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BF45A help needed

M

Midwest fisher

New member
Pulled boat from storage and carb problems from old fuel. Went through carbs and emulsion tubes and jets are clean now with no cracks but engine won't run without choke. I went back into the carbs as this just sounds like a plugged jet or emulsion tube but no. No vacuum leaks. Funny thing is it ran good last year for some unknown reason as the floats were set waaaay high. I'm about to set the floats stupid high again just to see if it will help. Is there any sort of test for the dash pot check valve in the fuel line?
 
Hi,
I haven't worked on one of these but I've cleaned plenty of Keihin Honda carbs. Just thought I'd offer some thoughts/ideas. Maybe something will click for you.

Looking at the Honda Marine Carburetion Manual there are two notes in the troubleshooting section for the BF45model under "Hesitation, stalls during acceleration".

Note one points out that there is a.Service Bulletin #6 but doesn't go in to detail about it.

Note 2 Indicates that if Service Bulletin #6 has been performed to raise the float level to 11.5 mm.

That might explain the high float you encountered.


How much attention/effort did you put into clearing the low speed and main AIR JETS? Those are accessed through the two passages on the front flange just above the carb throat. Low speed is the passage nearest the throat and main is just above that.

The low speed jet should pass pressurized cleaner through to the transition port orifices with the mixture screw lightly seated and low speed emulsion tube hole blocked.

I have found that it's often necessary to clear that circuit by "backflushing" using the spray straw directly over each transition orifice.

Actually, I highly recommend backflushing each orifice including idle, transition and main/high speed to get a reliable wash out.

The main air jet should deliver cleaner out of the main well and the decel hose spigot. Backflushing is a good idea for that circuit too while blocking one outlet and spraying through the other.

I don't know what a good evaluation of the decel check valve would be nor the dashpot diaphragm.

I suspect though that, since they're both primarily involved with anti stall, you may be able to simply disconnect and plug the hose to see if the engine runs differently without that system. I don't know for sure though and some care needs to be taken to prevent fuel leaking if you decide to try that.

Hope you get it sorted and good luck.
 
Thank you, that 11.5 mm seems like around the way I found the floats initially. I'm sure the circuit passages are clear but cannot in good faith consider removing the carbs for float adjustment without blowing out all passages again. Will advise.
 
Seemed to help but still too lean at idle. I'm starting to wonder if there is a screen missing from this engines muffler cover. Does anyone have a picture of there inside of both sties.? Looks like bf40 and bf50 shared the same muffler cover. Mine only has one large grid screen in it.
 
There's no reason that a missing flame trap screen would cause a lean condition.

Maybe it has a vacuum leak.
Try spritzing/misting water or carb spray at intake manifold and carburetor mount gaskets while running around 2500 rpm.
Water will make it stumble and carb spray will cause an rpm increase if you hit a leak.
The carb spray technique works best in my opinion.
 
Been around the intake and carbs with carb spray to no avail. Just putting my hand up the the air intake muffler without even really trying to close off the air seems to make the biggest difference. There is a very large opening screen in there just thinking I am missing something simple like possibly something that should be there and isnt..
 
Boat belongs to my farther so neither of us has seen it run on the water. Carbs were filthy but it did seem to idle better last year possibly due to the intake being filled with mud dobber nests restricting airflow.
 
Well, I don't know but I highly doubt the problem is is with the intake muffler. This thing could run with the muffler removed if you could figure out how to bolt up the carbs without it.

This is an old engine that you don't know so go back to basics and get yourself some data that you can depend on.

First thing I would do is check valve adjustment and timing.
Once you know, that's good, do a compression test.

If it checks out and you KNOW FOR SURE that the base engine is healthy and breathing correctly, then you might need to revisit the carbs.

You wouldn't be the first to have to go back and clean carbs more than once or twice or....well....more.

Those little buggars are TOUGH to get clean!
I wrote all that stuff about air jets and orifices and backflushing for a reason.

Good luck.
 
I had one of those things fill up the vent hole in a gas cap, a one way valve on a ride on mower. The hole was not much bigger than a sewing machine needle and I had removed the air cleaner and checked the carb and all the interlocks for clutch and seat. It would run and mow for a while, then quit and not restart. I finally looked closely at the gas cap and saw a hole, then discovered it was full of wasp mud.
 
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