Fuel pump relocation to under the seat?

[jermzfree]

I have a Walbro fuel pump and would like to relocate it off the engine. I already have water injection pump on the right side of the sub frame. It fits under the passenger seat, but am wondering if it would be sitting to high, and cause priming issues once the fuel tank ran about half way down. ??? Its not much higher than the side of the sub frame. I have heard the Walbro pumps can burn out very quickly if ran dry. Don't need that to happen

 

[RYC1966]

Can you or does anybody put a check valve in it? I believe the pump pushes more than sucks so it may be a concern...Are your concerns heat soak? You could wrap it up with some foil insulation or suspend it to get it off the breather / engine case area

 

[jermzfree]

Can you or does anybody put a check valve in it? I believe the pump pushes more than sucks so it may be a concern...Are your concerns heat soak? You could wrap it up with some foil insulation or suspend it to get it off the breather / engine case area

I had vapor lock the other day riding it for an hour and then parking it in the sun. Tried to start it and no fuel psi.

 

[RYC1966]

I have no clue...I have a pop can size fuel pump insulated sitting on the breather with no problems...I wish I could help you...I'll send you the sticky foil if you want it

 

[jermzfree]

Are you referring to that sticky foil that comes in a roll, for plumbing pipes? I have some of that stuff but wasn't sure if it would melt sitting on a 230 degree engine.

 

[OZBooster]

i pop the bottom out of a beer cooler , wetsuit type and slip it over the pump , main thing is to isolate it from contacting the cases

 

[jermzfree]

really? Like one of these?

 

[Rocketmn]

I have mine mounted under the gas tank to the inside of the frame. I also have a check valve on it...

 

[OZBooster]

yep, but a Jack Daniels one with flames

 

[jermzfree]

I should also mention I have boiling gas in my tank at the end of a highway ride. Maybe running a little lean?

 

[OZBooster]

probably bubbling up from the pump , you want to allow the pump to get rid of the air created by boiling fuel if you keep the pump under tank
try and get the supply to pump on an even slope or at least level so none is trapped

insulating helps a lot but occasionally even that is not enough, i have never been stuck, but have had to cycle the key a couple of times on the 100+ days
boiling points of fuels differ too ,

 

[jermzfree]

insulating helps a lot but occasionally even that is not enough, i have never been stuck, but have had to cycle the key a couple of times on the 100+ days
boiling points of fuels differ too ,

Yes I had a similar experience, no fuel pressure when I turned on the bike, tried cranking it for a while and did get it to fire up. Then 20 min into my ride the static fuel pressure started taking a dump. I pinched the return line and the fuel pressure immediately spiked up, so maybe an fmu issue as well.

 

[Boosted Cycle Perf]

I always mount the pump and filter underneath the subframe. I've sat in traffic in 110 degree Texas heat, stopped and gotten gas, and they always fire right up.

You can see the pump hanging down just above the nitrous bottle.

On another bike I built..

I always put it down low on anyone's bike I build that intends to street ride it. Under the tank works for most but sometimes it doesn't always.

 

[jermzfree]

Ok so I wrapped the pump and filter in insulation, still got vapor lock. Then I mounted the pump on the left side of the sub frame and still got vapor lock. Then I insulated all of the fuel lines in heat reflecting material, and that seemed to make a difference. In talking with the Walbro reps, it sounds like a big part of the problem might be the size of the pump I am using. The gsl392 is flow rated near 600 hp at 43 psi, which is way over kill! Too much hot fuel being pumped back into the tank, helping fuel temps go up. I won't know now until next summer if the problem is still around. If the problem comes back my next step will probably be to go with the gsl393 which is flow rated closer to 300 hp.

 

[Boosted Cycle Perf]

That doesn't make any sense. Do you still have the insulation under the tank?

Side of the Sub frame isn't a good spot for a pump because its usually above the bottom of the tank and leave room for fuel to drain back out of the pump when the bike gets shut off when it's hot, and fuel level is low. Fuel pump must be gravity fed, they can only do so much sucking.

As I posted before putting the pump were I have them pictured is the best way to keep them cool. It doesn't matter what size the pump is. The guy who told you that should be fired, and you should get your money back for ordering another pump.

 

[jermzfree]

That doesn't make any sense. Do you still have the insulation under the tank?

Side of the Sub frame isn't a good spot for a pump because its usually above the bottom of the tank and leave room for fuel to drain back out of the pump when the bike gets shut off when it's hot, and fuel level is low. Fuel pump must be gravity fed, they can only do so much sucking.

As I posted before putting the pump were I have them pictured is the best way to keep them cool. It doesn't matter what size the pump is. The guy who told you that should be fired, and you should get your money back for ordering another pump.

The Walbro inline pumps can suck fuel up hill. This is from a helpful Walbro tech. He sounded like he knew what he was talking about. I also tested it on my work bench, and it had no issues sucking up a two foot vertical with a 3/8 line. I haven't had any issues in about 300 miles since mounting it there, and I ran it down to the fumes while cycling it on and off just to make sure. Maybe its harder on the pump?

I was really perplexed as to why I was getting vapor lock with the pump and filter off the crank case. So I ran the bike in my garage for 15/20 min to get it at a good operating temp, and monitored the fuel temps. When the fans turned on the fuel temp started jumping and spiked to about 150 degrees. The fuel pump became hot to the touch too. All the hot air from the headers was being blown on the fuel lines and just cooking them. I thought I might have installed the auxiliary fan at a bad angle or something that would cause this. The second fan definitely pushes more hot air over the top of the engine. So I insulated the fuel lines in heat reflecting material and no more bubbles in the tank or vapor lock!!! I haven't had a good hot 90+ degree day to give the bike a real stress test, but so far the problem has gone away. It makes sense to me that using a smaller pump that's flowing less hot fuel back into the tank would aid in keeping fuel temps down.

 

[Boosted Cycle Perf]

Well guess I better call up that walbro man, and ask him for more pointers. I guys 10 years of building and tuning turbo street bikes as all been a lie.

Surprised the walbro man didn't tell you to relocate or insulate that big hunk of aluminum sitting directly above the header called an fmu...

 

[jermzfree]

Well guess I better call up that walbro man, and ask him for more pointers. I guys 10 years of building and tuning turbo street bikes as all been a lie.

Surprised the walbro man didn't tell you to relocate or insulate that big hunk of aluminum sitting directly above the header called an fmu...

I'm just regurgitating the info I have found, and what worked for me. The fmu is sitting on a thermo blanket

 

[mysticblu999]

I like under the seat or on the right side of the subframe the best.