Alternative carbs

[Shuriken]

Thanks for that info. You may be right. I will check parts schematics on that!

[randy]

An easy way to remeber that is:

Mixture screws on the engine side of the carb control fuel.

Mixture screws on the intake side of the carb control air.

[Shuriken]

I agree with Randy. After paying a visit to the garage tonight, I can tell you that the mixture screws on these carbs are fuel mixture screws. Loosen them enough and the plugs go black quick. Tighten them enough and the pugs turn white.

I have a color tune system and can determine combustion color. The lightest that I can get the color is light blue. With proper jetting, I think one should be able to mix the idle from a very light blue (or white) - lean - to a yellow/orange - rich. If you can't ever get the color white to orange, the pilots could be the wrong size.

As I mentioned, with screws seated, idle mix on my setup is light blue. This is okay for now because I don't have any reason to lean out the mixture any further than bunson blue. If I go to a lower elevation and need to richen the mixture, I can very easily.

So.... back to the ZRX carbs...

I have off/white plugs all through the range on my setup, so I assume the main jet to be close and also assume that the jet needle is close. I also assume pilot jets to be close.

Performance is night and day over my XS carbs. The only problem I have is a sub-2k stumble, which I haven't sorted out yet. With plug color good through the range, solving this stumble is becoming bothersome.

For those of you who may have frustrations getting these carbs to work on your XS, keep it simple. I did not change any jets or change float height! If the bike sputters, coughs, gags, etc, check the obvious things first. Make sure there is fuel. Make sure the vacuum ports are capped off. Make sure the carbs are clean, and synched. Start by setting idle screws at like 1 turn from seated, etc.

Now... anyone care to comment on my sub 2k stumble?

[trbig]

I see some Colortune kits listed with a 14mm plug, and some have a 12mm... is the one I need a 14mm?


Tod

[81xsproject]

14

[AlanB]

hi ae7f,

Sub-2000 revs is probably the pilot; have you tried the bike out on the road with the adjusters 1/2 turn further in (or out) from your "ideal" colourtune setting?

If that does not tune it out, the next step is the needle; When my Slingshots were set on the dyno, we ended up with the needles raised 1/2 of a groove...... Not as odd as it sounds; Dynojet do shim washers designed to lift the needle by "half a groove"

One groove was lean, the next was rich...... so 1/2 was best!

Good to hear that modern carbs are working well for you; I might try the ZRX carbs on one of my chops; Slingshots are getting hard to find!

What have you done with the Vac advance??

AlanB

[Shuriken]

Alan, you have a good idea. I will try the bike with a richer idle mix and with a leaner one. On my 80g, I would have trouble getting the bike to idle when color tune showed bunson blue. The bike seemed to want to run richer at idle. This bike idles fine with blue color tune, but you got me thinking.

Carb circuits are designed to overlap, but sometimes they don't do that very smoothly. If I am excessively lean at idle and the jet needle is normal or rich, the circuit may stumble on transition. I don't think I'd see this stumble the other way around as much - going from a rich idle to a lean mid, but what do you guys think?

I will try to do a chop at the "problem" spot and read the plugs. May be as simple as going a little richer on the idle than I want.

The vacuum advance does not work right when connected to #2 ZRX carb port. I got around this by cutting the vacuum hose and inserting a plastic restricter into it, then reconnecting the hose. I haven't checked for full advance at X rpm, but a cursory check shows that it is working. I will further test when I get a chance. The restrictor I am using came with the Carbtune tool. I made sure I saved a leftover piece to use on my vac advance.

[AlanB]

Hi ae,

You are probably on the right trail; the transitions are the hardest parts to get right. The manufacturers spend millions developing these parts; we are allowed to take a little while to do our adaptation! LOL.....

It is also perhaps having a look to check that the vac advance isn't pulling up a little at idle; The edge of the butterfly on the XS carb pretty much closes the vac port right off at idle, a port in any other carb stays open.

Unplugging the vac hose should make no difference to the advance at idle...... although you need to cover the vac port, or the idle will wander, and possibly move the advance.

keep at it!

AlanB

[Shuriken]

I rode the bike this weekend at an elevation 2-3,000 ft lower than the bike is normally at. This elevation difference is enough to lean out the mixture and I've observed that before.

However, the sub 2k rpm stumble was still present. I would have guessed that the elevation difference would have caused some observable difference in the way the bike would operate, especially if I have a fuel mix issue.

I could not detect any difference in the stumble due to elevation.

[planedick]

Elevation

It is (was) my understanding that these carbs were constant velocity which I was led to believe that elevation wasn't supposed to have any effect on the mixture. It would make sense, looking at the method of raising the needle, one would assume that atmospheric pressure changes would not effect the mixture, only the total volume at higher elevations. I would also assume that because of the lower pressure up there that the expansion would be equal so actual horsepower would be equal. Maybe some current Albert Einstien type could figure that out.... Guru's or such.....

I have a color tune system too, but at idle I couldn't get it to fire regularly. It seemed that the spark was too high up in the tube to fire reliably at idle. Was a long time ago I tried it and on another engine even. Maybe I will try it again on this motor, but I don't have any transition issues except immediately after a really high speed run on the freeway like when showing crotch rockets tail lights and license plates. He He But then it's only for a few minutes...

[Shuriken]

Planedick,

Where I live, I see elevations of 10,000+ down to about 2,500 as well. The bike really struggles the higher I go and opens up at the lower elevations. Haven't done it in awhile, but it seems I had to ride in 2nd gear at 10,000 and up.

[petejw]

im a believer

well i thought it was about time i installed
my carbs i got from a fellow xsive, thanks heaps matt,
heres the link
http://www.xs11.com/forum/showthread...ight=zrx+carbs

these carbs are something else,
i cant say enuff about them,

these werent plug and play like i have read recently,
but compared to our old carbs these were easy 2 work on and adj.

i was able 2 use the original throttle cable but nipped of about quarter inch of the outer sheath, the cable was able to fit in the original holder after a slight twist and tweak.

i used abou 6" of a universal choke cable ($8)
to attach the choke.

the carbs attach easily 2 our manifolds, albeit i have old carb holders, also makes it easier 2 attach when the motor is warm.
ive spent the past 2 days dialling the carbs in, there not spot on
but im gettin really close.

im not sure wat these carbs r off but they are way lean,
pilot jets are 35
mains were 95,
with this set up the bike would only idle whilst warming the bike up when cold,
with in minutes the bike died and i couldnt get 2 started,
the mixture screws were 2 turns out
the needles are non adj.

to cut a long story short (2 days worth lol)
my mains atm are 125 but i need to increase this,
the needles were shimmed with 3 washers
and the mixture screws are 4 turns out,
as i said im still in the process of fine tuning but im getting really close.
im going to try pgggs specs of 38 pilots and 130 mains
i definately need 2 go up 1 size on the pilots.
ive been using this set up atm with pod filters.

ive got 2 say, my bike has never run better or faster
the off idle and mid range has increased dramatically
unfortunately i havent as yet been able 2 take it out on the highway but it redlines nicely and pulls hard from 1st to 3rd.
i still have 2 fine tune, but im so happy with this mod
and well worth the money spent.

just wanna thank the guys b4 me who came up with this mod.

pics will follow soon

for any1 contemplating these or similar carbs arewell worth the time and effort to install, the most fustrating thing of this mod was attaching the throttle cable to the carbs each time.

[petejw]

i forgot 2 add,
out of necessity i ended up using
the mikuni jets, they sit a little higher
and a little tighter 2 screw in but a little oil on the threads
helped that.
heaps cheaper than the klien jets
the pilot jets arent interchangable tho.

[petejw]

cpl pics

pic of the choke set up
i used a spare throttle cable holder to hold the cable in.




jets but there blurry sorry
mikuni jets r the larger ones on the left

[petejw]

tourer to super sports

i took the bike out for another run on the freeway
and i cant speakly highly enough of this mod.
Its like a brand new bike,
the engine is stock standard with worn rings
it has plenty of blow by and little engine braking.
This bike is now scary fast, the improvement is so dramatic.
ill go thru how i set up the carbs to work and wat pifuls i found
on the way, these carbs were so easy to work on,
and adjust.
i started with 95mains and 35pilots, the float levels were all
factory set and untouched thru out this process.
the carbs pushed into and sat well in the boots, it always made it easy to put on when the engine was warm or hot. they slid in and sat well into the boots, my intake boots are old and pliable.
the first time i put the carbs on the bike was cold, with choke it fired straight up it ran and idled beautifully, but as it warmed up the bike slowly began to die and i couldnt restart it, the bike tried to run with choke but wouldnt run past the idle circuit without stalling, at this stage idle jets are screwed out 2 turns.
i screw these out 2 3 turns and the bike begins to idle, but stalls once given any throttle.
carbs come off
i chase around 4 kliehn jets from the local supplies they have none and told me theyed cost a fortune.
out of necesity I checked out the mikuni jets,
the mikuni jets have a larger and wider head,
i had a some concerns in using these in that with the larger head
it would sit closer to the fuel level thus making it run richer, how the needle would sit in the bottom of the jet and how this may affect transition of circuits, and how the jet would screw into the emulsion tube, i had a spare set 2 play with, the mikuni jets were a little tight to screw in but with a little dab of oil they had no problem,
the jet size i used were 110
i put it altogether and started it, it idled find i could now rev it pass idle but was feeling flat, by holding the choke out the bike had sum oumph behind it, took it out 4 a ride, idle circuit fine, mid circuit bike would die but then begin to pick up, with the choke out the bike started to have sum get up and go,
off with the carbs, i start to begin to shim the needle, these needles are unadj, i have no washers, so i end up using the little round auto electric earth thingy, i cut of the end bit and round it, i put 1 on each needle, put back on bike start it nice idle i can fully rev the bike now, i take it 4 a ride, the bike is rideable but very flat can still put on choke and bike pulls better.