Worn needle jets, carbs kaput?

[Fullmetal]

Hey guys, I've been trying everything to get the carbs on my xs360 running right. The bike was running too rich no matter what I did, especially in the low and mid range. I did a bit of digging, and I found some talks on a honda forum (blasphemy!) about worn needle jets. They were saying over time, the orifice at the bottom of the jet wears away and becomes rather oblong, allowing excess fuel to drip into the circuit. ALL the symptoms they listed were what are plaguing my bike (drop in mpg, low end/midrange richness, start with no choke, fouled plugs).

Sure enough, I tore my carbs apart again and the jets had indeed lost their circular shape. I never noticed it before, or if I did, I didn't think it would have some a prominent effect. The manual on the site confirms that the needle/jets wear over time and should be replaced every so often.

But this is where my problem lies. Both the needle and the jet are discontinued by yamaha, and I can't find any trace of any NOS parts. My options are rather limited, but I've narrowed it down to 3 routes:

1) Watch eBay for a set of a xs360 bs34s, but who knows how long that can take.
2) Buy Mikuni needle/jets with similar specs and try to get the carbs tuned right with those.
3) Fork over the money for a set of Mikuni VM carbs.

Any advice would be appreciated. I'm truly at a wall here, and I'm sooo close to getting this bike back on the road!

 

[xschris]

http://www.mikesxs.net/product/48-0656.html There was a member a few months ago that used these and said they worked fine. Make sure to use new o-rings for them. What do you have your idle mix screws set at?

 

[Fullmetal]

The idle mix screws are at 1 1/4 out, any more that and it becomes too rich. The manual says to replace the needle and the jet at the same time, so should I get http://www.mikesxs.net/product/48-0657.html to go along with it?

 

[xschris]

If the needles don;t show any wear marks you should be fine. 4fp21 is the needle for your bike. Using one not metered for your bike will make it hard to tune or even make it not run. I run xs360 carbs on my 82 sohc xs400 and it runs great with 1 turn out on the mix screws, third clip on the needle and 135 mains. Is your bike still all stock? If not post pics of the mods.

 

[Fullmetal]

My bike has uni pod filters and 2-into-1 exhaust with no baffles. I had a build thread around here before, but i haven't kept up with it haha. Jetting is stock (17.5 pilot, 135 main, needle clip 3 notches down), and like I mentioned, it runs rich in the low/mid range. Hell, when it's cold the low range isn't as bad but the mid range is always horrible. Float levels are 27.5 mm, it. ran waaay too rich at 26.5 mm. They're synced whenever the slightest change is made.

The needles I don't think are worn. They're still very smooth. I was curious since the 4fp21's are discontinued and the book says to replace both the needle and the jet at the same time. With the needle being a 4- series, i was told that getting another one in the same series should be tuneable, but it's merely speculation at this point. I'm not against keeping them, though, every penny saved is a penny earned.after all.

 

[xschris]

What do the plugs look like? How did you oil the filters?

 

[Fullmetal]

My plugs get fouled pretty much every time i start the bike. NGK Iridiums. I clean them after every ride.

The filters aren't oiled. I have k&n filter oil for my car's filter, though, idk how well it'd work on the foam.

 

[xschris]

They make uni /foam specific oils. Some also use 50/50 mix of 2-stroke and gas to oil them. With your setup my guess would be something wrong in the carbs such as worn o-ring for the needle jet or the choke circuit is not fully closing/sealing. Are the needles assembled in the slides correct? It should go in the slide, needle-spacer-spring.

 

[Fullmetal]

The needles are installed correctly. O-rings are fresh, i replaced them when i first rebuilt the carbs. I went ahead and ordered the z8 jets, I'm curious to see if they change anything.

 

[xschris]

What did you replace when you rebuilt them before?

 

[Fullmetal]

Not much but the o-rings and the float needle and seats. The PO rebuilt the carbs before, so they were in pretty good shape already. He had 2 different needle seats, though, one stock and one that wasn't, so I replaced those in tandum.

Tinkering around today, I pulled out my idle mix screws to make sure they're installed correctly. Well, i noticed one had a jagged edge and was bent slightly. I looked up the part number (1J7-14923-00-00) for comparison, and what I saw was different than what I had. In my infinite squidness, have I been running the wrong mixture screws the whole time? I thought maybe the tips broke off, but there's nothing stuck in the carb bodies.

Also took a pic of my needle jets, since this what the thread is about and I've yet to include a picture of them haha.

 

[XSLeo]

I get carb parts from Niche Cycle or Jets-R-Us. They sell genuine Mikuni parts.
Leo

 

[xschris]

There is your problem Make sure the holes for the idle mix screws are not large drilled out holes as this will cause big tuning issues. They should be around .95mm

 

[Fullmetal]

It took forever to get the idle mix screws in the mail, but they finally arrived. I compared them and the needle jets to what I had already in the carbs. The z8s are exactly the same as stock. I realized the old idle mix screws are broken and not different like i originally thought. The orifices look cleared out, idk if they've been enlarged or not.

Got everything installed, tried to start the bike but now it's running extremely rich. It bogs down unless the throttle is open and twisting the throttle doesn't make the revs budge at all. I've noticed the idle mix screws are uneven, one side is out a bit more than the other even though they're both 1 1/4 turns out. Took off the air filters to see if it was just a lack of air, and the left side carb was spraying fuel out?

 

[Wolfe_11B]

Floats set right? Needle/seat good?

 

[Fullmetal]

Floats were set to 27.5mm, which is within spec. I'll have to check the needle seats but one is just a few months old. I'm thinking I need to raise the floats a bit more.

 

[xschris]

The mix screw holes where likely drilled out and are now larger than the stock size. Don't worry if one seems out more than the other. Just go by the turns out from seated. I run a set of these carbs on a stock 400 and only need to turn them out one turn.

 

[Fullmetal]

I raised the float level to 28.5mm and it's still bogging down on idle. i turned the idle mix screws in all the way and they made no difference. Beginning to think the screw holes are letting in too much gas. If i turn off the fuel line (I have a inline shut off valve between the petcock and the filter), the bike will idle fine after a minute or two. As soon as the line is reopened though, it starts to bog.

I'm gonna raise the floats to 29.5mm as a last resort to see if that'll lean out the circuit. If that doesn't do it, I might have to come to terms with the fact that my carbs might be junk =\