91 vfr 750 - doesn't start, fuel pump only spits out a little fuel.

For some reason my 91 750 vfr will not start. I last ran it 1.5 weeks ago when I was riding on the last weekend of july and I haven't gone anywhere where the stuff I was picking up would fit on the bike since (went on some track days with my other bike) so I haven't ridden it but it was running fine when I parked it.

I checked spark on the rear plug by pulling the plug and grounding it against the engine and it's sparking, when I pulled the plug it was dry but i could smell gas. air is pumping through the system because you can feel it when you put your hand over the exhaust hole. I checked the air box, nothing foreign in there, there is gas in the tank. I can't remember if the fuel pump normally goes whirr when you first power up the bike but it's not going whirr now... I checked to see that fuel is getting to the pump and when I pulled the fuel line to the fuel pump it spews fuel no problems. i tried pulling the fuel line from the fuel pump and when I crank it spits out just a little bit of fuel. if i crank it long enough the bike goes woomph.

I've trailered my bike to toronto thinking that it was just a weak battery and I could probably charge it and get it going for the weekend (i've got some riding planned for friday, saturday & sunday).

I'm suspecting it's a fuel pump issue... is it possible that the fuel pump is air locked? that is something that happens on my ninja. if so how do I get it unlocked? I don't think it's the electrical to the pump because it's still spitting (not trickling) out some fuel.

 

Check battery voltage with your multi-meter. You might have a crapped out battery. Should be around at least 12.5 or so in sitting state.

How many miles on your Gen 3 bike?

 

battery is fine, have 90,600 km on the bike

 

There is an electronic relay that sends power to fuel pump, and i'd suggest that you use a jumper wire to bypass it for testing purposes.

With bypass installed, pump should click whenever key is on and fuel level runs low in carbs.

 

I by passed the fuel pump, got the bike going, once it's warmed up and going it runs fine.

how ever i don't know if it's the fuel pump or the power to the fuel pump, when i key on it jumps to 6 volts, when i crank it goes to 6 volts, it is possible that i haven't got the leads with the best contact as it is a pain to get them in there. I suspect if the pump was gettng 1/2 as many volts as it should there could be an issue.

 

where do i find the relay?

 

found it cleaned the contacts a bit works better now, going to get in there and clean them properly so i can be happier

 

If you're cleaning contacts you need to be extra careful not to bend the very weak supports.

 

well when your fuel pump does go, I have had great luck w/ these.
much cheaper then finding a factory pump.

There are all different kinds, this is just one example.

Electric FUEL PUMP - Universal 4-6 psi for VINTAGE cars | eBay

 

Hi

just seen your post, my fuel pump has cooked and I am on the lookout for replacement, do you mean that I could use one of those on the link, but which one for a 1991 vfr FM, would you know,

and would it be ok

Thanks for your time Steve

 

like this post, great questions. Similar problem on my 93 RC-36. talking to service at nearby dealership and reading different forums, i've found fuel pump likes to overheat and fail, but will run again after cooling down before complete failure. Also pump should only activate when cylinders 2&4 fire.

I can start my bike on choke but then it bogs out when I open throttle like its out of gas. Developed 30min into shoulda been 45 min. ride. Couldn't even start the next a.m. on choke. Hoping fuel pump fully failed or fuel filter is completely blocked.

I'm going to test fuel pump direct to battery, check fuel filter, drain carbs through nipple drain plug i've read about but not found, and check venting on the tank. Otherwise I don't want to have to get into the carbs. Hopefully we'll both figure it out.