Can I do a compression test with the intake manifold off?

[Petedacook]

I have a Tohatsu 2 stroke. The intake is currently off because I am replacing the reeds. The reeds are in the mail, but before I move forward with buying any other parts, I want to make sure the compression is good on the engine.

Can I do a compression test with the intake manifold off and reeds removed?

Thank you.

Pete

 

[gm280]

I'd say yes. But I am sure somebody has a good reason to say no. Being how you are measuring the compression of the piston compressing the air, the intake doesn't look like it would matter one way or the other. But I will keep watching your thread to hear reasons it won't work. JMHO!

 

[Sea Rider]

You can do what you plan on doing, the issue is if the reading in PSI will show real compression values. Tohatsu recommends compression test with engine warmed to normal operating temp, with throttle at fully opened position, with at least 4 compression strokes while ignition is disconnected. Compression for a 70 HP is 121 PSI.

Happy Boating

 

[Sea Rider]

According to a techie who happens to work with 2 strokes engines, making a compression test with complete reed valve assy removed will read less PSI on test.

Happy Boating

 

[Petedacook]

Thanks Sea Rider. I put Boyesen Reeds on it and closed the bottom end of the engine. Now I need my fuel pump to come from Australia.

Gonna try and patch the one I have to make it work for the test at least.

 

[Sea Rider]

Can you flip the reed valves that doesn't stay closed just for the test ? Are you changing complete Boyesen reeds assembly or just spare reeds ?

Happy Boating

 

[Petedacook]

I completely changed the reeds to Boyesen. The reed cage is still the stock cage.

I warmed the engine on the muffs. It ran fine. I did the compression test. I wasn't sure how the heck i could tell when it was cranked over 5 times. I can't see it spin or anything, it's too fast.

I cranked it over and counted to 5. About 110 PSI both cylinders.

Took boat out, ran ok at first. Didn't want ti idel at first, which is really not a new problem. We went out about 10 minuntes, to a post, stopped the motor and sat there fishing for about an hour,

Motor would not stay running after that. It would start, then die immediately before I could get it in gear. Messed with it doing this for a while, with no success. Changed the spark plugs. Tried a few more times, and got it going in gear.

Cruised around running throughout the throttle band for an hour or so. Every time we stopped after that, same thing, engine would cut off, then not run until I was able to get it into gear and the RPM would pick up before bogging down and dyeing.


I have another thread in Tohatus forums about this motor. I'll post this in there.....I was in a hurry to find out about the compression test with no reeds in, so I posted in here for a faster response.

http://forums.iboats.com/forum/engi...s/10236873-tohatsu-m70a2-stalling-won-t-start