Engine dies

[Winfried]

I ride a 2002 ST1100. Usually every morning when I drive to work, I get on the freeway and drive two off-ramps and get off. It is a very slight uphill, not steep, and just before I get off and at the top of the rise just before it levels off and then goes downhill, my engine loses power and then dies, but then I start to go downhill and slow down, my engine goes back to normal, and I don't have any more problems going to work or coming home. Work is 25 miles, and it happens about 7 miles away from home. And then this Saturday, I got on the Freeway in the opposite direction, and the Freeway goes uphill, not steep, about same uphill angle when I go the other way going to work, my engine started losing power and about to die, so I pulled to the shoulder, and started to slow down, and then my engine picked up, and I had no more issues for the rest of the day.

I was thinking that something must me in my gas tank blocking where the gas goes out, but I took a flashlight and looked in the tank and it looked pretty clear and couldn't spot anything.

Any ideas?

 

[raygks]

My bet is on the fuel petcock if it's still OEM. You can bypass the petcock for troubleshooting and see if the issue goes away to determine the root cause, thereafter either rebuilt or permanently bypass.

 

[dwalby]

My bet is on the fuel petcock if it's still OEM. You can bypass the petcock for troubleshooting and see if the issue goes away to determine the root cause, thereafter either rebuilt or permanently bypass.

agree that this is an easy fix to rule out, search on "vacuum fuel shutoff bypass" for details.

 

[Winfried]

I"m in sunny So. Calif. and the temperature has been fine, maybe upper 50s at night. But i do think it may have something to do with early morning hours, incline, and doing about 85 mph, and the first 10 minutes of riding. So the bike is just warming up.

 

[Bikeric]

Check that the vent pipe on your filler cap isn't trapped or damaged. If air can't get in properly, the fuel can't get out. Worth a quick look!

 

[Roger]

MM once wrote an explanation of how carbs. would ice in aeroplanes - and was also applicable to m'cycle engines...........

 

[Uncle Phil]

I'd start with the fuel cutoff bypass first, then look at the fuel filter, then consider the fuel pump and/or fuel pump relay I as long as you are sure it is not an electrical issue. Failing fuel pumps can do some 'interesting' things before they finally give up the ghost.

 

[Upt' North]

All above is great advice. It could be any of them of course. Next time you ride it can you leave the fuel flap open or off and just loosen the cap as you ride along just to rule out the cap causing a vacuum.
Good luck.
Upt'North.

 

[red one]

What everyone else has said but make sure your battery cables are clean and tight.

 

[Winfried]

Again it happened. I had spent Saturday rebuilding the Clutch Master Cylinder and on Sunday took it for a test drive. Got on the Freeway going uphill, and about 2 miles, engine started failing. Got on the shoulder, but kept going, and at the top the engine started coming back to normal. Rode on with no more issues. Going to try bypassing the fuel valve and see what it does on my way to work tomorrow morning, as it only happens when I the first ride of the day, going uphill going about 80. Then it reverts to normal.

 

[Winfried]

Just did the bypass. Then took the Fuel Shutoff valve apart and there is a tear in the diaphragm. Time to order a repair kit.

 

[dwalby]

Just did the bypass. Then took the Fuel Shutoff valve apart and there is a tear in the diaphragm. Time to order a repair kit.

or you could just leave it bypassed, many of us have bypassed that valve years ago with no consequences.

 

[paulcb]

or you could just leave it bypassed, many of us have bypassed that valve years ago with no consequences.

+1. Just bypass it. I’ve done it to both my ST11s, closing in on 100k miles like that.

 

[Uncle Phil]

250,000+ miles between my ST1100s with the bypass and no trouble.

 

[dtcoleman]

I would agree with Uncle Phil. I had the same thing but only after hours of riding. My '01 1100 would just bog down like being starved of fuel. Id have to pull over at the side of the hwy. Shut the engine off. Wait a few minutes. Start the engine n ride for a few more hours. Same thing. I was aso riding at high speed (120-130 klm/h or 75-80 mph). You can just remove the shutoff valve or diaphram all together. However you will have to plug the vacuum hose with a screw. The fuel hose match up to the fuel filter. You are good to go. If you carefully open up the diaphram you will notice a tear or hole in the rubber. Thats why you lose power. Another STOC member found me the repair kit. Thats also an option for you. Ill leave it with you. Good luck.

 

[Winfried]

I got the kit to replace the diaphragm in the valve and did it yesterday. Seems to drive good. Filled up the gas tank and found I got 41 MPG, which is what has been happening lately. Thought it might be because of the valve, but got 41 before bypassing the valve and same after bypassing it, so something else, because I usually get 44-46 MPG. Think it needs new plugs? Changed the fuel and air filter about 8 months ago, so what's up?

 

[dwalby]

I got the kit to replace the diaphragm in the valve and did it yesterday. Seems to drive good. Filled up the gas tank and found I got 41 MPG, which is what has been happening lately. Thought it might be because of the valve, but got 41 before bypassing the valve and same after bypassing it, so something else, because I usually get 44-46 MPG. Think it needs new plugs? Changed the fuel and air filter about 8 months ago, so what's up?

when my diaphragm got the tear in it I had the symptom where the bike had a strong raw fuel smell after shutting it off in the garage. Didn't know that was a symptom of a bad diaphragm, so eventually my #3 plug fouled pretty bad (from raw fuel getting past the diaphragm and flowing down the vacuum line to the #3 cylinder) and my mileage dropped by a few mpg. I bypassed the valve, cleaned up the plug and re-installed it and it went back to normal mileage.

 

[Winfried]

I will try that. I also just bought a 2006 Honda VTX 1800C a week ago. Found that I like switching between my ST and a V-Twin.

 

[Yves65]

Thank you all for this post and answers. I just replaced the valve ordered at Aliexpress