Fine tuning Carbs and Idle after installing a new/used set.

Brant · Aug 15, 2014

#1: Either name works, as majority know what that is referred to.
#2: Mixture screws are the only adjustable part pertaining to fuel supply.
#3: Mixture screws......pilot screws........dont' matter. "number of turns" may been referring to setting them where they were INITIALLY before carb dis-assembly......didn't go back and look at what that was referring to.
Either way, there is no such thing as a specified no. of turns out from seated, other than an initial bench setting if carbs were taken apart. That mixture setting will vary a tad depending on elevation bike is regularly ridden at

.....that's a given

.....and may very slightly on each carb(ain't no Four Musketeers here), depending on actual fuel levels in each bowl AND correct valve clearance/compression of each cyl. Apoligize for the confusion

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Bush: Seems you got too much free time on your hands.........nothin' a good long ride won't take care of

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Bush · Aug 15, 2014

Brant said:
Bush: Seems you got too much free time on your hands.........nothin' a good long ride won't take care of.

You got that right - too much free time because both of my ST's are in my sick bay at the moment, waiting on parts - nothing to ride!

Brant · Aug 15, 2014

Bush said:
You got that right - too much free time because both of my ST's are in my sick bay at the moment, waiting on parts - nothing to ride!

Bummer...............that'id get me to throw a little banter back and forth too

...........BTW, no offense intended.....it's all good

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mznyc · Aug 15, 2014

Brant said:
#3: Mixture screws......pilot screws........dont' matter. "number of turns" may been referring to setting them where they were INITIALLY before carb dis-assembly......didn't go back and look at what that was referring to.
.

Yup.That's what I was asking.The pilot screws are the only things that get restored back to a "set amount of turns" restored from where they started,and of course can be adjusted for fine tuning,but if the bike ran well before,should run well again if you get them close.
My problem was inconsistent idle.Still think it was a vacuum leak as first slow jet I pulled was clean.Even so,I'll replace all jets and pilot screws while the carbs are out as I have them on hand.

ST1100Y · Aug 16, 2014

mznyc said:
...should run well again if you get them close...

Sorry, I'm with Brant in this... should, could, might just won't cut it...
Either you don't touch the idle screws at all, and if, you do have to follow proper adjustment thoroughly...

#1 slightly too lean, #2 a tat on the rich side, #3 way too rich.... any idea how the engine will start to pound, knock and shake due such uneven cylinder outputs? What this will do to rings, cut, valve/seats, valve train and at some point to the bearings on the long run?

mznyc · Aug 16, 2014

Jeez not too condescending

Did in say I wasn't intending to follow procedure? I missed that,.....

Psst,... Pilot Screws,.....
I also understand how an engine works,do all of my own tuning on my FI bikes (Ducati,Moto Guzzi) and they run as good or better than I'll wager anyone's bike here ,so yes I'm not an idiot,just inexperienced with CARBED bikes that you grouchy old cogers who have tweaked for centuries !

afrymoyer · Aug 16, 2014

Brant said:
Just a FYI, anything that would get trapped in pilot jets STAYS there because of direction of flow, and atomiizing hole in end is to small for anything foreign to exit. I honestly can say I've never had these Kiehn's apart, but am a guru when it comes to the 4bank Mikunis on my 34yr.old Venturer1100 Yammy. All very similar in nature, and will cause similar if not the same running issues.....just sayin', from decades of experience with bike carbs.

Atomizing hole at the end of a ST1100 slow speed / pilot jet? Were? OK....Never mind....You've mentioned that you never had ST Keihins apart before....

Brant said:
No compromise needed. The sync is to be set with ALL intake as it runs in place.....period. Syncing carbs together is worthless unles you FIRST set idle mixtures......to highest in. vacuum....sync........re-set idle mixes to a T, and resync again. ANY varience of idle, as in 'floating around a bit at idle means carbs are NOT properly synced, which includes proper idle mixture settings.......with all intake in place.

BTW, that all IS to be done at lowest rpm it runs smooth at..........7-900rpm......and goes for ALL multi carb bikes.

Brant said:
First off......no grease on those boots before installation! It'll eventually rot the rubber. A shot of silicone spray is what's needed.
The term 'slow jets' is referring to pilot jets. Main jets are exactly that...main jets, or sometimes 'high speed' jets.
Lastly, there is NEVER a set number of turns for idle mixtures, not on ANY multi-carb bike. Those need to be set individually, using either a multi-vacuum gauge set-up, mercury manometer, or MorganCarbTune......with ALL intake(airbox, ect.) in place.
Same for sync.......sync reasonably close first......set idle mixes to highest in.vac.........re-sync.......double check mixture settings....re-sync.
Run a box fan in front of motor while doing this. It will prolong the time before cooling fan comes on. When fan comes on, stop process, shut motor down till it cools.
Reason being, the charging load of alt. from fan coming on changes vacuum AND fuel mixtures when motor is under even the slightest load.
FWIW, there's no such thing as a 10 or 15min. sync., not if CORRECTLY done. Anything short of that is just time wasted and not a noticable difference. Those that defer to 'above idle, sync makes no difference' are assuming just another urban myth....at best.

Twice in this thread, you have listed procedure's for setting idle mixture screws. However, the first one significantly differs from the second one, on were to start FIRST. Which one is most correct?

Brant · Aug 16, 2014

afrymoyer said:
Atomizing hole at the end of a ST1100 slow speed / pilot jet? Were? OK....Never mind....You've mentioned that you never had ST Keihins apart before....

Twice in this thread, you have listed procedure's for setting idle mixture screws. However, the first one significantly differs from the second one, on were to start FIRST. Which one is most correct?

Atomizing hole in end of pilot jet exist, no matter whether they are Kuni's, Kiehns, whatever
If you'll read, and not cop an attitude, you'll see I stated I haven't had THESE Kiehn's apart before........for that matter likely have have had apart more carbs(automotive and motorcyle) than you've ever seen

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BTW, if you'll actually READ, you'll see procedures are EXACTLY the same.........or if your REALLY on your game, you can set those mixtures using the 'lean-drop method'

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Just a nice way of letting you know your 'barking up the wrong tree'

Mznyc....seriously doubt your bikes run any better than my carbed bikes.......I'm anal particular, and you haven't a clue to my mechanical skill-sets as a PROFESSIONAL or as a hobby

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mznyc · Aug 16, 2014

Brant said:
Mznyc....seriously doubt your bikes run any better than my carbed bikes.......I'm anal particular, and you haven't a clue to my mechanical skill-sets as a PROFESSIONAL or as a hobby.

Once again,...off-course.Said my bikes "run as good or better",not referring to you or anyone specifically,but help members who want to help, understand I know how bikes work.So no need to go off throwing insults intentionally or not.But I can give many of examples of Guzzi's that don't run as well as mine.I guess it's just dumb luck.

Let's focus attention on the questions and try to solve problems.Ask a question about jets,get an answer about a carb sync.

. *** Just trying to keep the conversation moving,productive and streamlined.I want yours and others opinions,just don't want tit for tat bickering.Reminds me of being in junior high school.
If you think me or someone else is hopelessly off-course and it frustrates you ,I'd suggest ignore the post or thread and be happy.

Brant · Aug 16, 2014

mznyc said:
Once again,...off-course.Said my bikes "run as good or better",not referring to you or anyone specifically,but help members who want to help, understand I know how bikes work.So no need to go off throwing insults intentionally or not.But I can give many of examples of Guzzi's that don't run as well as mine.I guess it's just dumb luck.
Let's focus attention on the questions and try to solve problems.Ask a question about jets,get an answer about a carb sync.. *** Just trying to keep the conversation moving,productive and streamlined.I want yours and others opinions,just don't want tit for tat bickering.Reminds me of being in junior high school.
If you think me or someone else is hopelessly off-course and it frustrates you ,I'd suggest ignore the post or thread and be happy.

Looks like I did EXACTLY that, once I followed what you were specificly asking.......without making any personnel claims or attack

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afrymoyer · Aug 16, 2014

Brant said:
Atomizing hole in end of pilot jet exist, no matter whether they are Kuni's, Kiehns, whatever
If you'll read, and not cop an attitude, you'll see I stated I haven't had THESE Kiehn's apart before........for that matter likely have have had apart more carbs(automotive and motorcyle) than you've ever seen.
BTW, if you'll actually READ, you'll see procedures are EXACTLY the same.........or if your REALLY on your game, you can set those mixtures using the 'lean-drop method'.
Just a nice way of letting you know your 'barking up the wrong tree'

Mznyc....seriously doubt your bikes run any better than my carbed bikes.......I'm anal particular, and you haven't a clue to my mechanical skill-sets as a PROFESSIONAL or as a hobby.

Very arrogant of you to question the skills of other members that have actually had ST1100 carburetors apart, or their general mechanical aptitude. At this point, none of this helps the original poster getting his bike fixed by telling him that your bikes run better than his, AND that you are better than me.

The pilot jet in the ST Keihin, is nothing more than a metered orifice that is seated into the carb body. This jet only "supplies" fuel to both the idle mixture and the transitional ports at the throttle plate, were fuel then get atomized just below the venturi in the mouth of the carb.

I'm pretty sure I can read clearly. In your first quoted procedure you mentioned that "the idle mixtures have to get set FIRST, then synchronize, then re-set idle mixtue"... In your second quote you said " Synchronize reasonably close FIRST, then set idle mixes, re-synch, double check mixture settings, re-synch.... As you can see they do differ significantly. So this is unreasonable to ask which procedure of yours is more correct?

I must really be on my game. Thank you for mentioning it. No barking needed. I do own the #07MMA-MT3010B idle mixture screw tool along with an OTC 100S with inductive pick-up, and perform the idle drop procedure regularly on ST1100's.

mznyc · Aug 16, 2014

Brant said:
Looks like I did EXACTLY that, once I followed what you were specificly asking.......without making any personnel claims or attack.

Yes Adam, I meant to mention that,much appreciated.

Brant · Aug 16, 2014

afrymoyer said:
Very arrogant of you to question the skills of other members that have actually had ST1100 carburetors apart, or their general mechanical aptitude. At this point, none of this helps the original poster getting his bike fixed by telling him that your bikes run better than his, AND that you are better than me.

The pilot jet in the ST Keihin, is nothing more than a metered orifice that is seated into the carb body. This jet only "supplies" fuel to both the idle mixture and the transitional ports at the throttle plate, were fuel then get atomized just below the venturi in the mouth of the carb.

I'm pretty sure I can read clearly. In your first quoted procedure you mentioned that "the idle mixtures have to get set FIRST, then synchronize, then re-set idle mixtue"... In your second quote you said " Synchronize reasonably close FIRST, then set idle mixes, re-synch, double check mixture settings, re-synch.... As you can see they do differ significantly. So this is unreasonable to ask which procedure of yours is more correct?

I must really be on my game. Thank you for mentioning it. No barking needed. I do own the #07MMA-MT3010B idle mixture screw tool along with an OTC 100S with inductive pick-up, and perform the idle drop procedure regularly on ST1100's.

No difference,,,,,,pick one......idle mix or sync first........point being, process has to be repeated more than once to hold steady.
Read well, but comprehension may be the issue as I didn't even come close to questioning ones skills, or 'my bike is better than yours',,,,,,and overall, I believe he was satisfied with the answer.

Carry on, and you have a nice, safe weekend!......ATGATT

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Al st1100 · Aug 16, 2014

Denatured alcohol is the preferred lubricant for assembling rubber parts

John OoSTerhuis · Aug 17, 2014

Michael, you might be interested in Adam Frymoyer's moST excellent new AOW article on his ST1100 carb rebuild:
http://www.st-riders.net/index.php?topic=10249.0
Great pictures and descriptions!!

Major edit!: posted this before discovering I'd missed reading a whole new page of posts... sorry.

John

mznyc · Aug 17, 2014

Thanks John Adam sent the link.Wow! Fantastic write-up.

ST1100Y · Aug 18, 2014

John OoSTerhuis said:
http://www.st-riders.net/index.php?topic=10249.0
Great pictures and descriptions!!

I just admired the amount of goo in those carbs there... how did this ever get past the fuel filter/s?!
(when I did the carbs of the '94, their were clean like fresh from the factory...)

One addition: after removing the carbs, instantly crumble up 4 sheets of paper towel, kitchen roll or alike (I use workshop paper-wipes) and clog the intakes with them... you don't want to have anything falling into there...

afrymoyer · Aug 18, 2014

ST1100Y said:
I just admired the amount of goo in those carbs there... how did this ever get past the fuel filter/s?!
(when I did the carbs of the '94, their were clean like fresh from the factory...)

One addition: after removing the carbs, instantly crumble up 4 sheets of paper towel, kitchen roll or alike (I use workshop paper-wipes) and clog the intakes with them... you don't want to have anything falling into there...

The bike originally had one of those cheesy universal aftermarket "screen" type filter in it. Plus, the bike sat for a loooong time before I got it. I always stuff red shop towels in the intakes and they stay in there till the carbs go back in. For better picture reference, I took them out, took a snap, then put them back in, etc.

ST1100Y · Aug 19, 2014

afrymoyer said:
The bike originally had one of those cheesy universal aftermarket "screen" type filter in it.

OK, that explains it...
We only have a slight greenish stain on the inside of the bowls, etc... from the chemical additives/replacements in our unleaded fuel...
Washes off with regular brake cleaner, had yet no problems of any kind there.

I always stuff red shop towels in the intakes and they stay in there till the carbs go back in.

Thanx for clarification; none shown in the pix, nor mentioned in the text made me wonder... ;-)

We've an older Vacuumate (B/W LCD) with digital rev counter, which also serves very well for syncing and that "drop procedure"... (which takes quite some time done thoroughly actually...)

Brant · Aug 20, 2014

afrymoyer said:
Very arrogant of you to question the skills of other members that have actually had ST1100 carburetors apart, or their general mechanical aptitude. At this point, none of this helps the original poster getting his bike fixed by telling him that your bikes run better than his, AND that you are better than me.

The pilot jet in the ST Keihin, is nothing more than a metered orifice that is seated into the carb body. This jet only "supplies" fuel to both the idle mixture and the transitional ports at the throttle plate, were fuel then get atomized just below the venturi in the mouth of the carb.

I'm pretty sure I can read clearly. In your first quoted procedure you mentioned that "the idle mixtures have to get set FIRST, then synchronize, then re-set idle mixtue"... In your second quote you said " Synchronize reasonably close FIRST, then set idle mixes, re-synch, double check mixture settings, re-synch.... As you can see they do differ significantly. So this is unreasonable to ask which procedure of yours is more correct?

I must really be on my game. Thank you for mentioning it. No barking needed. I do own the #07MMA-MT3010B idle mixture screw tool along with an OTC 100S with inductive pick-up, and perform the idle drop procedure regularly on ST1100's.

Actually, that IS an atomizing office on other end of pilot jet, whether it be a Kiehn or Mikuni

. BTW, appreciate that part no. For the adjusting tool

.

Fine tuning Carbs and Idle after installing a new/used set.

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