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Need advice: adjusting my 4 stroke

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Paul
1st Mate

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57 Posts

Initially Posted - 05/28/2006 : 17:02:46

I'm hopeful my new Tohatsu 9.8 requires only a minor carborator adjustment. It starts cold and runs perfectly. After a couple of hours sailing, it will start again, but wants to quit when I give more gas than just idle.

Is there a smart method to fiddling with the 'mix' screw on the carb or is this just one of those things where you give it 7/8 of a turn until it sounds right? Based on the aforementioned symptom, should I start turning clockwise or counter-clockwise?

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Paul
1st Mate

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57 Posts

Response Posted - 05/28/2006 : 17:24:40

I meant 1/8 turns, not 7/8.

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atgep
Master Marine Consultant

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1009 Posts

Response Posted - 05/28/2006 : 18:10:47

"after a couple of hours "

The engine is cold at that point and will need a little choke to warm up. You did not mention if you were using the choke on the restart. These engines run on very tight tolerances and the engine needs to be warm to run properly with the choke off.

If you do find an adjustment is required, counter-clockwise will richen the mixture. Clockwise leans it out.

Tom

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tinob
Master Marine Consultant

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USA
1883 Posts

Response Posted - 05/30/2006 : 13:12:05

Paul...The smart way to fiddle with the carburetor is TO NOT FIDDLE WITH THE CARBURETOR MIXING SCREW

.

Choke to start and then advance speed slowly.

When my Nissan was just out of the box (October in the Northwest) it took some time to warm up. Now it's 85 degrees and it still needs choke to start but I can shut the choke off within a few seconds and it runs fine.

More greif is caused by inexperienced knob twisters.

Val on Calista # 3936, Patchogue, N.Y.

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Paul
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57 Posts

Response Posted - 05/30/2006 : 14:54:08

I couldn't locate a screw for adjusting the mix while hanging sideways from my stern rail. So I guess I was spared the opportunity to mess it up.

There are only two screws I found that appear designed for any adjustment; one for the choke idle speed and the other for the idle speed without choke. Again, the motor started cold (with choke) and ran as expected until it warmed up. Then it stalled and wouldn't restart for more than a few seconds and, eventually, not at all. No amount of fiddling with idle speeds mattered by then.

I have two other theories to test before figuring out how to get 100lbs of metal off the transom of a moored boat and into the shop. Both theories are related to the fuel tank.

I've left my gas cap on loose (old can, no vent) for about three weeks. A progressive build up of moisture in the tank would explain why the problem didn't exist from the start and has gradually gotten worse. But I also know there are opposing theories about whether condensation is a real or imagine threat to a vented tank.

I also wonder if the line/tank coupler has anything to do with it. I replaced the factory coupler with one compatible with a larger, older tank I had. I wonder if the old one is just different enough to create pressure that floods the motor; the prime bulb is full, so I'm pretty sure a vacuum isn't being created.

I'm thinking the most scientific approach would be to reconnect the original line coupler and run the motor from the tank it came with. If I get the same results, I'll add stabilizer to the fuel to see if moisture is in play.

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Sloop Smitten
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1181 Posts

Response Posted - 05/30/2006 : 16:23:28

Paul,
A lot of those fuel tank couplers look alike but are just different enough that they may be starving your engine. If I was in your shoes I would put the new coupler that came with the engine back on a fuel line I knew was clean and put some fresh gas in the new tank and try again. I am assuming you have a fuel filter that would stop any particulate coming from the fuel tank. If you can drain the carburetor bowl I would do that as well. If it won't start then I would spray some carb cleaner in the throat of the carb and try again. If it still won't start I would take it to a shop or call the dealer if I purchased it on-line. It's brand new and you don't want to screw it up.

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cks
Navigator

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126 Posts

Response Posted - 05/30/2006 : 21:06:30

i have a brand new mercury that i was told is a rebadged tohatsu. i have been having similar problems-stalling a few seconds after starting or not starting at all. the mercury has a "throttle" button that disengages the drive shaft so that you can open up the throttle without engaging the propeller. My manual suggested that before cranking, i try injecting a little extra fuel by turning the tiller briefly into "forward" while pushing the throttle button. i tried this this weekend an volla- the motor didn't stall. my manual also states that i should wait 3 minutes for the engine to warm up before moving.

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Paul
1st Mate

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Response Posted - 05/30/2006 : 22:37:43

Thanks, everyone. I reverted to the original fuel line, coupling, and tank. Then I adjusted the unchoked idle up a little higher than the factory setting. Thunderstorms preventing me from doing extensive testing, but I think I'm back in business.

The West Marine catalog arrived today and includes the 6.5 gallon tank that so many C25 owners recommend for $25. I'll pick one up tomorrow and throw away the old tank.

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.