I can't get my carb's tuned properly with exhaust and pods. ):

[3Phase]

Let It Flo

Yeah I was curious about that...
What does it actually really do?

YICS AND WHY YOU SHOULD LOVE IT:
"... the underlying theme is "greater fuel efficiency", and NOT one of more power or performance-—-although the two do go hand-in-hand."

Would syncing the carbs without it really be that bad?

It's difficult to almost impossible to sync the carbs on a factory stock bike without blocking off the YICS. With pod filters and the open exhaust I think you'd be wasting your time without blocking off the YICS ports.


Regarding the different carburetor specs here's a thread from our friends across the pond:-

Carb Specs by Model


A pair nicely chilled and stacked should help insure you extinguish your thirst for knowlege!



.

[Bonz]

YICS connects the intake tracts to help the mixture burn more completely. Vacuum is being "shared" and a true individual vacuum reading on each carb is not possible, unless the system is blocked off. I think that describes it?

[natemoen]

Yeah I was curious about that...
What does it actually really do?
Would syncing the carbs without it really be that bad?

It wouldn't be bad, it would just be pointless.

[Dylano*]

Good luck, Dylano!


I don't know if you're familiar with the YICS system on your XJ but while you have some down time you should take the time to learn how to clean it, then buy or make a YICS block-off tool for synchronizing the carburetors.

.

Yeah I was curious about that...
What does it actually really do?
Would syncing the carbs without it really be that bad?

[3Phase]

Good luck, Dylano!


I don't know if you're familiar with the YICS system on your XJ but while you have some down time you should take the time to learn how to clean it, then buy or make a YICS block-off tool for synchronizing the carburetors.

.

[Dylano*]

Idea is to quench those center running cyl. a bit richer since they run a bit hotter..........specially with your existing(or non existing) exhaust and intake combined.

The Venturer was set up that way, 2steps richer center two cyl. having the extra payload, even though having the oil cooler.......just an FYI.

That interesting. makes perfect sense. I'll give it a try.

Thanks again everyone.
I will be working on it this weekend.,
and again whenever those jets com in, probably NEXT weekend.
I will be reporting back with updates.

[motoman]

Sounds like a plan! I've had the carbs out more times than I care to admit adready, so I've gonnet great practice, hahaha

Why would it be a good idea to mix main jet sizes? Wouldn't I want them all running the same?

Idea is to quench those center running cyl. a bit richer since they run a bit hotter..........specially with your existing(or non existing) exhaust and intake combined.

The Venturer was set up that way, 2steps richer center two cyl. having the extra payload, even though having the oil cooler.......just an FYI.

[Dylano*]

Dylano,

Unless someone swapped the carbs, your XJ1100 does not have the cross-over passage in the casting between the main jet well and the pilot jet well.


Just a quick heads-up before you start changing main jets and drive yourself crazy: A basically open exhaust with pod air filters is basically not going to work right.


The slide needles (Jet Needles) in the XJ carbs are short, pointy little things with a taper that opens up the main jets fairly quickly in the mid-range and completely clear the main jets soon after that.

The main jets that will give you the best power and top speed will probably be so rich they'll make your eyes burn, and children and pets will cry when you ride by them on the street.


Put the stock 47.5 pilot jets back in the carbs and tune the top end first.

Start with the stock 112.5 mains in the outer carbs and put 115 mains in the middle carbs.

Next, try 115 all the way across.

Next, try 115 in the outer carbs with 117.5 in the middle carbs.

Next, try 117.5 all the way across.

Next, try 117.5 in the outer carbs with 120 in the middle carbs.

Next try 120 all the way across.

Next try 120 in the outer carbs with 122.5 in the middle carbs.

Next, try 122.5 all the way across.

You see where this is going, right?


After you get the top end dialed in, work on the low and midrange power/performance.

There are no Mikuni needles available for tuning the low and mid-range power on your XJ11 so you'll just have to deal with the needles you have now.

If the 47.5 pilot jets are too lean, try the the 50 jets.
Next, try the 52.5 but I think those will probably be too rich.

Yeah, it's a long process and you're probably going to be removing and installing the carbs a whole bunch of times before you get it close to where you want it.

Happy tuning!

.

Sounds like a plan! I've had the carbs out more times than I care to admit adready, so I've gonnet great practice, hahaha

Why would it be a good idea to mix main jet sizes? Wouldn't I want them all running the same?

[3Phase]

Dylano,

Unless someone swapped the carbs, your XJ1100 does not have the cross-over passage in the casting between the main jet well and the pilot jet well.


Just a quick heads-up before you start changing main jets and drive yourself crazy: A basically open exhaust with pod air filters is basically not going to work right.


The slide needles (Jet Needles) in the XJ carbs are short, pointy little things with a taper that opens up the main jets fairly quickly in the mid-range and completely clear the main jets soon after that.

The main jets that will give you the best power and top speed will probably be so rich they'll make your eyes burn, and children and pets will cry when you ride by them on the street.


Put the stock 47.5 pilot jets back in the carbs and tune the top end first.

Start with the stock 112.5 mains in the outer carbs and put 115 mains in the middle carbs.

Next, try 115 all the way across.

Next, try 115 in the outer carbs with 117.5 in the middle carbs.

Next, try 117.5 all the way across.

Next, try 117.5 in the outer carbs with 120 in the middle carbs.

Next try 120 all the way across.

Next try 120 in the outer carbs with 122.5 in the middle carbs.

Next, try 122.5 all the way across.

You see where this is going, right?


After you get the top end dialed in, work on the low and midrange power/performance.

There are no Mikuni needles available for tuning the low and mid-range power on your XJ11 so you'll just have to deal with the needles you have now.

If the 47.5 pilot jets are too lean, try the the 50 jets.
Next, try the 52.5 but I think those will probably be too rich.

Yeah, it's a long process and you're probably going to be removing and installing the carbs a whole bunch of times before you get it close to where you want it.

Happy tuning!

.

[Dylano*]

Went with BA80's suggestion as they are cheaper, and I hope I don't regret it!

Got these jets in THOSE ^^^ sizes

http://www.buyatvpartsonline.com/mikuni-carbs-jets-mikuni-genuine-oem-pilot-jets-c-699_707.html

http://www.buyatvpartsonline.com/mikuni-carbs-jets-mikuni-100604-main-jets-c-699_702.html

[Dylano*]

Just bought these jets


Mikuni Carb Parts - 100/604 - Mikuni Main Jet - Size 112.5
Mikuni Carb Parts - 100/604 - Mikuni Main Jet - Size 115
Mikuni Carb Parts - 100/604 - Mikuni Main Jet - Size 117.5
Mikuni Carb Parts - 100/604 - Mikuni Main Jet - Size 122.5
Mikuni Carb Parts - Genuine Mikuni OEM Pilot Jet - Size 47.5
Mikuni Carb Parts - Genuine Mikuni OEM Pilot Jet - Size 50
Mikuni Carb Parts - Genuine Mikuni OEM Pilot Jet - Size 52.5


SHOULD SUFFICE TUNING?! hahaha I hope so.

Don't tell me those mains are not OEM because they don't say so right there... -_-

[Dylano*]

I have to disagree with you on that Scott. The fuel flow from the needle jets is dependent on air flowing over the opening to create a vacuum to pull the fuel up and out of the bowl. The butterfly valves are all but closed letting just enough air through to mix with what little fuel is coming through the idle system. There isn't enough air flow there to create a vacuum in the needle jet.

That makes sense... From my minor understanding in fluid dynamics, I can't see that very light air movement creating enough vacuum to move anyhing up from the bowls... unluss we start talking on a molecular level... then yes of course it does, some fumes perhaps, but I would have to agree with your word usage on miniscule. Unless there is that crossover casting like motoman is talking about? Maybe that isencouraging what you are referring to? I honestly have no idea.

[motoman]

Not to hijack, but FWIW to some, the early 78-79 carbies draw fuel from both idle and main circuit thru ALL the rpm ranges since having the cross-over casting(that got plugged on the early 80 "bastardized" carbs. IMO, this is what seems to make them a bit easier to to tune with intake and exhaust modifications.

Aside from that, previous suggestions to start stock as a baseline(assuming there are no SECONDARY ignition voltage issues) is spot-on for a baseline to decifer what direction jetting needs to go, where AND how much.

[3Phase]

That's why I said, "miniscule."

In a nutshell: I did some main jet swapping to find out which ones my wallet likes and which ones Columbo likes -- fuel economy vs power and acceleration.

Changing the main jets made a very slight difference in the idle speed and I had to readjust the mixture screws. Looking in the carburetor inlets with the engine idling I could see the occasional micro-trace of fuel wafting from the needle/jet opening.


P.S. Never blip the throttle with the airbox off while you're looking into the carb inlets. DAMHIK!

.

[BA80]

Dylano,

Welcome to the site!


The carburetor slide needles never completely seat in and block the main jets so there is always at least some minuscule amount of fuel flowing through the main jets even at idle.

.

I have to disagree with you on that Scott. The fuel flow from the needle jets is dependent on air flowing over the opening to create a vacuum to pull the fuel up and out of the bowl. The butterfly valves are all but closed letting just enough air through to mix with what little fuel is coming through the idle system. There isn't enough air flow there to create a vacuum in the needle jet.