Tohatsu 90 2 stroke losing power

[skatz]

My Tohatsu 90 2 stroke, splutters a bit on idle but will rev to 4k - 5k revs, but under load will only go to 2k revs. I have had the carbs off and thoroughly cleaned them. Fuel pump diaphram replaced. New plugs. Compression test looks normal. New Fuel tank, new primer bulb. A friend mentioned lower seals gone or baffles ??? I am at a loss here. Please help, all those fish waiting to be caught and I have no engine

 

[TOHATSU GURU]

Re: Tohatsu 90 2 stroke losing power

You have to determine what system(s) on the engine are causing the problem. Use your service manual and start with the fuel system, then mechanical system and then ignition system.

 

[rogerwa]

Re: Tohatsu 90 2 stroke losing power

Whagt were the compression numbers and did you ensure you have spark on all cylinders?

When you pulled the plugs what did they look like? Were they normal and uniform across all cylinders or did one look different.

Is this a new problem?

 

[skatz]

Re: Tohatsu 90 2 stroke losing power

Its been a while since I did the compression test, but it was as the manual said it should be accross all three cylinders. The spark plugs all look ok and they are all sparking. I replaced the fuel line and tank and installed a water separator just in case. The problem just happened one day last summer as has been there since. What should I be looking for mechanically that would cause a problem like this ???

Thanks

 

[TOHATSU GURU]

Re: Tohatsu 90 2 stroke losing power

"Use your service manual and start with the fuel system, then mechanical system and then ignition system."

Anything from a bearing in the lower unit to a bearing on the crankshaft.

 

[skatz]

Re: Tohatsu 90 2 stroke losing power

I have loads of people telling me different stories ... It's a problem under the flywheel, it's this , it's that. Have you ever heard of "lower seals" causing this problem. Personally I think it's mechanical although that would not explain the spluttering

Thanks

 

[rogerwa]

Re: Tohatsu 90 2 stroke losing power

You need compression, spark, and fuel.. It will be related to one of those things. The reason I asked about compression is that is says a lot about the health of the engine. If you have good compression, It should come down to delivery of fuel or presence of spark.

On your engine there are a few things (failsafes) that will limit the RPM to protect it. For example a high temp or lack of water pressure will put it into limp mode. I assume you have a strong pee stream??

If you have good spark which you said you had and good compression, I would focus on fuel delivery. You could have junk in the tank blocking the pickup, you could have an air leak in a hose sucking air at high RPMs, you could have poorly adjusted floats in the carbs.. There are just lots of htings that if you don't understand the workings, make it very difficult to diagnose.

the only thing I can see related to seal is if you have a bad exhaust gasket that is letting exhaust into the engine cover, essentially choking the engine. Thats easy to test. Just run without the cover.

I would take another compression test just to make sure it is good.

 

[skatz]

Re: Tohatsu 90 2 stroke losing power

Apparently, the crank housing is pressurised in a two stroke, is this true. I have been told that the seals could be gone and that is where I am losing power ??? The electrical and fuel systems seem to be OK, rechecked the compression again - its good There is plenty of water coming through the system also.

Thanks again

 

[TOHATSU GURU]

Re: Tohatsu 90 2 stroke losing power

It's theoretically possible to have a lower main seal failure on a Tohatsu..I saw one once on a 3.5 hp. But, it could be virtually anything. That's why you start with one system and work your way through it by testing using the procedures in the service manual.