I’m having trouble finding Z8 needle jets on any site other than XS650 direct. Neither Nichecycles nor jetsrus has them. Anyone got an alternative supplier?
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Z8 Needle Jet
- Thread starter Wingedwheel
- Start date
MikesXS has 'em. If you look close at the pic, it looks like the Mikuni "square in a square" logo. Call 'em and ask?
https://www.mikesxs.net/yamaha-xs650-needle-jet-z8-oem-341-14941-88-00-1976-77.html
https://www.mikesxs.net/yamaha-xs650-needle-jet-z8-oem-341-14941-88-00-1976-77.html
They are labeled Mikuni on the listing so I’m going with it only because I’m needing them quickly. Funny how they are OOS on several different sites. I ordered jets, needles and orings.
Got the parts today and installed. Back story as to why I needed them. I’m 1200 mi from home in Texas taking care of some family business and I brought my ‘76 for my stop at the rally. I hadn’t ridden it last year because of my shoulder surgery and although I had taken it for a few short rides before I left for here I wanted to give it a good run to make sure there were no issues. I took off the other day and cruised a nice winding backroad I know here. The bike ran great for about 8 miles and I decided I wanted to take it out on the highway and take it up to 70-75 for the ride home. As I throttled down to turn I noticed a loss of power. Left cylinder had cut out so I was forced to turn around and limp back. I pulled the carbs off and looking in the left carb I saw that the needle had lifted completely out of the jet and was stuck. Well I had pulled those carbs apart back before the surgery, cleaned them and replaced the butterfly seals but they had run well before that and I didn’t remember messing with the needles. Upon inspection I found them to be incorrect( nobody to pin that on but me) and thus the order and replacement. When I first fired it back up it ran and idled well but as it warmed it would race when I blipped the throttle and not idle back down.I looked at everything I could think of, adjusting the cable, removing the cable all to no avail as it still wanted to rev up.it appears the throttle shaft is sticking and it’s obviously not the cable so tomorrow I will check the butterfly’s to see if one is sticking or slightly off but it just confounds me that it ran fine until the needle incident. Carbs were vacuum synced two weeks ago.
I didn't think it was possible for the needle to lift out of the needle jet. I thought the carbs were designed so that couldn't happen (long enough needle combined with tall enough needle jet). But you said you had the wrong needles in there? They must have been shorter than the correct ones? But a shorter needle would run rich.
5T I didn’t think so either but it appears I used some re-pop Y-22 which in your comparison pics is slightly shorter than the 4M-1 that is called for. The plugs showed it was running rich.
Upon inspection there is a slight side-to-side movement which doesn’t appear to hang up but when running the vacuum may affect things? I’ll try to loosen and adjust the butterfly’s.
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Butterfly’s adjusted and no more slop, returns nice and gaps all appear equal. I installed the carbs and got a decent idle but as it warmed it was still revving up. No air leaks so my next thought was look at the advance weights and this is what I found.
Of course this is all happening away from home but fortunately my BIL has a great shop(retired diesel mechanic/axle surgeon) and I brought a few tools. He has a buddy that runs the service dept at the local powersports dealer and works on older bikes so we headed up to see if he might have a spring lying around. Well he got on his computer and found two springs at a dealer in Louisiana about 90 miles from here. After a quick call to confirm they actually had them the parts tech told me they close early today so Monday morning we’ll take a road trip and pick them up.
All this happening while I’m not at my house is a little stressful because I need this bike ready for Arkansas.
Of course this is all happening away from home but fortunately my BIL has a great shop(retired diesel mechanic/axle surgeon) and I brought a few tools. He has a buddy that runs the service dept at the local powersports dealer and works on older bikes so we headed up to see if he might have a spring lying around. Well he got on his computer and found two springs at a dealer in Louisiana about 90 miles from here. After a quick call to confirm they actually had them the parts tech told me they close early today so Monday morning we’ll take a road trip and pick them up. All this happening while I’m not at my house is a little stressful because I need this bike ready for Arkansas.
Yes, grab up all the original advance springs you can find, they're like gold, lol. I've scored a few N.O.S. ones off eBay over the years and still look for them from time to time there.
3.5 hour road trip to pick these up. Spending the morning eating Cajun meat pies helped with that. Natchitoches LA. Small antebellum town with lots of history.
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Well it fixed the broken spring but not the issue. Bike will start and idle fine and you can even roll the throttle a few times but revving comes back as the engine warms. I’m baffled and a little frustrated right now because when I got here two weeks ago it ran well and I did take a spirited ride on it. That’s when the problem with the carb developed and since then it’s like chasing my tail. Carbs are clean and functional with no air leaks around the boots or seals. Throttle cable has been adjusted several times in case that was pulling when the handlebars moved. Found the bad spring and replaced both and while I was in there I greased the shaft and lubed the weights. They snap back with no sticking. I’m missing something here…
Carburettor butterfly shaft seals condition, perhaps?
Recently replaced and spraying around them yields no evidence of leaks.
What's your idle speed set at? You don't want it any higher than 1100 - 1200 RPMs (warmed up motor) or the ignition can start advancing. As that happens, the RPMs increase, which causes more advance, then more RPMs, etc. It's sort of a "self feeding" problem and the bike can end up running at 3K+ RPMs without you even touching the throttle.
Idle speed set at 1100 and it idles fine until it gets a touch of throttle then the revs start. I can shut it off and start it right back up and it idles fine. Touch the throttle and away she goes. Timing is spot on. I vacuum synced the carbs before I left on my trip but will do that again in the morning.
I'm with 5twins... that sounds like a runaway advance. Could be your tach is off a bit and you're actually at 14-1600revs. You have access to a timing light where you're at right now?
Yes Jim I have a timing light and I played with that a bit to make sure it was right. I’m not running a fast idle, I’m pretty sure the tach is accurate. What starts it is the throttle. It starts like a hanging high idle then escalates from there.
Edit: I do agree it’s acting like a runaway advance but with my idle set correctly what’s setting off the advance?
Edit: I do agree it’s acting like a runaway advance but with my idle set correctly what’s setting off the advance?
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Upon hindsight and since you guys know much more about this than me I’ll turn the idle screw down and see what happens.
What I was getting at is use the light to see if the advance start moving as soon as the revs do.
Let it idle, then use the idle screw (not the throttle) to slowly increase revs. Watch the light. Soon as the revs hit that magic point where they take off, watch and see what the advance is doing.
Might happen to close together to know what came first. On the other hand, might give us a clue.
Let it idle, then use the idle screw (not the throttle) to slowly increase revs. Watch the light. Soon as the revs hit that magic point where they take off, watch and see what the advance is doing.
Might happen to close together to know what came first. On the other hand, might give us a clue.
I turned the idle screw out and it cured the revving however I can’t get it to idle over 1K without the revving coming back when blipping the throttle. I have a few more adjustments to check but you guys were right about the idle setting off the advance. I’ve never had this issue but at least I’m headed in the right direction.
