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Honda bf-90 runs rough and stalls

D

DOCK DOG FRED

New member
Good evening, i ran across this web site and found the answer
to my starting problem that i had been pulling my hair out on.
Thanks so much.
I bought a pontoon boat the first part of the year, it ran in fresh water at sea level. I am running this boat at 5500'-6500'
in the mountain lakes. I have only had a chance to use the boat a few times so far, the snow just melted up high not long ago.
I have installed new plugs, drained carbs, drained fuel tank
installed new fuel, adjusted the valves, complete service, even installed two new fuel pumps and filter. Every thing checks out fine.
The motor starts out running great and keeps running fine.
But if you turn it off and it sits for 15-20 minutes and then you start it back up, the motor will run rough and not run up above about 1200 rpm. Then you have to play with the throttle, sometimes it dies, or just chugs along for a bit. If you can keep it running for 5 minutes or so, it will start to clear itself out and then run fine. I know i may need to reset for high altitude, also i can only get about 4200 rpm out of the motor under full load.
Will run up to 6000 rpm out of the water. I am sure i need a new prop with less pitch, could sure use some advise. Thanks so much.
 
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Since you are running at somewhat of an altitude you will be running rich. You are getting the same amount of fuel with less air. There are three different main jets for the 90's. I can not tell you which one you need. I have not had to deal with this specific problem.

Since you are running rich, your plugs may be getting fouled and it takes a while to burn it off....just a theory. Your power will be down, so to get full rpm, I would think that you have to lower prop pitch too.

Try to find a Honda dealer in that area. I am sure they deal with this all the time. If there are none, try to call one in Denver (the mile high city) for advice.

Mike
 
Thanks for the info, i will see who i can find in the area,
not many choices in the area for honda repair.
Do you have any starting point on a prop.
I am running a 3 blade aluminum 13.5x15?
Also, i was running the motor on the trailer today, at differant rpms. One thing i have noticed is if you just hold it at say 3000 rpm, you will get a small "pop" as the engine is firing time to time. I pulled the plugs and they looked clean, but like you said, they may burn off.
Thanks again for your time ,
 
The engine will generally pop if you run it up with no back pressure of the water. The altitude/jet thing may also be adding to it.

You said it ran good at sea level...what rpms were you getting at full throttle?

What rpms are you getting now?

You will need that info so the local dealer can make some suggestions.

I would think you need to get the proper air/fuel mixture first, then work on the prop selection.

Again, I have no experience in high altitude issues. It am only responding based on what I have read. According to the guidelines that I am seeing. Between 5000 and 8000 ft you should change to the next smaller jet. Your effective horsepower will be only about 80% of the normal horsepower. So your prop pitch will may have to be reduced to an 11 or 12 pitch...if my theory is correct.

All that being said...it is just theory. Check with someone who knows.

Mike

M
 
Hello again mike,
thanks for the info.
As far as the rpm at sea leval, I dont know.
I bought the boat from a private party and i cant get in touch
with him.
I think you may be correct about the popping, i dont recall noticing it when i run the boat in the lake.
I checked the engine with a hand held electronic tach today to check the dash tach, and they both matched.
Out of the water i can get 6k no problem. In the lake 4200 rmp max.
As far as the jets go, what jet do i need to change? The main,primary, or slow jet?
Also when i got the boat i also ordered the shop manual for the engine from honda, it came with a few supplements.
I noticed in one of that the primary jet in the supplement is a #80, and in the original manual it calls out a #52. I do not know what the differance may be.
I also found anouther posting with almost the same problem
as mine from dirty jets. This problem seem to be getting more common after i turn the boat off for about 15-20 minutes.
It just luggs and chuggs until it clears itself and the takes off and works fine.
I dont have any problem pulling the carbs, i just need to know what jet and what to look out for.
You have been a big help, thanks again,
steve
 
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the #80 is the main air jet. The jet I was referring to was the main jet. #132.

The guidelines say it should be reduced to the next smaller size to #128.

Mike
 
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