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bf8ah carb idle fuel mixture setting question

M

mickhodapp

Member
hi folks,the idle fuel mixture setting on my 1989 honda bf8ah carb is adjusted out 4 & 5/8's turns from being seated. it was just serviced by a new to me boat mechanic & it runs but sometimes idles way down & stalls.it is hard to start now when cold & it always needs to be choked whether it's cold or warmed up plus sometimes it stalls when accelerating in gear. is the idle fuel mixture setting wrong? new plugs .26 gap, fresh fuel, new inline fuel filter, good hoses,tank,connectors,everything is tightened up good, fuel pump filter is clean, & jets recently cleaned. any suggestions ? thanks in advance for any info ! Mick
 
If the motor is a BF8AH model, then it is a 1987. The idle mixture (or pilot ) screw should be 1 3/4 turns out from lightly seated.

It is possible that the mechanic missed part of the idle passage. This carburetor is pretty simple to clean, but screw #10 needs to be removed and that passage needs to be cleaned out with cleaner and blown out with compressed air. If that passage is clogged, the engine will not idle.

The motor also needs to come to temperature to idle correctly.

Both idle passage and temperature affects the acceleration.

If all is good and it is just the incorrect idle mixture setting, then you should see evidence of rich running by carboned up spark plugs.

One other thing that is very important is timing. If the timing belt has jumped time one notch, the engine will not idle correctly....acceleration will be bad....starting will be difficult .....but full throttle may seem ok once you get there.

This all assumes that compression is good in both cylinders. It should be around 151 psi.

Mike
Mike
 
pull plugs and take a look,is she running rich, Also try priming fuel bulb when running,if condition improves you have a delivery issue, possible weak fuel pump not sure on idle mixture setting, A little history on motor would help. Is engine new to you? Has she been sitting for a while in storage? Was carb disassembled completly and soaked in solvent overnight and rebuilt thoroughly,every nook and cranny cleaned.
 
Hondadude i dont think he has a manual I thought that idle mixture setting was a bit excessive. He might have trouble finding screw #10
 
Hello Mike & johnny, thank you for the information ! i got the motor started yesterday & let it run for two hours at idle,throttling it up in gear occasionally, while docked, & it quit once after warm when throttled up but restarted when choked but then didn't want to idle down without quitting. i shut it off & pulled out the brand new plugs (ngk dr5hs gapped @.026 & they were black & dry,i would post a pic of them but don't know how to do that yet,sorry. I haven't tried to re set the idle mixture screw yet because i'm not sure of the meaning of the word "turn". does it mean to count the # of 180 degree turns or is each turn a complete 360 ? my next trip to the boat i'll clean & re gap the plugs & set the idle mixture @ 1 3/4"turns?" out while the motor is cold, then start it up & keep it running until it warms up & then adjust it in or out 1/4 turn at a time & see what it does. then if it still doesn't want to idle right i'll try adjusting the idle speed in or out in 1/4 turns.I know where the #10 screw is & have sprayed carb cleaner in it & blew it out with compressed air but i can do it again. in regards to the question about familiarity with the motor, i have had it for 5 years & it only has approx 40 hours on it since it was completely rebuilt from the ground up by the po who was a very qualified boat mechanic. the motor has always been dependable for me except i've always had to start it with the choke pulled all the way out,whether the motor was cold or warm. what would be the cause of that? i purchased the boat in california & brought it here to puerto vallarta & thought that it might be issues with the gasoline they have down here. thanks again & if i don't hear back from you about the" turn" terminology i'll figure it out & i'll post my results. thanks again guys ! by the way, honda outboards are very rare down here so it's hard to find a qualified mechanic that knows about hondas. I think 4 & 5/8 turns (i'm counting 1 turn as 180 degrees) as extreme & am hoping this is the problem
 
Fact----The idle passage is very small.-----Many times it takes folks 3 tries to find and clean that tiny passageway.---------Do you have a magnifying glass ?
 
One turn is 360 degree (complete rotation).

After you play some with the adjustment....

If it continues to not run at idle, pull choke out a little and see if it keeps running.

If it does, then it is time to look at the carb again.
 
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