pilot screw initial setting for 40/128 jetting

[Ray Convery]

A bit frustrated trying to figure out what the initial pilot screw setting should be for my 2000 ST1100. Poring over the posts, I've read everything from 1 1/4 to 2 5/8 turns out. Seems a bit of a wide range. Anybody out there with some definitive info on this question?

 

[George]

I set mine to the initial stock setting and left them. STerling starts a d runs fine. Haven't gone far enough to get a mileage reading yet.

 

[SMSW]

I'm no expert, but I suggest you go by the Honda Shop Manual and see what that does.

Absent other guys with more knowledge than I have, look at this:

Mixture screw setting UK | ST1100-Carb Talk

Hey guys As I mentioned in my "introduction post", I have a 99 ST1100 which I bought about 3 weeks ago. I have been gradually servicing the machine as it was stood 5 years prior to me buying it. Up to now changed engine oil (Motul 5100 fully synthetic), genuine oil, air and fuel filters...

www.st-owners.com

You could also PM @John OoSTerhuis, @Igofar, or @jfheath, if they don't chime in soon.

 

[John OoSTerhuis]

Paging Adam Frymoyer….

 

[jfheath]

Not me. The carbs on the ST1100 are another thing for which expert status eludes me.

 

[Slydynbye]

Paging Adam Frymoyer….

That's the real answer.

 

[afrymoyer]

Hey Ray...

I see your in the deep south/Florida?
History of the bike?
What have you done to this bike other than change the jets?
ABS/California emissions bike?

 

[KSRider11]

A bit frustrated trying to figure out what the initial pilot screw setting should be for my 2000 ST1100. Poring over the posts, I've read everything from 1 1/4 to 2 5/8 turns out. Seems a bit of a wide range. Anybody out there with some definitive info on this question?

I just had my carb set off last weekend. I removed the slides, float-bowls, floats, float needles, jets, and pilot fuel screws. I blew out all of the passages and jets with carb/choke cleaner and compressed air. When I installed the pilot fuel screws I used new "O" rings as the old ones were compressed and hardened. I set the pilot screws to 1 and 7/8 out from fully seated. The bike idles and runs well but I may have compromised the air cut-off valve diaphragms with the carb/choke cleaner because now I get the occasional spit-back through a carb while cruising and a lot of back-firing while decelerating with the throttle closed. I changed the valves out last time without splitting the carbs but it is a MAJOR PITA!

 

[Al st1100]

I just had my carb set off last weekend. I removed the slides, float-bowls, floats, float needles, jets, and pilot fuel screws. I blew out all of the passages and jets with carb/choke cleaner and compressed air. When I installed the pilot fuel screws I used new "O" rings as the old ones were compressed and hardened. I set the pilot screws to 1 and 7/8 out from fully seated. The bike idles and runs well but I may have compromised the air cut-off valve diaphragms with the carb/choke cleaner because now I get the occasional spit-back through a carb while cruising and a lot of back-firing while decelerating with the throttle closed. I changed the valves out last time without splitting the carbs but it is a MAJOR PITA!

are you using the #40 low speed jet or the OE #38

 

[KSRider11]

are you using the #40 low speed jet or the OE #38

The stock size, which is the #38, I believe.

 

[Al st1100]

The stock size, which is the #38, I believe.

question was on the #40 jets

 

[Ray Convery]

Hey Ray...

I see your in the deep south/Florida?
History of the bike?
What have you done to this bike other than change the jets?
ABS/California emissions bike?

Hey, afrymoyer? I'm a BMW touring guy from way back, but I fell into this deal on a 2001 ST1100 with 4500 miles on it! Hadn't been licensed since 2007. Was stored under a carport with a bikecover/tarp covering everything but the front fender and forks. A little corrosion, a bit of elbow grease and few minutes with the buffer....done. Took the carbs out, found incredible amounts of green corrosion and mystery crud. Sent 'em off to a guy on ebay with a good reputation for a rebuild and jet conversion. The tupperware is perfect. Same with the seats and the running gear. Before the rebuild, it would fire if you primed it, but no idle and no acceleration. Original fuel pump shot, corroded and gunky. Aftermarket fuel pump. Got the carbs back. Fired right up. Still wouldn't idle and wouldn't accelerate past 3k rpm. Oh, and got fresh boots for the carbs as the originals were a bit stiff. Hoping that I've eliminated vacuum leaks and fuel delivery issues. Just need to sort this initial-settings thing. If that doesn't work, trucking it over to Honda, dropping my drawers, bending over and hoping for the best. Cheers!

 

[Al st1100]

A bit frustrated trying to figure out what the initial pilot screw setting should be for my 2000 ST1100. Poring over the posts, I've read everything from 1 1/4 to 2 5/8 turns out. Seems a bit of a wide range. Anybody out there with some definitive info on this question?

just finished installing the#40 jets, set the mixture screws at 2 turns. Did not sync yet but there is a big difference already. Idles smooth thru the whole choke range. Before if you took the choke off too soon the idle would get real low and always seemed to be too lean till warmed up. VERY SATIFIED SO FAR !!

 

[afrymoyer]

Hey, afrymoyer? I'm a BMW touring guy from way back, but I fell into this deal on a 2001 ST1100 with 4500 miles on it! Hadn't been licensed since 2007. Was stored under a carport with a bikecover/tarp covering everything but the front fender and forks. A little corrosion, a bit of elbow grease and few minutes with the buffer....done. Took the carbs out, found incredible amounts of green corrosion and mystery crud. Sent 'em off to a guy on ebay with a good reputation for a rebuild and jet conversion. The tupperware is perfect. Same with the seats and the running gear. Before the rebuild, it would fire if you primed it, but no idle and no acceleration. Original fuel pump shot, corroded and gunky. Aftermarket fuel pump. Got the carbs back. Fired right up. Still wouldn't idle and wouldn't accelerate past 3k rpm. Oh, and got fresh boots for the carbs as the originals were a bit stiff. Hoping that I've eliminated vacuum leaks and fuel delivery issues. Just need to sort this initial-settings thing. If that doesn't work, trucking it over to Honda, dropping my drawers, bending over and hoping for the best. Cheers!

Ray…Still need to know if it’s an ABS/Emissions bike to determine carb settings. I need this first.

Ok, this bike is a mess from sitting for years in the Florida heat and humidity. The green you saw is fermented rotten ethanol. Many “aftermarket” changes have been made to the bike all at the same time, with little to no results. Plus, two separate guys have worked on it, doing separate things. This may take a while to get straightened out, but we will…

Fresh airand fuel filters?
Have you spent the time to synchronize the carbs precisely? If not, do so.
Does it still have the auto fuel vacuum valve? If so, bypass it, take it out and throw it away.
Go back through your work and the rebuilders to triple check that EVERYTHING is secure and put back together properly.
Did the eBay carb rebuilder give you any specifications on what changes were made and how the carbs were set up?

 

[Ray Convery]

Ray…Still need to know if it’s an ABS/Emissions bike to determine carb settings. I need this first.

Ok, this bike is a mess from sitting for years in the Florida heat and humidity. The green you saw is fermented rotten ethanol. Many “aftermarket” changes have been made to the bike all at the same time, with little to no results. Plus, two separate guys have worked on it, doing separate things. This may take a while to get straightened out, but we will…

Fresh airand fuel filters?
Have you spent the time to synchronize the carbs precisely? If not, do so.
Does it still have the auto fuel vacuum valve? If so, bypass it, take it out and throw it away.
Go back through your work and the rebuilders to triple check that EVERYTHING is secure and put back together properly.
Did the eBay carb rebuilder give you any specifications on what changes were made and how the carbs were set up?

It's a non-ABS, bare-bones US bike. Carbs were "bench-balanced", 40/128 jets put in, accelerator pumps verified to be ok, all by the rebuilder. Fresh gas, fresh fuel filter. Final precision balancing to be done once an idle and warm-up is achieved. Awaiting a reliable initial setting and the arrival of the MotionPro pilot screw adjustment tool so it can be adjusted on a running bike. Thanks for the input!

 

[Ray Convery]

MANY THANKS TO ALL!! Almost everybody on point and thought out. Will advise as I go along.

 

[afrymoyer]

It's a non-ABS, bare-bones US bike. Carbs were "bench-balanced", 40/128 jets put in, accelerator pumps verified to be ok, all by the rebuilder. Fresh gas, fresh fuel filter. Final precision balancing to be done once an idle and warm-up is achieved. Awaiting a reliable initial setting and the arrival of the MotionPro pilot screw adjustment tool so it can be adjusted on a running bike. Thanks for the input!

First off, there are no accelerator pumps in the
Keihin’s. It’s all done with smoke, mirrors and rubbers…
If it truly is a 49 State bike, then going up to a #40 pilot/slow speed jet was the only upgade made. The #128’s come standard from the factory. So with that said, set all the idle mixture screws at 2 turns out from lightly seated, then leave them alone. This is just a touch fat for the Florida heat, but perfect for your other 3 seasons.
“Bench-balanced” don’t mean squat. They all run like crap after a complete rebuild and MUST be roughly synchronized at first start-up, then spend the time for perfection when at operating temp. I bench balance all mine too, but they’re still WAY off. Don’t touch the sync adjustment screws when the cooling fan is on. This will throw your readings off.
Another thing to remember is that with all of the air cleaner housings off and synchronizing, it’ll still pop and fart out the snorkel’s if you give it too much throttle. That’s normal because it’s running way lean with all the filter housings off. If it’s all done right, they’ll run perfectly after the entire intake system is fully assembled.

 

[Ray Convery]

First off, there are no accelerator pumps in the
Keihin’s. It’s all done with smoke, mirrors and rubbers…
If it truly is a 49 State bike, then going up to a #40 pilot/slow speed jet was the only upgade made. The #128’s come standard from the factory. So with that said, set all the idle mixture screws at 2 turns out from lightly seated, then leave them alone. This is just a touch fat for the Florida heat, but perfect for your other 3 seasons.
“Bench-balanced” don’t mean squat. They all run like crap after a complete rebuild and MUST be roughly synchronized at first start-up, then spend the time for perfection when at operating temp. I bench balance all mine too, but they’re still WAY off. Don’t touch the sync adjustment screws when the cooling fan is on. This will throw your readings off.
Another thing to remember is that with all of the air cleaner housings off and synchronizing, it’ll still pop and fart out the snorkel’s if you give it too much throttle. That’s normal because it’s running way lean with all the filter housings off. If it’s all done right, they’ll run perfectly after the entire intake system is fully assembled.

Yeah, I found the "bench-balanced" thing a bit off, hence the quotes. Probably mis-remembering the accel pump comment and he may have said that the choke circuit parts were fine. Thanks for the help on this. Cheers!

 

[Roger]

'bench balance', as I understand it...

 

[afrymoyer]

'bench balance', as I understand it...

Quite possibly the most half a$$ed way I’ve seen of bench balancing multi set carbs. At least she knew how to handle those little balls! LOL

I use a curved .010” feeler blade. Turn the idle speed cable till #4 carb is at open at .010”. Then set the rest of the butterflies to .010” clearance.