25hp Tohatsu random loss of power

[kevinwd1]

I have a 2006 25hp Tohatsu two stroke that randomly loses power at WOT .It’s as if the throttle has been pulled back to 3/4 power .The loss of power lasts only a short period of time then motor surges again maybe for 1minute or 15 minutes.
I took the boat out today for a two hour round trip and this occurred frequently on the outbound trip but improved coming home with it happening only twice in the last half hour.
Before starting the trip I replaced the spark plugs ,had fresh fuel and made sure fuel tank vent was open. The impellor is good as there is plenty of water flow .This problem has only started to happen in the last couple of trips.The motor has heaps of power and the boat jumps onto the plane
I’m going to remove and clean carby as it seems likely it’s a fuel problem .I’ve been told that the fuel pumps are near bullet proof so is unlikely to be the problem
Any feedback on other possible causes appreciated
​​​​​​​Regards Kevin

 

[pvanv]

What is your actual model (not year?).
Possibly have a bit o junk in the carb.

 

[kevinwd1]

Model M25C3

 

[pvanv]

That model was not available in North America at that date; however, the usual applies. Start with the fuel system, from tank vent through o-rings on fuel hose, to pump and carb. If all are perfect, test electrical components.

 

[kevinwd1]

What size are the fuel hose o-rings? Do they need to be a particular type of rubber to cope with petrol
I removed the carb today, and the bowl was like new with no dirt at all. I will remove and clean the main jet tomorrow at work. Is there anything else I should check on the carb?

Yesterday I noticed a small drop of milky liquid on the bottom of the old spark plug. I assumed it was condensation as the motor had been sitting for three weeks. Maybe I should do a compression test? .Is it worth checking while carb is off ?. I wouldn't think symptoms would indicate a head gasket issues, but I'm no mechanic

Thanks for your help

 

[pvanv]

Fuel hose o-rings are not available separately; you would replace the hose end.
Fully disassemble the carb (including jets and emulsion tube, and soak overnight in real carb dip, then blow out all passages with generic carb spray, then carefully reassemble checking float height.

 

[kevinwd1]

The carby was spotlessly clean so I don’t think that it was the problem.
Does the plastic Tohatsu fuel tank have a filter on the uptake hose and if so can you remove and clean them
I have managed to get some orings from an engineering supply shop .A genuine replacement hose cost $140 so that’s not an option

 

[pvanv]

Yes, there is a strainer in the scepter tanks (US)

 

[pvanv]

You can get individual end connectors if you can't get o-rings.

 

[Sea Rider]

The individual end connectors are darn expensive too, probably will only save just $ 30 buying spare parts. Some issues : When you bought the motor, was brand new, second hand, it's used in salt water as to check the motor's background ?

That motor is a 13 year oldie, if used in salt water, do you see thin white salt lines formed around the cylinder head gasket contour or rust on any of the spark plug tips ? If so, gasket has ceded a bit, was not retorqued back to specs soon after the break end period ended. Nothing strange, nobody does so LOL!!

Clean the whole internal tank before assembling back the pick up fuel tube along the main fuel filter located near the fuel pump. Spare connector's o'rings must be 100% fuel compatible, if not will be degraded soon.

Happy Boating

 

[kevinwd1]

I brought the motor secondhand about six years ago. It's used in salt water but always flushed out and run until carby is empty. I never use ethanol fuel.
The motor still starts easily and runs the same as when I first got it except for the random loss of power
There was no rust on the tips of the spark plugs and no salt around the head gasket, it feels like a fuel starvation issue?

 

[Sea Rider]

Need to discard if already being a fuel starvation related issue, is the current fuel line the original one ? got the new connector o'rings ? if not, will need to troubleshoot the original o'rings if having hidden issues and go from there...

Happy Boating

 

[Sea Rider]

This is a simple DIY way to troubleshoot if having bad internal fuel connector o'rings.

​


Unscrew CCW the fuel pick up assy, wrap tight rounds of a single length piece of electric, duct tape as seen in picture. Do same at motor connector end. Check if issue has gone, if so, will need to buy 2 new fuel o'rings same diam and size, check car parts shops for them. Report your findings..

Happy Boating