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Steve, Motorcycle Mechanic
Category: Motorcycle
Satisfied Customers: 6816
Experience:  30+ yrs. experience, MMI, HD technician, HD early, engine rebuild/performance, bike builder, kit bike program manager, CCI 2001-2004
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Just bought a 2001 FXSTi that the prior owner said should

Customer Question

Just bought a 2001 FXSTi that the prior owner said should only be filled while the bike is standing straight up, and if on the side stand while filled, it will run out of fuel once driven off. Never heard of such a thing on the many Harleys I've owned, so topped it up this morning on the side stand, drove about 100ft, and it ran out of fuel. Restarted a few times, but would run out again once throttled. An evap hose or gas cap issue? Never had a EFI Harley starve after a fill, always topped off on the side stand.
Submitted: 3 months ago.
Category: Motorcycle
Expert:  P.J. replied 3 months ago.

You're on the right track for sure.

I've heard some strange things over the years but this one is way up there on the list of odd ones. Filling the bike vertically versus on the side stand isn't your problem.

The tank on your bike, assuming it is stock, is a single tank. It has no split in the center and has one filler neck. In the past there could be issues if a crossover tube was blocked and the fuel didn't transfer but that is not an issue with your bike.

My guess is that your problem is caused by a blocked tank vent. If it gets blocked then air will not enter the tank and, as the fuel is drawn out, a vacuum is formed and the fuel flow can stop. When the tank is full this vacuum will form much more quickly.

The simplest way to know if this is the issue is to recreate the stall and then open the fuel cap to allow air in. You may hear air being sucked in. If the bike starts back up immediately then you know you have a vent issue. The vent is a small curved tube on the top front of the tank toward the right side of the frame. There should be a rubber hose attached to it. There is also a check valve in that line back near the seat area. It can stick closed. I would check to insure this is open.

If the venting is not the problem then the fuel pump or lines are the likely issue. Some more in depth troubleshooting will need to be done to determine where the problem lies.

I hope this helps. Please let me know if I can be of further assistance. Also, please leave a positive rating for my service today. Thanks, P.J.

Customer: replied 3 months ago.
Don't yet agree with a clogged vent line, as it would continue to be a problem until the fuel level drops. Stock one piece OEM tank, one cap on the right side, crossover hose at the front bottom to balance each side while using fuel, EFI 88", looks to be a Delphi system, stage one upgrade done when new by selling dealer. If a plugged vent, it should just about always starve when full of fuel. Barely made it one block to my shop, drove a second time and burbled out of the driveway, and ran perfect for the next 6 miles, uphill runs under heavy load. Ran perfect home and back for my first 42 mile run on 3/4 tank, didn't have an issue until topped off on the side stand. Cap breaths in when sucked on, so air can travel into the tank when the fuel level drops, vent hose is designed to be for evap system to breath out into a canister for vapor storage, to be re-burned later. I'm 40 years in the auto biz, prior owner was a sharp guy who thought it was aerated fuel getting into the pump, causing a fuel starvation into the pump until run through.
Expert:  P.J. replied 3 months ago.

Ok, if you're confident the tank venting is properly working then I would suggest a fuel pressure check.

It should pressurize to 55 - 60 psi and hold this for a minimum of 3 minutes when the bike is off. It should maintain 55 - 60 psi while running at any RPM. Check this and let me know what you find.

Thanks, P.J.

Customer: replied 3 months ago.
Double checked the fuel cap, sucks in, won't blow out. Disconnected the vent line at the tank, and passes air both ways, so don't believe it's vapor locked, or unable to draw air into the tank to let the fuel level drop, and draw into the pump pickup. I'm trying to find out if this is a pump or screen issue, possibly mis-mounted inside the tank, and allowing air from the fuel fill to enter the pickup in some way. Runs great once the air was purged from the pressure line, no different than if ran empty and re-filled. Wasn't empty, about 5/8 when filled, and did just what the prior owner said it would.
Customer: replied 3 months ago.
Hoping to hear from someone who has experienced this "filled on side stand, not straight up" issue, and resolved it.
Expert:  P.J. replied 3 months ago.

You won't hear from anyone who has experienced that issue because that isn't the issue. I can't stress that enough. You're chasing a ghost.

Check the fuel pressure as stated above and then the next person may be able to help you further if you are willing to open your mind to accept the help.

Best of luck.

Customer: replied 3 months ago.
Have an open mind, thus asking a for pay forum for someone with experience in this issue. The issue is it ran out of fuel when topped off on it's side stand, said by the prior owner would happen, and not to be an issue when filled standing up. I'm imagining that the aerated fuel is entering the tank directed at the fuel pump, and if filled straight up, is directed to the bottom of the right side tank. Poor fuel pressure should affect drivability at any fuel level. This problem only occurs after a tank fill. Seems like it's sucking air after being filled, and runs fine after it purges itself when running. Haven't filled straight up yet, really doesn't make any sense to me, but according to the prior owner, makes all the difference. Fuel pressure issue should be a constant one, not related to the type and angle of fill. A crazy problem that I've never heard of before, but wanting to correct it as it doesn't seem to be a normal occurrence after filling the hundreds of Harleys I've bought and sold.
Expert:  Steve replied 3 months ago.

this isn't a forum.

this is a place t contact an expert to help you deal with your issue.

you didn't "fill up on the side stand and run out of fuel" in 100 ft.

there is no "filled on the side stand, not straight up" issue.

it didn't happen. it's not possible. didn't fill it up, or your fuel system has an issue providing fuel to the throttle body.

if you're open to determining the cause of the issue, I can help you.

but if you're stuck on thinking you filled up on the side stand and ran out of fuel within 100 ft, good luck.

let me know if you need more help.


Customer: replied 3 months ago.
The tank was indeed topped off, and ran out of fuel within a 100ft. Something I've never experienced on any bike. I talked to the prior owner again, who was a first time Harley owner, who bought from a friend, also a first timer. The issue has been with this bike from the first owner, and both newbies figured that filling straight up was the proper way to re-fuel. he also stated the tank ha never been off, or the fuel pump removed. After all my years wrenching, I thought it was impossible too, so my first fill from over a half tank was on the side stand to see what he was disclosing firsthand, with the results he disclosed. Ran it hard before and after, without a hiccup under heavy load, so don't feel it's a fuel pressure or delivery issue. After reviewing the parts diagram of the fuel pump last night, I'm figuring a defective from new, partially clogged, or mis-installed fuel pump pre-screen that's allowing air from the aerated fuel fill to get trapped under the screen when filled leaned to the left. Wouldn't happen when filled straight done to the right side of the tank when standing straight up. The fuel fill would then be directed at the pump, possibly allowing air to get trapped under a faulty/clogged screen. Once started, the fuel within the system would allow it to run a bit, and once trapped air made it's way through the system, would start to temporarily run out of fuel until it purged itself out. So not an impossible scenario, just one that you and I never heard of, or could even imagine. I'll repost you once I burn some fuel out of it, and take the pump out for a look and repair.
Expert:  Steve replied 3 months ago.

you said you ran out of fuel. that means the tank was empty. so what you really meant was the engine stopped after 100 ft while full of fuel.

I will step up and say the scenario you posted of air entrapment and binding of the fuel pump is indeed an impossible scenario.

It's never happened to anyone else ever and MOST people fuel their motorcycles on the side stand.

why are you focused on fuel?

it's just as likely you have an intermittent loss of ignition spark.

your engine needs only 3 things to run:

- spark

- fuel

- compression.

I would install a spark tester on the engine and try to repeat the scenario.

then, when the engine dies, check for spark.

let me know what you find.


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