hitachi (i think) carb question...

on the top, engine side of the carbs, there is what looks like a fuel screw. i just got this bike, these are new carbs to me. i have the cabrs out and cleaned them, and noticed that the screws were 3.5 turns out. for all of the other cabrs i am familiar with (kehein FCR is my fav.) anything more than 2.5 turns requires a rejet.

is this a pilot screw, and how many turns out should it be??? (i know not all bikes are the same, im just looking for a starting point)

 

Those are the Pilot Mixture Screws.

XJ-Bikes were set-up slightly Lean at the Factory ... 2.5 ~ 2.75 Out.
Factory Pre-set.

After a generous amount of feedback from members who have Colortuned ...
the consensus is that the Pilot Screws NEED to come OUT to 3.0 (Or greater) to achieve a smooth Idle and to have enough Richness to sustain Ignition when the Throttles are opened for the brief duration of Fresh Air preceding the Main Jet Supply.

The Final Analysis is on an Engine to Engine basis.
Read your Plugs.
Adjust one or more of the Carbs to achieve the correct coloration.

This means you might have to Enrich or Lean-out individual Carbs.

That's OK ...

We're Issuing YOU a License to TWEAK!

 

ok then, THANKS!

 

Rick, MiCarl has my 550maxim and when he got it tuned, he was 0.5 from fully closed...

those babies were running awfully rich apparently at 2.75 out...

ive not ridden it yet (waiting on better weather and a few other little things) so we will see how it runs but theres quite a difference between 2-3/4 and 1/2...

 

What size pilot jets are you running? Sounds like maybe you could drop down in size? Just asking....I'll sit back and wait for the experts to weigh in.

 

LT:

I'm not exactually sure about this ... but, when I put the NEW Pilot Jets in your Carbs, they were different from the Bad ones we scrapped. I wish I saved themm to be able to know for sure ... but, I do know that the ones we put-in were probably a size up ... because they were the ones with the side holes inn them and the ones we couldn't fix didn't have side holes.

I had to drill-out two of them ... so I never looked at them close.

I'm glad MiCarl is out Central US Agent and got you Dialed in.

It would be nice to have Regional Carb People that Members could visit and get tuned-up like MiCarl did for you.

There doesn't seem to be too many Members from New England anyway.

 

i noticed that!

now to hijack my own thread... has anyone changed to a pumper style flat slide carb? these vacuum slide carbs are the first thing we throw away on the quads, for performance reasons (no throttle response or power!)

im thinking that 2 kehein FCR 40mm's would feed this 750 just perfect, and they have a kick ass whistle sound to them at part throttle.

any thoughts?

 

I have never seen anyone hang a set of those Flat-side Rollers on a XJ-Bike

I know the Carbs you have in mind. The Choice of High-Performance Racing Teams as of late.

You might find there is a Kit, complete with Intake Manifolds available.
If there is ... Tuning for the 750 is going to be a situation where you'd want to have them Dyno-ed.

If you have the scratch to make it happen ... all the more Power to you, my friend. You'll be living at the high-end of the tach most of the time!

You won't have the restrictions that trying to re-jet Hi-Tots have.
Those Kay's have a whole board of Jets and squishers to make lots of power happen; fast!

Just hanging them on your Bike is going to be the tough opening act.

(Be really careful taking-off the Stock Intake Manifolds. The Cap Screws holding-on the Manifolds are crap soft steel and will BREAK right off if you sneeze on them wrong. Don't break-off a Manifold Cap Screw or you could be wishing you had a Race Team to help you do the Drilling-out of the broken fasteners.)

 

bought the bike with 3 broken bolts, 2 were for the right boot and it was gorilla glued onto the engine. driling them out is todays project!

 

Zookie:

You got your work cut-out for yourself. Do you think the Kay's are going to fit the Yammie without a custom manifold of some kind?

That could be more than you bargained for.

I;ll keep my eye on this thread and wish you luck!

 

It will be interesting to see how this plays out. I'll be watching intently.

 

well i thought long and hard about it, but for a first time on road bike rider, i dont need the "race" characteristics of FCRs for my first season out. maybe for the winter rebuild? i really think it would be easy to do, and undoubtedly would have a power increase over the vac jobs.

as for the broken bolts.....DAMNIT!!! i hate this kind of work. and i checked the other bolts before i packed it in for the night...they are going to break. so im raiding my toolbox tomorrow and im going to bring home my "bag of tricks"....the snap-on air chisel with the 3/8 socket attatchment. im going to see what happens after i pound on the bolts for about 5 minutes. im hoping they get scared and fall out.

if more bolts break i think i may pull the head, its really tight in that frame with a drill!

 

almost forgot todays carb question......

WTF are the "jets" that stab through the intake boots (box side of carb) and run a hose to the bowl ? are these needed or can i junk them and cap the bowls? i dont see how they can do much of anything unless the engine is turning at 10k. maybe im wrong, but i figured id ask before i chucked them.

 

Those are "Dial a Jet" External Jets for many applications.

Don't trash them.
Stick 'em in a box and send them to me.
I'll be happy to find a use for them.

Dibs.

 

so were they factory, or a previous owners attempt at getting the thing to run?

 

PO.

Aftermarket all the way. You are supposed to be able to Dial-in the extra Fuel you need from being lean by hooking-up the Fuel Bowl to the Manifold.

You see them more on the really big bikes than you do on anything less than a 1,000 cc.

http://www.thunderproducts.com/dial_a_jet.htm

 

well i'd like to hang on to them until i get the bike running, but once its running trouble free without them, they are yours rick!

im not sure if i should continue in this thread or start another with this question.......

i will be doing pod filters, and harley sportster mufflers. these are set lean from the factory (i think all bikes/sled/quads are...), so going from 120/40 to 125/45 jets would be high/low/good start ????

on the atv forums i frequent we have a "jetting database" thread, where everyone posts up thier engine mods, altitude, exhaust setup, carbs, and what jetting/screw turns you are running. is there a thread like that here? i looked, came up with nada.

 

Mainly because that are a slim few that have nailed it down.

The Pods and Jets can be orchestrated to give you good Low-end and Wide Open Throttle.
What happens inn the middle is the realm of the Diaphragm Pistons and the Needle Valves they lift out of the Main Jet Emulsion Tube.

To get the Midrange you will want ... You will have to alter the Emulsion Tube's air Holes and "Do something" with the Main AIR Jet. Probably a larger one I would suspect.

Although I know WHAT needs to get done. I have never once done it and therefore have NO advice for you on what or how to get the Midrange performance that will be hard to tune-in once the Pods are on the Bike and the Stock Airbox system abandoned.

It would seem logical that the Emulsion Tubes would need to be altered to allow move Main Air in to draw-up additional Fuel when the Diaphragm Piston Rises.
Perhaps having the holes on the Emulsion Tube graduated from Stock to a Larger diameter toward the top is in order.
Certainly more AIR needs to be introduced to affect the amount of Fuel Drawn-up through the Tube.

That my friend, is the Experiment you need to solve. A mystery without clues so trial and error is the only method.

Not so elementary ... My Dear Watson!

 

so what you are saying is i should just buy the dynojet kit, because it sounds like an aggressive needle profile would solve the mid-range woes. i WILL get this perfect (carb perfection is what lets me win my races against heavier built machines), and i will post up my findings for others to copy.

still have some hitachi questions....these are still a little foreign to me. they are nothing like the mikuni cvk's that are the only other vac slide carb i dabble with.

maybe we call it something different, but what is the emulsion tube?
also, the main air jets are the ones found under the plate under the diaphram? if not wtf are those little guys, and where are these air jets?

 

The Emulsion Tube is the Brass Tube the Diaphragm Needle slides down into when the Piston is all the way down.

You remove it by pulling the Main Fuel Jet and Washer and pushint it uo through the top of the Carb.

Maybe you call them Nozzles.
Most Old School people refer to them as Nozzles.

The two AIR Jets are topside under the plate.
The Large one is Pilot Air
Smaller one: Main Air

You can ditch the plates when you assemble the Carbs.

 

nothing feels better than chucking useless parts!!!

thanks for all the help/clarifications!