Carb Technical advice needed pls.

[Mitch 570]

Hi, im after a little advice on my carbs if anyone can help at all please. Its a ST1100AX 99plate UK model.

I have stripped them down and thourougly cleaned them with carb cleaner and compressed air and put them all back together. The only thing i did not do was split them apart. I did however manage to get all four air-cut valves out before cleaning to avoid damaging the diaphrams.

Q1On rebuild i noticed that the choke linkage bar has a little play in it making carbs 1 and 3 uneven to 2 and 4 (the control side) opening slightly after and a little less untill full choke. Has anybody come across this previously and if so how did you resolve it?

Q2 My idle adjustment screws range from 1 turn to 1 and a 1/4 when checked before removal which seems a little odd. My Trusty Haynes Manual says "Initial setting 1 and 5/8 out then Final setting 7/8 out (see text)" Guess what no text apart from the general information which basically says if unsure take it to Honda. Any Ideas on this?

I dont really fancy putting it all back together to find its wrong and have to start again. I have already bench set the butterfly valves and will do a full sync when back together.

 

[Josephm32156]

I haven’t taken my carbs apart yet because they run fine but as far as the linkage bar, I noticed mine entire choke was stuck when bought the bike and if the coke is stuck and you try to open it then you will just bend that linkage bar and it was make your choke uneven like that. I got the choke repaired and lubed but if the linkage bar is bent you will have to either bend it back perfectly or I would recommend buying a new one if it’s really bad.

 

[John OoSTerhuis]

I’m no carb expert (maybe Adam F will chime in) but I’d probably leave the pilot screws where the factory set them and then do the idle-drop procedure after the carbs are installed and the ST running again, if you must; but, the Honda Service Manual sez there’s no need to do the procedure unless the pilot screws are replaced. Or if you’re operating continuously above 6,500 feet.

My Trusty Haynes Manual

will do a full sync when back together.

N.B. don’t follow the Haynes sync procedure. The ST1100 cylinder banks are NOT balanced to each other. Each cylinder is balanced to the #4 carb individually in any order. Adjust the idle speed back to spec during the sync as necessary.

Good luck.

John

 

[Mitch 570]

I haven’t taken my carbs apart yet because they run fine but as far as the linkage bar, I noticed mine entire choke was stuck when bought the bike and if the coke is stuck and you try to open it then you will just bend that linkage bar and it was make your choke uneven like that. I got the choke repaired and lubed but if the linkage bar is bent you will have to either bend it back perfectly or I would recommend buying a new one if it’s really bad.

Thanks for your reply. Idid notice that the choke plungers were a little scuffed and have polished them up best i could so what you say makes pefect sense. I will try bending the bar as suggested to ballance the choke plungers. Can I ask what you used to lube with and was it just the linkake or the choke plungers as well?

 

[Mitch 570]

I’m no carb expert (maybe Adam F will chime in) but I’d probably leave the pilot screws where the factory set them and then do the idle-drop procedure after the carbs are installed and the ST running again, if you must; but, the Honda Service Manual sez there’s no need to do the procedure unless the pilot screws are replaced. Or if you’re operating continuously above 6,500 feet.



N.B. don’t follow the Haynes sync procedure. The ST1100 cylinder banks are NOT balanced to each other. Each cylinder is balanced to the #4 carb individually in any order. Adjust the idle speed back to spec during the sync as necessary.

Good luck.

John

Thanks for your reply. Will leave the Idle screws as are then as where I live is only 265 ft above sea level and doesnt change much for miles around. Looking forward to the sync as when i stripped the carbs the butterfly valves were all over the place but didnt seem to run too bad apart from a hessitating stutter comming out of corners which made me strip them in the first place.

 

[Josephm32156]

Thanks for your reply. Idid notice that the choke plungers were a little scuffed and have polished them up best i could so what you say makes pefect sense. I will try bending the bar as suggested to ballance the choke plungers. Can I ask what you used to lube with and was it just the linkake or the choke plungers as well?

I just used some gear oil to lube up the choke linkage and plungers as well. it last long and doesn't collect dust. Lube any and every external moving part.

 

[afrymoyer]

John OOST texted me to have a look at this...

Hopefully the carbs are still out...

Don't bend anything yet! I've never had to bend any linkages for adjustments. The whole system should work as smooth as butter with your thumb working the main lever back and forth(where the choke cable hooks up). Something is probably sticking. Be certain that both of the choke/enriching linkage pivots are moving feely. Same as the choke plunger actuator rods. The rods get gummed up. Don't be afraid to remove them and give them a light sanding were they slide in the carb body. Also clean out any oxidation in the carb body. Lightly lube the rods with grease. The choke plungers themselves could be gummed up and sticky in the carb. These are easily removed, rubber seal pulled back, cleaned and lightly lubed. Usually you can get everything cleaned up lubed and working freely. The plungers are expensive, so be careful with them! I've had to buy several of them over the years.

You can adjust how the plunger rods sit in the plunger groove itself. Make sure all plungers are fully seated/closed in the carb body. Loosen the phillips head screws on carbs #3 & #4 actuator rods. Pull the rods back, so that the rods on carbs #1 & #2 are butted up against the plunger base (rear of the plunger groove). Then do the same with the loosened adjusters. Make sure they are butted up against the pivot arm/cam and plunger. Tighten the screws. Done....

I am attaching some pix of a spare bank of ABS emission carbs that I have sitting around. They are the same set up as yours. Hopefully this will help explain what I'm pointing out more clearly.

 

[afrymoyer]

I've looked in all of my manuals and notes, and am having a hard time trying to find out what bike you have. With the factory settings 1 5/8 turns out on the mixture screws, Im assuming you have an "International" non-emission bike? You should have #40 pilot/slow speed jets and #128 main jets from the factory? If this is the case, then I would start out at 1 3/4 turns out on the mixture screws. Set them all evenly across the board. If this is not the case with the jets, please report back. I'll keep an eye on this thread for a while and make sure you get it sorted out.

 

[John OoSTerhuis]

Hey Mitch, have a look at Adam’s great carb rebuild article in the AOW:

Carb Removal and Rebuild ( ST1100 ) *

Carb Removal and Rebuild ( ST1100 ) *

www.st-riders.net

 

[Mitch 570]

I just used some gear oil to lube up the choke linkage and plungers as well. it last long and doesn't collect dust. Lube any and every external moving part.

Spot on thank you

 

[Mitch 570]

John OOST texted me to have a look at this...

Hopefully the carbs are still out...

Don't bend anything yet! I've never had to bend any linkages for adjustments. The whole system should work as smooth as butter with your thumb working the main lever back and forth(where the choke cable hooks up). Something is probably sticking. Be certain that both of the choke/enriching linkage pivots are moving feely. Same as the choke plunger actuator rods. The rods get gummed up. Don't be afraid to remove them and give them a light sanding were they slide in the carb body. Also clean out any oxidation in the carb body. Lightly lube the rods with grease. The choke plungers themselves could be gummed up and sticky in the carb. These are easily removed, rubber seal pulled back, cleaned and lightly lubed. Usually you can get everything cleaned up lubed and working freely. The plungers are expensive, so be careful with them! I've had to buy several of them over the years.

You can adjust how the plunger rods sit in the plunger groove itself. Make sure all plungers are fully seated/closed in the carb body. Loosen the phillips head screws on carbs #3 & #4 actuator rods. Pull the rods back, so that the rods on carbs #1 & #2 are butted up against the plunger base (rear of the plunger groove). Then do the same with the loosened adjusters. Make sure they are butted up against the pivot arm/cam and plunger. Tighten the screws. Done....

I am attaching some pix of a spare bank of ABS emission carbs that I have sitting around. They are the same set up as yours. Hopefully this will help explain what I'm pointing out more clearly.

Nice write up and much appreciated thank youWill re do it and hopefully get it sorted. It does feel a little stiff.

 

[Mitch 570]

I've looked in all of my manuals and notes, and am having a hard time trying to find out what bike you have. With the factory settings 1 5/8 turns out on the mixture screws, Im assuming you have an "International" non-emission bike? You should have #40 pilot/slow speed jets and #128 main jets from the factory? If this is the case, then I would start out at 1 3/4 turns out on the mixture screws. Set them all evenly across the board. If this is not the case with the jets, please report back. I'll keep an eye on this thread for a while and make sure you get it sorted out.

Yes it's uk spec. When I get home I'll look at my notes and verify the jet sizes and take a pic of the manual mixture screw settings. I don't understand why mine were set so low.

 

[Mitch 570]

Hey Mitch, have a look at Adam’s great carb rebuild article in the AOW:

Carb Removal and Rebuild ( ST1100 ) *

Carb Removal and Rebuild ( ST1100 ) *

www.st-riders.net

Thank you for that. It's a great in depth job. Without it I don't think I would have attempted it as this is my first carb job.

 

[Mitch 570]

I've looked in all of my manuals and notes, and am having a hard time trying to find out what bike you have. With the factory settings 1 5/8 turns out on the mixture screws, Im assuming you have an "International" non-emission bike? You should have #40 pilot/slow speed jets and #128 main jets from the factory? If this is the case, then I would start out at 1 3/4 turns out on the mixture screws. Set them all evenly across the board. If this is not the case with the jets, please report back. I'll keep an eye on this thread for a while and make sure you get it sorted out.

Just got home and checked the jet sizes. They are pilot 40 and main 125. I have also taken pics out of my manual showing my model. The only mod I have found on the bike so far is that there are MOTAD stainless steel exausts type M11STL fitted instead of stock. Not sure if the jets should have been changed for this. Will have to look into it. Does this shed any light on the mixture screws at all?

 

[afrymoyer]

Emission standards in the UK sure are different. I’ve never seen an ST tuned that way from the factory(here in US). However, there are a bunch of ABS emissions bikes here that the owners have installed the #40 pilots and kept the 125 mains. So with that said, keep the 1 3/4 turns on the mixture screws. The exhaust you have is similar to stock, so keep the same jets.

Thank you for the pictures. I will keep for my notes.

Sent from my iPhone using Tapatalk

 

[Upt' North]

Mitch, their is no need to re-jet for the Motad's. Standard carb settings are just fine.
Upt'North.

 

[Mitch 570]

Emission standards in the UK sure are different. I’ve never seen an ST tuned that way from the factory(here in US). However, there are a bunch of ABS emissions bikes here that the owners have installed the #40 pilots and kept the 125 mains. So with that said, keep the 1 3/4 turns on the mixture screws. The exhaust you have is similar to stock, so keep the same jets.

Thank you for the pictures. I will keep for my notes.

Sent from my iPhone using Tapatalk

Thanks for your help on this. Have done some looking up as well and all I can seem to find is that in the 90's Honda factory set all bikes to a lean-ish mixture setting for emmission purposes and of course they cant set up seperatly to cater for all temps and altitudes. So what youve said sets my mind at rest and will go with your recomendation and see how we go.

If you need any further bits for your notes let me know and I will post up what I have.

 

[Mitch 570]

Mitch, their is no need to re-jet for the Motad's. Standard carb settings are just fine.
Upt'North.

Nice one thanks for that. This jetting stuff is all new to me. Learning as I go.

 

[Walleye]

early 70's we were always checking exhaust tip color after finishing a spirited ride, light gray or light tan was to lean, black or dark brown to rich, I had a spirited ride Saturday just because I haven't had one yet on this bike, 85 to 110 to and back, it ran pretty well, but my exhaust is black, no color, I have two bros slip ons, guess someone over richened it.

 

[Mitch 570]

Just a quick update. Thanks to you guys the carbs are all bench set with everything working as it should. Big thumbs upThe choke plungers were sticking and the linkage was slightly bent I guess due to the pressure of the sticking plungers. Carbs are back on the bike now. Can't go any further now though as the alarm/immobiliser has packed up and is stopping me striking it up. That's my next job then.