Fuel Level When Pump Isn't Required

[bluesman77]

I was riding my '97 M750 w/ Kehin FCR's the other day on a long stretch of road that goes downhill for over a mile. As I approached the bottom of the hill, the engine quit. I pulled into a driveway and looked at everything I could think of that might have caused the failure, but found nothing. I tried starting the engine after about 10 minutes of looking and it fired right up, so I headed for home. As I went down another over mile stretch of downhill road, the engine quit again. There was between a gallon and a gallon and a half of fuel burned based on the trip odometer. I moved the bike to a level spot and tried starting it again, but was unsuccessful. I called my wife to come get me so we could come back with our trailer and asked her to bring a gas can in case the Mikuni pulse fuel pump had taken a dump. We filled the tank, after which the engine started right up and ran fine all the way back to the house. I have since rebuilt the fuel pump, which takes about two minutes. I was able to blow into the inlet and outlet before the rebuild, but only the inlet after the rebuild. I then drained the tank by about 2 gallons and let the bike sit for a week. I didn't ride, but fired it up today and it runs great - actually idled much quicker than normal. As I knelt beside the bike looking at the gas tank in relation to the flat slides float bowls, it seems like the tank should flow w/o need for a pump, but I know that's not the case. My question is,  what fuel level is required to get fuel to the carbs w/o a pump? I'm trying to determine if the pump was the root of my problem.

[Ddan]

I don't know the answer to your question, but is it possible that the down hill was long/steep enough the the floats closed and you just drained the bowls?

[ScottRNelson]

I figure that if Ducati felt the need for a fuel pump on the carbureted Monsters, it probably needs one to run right.

The don't put them on dirt bikes, though, like my XR650L.

[Howie]

I don't know the magic number, but at some point the fuel leve in the tankl is lower than the float bowl in the carbs, so it will no longer gravity feed.

Where did you get the kit for the OEM pump?

[bluesman77]

I don't know that the pump I have is the original as someone else "built" the bike, It's the rectangular Mikuni pulse pump used in many applications from snowmobiles to ultralights. They're available from many places including eBay - I was able to pick one up locally for $6.

[Howie]

That is an after market pump.  The stock pump is pentagon shaped.

[The Mad King Pepe']

I'm having a similar problem (at least I hope so, or else I don't know where to bang my head ).

I have a m900 with FCR's and no fuel pump. Everything seems to be running fine until the tank gets down to about 1 gallon in it, and then the engine starts sputtering and seems to have problems running. This is much more evident when the bike is not level.

At first I thought the fuel tank needed to be cleaned, but as I refilled the tank the problem went away and I was able to ride again until the fuel went down to about 1 gallon. Also the fuel filter is made of clear plastic and I don't see any residue accumulating inside.

In my case the fuel lines are nice and clean and new so I don't think they can be part of the issue. I'll have some fun checking the bike this weekend, and if the weather allows me to I'll take the bike for a long ride and see if it starts sputtering when there's about 1 gallon left in the tank. Then I'll put the fuel pump back on and see if that changes anything.

[koko64]

I'm having a similar problem (at least I hope so, or else I don't know where to bang my head ).

I have a m900 with FCR's and no fuel pump. Everything seems to be running fine until the tank gets down to about 1 gallon in it, and then the engine starts sputtering and seems to have problems running. This is much more evident when the bike is not level.

At first I thought the fuel tank needed to be cleaned, but as I refilled the tank the problem went away and I was able to ride again until the fuel went down to about 1 gallon. Also the fuel filter is made of clear plastic and I don't see any residue accumulating inside.

In my case the fuel lines are nice and clean and new so I don't think they can be part of the issue. I'll have some fun checking the bike this weekend, and if the weather allows me to I'll take the bike for a long ride and see if it starts sputtering when there's about 1 gallon left in the tank. Then I'll put the fuel pump back on and see if that changes anything.

That's the classic symptom of a failed fuel pump or no pump. It basically means no reserve gallon. Part of the tank sits low enough in relation to the carbs that there's no gravity feed at that point. Clogged tank outlets, filters or lines can display similar symptoms,  but you removed the pump which helps overcome gravity for the last gallon or so. Left hane corners with low fuel and no pump are interesting as the feed pipe comes out the right, lower, rear side of the tank! Head downhill and the fuel rushes to the front of the tank and the lines sucking air.

I want to remove mine coz it's the butt ugly stocker but reluctantly leave it on. If it fails I'll buy the rectangular one as the stocker is over a hundred bucks in OZ.

The aftermarket rectangular pump looks like it may be easier to hide. Its bloody cheap and cheerful too.
Aren't FCRs beautiful.