BF90 Stalls on hard acceleration

[Sandiford]

Gentlemen<br /><br />My BF90 stalls if I try to accelerate hard from standstill. If I ease the throttle through the first 2,000 rpm or so, I can then shove the throttle wide open with no problems. <br /><br />I have read a couple of threads which refer to the acceleration diaphragm assembly. Could this be the cause of the problem? How does one go about testing this device?<br /><br />As far as I can tell, the diaphragm injects air (not fuel) into the carbs when the throttle is opened thereby leaning up the mixture temporarily. the diapragm itself seems sound (it will hold air pressure).<br /><br />Is the valve between the diaphragm and the carb. supposed to act as a check valve? mine allows air flow in both directions, but flow back from the carb to the diaphragm is certainly restricted.<br /><br />I hope that I have explained this clearly.<br /><br />Any advice or comments are much appreciated.<br /><br />Thanks

 

[MajBach]

Re: BF90 Stalls on hard acceleration

I've had this problem on my 90, but after ignoring for an entire season, the problem seems to have gone away on its own.

 

[Sandiford]

Re: BF90 Stalls on hard acceleration

Thanks, MajBach<br /><br />I guess I will stick it out until next season and hope things improve.<br /><br />Did I understand the function of the diaphragm correctly?

 

[MajBach]

Re: BF90 Stalls on hard acceleration

I have no idea how it works. I actually had this problem the first season I owned the motor. I mentioned something to the mechanic and I saw him make an adjustment that seemed to correct the problem. The following season the problem reappeared and I asked him to fix it again but he ( nor I ) recall what he did, ( I thought it had something to do with an accelerator pump ). Anyway, around the same time I was informed of a TSB for this problem and the fix. I didn't have the cash ( it was a warranty coverage I think too ) so I thought I would just lay off the hard starts. I noticed that the problem occurred most frequently when I had a heavy load or used my coarse prop. From this, I assumed the fuel wasn't being delivered as fast as the air was as this is also a problem on piston driven airplanes. Anyway, maybe the diaphram rectifies this problem. But this season, the engine died only twice early in the year and never since so somehow the problem is gone.

 

[rodbolt]

Re: BF90 Stalls on hard acceleration

the diaphram actually pushes air into the bleed chamber and makes the fuel mix richer. it forces extra fuel up the main nozzle. it works on the priciple that the air presure in the flaot bowl is higher than at the top of the main nozzle. with a small boost in air pressure at the bottom of the nozzle more fuel will be expelled.<br /> check your service manual cause I belive there are inline check valves to prevent fuel from being drwan back into the lines.

 

[vikingham]

Re: BF90 Stalls on hard acceleration

Just want to be sure I'm clear - the diaphragm is that round gizmo about 2-3 inches across that's linked to the throttle linkages on the carbs, right? It seems like the shaft operates when the throttle is opened beyond a certain point (maybe 1/3 to 1/2?)?<br /><br />I had wondered what it was doing there.

 

[rodbolt]

Re: BF90 Stalls on hard acceleration

without looking at it it could be a dash pot or an accelerator enrichment device.<br /> best thing is buy a manual.<br /> but if you can get a clear pic I may be able to help. I dont deal much with honda anynore but they always had a well engenered and reliable product.

 

[Sandiford]

Re: BF90 Stalls on hard acceleration

Gents<br /><br />Many thanks for your input. From what I can saw in the manual, I think rodbolt has a good explanation of the operation.<br /><br />When I can get my hands on my manual again, I take a closer look.<br /><br />Thanks again!

 

[prdebusschere]

Re: BF90 Stalls on hard acceleration

my 99 honda 90 also stall with fast acceleration. i have done the stc. also all carbs have been taken off and soaked in a carb cleaner twice by the dealer. this has been going on for over 2 years. the dealer says to replace the carbs or find an ultrasonic carb cleaner. what should i do

 

[MajBach]

Re: BF90 Stalls on hard acceleration

This is not a carb problem. There is a recall on a part the causes this. See an experienced mechanic about it or contact Honda.