ST1100 Carb 101- STAGE 2 jet kit

[Josephm32156]

So I recently overhauled my carburetor on my 96 ST1100 and the bike runs much better but there still seams to be a slight idle issue as well as some minor backfiring at decel. I have been doing research and found you can buy a stage 2 jet kit for slightly modified exhaust ( mine has slip-on mufflers but stock pipes from the mufflers up).
ANYONE HAVE ANY SUGGESTIONS ON UPGRADING THE JETS?

 

[Slydynbye]

Idle jets and shims are worthwhile but going to 130 main will do nothing for top end and give poor gas mileage in my opinion.

 

[Roger]

Does the bike warm up cleanly without popping and banging as you take the choke off?

 

[Hibobb]

My two cents is that the stock carbs are great when clean (Even with slip on muffler).
You may have been able to squirt cleaner thru the old jets, but that doesn't mean they are still the correct ID (Think of a water pipe with calcium buildup).
Even with brand new jets, there are passages in the carb that could be restricted. I am now guesing, but most carbs have a fuel screw that must be taken out and passages checked.
There may be other guys that disagree with me, but I say the japs that designed this bike are way smarter than most of us will ever be.

 

[Josephm32156]

Does the bike warm up cleanly without popping and banging as you take the choke off?

Yes, it warms up pretty clean but only started it a couple times becuase I waiting for more coolant to come in. Still have to finish running a dose of seafoam.

 

[afrymoyer]

I’ve looked at your other threads and all your pictures. You have an emissions bike. I can see all the vapor recover plumbing on the carbs. I also saw that the PAIR system is still installed. It is not uncommon to have a mild decel pop or bubble. The emission system is doing its job and burning off any residual fuel in the exhaust system.

Because you have an emissions bike, I would recommend against the jet kit. You can however, go up on the pilot jets to the #40’s. If that is a picture of your bike with those little fart can mufflers, you could get away with a #128 main jet and start at 1 3/4 turns out. No more that 2 turns out on those mixture screws... This should get you real close.


Sent from my iPhone using Tapatalk

 

[bdalameda]

I just finished rebuilding my carbs and installed new jets as it has been almost 10 years now since I have had the carbs off. The California model St1100's as well as 96+ US models (I think) came with 125 main jets and 38 pilot jets. I upsized to the Canadian and Euro standard jets at 128 main and 40 pilot jets with 1 shim under the slide needles. All US bikes were fitted with a PAIR system which injects air into the exhaust stream to completely burn any unburned hydrocarbons - the PAIR system causes most of the deceleration popping, though it has no effect on the engine performance at all. I removed my PAIR system as it had deteriorated diaphragms etc. while I was in there. I also replaced the air-cutoff diaphragms while I had the carbs out. I also reset the float height at 7mm as the float height as measured was between 8mm and 9mm. I set the idle mixture at 1 3/4 and did an thorough carb sync. and idle drop adjustment on the mixture screws.

I can report that my ST runs better than it ever has - I mean noticeably better. I expected to lose some fuel economy but to my amazement I can report at least a 2mpg improvement after this. Surprising with the larger jets and float height adjustment but it absolutely has improved. Noticeably harder mid range pull and better top end.

Dan

 

[Al st1100]

some minor backfiring at decel ( depending on your definition of minor ) is normal , there are many threads on this subject. I have a 96, did it from the day I got it . Have no concerns about it.

 

[John OoSTerhuis]

Sure wish you had before and after dyno results, Dan.

About the PAIR system causing decel popping - if the diaphragm in one or both of the Air Suction Valves was torn, the ST would run like shite... think about it! Air leaking into the #2 and #4 cylinders intake manifolds, just like a bad carb boot or disconnected/cracked carb sync hose.

If you had decel ‘burble’ before removing the Seconday Air Supply System (Exhaust Emission Control System, aka PAIR), you’ll still have it after because in both cases there is NO air being added to the exhaust manifolds. No one who’s done it admits this...

If STriders wish to remove the “PAIR” system just do it, don’t rationalize it over the long perpetuated “backfire” (afterburn) trope.

If you have an Air Suction Valve diaphragm that’s torn/holed, poST a picture, AND report the running symptoms throughout the rpm range and load.

Sorry... pet peeve.

John

 

[bdalameda]

I did note that after the float adjust, rejet, air-cutout replacement, tune, and PAIR removal, I have not one bit of deceleration popping anymore. My ST always did it before, a little bit, but it never was an issue or concern. I attribute this to the PAIR removal but who knows, being I did so many things. I believe my increase in fuel economy has something to do with the increase in mid range power and not having to open the throttle as wide to maintain speed etc.. Can't figure any other reason to improve mileage with everything set richer. The best I could ever get mileage wise with our stupid California fuel blends was about 41.5 mpg - now for the last two tanks of fuel averaging 43.5 to 44 mpg with a mix of semi spirited riding.

 

[John OoSTerhuis]

From page 5-2, Fuel System Troubleshooting, in the Honda Service Manual under:
Afterfire when engine braking is used

• Lean mixture in slow circuit
• Air cut-off valve malfunction
• Secondary air supply system faulty
• Hoses of emission control system faulty

Keep in mind this is NOT normal decel burble, it’s loud scary sounds.

FWIW

John

 

[John OoSTerhuis]

PS The quick test to rule out the PAIRs is so simple it’s ridiculous - disconnect the PAIR hose from the ‘T’ between the #2 and #4 cylinder intake manifold hoses. With a short extension hose inserted into the PAIR hose, apply suction with a MityVac (or even just with your mouth!). If it holds/doesn’t bleed off, THE PAIRS ARE OK!

Page 5-17 in my Honda Service Manual, plus page 7-8 in the Honda Common Service Manual.

Again, FWIW

John

 

[Walleye]

I just finished rebuilding my carbs and installed new jets as it has been almost 10 years now since I have had the carbs off. The California model St1100's as well as 96+ US models (I think) came with 125 main jets and 38 pilot jets. I upsized to the Canadian and Euro standard jets at 128 main and 40 pilot jets with 1 shim under the slide needles. All US bikes were fitted with a PAIR system which injects air into the exhaust stream to completely burn any unburned hydrocarbons - the PAIR system causes most of the deceleration popping, though it has no effect on the engine performance at all. I removed my PAIR system as it had deteriorated diaphragms etc. while I was in there. I also replaced the air-cutoff diaphragms while I had the carbs out. I also reset the float height at 7mm as the float height as measured was between 8mm and 9mm. I set the idle mixture at 1 3/4 and did an thorough carb sync. and idle drop adjustment on the mixture screws.

I can report that my ST runs better than it ever has - I mean noticeably better. I expected to lose some fuel economy but to my amazement I can report at least a 2mpg improvement after this. Surprising with the larger jets and float height adjustment but it absolutely has improved. Noticeably harder mid range pull and better top end.

Dan

This is true carb porn at its finest, you dont here this kinda talk much anymore, love it, good job. Now has anyone tinkered with the ST timing.

 

[afrymoyer]

"Factory" brand used to make a timing advancer for the ST years ago, and they only sold it for several years. It didn't do too much, other than sharpen up the throttle response a little. Worked better with re-jetting the bike, but wasn't that effective at stock settings.

 

[Walleye]

Just curious, it use to be common to change jets , carb work, ignition timing and cam timing and exhaust mods and get significant gains, anyone out there pushed it to the limit with the ST1100. These are low cost mods. How far can you go within reason ?

 

[Josephm32156]

I just finished rebuilding my carbs and installed new jets as it has been almost 10 years now since I have had the carbs off. The California model St1100's as well as 96+ US models (I think) came with 125 main jets and 38 pilot jets. I upsized to the Canadian and Euro standard jets at 128 main and 40 pilot jets with 1 shim under the slide needles. All US bikes were fitted with a PAIR system which injects air into the exhaust stream to completely burn any unburned hydrocarbons - the PAIR system causes most of the deceleration popping, though it has no effect on the engine performance at all. I removed my PAIR system as it had deteriorated diaphragms etc. while I was in there. I also replaced the air-cutoff diaphragms while I had the carbs out. I also reset the float height at 7mm as the float height as measured was between 8mm and 9mm. I set the idle mixture at 1 3/4 and did an thorough carb sync. and idle drop adjustment on the mixture screws.

I can report that my ST runs better than it ever has - I mean noticeably better. I expected to lose some fuel economy but to my amazement I can report at least a 2mpg improvement after this. Surprising with the larger jets and float height adjustment but it absolutely has improved. Noticeably harder mid range pull and better top end.

Dan

Hey quick question, what angle do you hold the carbs to get a proper float height adjustment? The bike is runny much better but still having choke issues and high idle. I did not set the float heights so I think that may be the problem with the new float needles in.

 

[bdalameda]

You must measure the floats when the float tab just touches the needle seat pin which is spring loaded. This can be done by had or rotate the carbs so that the floats are not depressing the pin on the needle seat. I set my float level to 7mm as measured from the bowl sealing surface to the top of the float.

 

[bdalameda]

You may need to replace the Air Cutoff diaphragms if you are having idling issues as bad air cut-off will cause an air leak that can effect the idle.

 

[Josephm32156]

You must measure the floats when the float tab just touches the needle seat pin which is spring loaded. This can be done by had or rotate the carbs so that the floats are not depressing the pin on the needle seat. I set my float level to 7mm as measured from the bowl sealing surface to the top of the float.

Thanks man

 

[sjsavin]

I just finished rebuilding my carbs and installed new jets as it has been almost 10 years now since I have had the carbs off. The California model St1100's as well as 96+ US models (I think) came with 125 main jets and 38 pilot jets. I upsized to the Canadian and Euro standard jets at 128 main and 40 pilot jets with 1 shim under the slide needles. All US bikes were fitted with a PAIR system which injects air into the exhaust stream to completely burn any unburned hydrocarbons - the PAIR system causes most of the deceleration popping, though it has no effect on the engine performance at all. I removed my PAIR system as it had deteriorated diaphragms etc. while I was in there. I also replaced the air-cutoff diaphragms while I had the carbs out. I also reset the float height at 7mm as the float height as measured was between 8mm and 9mm. I set the idle mixture at 1 3/4 and did an thorough carb sync. and idle drop adjustment on the mixture screws.

I can report that my ST runs better than it ever has - I mean noticeably better. I expected to lose some fuel economy but to my amazement I can report at least a 2mpg improvement after this. Surprising with the larger jets and float height adjustment but it absolutely has improved. Noticeably harder mid range pull and better top end.

Dan

Dan, what size shim did you put in?

Stuart 97 ST1100