What did I do Right or Wrong

[bob]

Tecumseh HMSK105 engine off of a snowblower. Started good but did not run smooth at high speed and did not idle. Cleaned carb a couple of times but no better. Decided I would try setting valve gap. Did that at .010 and I also cleaned carbon from head of piston and valves. Lapped valves. After finishing it would only start from electric starter, not pull start but to my surprise it ran good at high speeds and low idle. But it will not start using pull start. I can tell by pull start there is very resistance, so very little compression ( which It probably had from start but I just never noticed). My question is what did I do to make it run good and what did I do to make it have very little compression. Thanks

[RoyM]

I am wondering what position the piston was at when you adjusted the valves. It should be a quarter turn past top dead centre on the power stroke so the lifters are completely clear of the cam lobes.

[KE4AVB]

RoyM » Sun Apr 25, 2021 22:22
I am wondering what position the piston was at when you adjusted the valves. It should be a quarter turn past top dead centre on the power stroke so the lifters are completely clear of the cam lobes.

Hmmm I thought it was a quarter inch pass TDC compression.

But any way this old fart still prefer to do it the old way of adjusting each closed valve when the opposite valve is fully open. I know it takes longer but I have better results and I don't need to hunt TDC compression or find a measuring stick and remove the spark plug.

[38racing]

RoyM » Sun Apr 25, 2021 22:22
I am wondering what position the piston was at when you adjusted the valves. It should be a quarter turn past top dead centre on the power stroke so the lifters are completely clear of the cam lobes.

Hmmm I thought it was a quarter inch pass TDC compression.


But any way this old fart still prefer to do it the old way of adjusting each closed valve when the opposite valve is fully open. I know it takes longer but I have better results and I don't need to hunt TDC compression or find a measuring stick and remove the spark plug.

I think compression and power are the same stroke in a sense wrt to tdc. Piston approaching tdc on compression and leaving tdc on power. So technically 1/4 past tdc compression means you have started power stroke.
Tecumseh manuals actually say valves are set at tdc. Maybe they work the compression release into their clearance spec. I have a thread about a briggs blower engine. Starts fine on pull cord when cold. After running for even a short time it won't start will pull start, just with electric. On hold as spring as arrived.

[RoyM]

As long as it is on the power stroke both valves are completely closed so we are golden.

[bob]

I figured out what I did wrong. Took a second look at valves since you guys seemed most concerned about adjustment. I had set clearance orginally with both valves closed and checked clearance this time with one open and one close. Both ways showed good clearance. And then I remembered the keeper at the top of the exhaust valve had come shooting out when I did it orginally. I now saw saw I had put it in the wrong way. I had placed it with flat side going down and should of went up. Now it starts with pull cord. I still think there is not a lot of compression but it is working. Thanks