XS360 needle jets

[cosworth]

So recently I discovered mine were worn out. Badly worn needle jet and badly worn jet needle.

The XS360 had an X-6 needle jet or "emulsion tube" stock whicxh are discontinued. But the X8 apparently works in place and you can buy NOS X8 jets still from the XS650 vendors. But these are in limited supply.

I poured over the available spreadsheets that show the dimensions for the needle and found that an XS650 needle LM1, dropped down to slots will produce numbers that should compliment the carbs with the obvious non-stock exhaust most of us run.

Looking at this spreadsheet I pared down, you can see the critical variable dimension highlighted is 16.9mm. Stock it is 14.9mm. changing this number on my spreadsheet moves the numbers on the left for the LM1 needle closer to the 4FP21 specs that the XS360 uses. Dropping the needle profile 2mm into the jet gets it close enough. I have ordered some needles and am waiting on some X8 jets. Living in Canada sucks ass sometimes because mikesxs won't sell to me. But there are other ways to get a mikuni X8 here within monetary reason lol.

Of course using the needle assumes you want or can utilise a bit richer midrange fuel delivery. I'll report back soon with some results.

 

[cosworth]

I also have the spreadsheet here

$fixedlink$

 

[BBS360]

Any luck with the alternate needles?

 

[xschris]

https://www.mikesxs.net/yamaha-xs650-needle-jet-z8-oem-341-14941-88-00-1976-77.html I think there was a member that used these and said they looked the same as stock. No word on the needles.

 

[cosworth]

I installed those z8 tubes at a hefty price since I am in Canada and mikes a won't ship here and their "Canadian" site won't stock them. I can't be bothered with business practices like that.

I digress. Ok so the z8 are in and the other needles ran like shit. No go. I'll scout eBay and take a gamble on finding some buried in a low mileage carb. I have two sets of xs400 carbs sitting here but I'm trying to keep it stock.

I have a friend who is amazing at metal casting very small parts, he does jewellery. He has an xs400 too lol. He said even if I found brand new ones for him to copy, the shrinkage after cooling would render them useless.

It's been suggested to cover the non worn area and plate the word area, then sand with 2000 grit to blend. Seems extreme, but you just cannot buy these any more.

 

[xschris]

I read some of your old posts and you said you are running larger main jets. What jets are you running now and what clip are the needles at? The original problem was fouling a plug and hesitation at higher rpm's.

 

[cosworth]

I have the carburetter jets all stock. The new needle is set one ring down in order to emulate the stock needle. In this combination it still runs like a dog. 135 mains.

Putting the carburetter back to totally stock, with stock needle runs best of all combos, but not very well. 132.5, 135, 137.5. Screws between one and three turns out. The LM1 needle on the second clip is the closest emulation of the 4FP21 stocker.

Long term, if I were judging a concourse event, and saw an xs360 with xs400 carbs, I'd cut them slack.

 

[xschris]

Have gone through the ignition well? Points, timing, condenser and ATU. If your ATU has not been taken apart, cleaned well and lubed your timing will not advance as it should and you will have poor power. Have you done a compression test on the motor?

 

[cosworth]

The motor is in great shape. Compression is excellent, bright spark, points are great. The needles are worn. Not sure how that is not getting across. Idles great, full throttle is good. 1/4 throttle to 1/2 throttle it's rich and boggy. The needles are really worn. It needs new needles so that it doesn't run rich in that range.

My experiment with the LM1 wasn't good enough. And that is as close as we will get unless someone magically gets some made.

 

[BBS360]

I was looking at the chart on the weekend. The XS400's 5Z1 needle looks closest to me. Slightly richer but closer than anything else unless you go to a leaner needle.
You can actually punch the needle numbers into the angle chart and it fills the lines in to compare needles visually. The chart isn't a totally accurate visualization but pretty good to compare.
There are some others that look close but none that are available.

The LM1 needle tapers to a much, much larger angle, making it much richer once you get to that RPM.

Might be feasible to machine/hone a leaner needle to the correct angles.
Probably a difficult item to machine from scratch even with the chart numbers.

Speaking of, the spreadsheet lists two different taper angles for the 4FP21. One page says 1.5 while another says 1.3.

 

[xschris]

The 5z1 needle is much longer than the xs360 ones.

 

[BBS360]

According to the spreadsheet only 6mm longer.
The 4FP21 diameter at the tip is similar to the diameter at the matching point on the 5Z1.
I'm just suggesting that if someone is desperate it could be used.
If it's even necessary it'd sure be easier to trim a few mm of the end than it would be to hone a larger needle down or machine one from scratch.

For that matter, the XS250's 4Z1 or 4HX15 are real close too. Much closer than the LM1.
The 4HX15 might be even better than the 5Z1. Only 1mm longer than the 4FP21. Tapers both start 1mm sooner but the clips could be adjusted.
Slightly richer at the first taper than 4FP21/5Z1 but right between the two at the second taper.
A good compromise in a world where 4FP21's don't exist new, and Keyster makes a kit for the 250 with their 4HX15 replacement.

 

[cosworth]

So after a lot more fiddling and messing about with metric o-rings, I had found that the stock x6 is quite a bit different than the z8. I measured with a digital calliper and they appeared the exact same. I got out my fancy numbered drill set and my welding tip cleaner. The x6 emulsion holes aren't the same as the z8 and the spacing is very very slightly off.

Long story short, worn 4fp21 needles will work with NEW z8 emulsion tubes. But drop them one clip down to lean it out since the z8 will run rich. And one half turn more on the fine adjustment screws. 2 out for me at sea level and sorta chilly.

Runs way, way better than the totally stock and worn out setup. The LM1 needles all the way down we're still too rich. Knowing the z8 tubes are that much more richer I may look at some other needles. But for now it runs with worn needles but new emulsion tubes.

 

[BBS360]

Seems like a lot for slightly worn needles. Mine have similar looking wear but I can't detect any actual depressions or narrowing of the needle.
Seems like it'd have to be pretty significant wear to affect things much.

I did happen to come across an ad for a CNC service for milling small parts.
Don't have a quote but with the needle specs from the spreadsheet it may actually be feasible to get new needles milled.

 

[cosworth]

Yeah my close friend has a 5 axis cnc. For now I'll take the bike as it runs.

I should be looking for another tank decal set, piston set, gasket kit and needles if I want to keep it as long as I do.

 

[cosworth]

Ok, a little update. After spending a bunch of time messing with clip height in the spreadsheet, knowing the Z8 runs rich, the nearest is the 4HL12. Putting the digital calipers on the worn needle though, shows that using a worn needle is better than using a 4HL12.

 

[cosworth]

Real update.

I chucked some brass rod and turned it down to 0.137", then drilled the needle jet with a numbered drill. Heated up the jet and press fit the rod in. Then redrilled the needle jet. Tidied it all up in the lathe as close to stock as I could. Also, I anodized the needle, the bike runs great now with the plug showing dead on jetting.

There is a hesitation at 6000 rpm I need to sort out as either fuel or spark related. I'll put a one step bigger main jet or some coils from my other harnesses. Or try a colder plug. Or a warmer plug. It feels like flameout, but who knows.

It felt good to know that the wear items in the carb can be maintained.