Small 2-cycle compression

[bh357]

Older ~1980's Toro snowthrower with a small single cylander 2-cycle engine. What is a good compression reading for this type of engine? It looked like it was peaking around 60-70 psi, but the needle was jumping all over the place when I was cranking it. Runs pretty good, but bogs slightly under more than a few inches of snow, and doesn't throw it more than about 10 feet, and not that high. She's soaking in some SeaFoam right now (garage looks like a Cheech & Chong movie )<br />I have another similar vintage Toro with a similar type of engine, that when pulling over by hand feels to have higher compression (haven't checked that yet). So, worst case scenerio is that I can swap out motors.<br />Thanks for your help in advance.

 

[rwise]

Re: Small 2-cycle compression

is there a check valve on your gauge? if not it may be the gauge is not giving you a good reading. it should hold the presure so that you can crank the engine 5 or so times to get to the max reading. 60-70 is bit low for me I want at least 80-90 or higher. the seafoam may help it.

 

[ED21]

Re: Small 2-cycle compression

Some 2 strokes have a compression release to ease starting. I don't know what to look for to be able to tell, except maybe owners manual.

 

[pjc]

Re: Small 2-cycle compression

also have throttle at wide open during cranking. you also can pour one teaspoon oil in plug hole to see if comp. is higher. if higher, ring (s) are worn. btw, 60-70 is low, agree you want 90+.

 

[bh357]

Re: Small 2-cycle compression

Thanks for the input so far. I ran the sea foam out this evening and it feels like it takes a bit more effort to pull. Ran out of light so I didn't get a chance to check the compression again. That 70lbs was just a guess as to where it was hitting - may have actually been a bit higher. Yesterday when I tried to check the compression, I did add a bit of oil to the cylander, and it didn't seem to make any difference.<br />As for having it at WOT, it has a governer on it (spring I think). I'll have to rig the throttle to stay open when I attempt to check the compression again. How much of a difference does the throttle position make in the compression reading?

 

[pjc]

Re: Small 2-cycle compression

the throttle not being full open makes enough difference in that you will not measure the true cranking compression. you should be able to zip tie or wire carb butterfly open.

 

[bh357]

Re: Small 2-cycle compression

Thanks for the advice guys. I checked the compression yesterday evening (throttle at WOT), and measured between 90 and 100 psi. Guage was still fluttering though.

 

[WillyBWright]

Re: Small 2-cycle compression

The gauge should gain compression in steps, then level off and hold. If it leaks down, there's a leak in the gauge. 2-strokes aren't usually too picky whether the throttle is fully open or not (on 4-strokes it's critical). That motor has a compression relief port to help starting. I like the S-200. I have an S-140 and it's really tippy. The last few years we haven't had enough snow to bother buying the gas for it. <br /><br />I got a Gilson too. Lawn Boy used them too, and the blower was good but the Lawn Boy motor was crap. The Gilson used the same blower, but the Tecumseh motor in it is much better. Same motor as your Toro's. I might try adapring one to my son's go-cart, but not convinced a centrifugal clutch would work so hot on a 2-stroke.<br /><br />I worked on a really flooded S-140 once. Took the carb off to rebuild it, then pulled the motor over to pump out the gas. It Started! It Ran! Rather well for quite a few seconds. At first I looked like this . The longer it ran, the more I looked like this . Quite a bit of gas can puddle in the bottom of the crankcase, and apparently it had. It just kept running ... and running ..... and running ....... with no carb.