compression test

[inthegulf]

just wondering the effect on reading of not having throttle wide open?

 

[LubeDude]

Re: compression test

The throtle must be at least partially open so that the engine gets enough air to load the cylinders with air so that when the piston comes up with the valves closed you get a full cylinder of air to give you an accurate reading! Less air, lower reading!<br /><br />LubeDude

 

[R.Johnson]

Re: compression test

I have never really noted any real difference in this respect. A compression check on a 2 cycle engine can be misleading, as an example I have found the high reading cylinder to be the one that is damaged. Though I certainly use a compression test, I also follow with a leak down test as this can be a better indicator. If you want to save a lot of headache, and expense, as when dealing with an older motor, pull the cylinder head or by-pass cover. Before starting any repairs, or tune-ups you have to know that you are dealing with a sound engine to begin with. Since following this board, I have seen people pumping a lot of time and money into the unknown

 

[Walker]

Re: compression test

I've taken readings both ways and have found no difference at all. There aren't any valves in a 2 stroke engine cylinder. There are reed valves in the intake manifold but they have nothing to do with compression. I guess its possible that a reed could be stuck shut and sealed with varnish from old gas, but not likely.