1989 XT600 - Needle Question
 

Hey Folks,

I'm in the middle of tracking down why my bike is running to lean. I'm pretty sure I've got an air leak around the throttle shaft through the carb and have order a few parts and gaskets to resolve.

After looking over everything I notice that the needle on the primary carb has some play in it, up and down. Not much about 1/8" up and down. Is this normal for the needle to be loose? The holder it's in is as tight as it goes. I was going to move the the adjustment clip down one notch to try and move more to the rich side.

Symptoms of my bike include the secondary not closing (stuck throttle around 3500rpm) inconsistent idle, popping or sneezing through the intake and a good backfire on deacell. I did the find the leak with carb cleaner and the idle changes when I spray up around the top of the carb. Also, after thinking my cables were gunked I replaced them, however this didn't solve the issue. If the throttle is wide open it will snap close, if the throttle is half open it won't snap closed, almost if it doesn't have enough force to close the throttle when only opened half way. This is what is leading me towards the throttle arm, or perhaps the spring (which is now obsolete).

Here's what I've done so far:
- Cleaned Carb
- Replaced gasket on bowl and top cover (primary)
- Intake boots good
- Replaced throttle cables
- Ordered: needle valve set, main jet (#125), jet gasket, pilot screw set, throttle arm gaskets, short hose between carbs.

Any help would be greatly appreciated!

Dont worry thats normal. The needle is getting bigger at the end but if its out very far it has some space so the air/petrol can get around it ;)

If it's truly an 1/8" up/down that too much . You should check that all the parts are there above the needle to hold it down . It should have a little movement(maybe .015-.02"IIRC) but no 1/8" from what I remember with mine, has been a while since I had any of mine apart and am used to FCR's lately .

Here's the parts that you need . Yamaha Motorcycle Parts 1987 XT600T CARBURETOR Diagram


There should be a gasket under the cap on the primary carb to stop air leaks , The seal on the throttle shaft do go bad so it is quite possible they're leaking .

If your secondary carb is clean inside and the bore smooth with no corrosion pitting you likely have a weak spring for the slide . You can use springs from modern Mikuni CV carb but it is tough to know which spring rate to use , trial and error . I'd try this one , http://www.partzilla.com/parts/detai...286-00-00.html

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That's the diagram I used to order the other parts (through Boats.net). There are a few that I wanted to order that are now obsolete, including the Jet Needle Assembly. Which I also can't find any photos of as to see what I'm actually missing. Heres a picture of what my carb has, I believe I'm missing a second poly washer and maybe a small spring? I can't find photo's of one anywhere. I also wanted to replace the choke assembly as it doesn't seem theres an gasket or o-ring so maybe the shaft is worn out and leaking air. I've tried calling my dealer to try an order both 49N-1490J-10-00 and 5Y1-1410A-00-00 and they can't find anything. The parts cannot be crossed referenced. Ugh..

http://i.imgur.com/TwO9Dam.jpg

The secondary slide moves freely up and down and does return to the top. The spring on the shaft snaps back nicely. The only thing I noticed was the butterfly valve, when at WOT is not horizontal. It goes past that position, so maybe I can align this once the carb is back together. Any idea how to do this? I know there's an adjustment screw but I believe that is for setting when the secondary turns on.

Here's a picture from my Clymer. I do believe I'm missing a couple of pieces, I assume a previous owner let that spring get away on them. I'm at a bit of a loss since I cannot order a replacement. I'm wondering how tolerant the pressure on the spring is and if I can replace with something similar, this might sound stupid but it looks to be the same size as something you'd find in a pen, just shorter.

http://i.imgur.com/DO2ZgIW.jpg

Ya your missing the spring and a plastic spacer about 1/16" thick that goes under the spring on top of the needle, there is another plastic washer that goes under the needle clip as well but can't remember exactly . From memory a pen spring will probably work , the original Yamaha one isn't that strong and is about 10mm long . Main thing is that it keeps the needle pressed down and help stabilize it from vibs , right now yours is probably bouncing around and playing havok with jetting .

For replacement parts like this I used to have a spare carb set but it's been mostly scavenged of useful parts . About all that's left is buying an overpriced setup off ebay . I'd try the pen spring , I've used those springs for quite a few things over the years , surprising how useful they are and why before throwing an empty pen away I usually grab it and toss it in my junk drawer .


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Quick Update - I got my parts this morning and got them all installed in the carb. Bike is working top notch, no hiccups, no irregular idle, and no throttle stick! Adjusted when secondary opens and adjusted idle screw. F@CK YEAH! Purrs so nice now and I can even drop the idle speed to the proper 1300-1500 rpm and run smooth.

One thing I wanted to find more information on was tuning the carb. I noticed a slight drop in power (might be my head). When I got the bike the carb had a #130 jet in it. I replaced it to stock - 125. Would this drop my power a bit? Can I put in a #150 jet and get more power?

They should be plenty rich stock, like most aircooled bikes. Dont go above the stock size.

It'll make the most power at 12.8 a/f ratio , don't know what they are stock but I'd say it's somewhat leaner than that . A 150main would be way too far , I'm only running 125's in my heavily modded motor and it is running low 12's on my wideband .

Hope the link works, this is my bike at around 50.000km
Snorkel removed, the end of the exhaust removed, and pipercross foam-airfilter installed. Otherwise totally stock, and pleeenty rich at the mainjets.

Yamaha XT 600E

I know it's been a while...
 

Hi, I know this page hasn't been touched for 3 years but...
mesheau did not specify what was making his throttle stick or if he managed to adjust the butterfly valve back to horinzontal instead of slightly past it.
My bike has the same issues... slightly stick throttle and the butterfly goes past the horizontal at FOT.
Thanks!
David

OP had only a few posts on this thread then gone.
in short, sort out the stickiness by disconnecting stuff and seeing where it happens or when it stops.... often it's just the cable routing and its internal lubrication.


dont worry too much about the valve plate angle, how many times do you apply full throttle anyway? :)


if memory serves me right, you can tune the plate angle between the carbs while holding full throttle