After hour ride, bike starts stuttering or missing.

[Winfried]

I have a 2002 ST1100 with 87,000 miles. About 2 years it started. Runs great, then after an hour averaging 75 mph, engine starts stuttering like it's not firing properly. I keep it at same mph and I keep it going until I reach my destination as I'm usually within 25 miles when it happens. After a rest and it's cold, making return trip, same thing happens. My guess is fuel issue rather than electrical, but it has to be one or the other. Ordered Seafoam from Amazon just now, as why not? So any recommendations as to what is going on.

 

[Larry Fine]

Clogged fuel-cap vent?

 

[Dbar]

I have a 2002 ST1100 with 87,000 miles. About 2 years it started. Runs great, then after an hour averaging 75 mph, engine starts stuttering like it's not firing properly. I keep it at same mph and I keep it going until I reach my destination as I'm usually within 25 miles when it happens. After a rest and it's cold, making return trip, same thing happens. My guess is fuel issue rather than electrical, but it has to be one or the other. Ordered Seafoam from Amazon just now, as why not? So any recommendations as to what is going on.

Could be the fuel vacuum cut off. Common problem with 1100's. Can be bypassed or repaired.

 

[Al st1100]

fuel valve bypass and replace the fuel pump( it's 20 yrs old). replace with aftermarket fuel pump. look thru all these posts on how to, fairly simple. https://www.st-owners.com/forums/threads/st1100-fuel-pump-replacement.89040/

 

[Ron]

I doubt it is the filter. It sounds like the pump can't keep up and the carbs are running out of fuel. Have you tried running at a lower speed (~50mph) to see if and when it happens? Some times the vac. valve has a perforation in the diaphragm and it doesn't open all the way reducing fuel flow. The carbs fuel bowl starts running lower and lower causing the stuttering. Have you tried to add "choke" when it starts stuttering?

Put the Sea Foam in the fresh gas, bypass the vac. valve, leave the fuel tank cap loose and go for a ride. Note if anything changes.

The vac. fuel valve fix is immediate in it's affect. read this "how to". Don't forget to plug the vac. hose.

Vacuum Fuel Valve Bypass Method ( ST1100 ) *

Vacuum Fuel Valve Bypass Method ( ST1100 ) *

www.st-riders.net

The loose fuel tank cap fix is immediate in it's affect.

The Sea Foam and fresh gas take a full tank maybe two.

The above are free or cheap to try. If there is little or no change, you made need a new pump. The pump is cooled by the gas in the tank. Usually it becomes erratic as it warms up. Either from use or if the fuel drops below 1/2 to 3/8 level. A new pump assembly is available from Honda for a mere $500 or so. Read the thread linked above a couple times (I think there is more than one, maybe do a search.) for a cheaper alternative.

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[Larry Fine]

Put the Sea Foam in the fresh gas, bypass the vac. valve, leave the fuel tank cap loose and go for a ride. Note if anything changes.

Note about note: When troubleshooting, you should only make one change at a time and test, especially if you want to determine what the cause of the problem was.

 

[Winfried]

Regarding the diaphragm as I replaced that awhile back, and it is the first thing I checked when it started happening. As to trying each suggestion and going for a test after each, the stuttering doesn't happen until after over an hour driving, which is about 70 miles. Well, you know how long that would go before getting old, and you have to let the bike cool down before going to the next suggestion.

 

[Ron]

Ron said:
Put the Sea Foam in the fresh gas, leave the fuel tank cap loose, bypass the vac. valve and go for a ride. Note if anything changes.
Click to expand...

Note about note: When troubleshooting, you should only make one change at a time and test, especially if you want to determine what the cause of the problem was.

Note about note about note: Notice the big goofy grin? I worked in maintenance for over 40 years with most of that time trouble shooting broken equipment. Been riding 1100s for over 25 years/2-300 K miles. It's how I would approach it on my bike. I'd rather ride than wrench.

I'm more interested in riding than wrenching. Do all these easy things at once and start undoing them one at a time when the ride last longer than an hour. They all are easy to un-do.

It has happened numerous times so the gas probably is somewhat fresh.

The bike runs OK for an hour or so then starts stuttering. The carbs are probably OK. The Sea Foam might help but probably isn't needed. Don't worry about the Sea Foam, it'll be OK to leave it.

Tighten the cap and ride another hour or more. Easy to do and after it runs OK for more than the hour, easy to un-do it (tighten cap). If it doesn't run OK after tightening the cap, loosen it again. Leave the tank flap cover unlocked and loosen it while riding, if you can. The cap being loose keeps a vacuum from forming in the tank as the fuel is used. The cap allows air to flow into and out of the tank. Cap repair:

Fuel Cap Repair/Rebuild ( ST1100 ) *

Fuel Cap Repair/Rebuild ( ST1100 ) *

www.st-riders.net

The vac. valve bypass test isn't too difficult and can be undone just as easy. "It was repaired before the problem." Why was it repaired? How long did it run, without problems, after the repaired? Many guys have tried and the repair failed or didn't last. It takes 10 minutes to remove plastic, 10 minutes to bypass valve and plug vac. line, 10 minutes to install plastic. Or save 10 minutes and run without the plastic. Easy to undo the bypass.

If nothing changes, that leaves the pump. At $500 from mother Honda, that would be a considerable thought process for me. I would futz with the several alternatives on this site first. But the question is do you have more time or money.

That's about all the mechanical fixes. What are the electrical possibilities? Fuel pump relay or coil intermittent when hot?

 

[Popeye]

Ron said:
Put the Sea Foam in the fresh gas, leave the fuel tank cap loose, bypass the vac. valve and go for a ride. Note if anything changes.
Click to expand...

Note about note: When troubleshooting, you should only make one change at a time and test, especially if you want to determine what the cause of the problem was.

Note about note about note: Notice the big goofy grin? I worked in maintenance for over 40 years with most of that time trouble shooting broken equipment. Been riding 1100s for over 25 years/2-300 K miles. It's how I would approach it on my bike. I'd rather ride than wrench.

I'm more interested in riding than wrenching. Do all these easy things at once and start undoing them one at a time when the ride last longer than an hour. They all are easy to un-do.

It has happened numerous times so the gas probably is somewhat fresh.

The bike runs OK for an hour or so then starts stuttering. The carbs are probably OK. The Sea Foam might help but probably isn't needed. Don't worry about the Sea Foam, it'll be OK to leave it.

Tighten the cap and ride another hour or more. Easy to do and after it runs OK for more than the hour, easy to un-do it (tighten cap). If it doesn't run OK after tightening the cap, loosen it again. Leave the tank flap cover unlocked and loosen it while riding, if you can. The cap being loose keeps a vacuum from forming in the tank as the fuel is used. The cap allows air to flow into and out of the tank. Cap repair:

Fuel Cap Repair/Rebuild ( ST1100 ) *

Fuel Cap Repair/Rebuild ( ST1100 ) *

www.st-riders.net

The vac. valve bypass test isn't too difficult and can be undone just as easy. "It was repaired before the problem." Why was it repaired? How long did it run, without problems, after the repaired? Many guys have tried and the repair failed or didn't last. It takes 10 minutes to remove plastic, 10 minutes to bypass valve and plug vac. line, 10 minutes to install plastic. Or save 10 minutes and run without the plastic. Easy to undo the bypass.

If nothing changes, that leaves the pump. At $500 from mother Honda, that would be a considerable thought process for me. I would futz with the several alternatives on this site first. But the question is do you have more time or money.

That's about all the mechanical fixes. What are the electrical possibilities? Fuel pump relay or coil intermittent when hot?

My best guess would be fuel line getting hot. Try putting aluminum foil between any fuel lines and engine parts.
Did someone work on bike, maybe move fuel lines around?

 

[Ron]

It's all kinda moot. He never got back on the matter so who knows.

 

[mortenk]

Yeah, it's always sad when people don't follow up on their findings and resolutions. My 1991 ST had the same exact issue, which I solved with an open gas cap.

 

[diferg]

Bummer, I was hoping he would respond to Ron and mortenk comments. Many of us will benefit to learn the solution.

 

[cc2larke]

Hello! This sounds a lot like a problem that recently developed for me. Rode to work in 80+ degree weather, no problems, about an hour riding. On the way home (spirited riding, much cooler in the evening), each time less than 75 miles on a full tank, within about 10 min I experienced a gradual loss of power (feels like a petcock bike before you switch to reserve), got to the side of the road, pull the clutch in, bike died. After maybe a minute (I'd power cycle the key), the bike would start with choke (not without, though it sounds like it wants to), run rough for about 15 seconds, and then smooth to a high (warm) idle. Choke off, bike ran normally. This seems like a fuel problem, didn't notice any difference in lights (dimming or anything, it's night, so easy to see).

I have about 32K miles on it, have been replacing all the consumables (fluids, brake lines, air filter, spark plugs, etcetera). Thought maybe I pinched something last time I took off the "fuel" tank, and was going to dive into it today. It's an inconsistent problem (happened maybe a week ago, and then again last night), so I'm trying to see what was similar between the two rides, and hopefully not get stranded (it's a little heavy to throw in a truck!). I know the tip sensor was replaced, though this doesn't seem electrical.

Thanks in advance!

 

[Larry Fine]

First suspect is fuel cap venting.

 

[cc2larke]

I hope you're right, as that seems like an easy fix, and it seems to be happening when the tank is full (ish), and smaller changes in fuel level will result in higher changes to air volume (and pressure). While it's difficult to hear on the highway, will I hear vacuum through the cap as it releases?

 

[Larry Fine]

I hope you're right, as that seems like an easy fix, and it seems to be happening when the tank is full (ish), and smaller changes in fuel level will result in higher changes to air volume (and pressure). While it's difficult to hear on the highway, will I hear vacuum through the cap as it releases?

I do when I open it. Try riding with the cap loose (and tank not full).

 

[cc2larke]

Took the cap apart, nothing too gross inside. The little piece inside does not have the spike on it, just a lipped hole that the spring fits around, and it seems to move freely. The cap doesn't seem to restrict air flow through the breather nipple on the outside in either direction.

 

[Al st1100]

it's not vaccuum when you release the cap , it's pressure. The gas fuel expands due to the heat being right behind the engine. If you have eliminated the fuel cut valve then it's the fuel pump, very comon.

 

[cc2larke]

The cut valve is tomorrow's project (or nearly). I ordered a rebuild kit for it, figured I'd eliminate it as a problem, but we'll see how long it takes to ship. I may have pinched something when I had the cover and everything off (I had to take it largely apart to get at the rear brake line), so I may take it apart tomorrow to see if that's the problem. I don't have a concrete way to make it starve, it's only ever happened those two times, so I can't just monkey with something and see if that fixes it, I have to wait for it to fail which is annoying--I hate not trusting it, it's a freaking Honda.

 

[cc2larke]

Anyone have experience with the QFS replacement pumps? I've seen reviews that say they work great, and some that say they work too well, and flood the carbs. They claim to be designed to work in ethanol fuel, which sounds great, since the one that's in there wasn't. Oh--should mention that even though it's an old bike, it only has about 35K miles on it. Still waiting on the petcock parts, so I haven't torn into it yet, but maybe this weekend.