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jshep 03-02-2008 09:14 PM

tohatsu 3.5 won't run without choking

I have a 2002 3.5B2 3.5HP 2cycle that I purchased used last year. Worked great for 2 outings. Died the 3rd.

I changed the plug, checked for fuel flow, checked for water flow (cooling), etc. New gas, new oil. 50:1.

It starts great with the choke on. Whenever I move the throttle up or completely turn off the choke, it dies. Sounds to me like a fuel flow problem, but the line seems to be fine into the carb. Carb spray did nothing. My guess is that I need to get a rebuild kit for the carb, but before I start looking for one and go to the trouble, I wanted to ask for some friendly advice.


Faster 03-02-2008 09:22 PM

Does it "wheeze" when it dies? We have had periodic problems over the years with one of our 5 hp nissans and always found some crud in one of the jets in the carb.

Don't think it's necessary to get a carb kit unless the engine is quite old. Pay attention as you disassemble it, don't lose any bits, and take out all the jets, inspect them and blow them out. As long as you haven't damaged the gaskets you should be able to reassemble it and be good to go for a while.

Very simple engines, most likely a carb problem.

Quickstep192 03-02-2008 10:41 PM

I had the same problem on my Honda. The jet orifices on these little motors are tiny and the tiniest bit of crud can clog them. I think it's likely to be the main jet which is generally accessed by removing the float bowl. You may find that the float bowl and/or the float valve are gunked up. You'll want to clean the entire carb, otherwise another piece of crud might find it's way right back in there. I've usually found disassembling the float bowl to be a dicey operation as the float valve can fall apart and its re-assembly might not be intuitive. Some companies sell a carb re-build kit which includes the jets and gaskets. Carb cleaner can be pretty hard on some of the gaskets and o-rings.

ysabelsdad 03-02-2008 11:24 PM

I have a 5 horse Mercury that is doing something very similar. Can anyone recommend a decent book on maintaining and repairing small outboards. Most of the book I have seen seem to be oriented to larger engines.

Faster 03-03-2008 12:10 AM

Here's a link from a google search... don't know anything about these books but maybe something here will look helpful....
Outboard Motor Manuals and books about Outboard Motors

Sapperwhite 03-03-2008 12:11 AM

Seloc Marine has a book on about every engine out there.

ysabelsdad 03-03-2008 12:30 AM

Bingo. Seloc is it.

The outboard motor book store doesn't seem to carry anything on Mercury engines built passed the late 90s.

camaraderie 03-03-2008 09:15 AM

I agree that the carb bowl and float are the likely culprits if you have good flow up to that point. It is pretty straightforward work to disassemble and clean and does not require a manual if you just go slowly and try not to have any pieces leftover when you put it back together! :D

eherlihy 03-03-2008 09:40 AM

To clean the jets, I have always found that a blast of WD40 (Water Displacement formula 40) works wonders. If the crud is really stubborn, I have some wire-wrap (stiff, thin guage [AWG 30] wire) that I use to poke the crud through the holes in the jet. You can probably pick some of these up at your local electrical hobby store (Radio Shack, etc.).

chucklesR 03-03-2008 10:05 AM

Sounds like fuel air mixture, but may not actually be the carb/choke.

How about the gas cap - most have vents that need to be opened when running, closed when carrying? Do / did you remember to open yours?

Look for simple solutions first, then start poking around with tools.

How much time elapsed between running it the second and third time? Is the fuel bad? If the carb isn't varnished (brown coating on the metal) it might be just a blow out the jet's issue, if it's varnished soak it as a unit and try it before taking it apart.

Did you refill with E85 and melt the innards?

Is the choke set and operating properly (not sticking, popping once hot etc..). Again, going with the simple solution first make sure it's operating correctly since the engine shuts down when you close it, or speed up the throttle. - it might not be fuel, it might be air :)

It might be fuel, but look for the easy, single answer to a single problem solution first.

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