Fuel Pump Question

Ivory Ghost · Jul 2, 2014

Hey! New to the Forum; hoping for some good feedback.

I have an '85 VMax that's been rebuilt top to bottom and has worked perfect the last 3 years. This morning it left me stranded for the first time. I was in a haul ass hurry because I was late for work so I'd been cruising at about 85 (faster than I've been riding it around town this year) for just a few miles when all of the sudden it started to bog down and I basically could only get it to idle. It was only about 60 degrees out and I'd only ridden 5 miles, so overheat, vapor lock, etc. is not what I'm worried about.

After getting it on a trailer and home after work I began looking into the fuel pump; it was clicking fine, but I only get about 2 ounces of gas in the first few seconds after turning on the key (then it stops). I tried finding answers as to how much is should pump but still have no clue on that; any info would be appreciated.

Anyway, I put it back together and got it running fine, but I still don't think it's right. I've changed the fuel filter so I don't have that as a variable, but I'm no where near confident it can get me down the highway on a long ride.

OK, so here's what I can tell you it's doing. With the fuel line unhooked from the carbs and dumping gas into a small bottle (therefor no back pressure is being built up) it clicks for just 3 seconds after I turn on the key, then it stops. Also, with the gas lines hooked to the carbs, it runs for the same 3 seconds and stops...EVERY time! I can turn the key on (without starting the bike) 100 times, one time immediately after another, and it always clicks for 3 seconds and stops!

I would think that if it was working right it would build up pressure and only click a second or less after 3 or 4 times of turning on the key. I'm doing it as fast as I can and the battery is charged up so it's clicking as fast as I think it ever has. So, since it's not building up enough pressure to turn itself off quickly after consecutive "key-ons" (as it's filling the carbs - and no, they're not leaking gas out anywhere), I'm wondering if there's a good chance that the pump is only working marginally and possibly the diaphragms or seals inside are letting some gas back into the tank.

Bottom line, does it sound like a fuel pump issue; should I just replace it?

maleko89 · Jul 2, 2014

The fuel pump and relay are working fine. The fuel pump relay has an ignition feed so that it'll shut off after a few seconds when the bike isn't running. This is a safety feature. If your bike was running the relay/pump would run continuously to keep the bowls full of fuel. I would try running the bike again. Stay close to home and if it happens again take your gas cap off. Listen for a whoosh of air. Also, check your fuel tank vent line/tip over valve. Drain the float bowls...one at a time and make sure you have close to an equal amount of fuel in each one. Silly question, you sure you have fuel in the tank? Is it low? Perhaps reserve switch circuit isn't working and/or low fuel light isn't lit?

Ivory Ghost · Jul 3, 2014

Bike was low on gas the day before; started to miss a little and the tank mounted fuel light was flickering; flipped to reserve and it came back to life like always. Rode another 5 or 6 miles, filled up, flipped reserve off and rode several more miles before heading home. The next day is when is weirded out, but it's got a full tank.

What's the significance of the 'swoosh of air'? Also, where's the tip over valve?

yubamike · Jul 7, 2014

The swoosh of air would suggest a plugged vent for the fuel tank. As the gas is pumped out of the fuel tank, air has to be sucked in to replace its volume or it will eventually create a vacuum in the fuel tank. As the vacuum increases, the amount of fuel the pump can move decreases to the point the carbs run dry. The swoosh is the air rushing into the tank to fill the vacuum. Once tha vacuum is eliminated, the bike will start and run normally and the process starts all over again. I don't know where the tip over valve is but it is usually on or near the top of fuel tank and will have a U or J shape. This thread is also posted under the heading for problems with the website. You will get a lot more responses if you post it under the correct heading. Good luck!!

davesax36 · Jul 7, 2014

The tip-over valve is attached to the front of the battery box. It's a little white cylinder that's fed from the vent line on the top of the tank.

At least I think that's what that thing is...

dodgediesel59 · Jul 8, 2014

Im not sure about everyone elses bike, but the 4 or 5 I have dealt with are different than OPs relay operated. My bike if you had empty carbs will run the pump for the 3 seconds each key cycle, but as the bowls fill and pressure starts to build up the pump will start working hard and building pressure and the clicks will become farther apart and or not click at all when the key is turned back on.

tugla · Jul 9, 2014

yup thats normal. I find if the bike lost its prime the three seconds isn't enough to get fuel to fill the bowls. so I prime the pump and line then the three sec is enough to push fuel to carbs ans with carbs full tou should not get any more clicking....til it is low again like couple days of not riding. this only happened to me once.