Almost stalling starting out

[Scott Wood]

I've a 2002 ST1100A bought new. It has been well ridden (plus 130K miles) and well taken care of. I ride it pretty much daily. Use gas additive periodically, plugs and oil changed regularly.
Wonderful ride, would love to get it purring again.
Replaced the vacuum fuel shutoff last year or so, due to a leak in the diaphragm, shutting off fuel delivery. That fixed it. Ran fine until a few weeks ago.
Starting out in 1st, the engine has no power and putt putts until higher RPM 4K or so. Cruising at 3-4K I can jump on it and it responds without power loss. Adding choke seems to help getting off a dead start.
Bypassed the new vacuum shutoff just in case, though the diaphragm looked good. Replaced the plugs. Still no change. From what I'm reading, it maybe carburetors?
Any guidance, though I've only weekends free, working daily M-F... and riding.
Gig Harbor WA rider.

 

[Larry Fine]

Symptoms suggest clogged pilot jets.

 

[GGely]

+1 on Larry’s comment.

I’ve had good results using either Seafoam or Star Tron in a high concentration. I’ll run the engine for a while to make sure it’s well into the carbs then let it sit for a bit and that usually does it.

A maintenance trick I got from the CX500/CX650 forum is to alternate MMO and Seafoam in each tank. For the time I had my GL650 Interstate and the ST1100, I never had any issues with the carbs, ever.

 

[Larry Fine]

Years ago, my Nighthawk had the same symptoms. If I could just baby it, finesse it, add some choke, and finally manage to get the RPMs up, it would then take off like the proverbial bat.

 

[Ron]

Another forum I'm on suggest water craft synthetic 2 stroke oil at 1 oz. per 5 gallons (US) gasoline. I used it in a used bike I bought for about a half dozen tanks. It runs better but I don't know if it's the oil, fresh gas, being run regularly or my imagination.

I think I'm allergic to working on carburetors.

 

[Uncle Phil]

If it idles fine but fast with the 'choke' on and idles fine once warmed up with it off, it's not your low speed jets.
If the bike has not sat for a good period of time, you could have a torn carb diaphragm.
Especially if you have been running it regularly and it just happened all of a sudden.
If it acts like it is out of gas, you could have a fuel pump going south on you.
Or it could be simply a bad tank of gas - drain it and start with fresh.
Also check the plugs you pulled out to see what the color looks like on each one.
That might point you to a particular cylinder with the issue.

 

[Scott Wood]

Ron is allergic to carburetors as I am. Unfortunately, a 2002 Honda is too old for the shops I've been using to work on it any more. However, willing to dig in as I have over the past 2 decades. I've a shop manual, though any suggestion for a possible kit (or replacement parts) I my need? Seems parts that old, take some time to find and I'd hate to have to wait once I've torn into the carbs.
Note the recent sparkplug change, show pretty darkened plugs.
Also, for sometime now, I could smell that it maybe running rich, though mileage has not significantly been reduced.

 

[Uncle Phil]

Does the bike have the original fuel pump or an aftermarket one?
Several of the aftermarket ones produce too much fuel pressure that will 'overrun' the carb floats.
On the 'in the tank' ones I use I put a fuel pressure regulator to solve the problem.

 

[Scott Wood]

Does the bike have the original fuel pump or an aftermarket one?
Several of the aftermarket ones produce too much fuel pressure that will 'overrun' the carb floats.
On the 'in the tank' ones I use I put a fuel pressure regulator to solve the problem.

Original fuel pump. Thanks for the heads up.

 

[Uncle Phil]

Original fuel pump. Thanks for the heads up.

Then you may have a torn carb diaphragm(s) - but that's just a guess.
Is it hitting on all four cylinders or can you tell?
If any one of the four is not firing it will have hardly any power at all.
You have to really thrash it to get it going at all and it will have no top end.
How does it idle once it is warmed up?
Could a vacuum line be loose somewhere?

 

[Scott Wood]

Still needing choke coming off a stop. Once warmed, does help reduce the issue. Seems to power through at higher RPM without noticeable drag. I'm going to look at trying to dig into the carburetors and replace what may have worn-out. But it will have to wait for a long weekend and parts. Any more suggestions on what to check and potential carb parts?

 

[Uncle Phil]

Sure sounds like your low speed jets are clogged.
That just requires removing the carbs and cleaning them out.

 

[Upt' North]

No one seems to have suggested a blocked air filter. Have you tried new OEM filter?
Upt.

 

[Larry Fine]

No one seems to have suggested a blocked air filter. Have you tried new OEM filter?
Upt.

Wouldn't a dirty filter behave like a choke being on?

(Yes, I know we have 'enricheners')

 

[DannoXYZ]

Also dirty filtre blocks most at higher RPMs with higher flow-rates. At idle and low throttle, wouldn't affect a thing.

Definitely idle and pilot circuits need cleaning. Not just jets, but entire hidden secret passages in carb-body between jets and bleed-holes in carb-venturi. Everyone thinks JETS! JETS! JETS!!!, but it's like focusing just on sprayer nozzle on your garden hose. What about the 20 golf-balls stuck in hose along way? That's contributing way more to lack of flow than sprayer at end...

 

[Scott Wood]

+1 on Larry’s comment.

I’ve had good results using either Seafoam or Star Tron in a high concentration. I’ll run the engine for a while to make sure it’s well into the carbs then let it sit for a bit and that usually does it.

A maintenance trick I got from the CX500/CX650 forum is to alternate MMO and Seafoam in each tank. For the time I had my GL650 Interstate and the ST1100, I never had any issues with the carbs, ever.

Used fuel treatment and soon after that is when the problem started. Continued multiple rounds of fuel treatment. Will have to try Seafoam. How concentrated is safe?