Fuel Starvation Symptoms ? 11/99 Build Date

[OffShore1V]

Hello

I have a ST1100 with a build date of 11/99 and 93K miles. I was told it was a 2002, but based on the 11/99 build date, I think it is a 2000 model.

Currently, the bike will not take more than 1/2 throttle before it bogs and seems to "run out of fuel," completely loosing all power and refusing to rev until the throttle is reduced. It will then slowly rev but will start to break up as the revs climb. The bike then completely signs off between 4000-6500 rpm, refusing to rev any higher, regardless of throttle position or gear selection.

When I got the bike it would take only about 1/4 throttle.

1. I first found a nearly plugged fuel filter- Changed and had no improvement.
2. Next, I found a torn Auto Valve Assembly diaphragm ( Automatic petcock) - I replaced the assembly & the bike now will allow 1/2 throttle before the sensation of "running out of gas" occurs.

Some further details for your consideration-

• I tested the electric fuel pump by disconnecting fuel line from outlet of fuel filter and observing the following- When the key is turned on and the "run" switch placed in the "run" position the Fuel Pump can be heard to prime and flow is observed.
• When the start button is pressed, Fuel flow seems to be sufficient and consistent.
• The bike starts and idles in a seemingly normal manner. Choke is required when cold, but it warms to idle after a few minutes.
• The idle adjustment screw seems to function properly, allowing idle to be set where desired once engine is warm.
• Without load- (in neutral on the stand) the throttle can be opened further than 1/2 throttle without the problem occurring

I have read here, and discussed with other mechanical friends the following possibilities-

1. Torn Carb Diaphragms
2. Air Cut Off Valve (not sure where these are, how they work, or how to test)
3. Vacuum Problems
4. bad or clogged "charcoal canister"

I am pretty mechanically inclined- riding, wrenching and racing the last 25 years- HOWEVER - this is my first rodeo with an ST1100 and it's more complex vacuum and CA emissions systems. I am hoping you good folks might describe some trouble shooting processes, and/or post some links to fixes or tests.

1. My first hope is that you can suggest what the most likely culprit might be from your experiences and my symptoms.
2. Second, my thought is that you may be able to help me with the easier steps to eliminate what it is not- so I can avoid going to the step of removing and disassembling the carbs without knowing for sure what the problem is.

Thanks
David
OffShore1V

 

[BuddingGeezer]

If you have sufficient fuel flow, 2 things come to my mind. Torn carb diaphragms and an extremely lean fuel mixture. My '91 will not rev beyond 5500rpms in neutral on the center stand with the air filter removed. I have an Aimsoil foam air filter and with it properly oiled my bike will run out of power the last 1/8 WOT (wide open throttle) because the A/F mix is too lean. Are you sure the bike has an air filter installed? A K&N or Aimsoil filter with no filter oil, torn?

The small filter that supplies the air to the carb diaphragms in good condition?

Maybe someone with a CA emissions bike can clue you in the charcoal canister.

Let us know what you find.

 

[Mark]

1st step:
Take the vacuum fuel cut off out... you can put it back in if you care to after making sure it isn't the cause of the issues.

I had a little issue with it, here is a link to how to do the deed.

 

[OffShore1V]

1st step:
Take the vacuum fuel cut off out... you can put it back in if you care to after making sure it isn't the cause of the issues.

I had a little issue with it, here is a link to how to do the deed.

Thanks- - the diaphragm in it was torn- so I installed a brand new one as mentioned above. Bike is better, now takes 1/2 throttle- instead of only 1/4 throttle - but still "runs out of gas" over 1/2 throttle.

 

[OffShore1V]

If you have sufficient fuel flow, 2 things come to my mind. Torn carb diaphragms and an extremely lean fuel mixture. My '91 will not rev beyond 5500rpms in neutral on the center stand with the air filter removed. I have an Aimsoil foam air filter and with it properly oiled my bike will run out of power the last 1/8 WOT (wide open throttle) because the A/F mix is too lean. Are you sure the bike has an air filter installed? A K&N or Aimsoil filter with no filter oil, torn?

The small filter that supplies the air to the carb diaphragms in good condition?

Maybe someone with a CA emissions bike can clue you in the charcoal canister.

Let us know what you find.

Thanks for this - can you tell me where is the "small filter that supplies air to the diaphragms" you mention located ?

 

[vinny]

can you tell me where is the "small filter that supplies air to the diaphragms" you mention located ?

The sub-filter that supplies the air for the diaphragms is the small rectangular enclosure in front of the air filter enclosure. It has a small foam filter that is prone to deterioration. It has two 3/8" hoses running to it, one from either side.

After you check that, check the carb isolators. The isolators can harden and crack, letting air leak in and causing a lean condition at higher rpms. If the clamps are loose, that's a good sign they need to be replaced.

 

[OffShore1V]

The sub-filter that supplies the air for the diaphragms is the small rectangular enclosure in front of the air filter enclosure. It has a small foam filter that is prone to deterioration. It has two 3/8" hoses running to it, one from either side.

After you check that, check the carb isolators. The isolators can harden and crack, letting air leak in and causing a lean condition at higher rpms. If the clamps are loose, that's a good sign they need to be replaced.

The filter is fine- Isolator I have not checked yet but will do.


Noticed an enormous pressure built up when I removed fuel cap- as if its not venting. This is a Cal Spec bike so I am going to check charcoal canister at the reccomendation of a good friend who is Honda certified - His logic is that if this canister is blocked, since it is where the float bowls & gas tank vent to this might be the culprit- because if the float bowls can't vent fast enough - then they can't fill fast enough to keep up with demand. Will keep you posted.

 

[jvick98]

A friend's 2002 ST1100 acted just like this. A good dose of Seafoam soaking for a few days cleaned it up! Add 1 oz per gallon to fuel, run for 30 minutes or so.
Easiest things first.
Jim

 

[Basic]

Are you sure this is fuel related? I just experimented with the K&N air filter and found that when the foam collar is added, this blocks about half of the air channel to the filter. As a result you get the exact same symptoms you described above.

Grts, Rob

 

[sterjll]

It's time to check your carb diaphragms.

 

[STPaulK]

A friends 99 had the same problem a few years back. After going down the path of fuel delivery problems, I finally went another direction and found the secondary harness to the coils were making a bad connection at the crimp at a connector, This connector is located on the frame under the left side fairing pocket. It was a poor crimp from the factory where the insulation was crimped inside where it's supposed to just be conductor. Recrimped and all has been well since. We think it was causing a very weak spark on two of four cylinders.

 

[OffShore1V]

It's time to check your carb diaphragms.

Agreed - Today's project.... keep you posted....
also- it appears the charcoal canister was removed by someone in the past....

 

[OffShore1V]

A friends 99 had the same problem a few years back. After going down the path of fuel delivery problems, I finally went another direction and found the secondary harness to the coils were making a bad connection at the crimp at a connector, This connector is located on the frame under the left side fairing pocket. It was a poor crimp from the factory where the insulation was crimped inside where it's supposed to just be conductor. Recrimped and all has been well since. We think it was causing a very weak spark on two of four cylinders.

Thanks- I'll check this while I am there

 

[OffShore1V]

Are you sure this is fuel related? I just experimented with the K&N air filter and found that when the foam collar is added, this blocks about half of the air channel to the filter. As a result you get the exact same symptoms you described above.

Grts, Rob

hmmmm- not sure what foam collar you are referring to - this bike has only a round automotive style air filter in it, which sandwiches between the upper and lower parts of the airbox - explain further or perhaps post a photo ? Thanks

 

[Basic]

Here the K&N air filter like it should be.

The same filter, is often delivered with a foam collar, seen in this picture. This collar will partially block the air intake (both by blocking the intake openings and leaving to little space around for air flow)
With this collar mounted, you should get exactly the same symptoms you described above.

 

[Uncle Phil]

Just for grins you might pull one or two of the spark plugs and see what color the electrodes are. Only takes a minute and could provide some valuable information.

 

[Basic]

Don't know if you found a cause yet. If it was a collar over your airfilter, you might find my findings from today usefull:
http://www.panzerbasics.com/index_files/98-ST1100/KNfilter.htm
If not in the air intake, then surely, it will indeed be a fuel problem.

/Rob

 

[the_gr8t_waldo]

you mentioned that the fuel flow was observed....this does not qualfy as checking the fuel pump. it should deliver a prescribed amount of fuel over time. this last summer i had a fuel pump go south on me. it would run fine when filled over 1/2 tank( for this reason i would suggest that you set up the fuel delivery test to include a few inches 6-8" of vertical lift before discharge into the measuring container), but under that the engine just couldn't run at freeway speeds. and if i were quick enough to disable the C.C., i could keep it running at 45-55 mph with a lot of coughing and sputtering., untill i topped off the tank again- good luck on this problem

 

[sofawizard]

ive had similar problem on my 99 it turned out to be the white conector bellow the left fairing infill wa the cause did everything short of replace the engine brfore that was diagnosed be warned . i discovered it by running the engine and twisting the conector ..

 

[STPaulK]

ive had similar problem on my 99 it turned out to be the white conector bellow the left fairing infill wa the cause did everything short of replace the engine brfore that was diagnosed be warned . i discovered it by running the engine and twisting the conector ..

https://www.st-owners.com/forums/showthread.php?123386-Fuel-Starvation-Symptoms-11-99-Build-Date&p=1555988&viewfull=1#post1555988