Tecumseh Model: HMSK105, Spec: 159908C carb issues

[jwales]

Hello Sky. You are correct, this unit is a solid state ignition with alternator under the flywheel for the light. I am assuming the valve clearances should be checked at TDC on compression stroke (both valves closed)?

I did remove the intake elbow when I removed the carb. I also had cleaned both surfaces and inspected the gaskets before re-assembling. No imperfections noticed.
Thanks

[Skywatcher]

Hi Once Again J.

The general recommendation is to check the valves with the engine just past TDC compression stroke. The usual term that's used is ¼" past TDC. I assume this means the piston has traveled ¼" down the cylinder after having crested TDC which puts the flywheel about 20º past TDC. The magnets on the flywheel will align with the ignition coil about 20º before TDC to give the correct ignition timing. If the magnet aligns with the ignition coil at TDC, the flywheel key has partially sheared. Hope this points you in the right direction,

Sky

[jwales]

I tried adjusting the carb with the governor rod to the throttle plate disconnected (thinking maybe the governor is the problem). It took a while but was able to adjust the idle and high speed(full throttle) and was able to run the throttle at full and then down to idle back and forth without the engine dying, so I think the carb is OK.
I connected the governor rod back up and tested and needed some more adjustment, which I could get it to idle down but at full throttle it would not get high enough RPM (by sound) and testing it in the snow bank started to die under load.

Since I was taking the carb off again to clean and adjust, I removed the muffler and opened the valve cover. I attempted to measure the gap/clearance of the intake and exhaust valves. I could only get a .004" under the intake and could not get the .004" under the exhaust. Measured approximately 1/4 past TDC (and other positions also). So I think there is a valve issue and I told my friend he needs to take this to a professional with the right tools.

Thanks for all your help!

[Skywatcher]

Hi J.

Glad we were able to help you get to the root cause of the engine troubles that have been plaguing this machine and you for a while now. As you say, now you just need to find a shop that actually knows what they are doing and are willing to listen to you so they don't charge you an hour for unnecessary diagnostic time. They can go straight into the engine and get the valves adjusted to spec (.010" ± .002") for both valves. All the best,

Sky

[38racing]

Jwales.
Anything to update on this? I have an old hm80 on a snowblower that I can't get to run right. On third carb. Won't run unless choke is part closed. Will blow some snow and then it starts puffing and struggling. Open choke it changes to surge back fire. Put on some choke and it runs ok for a bit. Last year when I had the adjustable carb it was just continously changing lean to rich and back to lean to use. Thinking maybe I should check the valves too.

[bgsengine]

38, check your intake gaskets and fasteners and intake manifold. Had a Troy-Bilt tiller that ran like you describe, the carb to intake mainfold bolts were just slightly loose, when it warmed up, the carb was just loose enough to leak air so we had to adjust the mixture as it got warmed up. Wasn't really noticeable because of how the engine vibrated, it was hard to tell carb was shifting until I happened to spray a little penetrating oil on the linkages (thinking maybe a little rust) and engine speed changed.

[38racing]

38, check your intake gaskets and fasteners and intake manifold. Had a Troy-Bilt tiller that ran like you describe, the carb to intake mainfold bolts were just slightly loose, when it warmed up, the carb was just loose enough to leak air so we had to adjust the mixture as it got warmed up. Wasn't really noticeable because of how the engine vibrated, it was hard to tell carb was shifting until I happened to spray a little penetrating oil on the linkages (thinking maybe a little rust) and engine speed changed.

everything tight. Gaskets in good shape.

[jwales]

Sorry 38. Working on the valves was above my experience level and I gave it back to the owner and said you need to take it to a professional. Its sad but he chose to toss/scrap it I found out later.

Happy holidays everyone!