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Help - Fuel Starvation?

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grl3760

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Hello. I have a Tohatsu 2.5 hp 2 stroke that I use to power a small sailboat. When I move the throttle lever past 40-50 percent the engine begins to lose power and shuts down after 10 seconds or so. I can keep the engine running if I use the choke - at about 50 percent closed. At WOT with the choke at roughly 50 percent on the engine will run at about 85 percent of max rpm.

I have completely disassembled the carburator - twice. All clean inside. Float floats, the little valve that controls fuel flow to the bowl clean and moves easily in its slot. Blew out all of the passages in the carb body I could find - all clean and clear.

Fuel tank outlet, shut off valve, hose to carb checked - blew out - all clean and clear.

Spark plug had a little bit of oily residue on it. I cleaned, touched up the edges with a small file and checked gap - all ok.

Amazing thing is that it ran when I put it back together, but no improvement in the situation I describe above.

I would appreciate any thoughts on what I can try next.

Thanks!

George
 
Sounds too lean. Probably still varnishing in the carb. Do a complete carb disassembly, and a 4-hour bath in carb dip. Real carb dip. Check the adjustment of the richness of the slide as per the Factory service manual. In the future, always run the carb out at the end of the day to reduce that varnishing.
 
Thank you for your response Paul, will do the carb cleaner exercise this weekend. I do not know how to adjust the richness and do not have a factory service manual. I guess try the carb cleaning first. If that doesn't solve the problem we can work on the richness.

The engine is 5 years old, lightly used and I do run the carb dry....unless I forget.

Thank you again.
 
The small (2, 2.5, and 3.5) 2-strokes have a spring-loaded cable to move the slide, and it engages a retainer. You have (I think 3) different setting points that seldom need adjustment, but I have had 1 or 2 motors that worked better after changing it. A Manual would definitely help. Where are you located? The 2-strokes have not been available in North America for some years now.
 
I am in Atlanta, sail on Lake Lanier. Purchased my 2 stroke as they were phasing them out, liked it mainly because it is light - 27 lbs. - weight counts when racing..... I have no idea whether it has agood reputation or bad - it has done well for me until now.

I am familiar with the slide and spring - came out when I unscrewed the top of the the card. before any disassembly by me, at WOT (lever moved as far as it will go) the slide still covers about 1/2 of the carb intake throat (which I thought was weird - one would think it would be...wide open!).
 
I'm assuming you have an M2.5A2. That is the same block/piston as the M3.5A2. The big difference is in carburetion. If you ever need more power, I just gave you a hint. Yes, we sold tons of those to small boat sailors, primarily because of the light weight and compact size. The same corollary holds true today in the four-stroke 9.8... Much lighter than the four-stroke 9.9. Your motor is sought by many a J22 owner today for the weight advantage. Unfortunately, the EPA has made us use the 4-stroke version of that motor for several years now, and it's a lot heavier -- plus can't just be tossed below when racing -- it must be placed on the correct side, or crankcase oil runs into places where it shouldn't. I have actually replaced power heads on the old 2-strokes, even though it isn't cost effective, because the owner wants to keep the weight advantage.
 
We have a Wavelength 24. In calm conditions I can get 6.1 - 6.2 mph - gets us back and forth to the race course just fine. Thank you for your help. I will let you know how the carb cleaning goes.

George
 
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