Logo
FULL SITE MENU

Rpm drop

G

glaspro19

New member
I have twin BF40AX XRT's went out this weekend and 4 hours into trolling at 3000 rpm's one of my engines decided to act funny on me. RPM's dropped to 2500. I tried brining it back up got it to 3k for a couple of minutes then it drops to 2k starts to vibrate alot and couldn't hold a steady rpm. I then tried to upthrottle got a good respone at 4500 rpm's and thats how I got home. Got to the harbors entrance dropped throttle and the engine died. docked with one engine. Tried to start the engine again but would only start with the fast idle lever in upmost postion, tried to lower it to regular idle speed to no avail it kept dying. Washed the boat up and drove home (apporx 2 hours later) at home I looked at it, everything seems to be in place all hoses connected properly, no vaccuum leaks, I tried to hook up my syncronizer and all three carbs are in sync. Idle is at 1000k.

It will hold idle now for a couple minutes then wants to die. but when i rev it at home it still cant hold a 3k and will "bog".

I just did a carb rebuild and sync on both engines a couple of months ago and no problems till now. I have fresh gas new fuel filter/water seperators new spark plugs.

I'm stuck. Could it be a bad coil or wires or even a bad CDI unit?

Another question, what is the proper way to sync your carbs? I've read on here Hondadude recommends you to pich off the hoses between carbs but my manual doesnt state that. Also I think i read where they say to start with #3 carb and adjust the pilot screw 3 1/2 turns out from seat but my manual says 2 1/8 turns from seat.

any help at this point would be greatly appriciated.

thanks in advance
 
The later models have the hoses that need to be pinched off. Yours does not...so you do not have to worry about that.

My spec book says that the idle mixture screws for 40A with serial number 2007400 ~ later should be 1 5/8. Based on your Model number (AX), your serial number should be in the 3000000 series. Thus screw set at 1 5/8.

For others looking at this thread with 40's .....here is the variations to the idle mixture screw based on vintage.

2 1/4 turns out for engines BAYE-2000001 - 2007399
1 5/8 turns out for engines BAYE-2007400 and later
3 1/2 turns out for engine models BF40A4 and later (these have the vertical hoses between the carburetors.

Therefore, at idle you may be running too rich.

To sync the carbs, #3 is the reference....so you match the other two up to #3 (whatever vacuum it has). Make sure you sync after the engine is to temperature and keep the idle around 950 plus/minus 50.

If you think it is spark.....put a timing light on each of the plug wires as it is dying and see what the spark does.

It could just be, that there is some debris back in your carburetors. If you have not changed the small hoses on the motor, the hoses may be deteriorating and piece coming off inside.

Also, if you cleaned the jet sets (skinney tubes going up through the carb), they may be clogged again or may also have small cracks in them, causing erratic behavior.

If your spark looks ok (the same on all cylinders), disconnect your choke linkage that connects all of the carburetors. That way you can manually choke each carburetor individually to see if any of the cylinders pick up as you vary how much choke that it has. Choke it little by little. If there is pickup, you most likely have a carb problem.

All that being said, you should check the compression to be sure that all is well in that part of the engine.

Mike
 
Hondadude sorry for the long delay...

Finally got to look at the engine this past weekend. I had taken pictures and videos of the motor and how it was running and with my luck my iPhone crashed yesterday before I got to back them all up. I lost everything....

First off I have a question I looked on the back side of the block and stamped on the block was the serial number BAYE 1000147 I think it was I am certain of the BAYE 1000 I cannot remember the last three digits off the top of my head. Had it in my notes on me phone but thats all gone now. Just was wondering what your manual says about Idle screw adjustment on this model, you didnt seem to list it earlier.

I HAVE ISOLATED THE PROBLEM TO #2 CARBURETOR

This is what I have done. Power balance test. #2 no change. Started to play with the idle adjustment screw took it out almost all the way it was hanging on by a thread or two then the engine started to even out a bit. Pulled #2 Cyl coil and finally heard and saw some change in rpm drop.

Im thinking that it may be plugged again? Pulled out the screw all the way and heard some very good "sucking" air intake. Took out #1 and #3 screws to compare and they all sound the same so I can't really tell. When I removed #1 and #3 screws the engine wants to eventually die. With #2 it still runs just rough.

Do you have any other suggestions before I actuallty take the whole thing apart again and try to clean it out? Not sure if that is even the problem I'm just guessing here.


Thanks for all of the help.
 
Yes.... First of all, your model is a BF40A. 1995 or 1996.

Idle mixture screw setting is 2 1/4.

It is very possible that the slow speed air jet is clogged.

Try this. Drain the carburetor bow. Take out the idle mixture screw and spring.

Shoot a few shots of brakekleen into the idle mixture hole. Then take some compressed air and give it a few shots of air. Then do the brakekleen/air shots again a couple of times.

Leave the bowl drain open and squeeze the fuel bulb and flush it with fuel, clearing out any debris that may have gone into the bowl.

Put the idle mixture screw back it and give it a try.

You might get lucky.

Mike
 
Back
Top