# 2008 BF 750i Weak? Fuel Pump



## smutty11 (Jul 2, 2010)

Hey all. Looking for help with my newly purchased used Brute. After i first start it up it runs great. After 2-3 minutes when I attempt a WOT run I can only get about 25mph out of it and a bunch of backfiring. Here's the interesting thing. If I shut it down and then immediately turn it back on and attempt a WOT run it runs awesome again for 2-3 minutes. I can only think of a couple potential problems and was hoping for some input. It's as if the bike is running off the fuel that is being pressurized at ignition turn on and then not by the ECU. I can hear the fuel pump running when I turn the ignition to run. I don't have an FI light on the dash. It is snorked but I don't know how this would cause these symptoms. It runs great by cycling the ignition when it's both cold, warm, and hot (while the fan's running). I'm leaning towards fuel pump because of how the condition goes away. If it were injectors or some other sensor (TPS) i don't know that cycling the ignition would fix those. Does the ECU "learn" anything in the first couple minutes of being on every time or does it just give a certain timing and fuel map based strictly on sensor input. I know there's two different timing maps for low and high throttle, but again I don't think the TPS is the cause. Any ideas???? Thanks....and I'll get a sig up soon just joined yesterday and goin out to load her for a ride today, limp her around the woods.


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## hondarecoveryman (Feb 28, 2009)

It is a crack in the pump housing , causing a pressure drop , I had one in my shop doing the same exact thing , but you cant buy just a housing , you have to buy the whole assy.


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## smutty11 (Jul 2, 2010)

Thanks HRM....The machine's got 94 hrs on it. Any ideay what I can do to keep this from happening again? Is the crack something I can see on a visual inspection once I get the assembly out of the tank? I'm not challenging your suspicion, but would like to confirm it before I go throwing parts at it.


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## smutty11 (Jul 2, 2010)

The kick in the junk of it all was that there was no way I could have identified this when I test drove it in the parking lot of the mower repair shop it was for sale in front of before I bought it.


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## hondarecoveryman (Feb 28, 2009)

Yeah there was no way you would have noticed it in a parking lot :nutkick: It is not something you can see, I heard fuel spraying back into the tank on the one I worked on , rode it untill it started messing up , removed the fuel cap (dumb luck) and thats when i heard it . I tried univesal pumps,fuel regulators and every combination of the 2 before buying a new pump :34:


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## Rack High (Feb 23, 2010)

Smutty, 3 months ago I rolled mine in a raging river current. Long story short, my bike acted just like yours where it would run good out to 1/4 throttle but anything past that or quick WOT and it would bog down, backfire etc.. Turns out sand had gotten into the fuel tank, picked up by the fuel filter clogging the fuel line and injectors. After a complete purge, she's running great now. Just another possibility.


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## smutty11 (Jul 2, 2010)

Thanks for the input Rack...Based on both your and HRM's suggestions, I'll be pulling the fuel pickup out today for a filter cleaning and pump inspection. I'd like to get a WOT fuel pressure reading before and after but I'm not sure if it's worth the effort. Wish I had my own dyno.


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## smutty11 (Jul 2, 2010)

....and clogged injectors. How'd you fix that? Did you clean them yourself or send them off?


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## smutty11 (Jul 2, 2010)

Just looking for backup on eliminating another possibility. In the service manual it states that with certain sensors failed or out of range that the ECU would lock into the "low speed" map. If this were the case my FI light would be on correct?


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## Crawfishie!! (Dec 9, 2009)

Man, sorry bout ur luck with ur bike. unfortunately when i bought my 08 i waas having the exact same issues you are having. i removed my fuel cell, then pump to find the the coupling on top (where the fuel line connects) was cracked. i tried jb weld, plastic steel and several different applicatons only to find out that none of those will hold up to the pressure that little pump puts out. in the loong run, i had to break the bank and go spend $700 for a new fuel pump and relay. after complete disassembly of the fuel pump i found a screen on the bottom that can be cleaned as well, i would try cleaning that screen first and running it again just to be sure you dont throw away that kinda ducks. just my 2 cents and what i went through with mine.


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## smutty11 (Jul 2, 2010)

Crawfish...Right on!!! That's what I spent most of yesterday doing. For now it's dramatically increased the performance. When i first tested the pump, before removing it from the tank, it was barely trickling out. After cleaning and reassembly I thought I had bigger issues because it still only trickled after a good quick spurt. Something for those who may be in the same boat....Make sure you fill the tank enough to get the fuel going into that little plastic resevoir on the bottom from all sides. If you don't fill it enough it only gets in through the little bottom holes, I suspect for operator awareness of fuel status at WOT, and will starve the pump.

All, thanks all for the info and getting me down the right road....

This thing kicks now and runs better than since I purchased it.


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## Rack High (Feb 23, 2010)

An ATV shop in my hometown cleaned them out. Mech said they were definately clogged with sand.



smutty11 said:


> ....and clogged injectors. How'd you fix that? Did you clean them yourself or send them off?


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## Crawfishie!! (Dec 9, 2009)

smutty11 said:


> Crawfish...Right on!!! That's what I spent most of yesterday doing. For now it's dramatically increased the performance. When i first tested the pump, before removing it from the tank, it was barely trickling out. After cleaning and reassembly I thought I had bigger issues because it still only trickled after a good quick spurt. Something for those who may be in the same boat....Make sure you fill the tank enough to get the fuel going into that little plastic resevoir on the bottom from all sides. If you don't fill it enough it only gets in through the little bottom holes, I suspect for operator awareness of fuel status at WOT, and will starve the pump.
> 
> All, thanks all for the info and getting me down the right road....
> 
> This thing kicks now and runs better than since I purchased it.


Since you have the tank you, I would go ahead and clean the inside the tank b4 putting that pump back in....just my 2 cents worth


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## brute21 (Mar 12, 2010)

go ahead and route that gas check valve to the top of the pod too. That will prevent this from happening again. I believe they have an explanation on the how to's


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## smutty11 (Jul 2, 2010)

brute21 said:


> go ahead and route that gas check valve to the top of the pod too. That will prevent this from happening again. I believe they have an explanation on the how to's


 
Definitely gonna do this....There's sand/mud inside the frame tubing....not good.


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## smutty11 (Jul 2, 2010)

Crawfishie!! said:


> Since you have the tank you, I would go ahead and clean the inside the tank b4 putting that pump back in....just my 2 cents worth


 
Did that....Thanks Crawfish.


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## smutty11 (Jul 2, 2010)

smutty11 said:


> Crawfish...Right on!!! That's what I spent most of yesterday doing. For now it's dramatically increased the performance. When i first tested the pump, before removing it from the tank, it was barely trickling out. After cleaning and reassembly I thought I had bigger issues because it still only trickled after a good quick spurt. Something for those who may be in the same boat....Make sure you fill the tank enough to get the fuel going into that little plastic resevoir on the bottom from all sides. If you don't fill it enough it only gets in through the little bottom holes, I suspect for operator awareness of fuel status at WOT, and will starve the pump.
> 
> All, thanks all for the info and getting me down the right road....
> 
> This thing kicks now and runs better than since I purchased it.


 
I have bigger issues. The fuel pump cavitates after about 3-5 minutes of running. I direct wired it to the battery and let it sit for a while under pressure. after a couple of minutes I could hear a distinct change in the pitch of the pump whine. It went from low pitch to high pitch as if it got really easy for it to pump fluid. The pump's toast. 

Here's the history. I checked the entire assembly in a big plastic coffee can with gas in it. It would pump fuel fine at the shop manual advertised rate. I let it pump back into the coffee can for about 15 minutes. I ran it off a car battery. I even put my finger on the outlet barb a couple of times to "check" for leaks in the rest of the assembly. It had good pressure, enough to make a fine mist when I pressed my finger against it and it wasn't "easy" to stop it completely. Not enough to make the relief valve open but no leaks. So I put it back in with a new filter screen off a 85 Galant. Same darn thing, it would lose power after a couple of runs. So the next step was to let it run pressurized as mentioned above. There was a distint change in the pitch of the pump. It's TOAST!!! 

So I went the same route as some of the other links to fuel pump issues suggest, and wired/plumed in a regular fuel pump. So far works great. It's rated at 45-60psi. It's enough to make the pressure relief valve funtion. It's a very distinct sound. The best way to describe it is a chirp. I'm gonna get some time on it on the farm this weekend and then a trip to the woods next weekend. I'll get some pics on the pre-woods inspection.


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