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6hp ,4 stroke,problems on high lakes

Y

YORKY

New member
Had trouble starting motor on high lakes ,so took it back to dealer, who drilled out mixture screw plug, and leaned out mixture.Starts better now but idles, too fast for trolling, and slowing down idle results in stalling.Dealer suggested going to a #6 prop, but I also use this engine as a main motor on my 10ft porta bote, and I d'ont want to get into swapping props back and forth.Could drag a bucket but thats not a real solution.Any ideas out there?
Tony
 
Sounds like the idle mixture is way too lean, and the motor is running on the main circuit only -- hence no idle. Those carbs are VERY sensitive to even slight changes in the idle circuit.

It is usual and normal to swap props when changing boats/loads. Likewise, if there is a big altitude change, it is typical to either swap jets or change to a carb that is jetted correctly for the specific altitude. You can't have it both ways, but you can try to hit a middle ground -- setting up in a manner that is not best for either, but tolerable for both.

What specific model is the 6? If it's a B model, you may get a little more tolerance for different altitudes by running the carb from the A model.

There are 2 jet kits available, about $42.00 each. The kit for 3,000-6000 ft includes 3R6032540M PILOT JET #35 and 3R1032511M MAIN JET #68 HIGH ALT; The kit for over 6,000 ft, includes 3R2032510M MAIN JET #62 and 3R6032540M PILOT JET #35. The difference between the kits is the main jet.

Don't know what performance you need from the portabote, but there is a slow-speed, large-blade, high thrust prop available (used on sailboat applications), 399B645121 PROP 4/5/6HP, 8.375" DIA X 6" PITCH (ELEPHANT EAR), about $72.00, which may slow your trolling idle enough, yet have enough top speed for the portabote.

However, if you are jetted for high altitudes, running at sea level will still be the wrong mixture, and vice versa if running at high altitudes with sea-level jetting.
 
Thanks for the reply panv,
Engine model is mfs6bs 3r4 .Dealer tech told me that the problem with this engine is that there is no idle circuit.The only mixture adjustment was, the screw they showed me how to adjust, after they had drilled out the plug blocking it.So between the mixture screw, and the idle stop screw, that's all there is to work with .They said nothing about changing jets.
Tony
 
Better get that dealer tech to verify what he told you. He is mistaken. Those are indeed the high altitude jets for that motor. That mixture adjustment they showed you, sometimes referred to as a pilot screw, is indeed the idle mixture screw. It's set by instrument in Japan, then the anti-tamper plug is installed to satisfy the US EPA.
 
The air mixture port should not have been drilled out as it was completely unnecessary and a violation of Federal Law...The high altitude jet change out is the legal and ONLY correct method. Retarded dealers cause more problems than they solve:)
 
Thx again guys,this is disappointing news, when I thought they were experts.Do you know how to set that pilot screw back into the ballpark again.They told me the normal position for that screw is 2turns out from fully seated, and to turn it back in 1/2 turn to lean it out, so I guess it's all screwed up now.
Tony
 
Unfortunately the factory does not publish initial settings for the idle air mixture screw (since we're ideally not supposed to be adjusting it). So... it will need to be set by trial and error, and "dialed-in" like we used to do 40 years ago. FWIW, I have seen them (from the factory) as far out as 3+ turns or as little as 1 turn. Tiny differences (less than a quarter turn) can make noticeable overall differences in low speed and idle, but will not affect high speed operation substantially.

If they claimed that it was originally set at 2 turns out, that's a good place to start. Then test the motor... cold starting, warm idling, etc. A good shop tach can show small differences in idle RPM, but setting by ear is OK if your hearing is good and you are very careful.

Listen for warmed-up idle speed. When set correctly, idle will be at its fastest, with no popping through the intake. As you lean out the screw too far, you will hear the motor slow down, and as you richen it too far you will also hear the speed drop off. You will need to adjust the idle stop screw as you change the mixture, to maintain a consistent low idle, and throttle up/down after every change to reseat the tang on the idle stop, and blow off any carbon that accumulates on the plug. Be patient. Once you achieve a stable idle, you are almost home. Then, for driveability, you need to richen it up just a hair. Back it out maybe 1/8 turn and test again.
 
What Paul said and I will add that the setting is variable to each individual engine so it can only be set by the ear of a competent tech or by puter at the factory. The danger with tampering with ANY air mixture screw is that unskilled techs or foolish consumers will set the carb too lean causing damage to the engine. They are always, 100% of the time, set correctly at the factory. By setting the carburetor unnecessarily rich you simply burn more fuel, subject yourself to a $10,000.00 fine and foul out your spark plug(s). Altitude adjustment needs to be done by jet replacement...Never by screwing around with an air mixture screw. As fewer competent technicians are entering the marine marketplace everyday I fear that we will see more of this type of mistake. The sad thing is that these unskilled techs are everywhere and don't even understand that they are making mistakes. In the 60's and into the 70's you would generally walk into a mom and pop boat dealership and find one tech who had been doing this for 15 to 25 years. Now you walk into a dealer and find an immaculately clean repair shop with three factory trained techs who have an average experience base of 5 years. They simply do not have a clue as to what to do unless a computer diagnostic tells them what to replace.
 
Thx again guys I will follow youir suggestions, and I am going to have a real long chat with the dealership ,especially since they charged me $50.OO for messing it up.
Tony
 
Paul

you stated: ...The kit for over 6,000 ft, includes 3R2032510M MAIN JET #62 and 3R6032540M PILOT JET #35...

I have a 6 hp, 4 cycle Nissan and intend to use it on high altitude lakes. Where Can I find these jets? I tried the parts people here and the guy I talked to can't find them.

Thanx

Gene
 
Any Tohatsu/Nissan dealer can order them in for you. Currently, the pilot jet is out of stock in Dallas (the US headquarters for parts).
 
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