1998 Honda bf90 fuel starvation at higher rpms

Just got my motor back from the mechanic for a carb clean. He said the carbs look clean, and that two carbs floats heights had to be adjusted. I got the motor back and it starts and idles great, but when I hit anything above 5000 rpms it starts to rev down and up. If I squeezed the fuel bulb it did pick up speed, I try this again and it didn't have any effect on it later in the day. I ask him if he had to sync the carbs and he said he did not. And he also had to make a intake manifold gasket, could a leaking mainfold gasket be the culprit?

I gonna try and replace the fuel filter in the motor. I am hoping that it is not a electrical problem, but from what I read rpm's that fluctuate at high speed can be electrical.


Thanks gulfcoastsurf

How does he know that he did not have to sync them, if he did not put any gauges on them?

The homemade intake manifold gasket is suspect. Why did he not use the proper gasket? $11.00. If the surface for the intake manifold gasket is not clean and the gasket is not sealing perfectly, not only can extra air be being sucked in, it is possible that some water from the water passage could be sucked into the combustion chamber.

Was the fluctuation above 5000 rpm the reason you took it in for repair in the first place? If so, why did he not water test it. That is the only sure way to see if the trouble is fixed.

Did he check compression?

Spark?

Why did he not change the fuel filter?

Did he install new NGK DR7EA spark plugs (only use NGK DR7EA's not Densos)?

If you momentarily hit the choke switch, does it pick up?

I would get those unknowns resolved before you look at electrical.

I would also be sure all the hose connections on the motor and going to the motor are tight with no leaks.

Also, check your fuel, drain one of your carburators into a glass jar and check for any water.

I know....there are more questions than answers.

Mike

Thanks for the response, took the boat to him because at idle it was not firing on two cylinders, he adjusted the floats and it now responds when you

pull the spark plugs boots. It also at wot would only get up to 4500 rpms. and just stay there no more or less.

I change the spark plugs to the recommended NGK DR7Ea and check to make sure they were gaped to manufacturer specs. I today change the internal

paper fuel filter and it looks yellow and possible no good, I did not get to water test it today because of a afternoon storm, but am feeling pretty

confidence that the old filter was hindering fuel flow. He did not check the compression, it was check in April and was about 186 on each cylinder. I

have not try the choke to see if the motor pickups when it stumbles. Spark as far as I know is OK, as for the mainfold gasket I do not know why, have

one ordered and will have it switch out. I will report back tomorrow with the results from the new fuel filter and checking all the fuel lines and fittings

from the tank to the motor.

Thanks Gulf Coast Surf

Well he is a quick update, ran exactly the same fluctuation speed at first then a steady 4000 rpm, flipping the choke makes it stall even more, the fuel filter did not fix the problem. And discover that the number 3 cylinder is not firing now. The next step would be changing out the intake filter. I also could kind of smell a hint of gasoline in the oil, it may just be my nose playing tricks on me.

Hook it up with the a portable tank and was able to run it for about 15 minutes before the afternoon storm ran me off the water, not even the slightest stumble, so the problem I believe lies in the spin on fuel filter, tank pickup, or possibly some sour fuel. Thanks for all the tips Honda Dude they are greatly appreciated.

Gulf Coast Surf

Sounds like you might be on the right track. Keep us posted.

I do wonder that would have caused you to lose #3 cylinder.

Let's hope the solution is simple.



Mike

Forgot to add that I checked after running it today and now have the number 3 cylinder firing again. I will report back tomorrow with the final report.

Ran the boat for about 4 hours today, ran flawless, change the spin on filter for a racor sight bowl, dump the old fuel that was only 2 weeks old and check the intake screen on the tank. Is it possible that the sierra removable filter was clog only after 3 month? Anyway the motor up and running great. Thanks Honda Dude for the tips.

Gulf Coast Surf

Yes...could be hose coming apart from ethanol in fuel and the parts are ending up in the filter. Just had one of those myself.

Glad things worked out.

Mike

Even with everything running well, make it a habit to change out the Racor filter element every season or every 200 hours, whichever comes first. They do get clogged up occasionally.

I have found on my two BF90s (a 2005 and 2006) they respond really well to being run with the Stabil Marine Ethanol stabilizer (blue in color). They were hard starting SOBs even after being run some. Draining the carbs only helped in the very short term. Now I don't have to drain them at all. I have racors on both and was still getting bad fuel to my motors which caused problems.

Sobie2