will not likely run or if it does run it will not run correctly. If you look down through the top center of the bolt you should be able to see the small hole or jet that I am referring to, it will be in the center near the bottom, it actually runs down into the passage the is between the two larger holes in the outside lower part of the bolt. You can run a small needle or wire down through it and you should be able to see the needle/wire sticking down into the passage of the larger parallel holes.

The valves do seat at an angle and can be slightly raised above the block surface. At this point I am not concerned about the valves based on your compression information. At 60psi you don't have a compression problem on this engine.

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