Need Favor/help with carbs...

Sci85

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Hi guys,

I've been fighting a high idle issue since I rebuilt my engine. I've cleaned my carbs several times, put in all new jets, inspected the diaphragms, replaced the shaft seals, new intake boots, etc, etc. I even bought a 2nd set, rebuilt those, replaced the shaft seals on those as well and both sets exhibit the exact same high idle.

I'm really at a dead end at this point. I'm beginning to wonder if I have some kind of weird electrical issue or a crack in the head or something. All indications point to a air leak but after trying two sets of rebuilt carbs that act exactly the same way, I'm beginning to question if this is indeed a carb issue or not.

So, I have an personal request/favor to ask:

Would someone be willing to install my carbs on their bike and see if they operate normally? Or, if you have a KNOWN good working set that you would be willing to let me try on my bike? I will pay for shipping both ways. I just don't know what else to try at this point and this seems the only way to determine if possibly there is some other thing going on.

Please let me know. I would be forever indebted for your assistance.

My bike is a 1980 model running BS34 carbs.

Thanks,
Sci85
 
I would be willing to do it, but GGG or 5T or ol' Griz would be the guys you need. They might spot something and have the parts handy to fix it.
 
Uh, thanks for volunteering me, xj, but putting one of those carb sets on my modified motor wouldn't accomplish much. Sci, I can't promise to find the gremlin, but if you want to trailer that scoot 100 miles or so I'll give you an afternoon of free troubleshooting. Send a PM with a phone number and we'll talk.
 
I would be willing to do it, but GGG or 5T or ol' Griz would be the guys you need. They might spot something and have the parts handy to fix it.

Thanks xj. I've replaced all the wear out parts except the diaphragms (which I've checked on both sets and patched). I don't think will need any parts. I just need to determine once and for all if it's these carbs or something else. I know it's kinda drastic but I don't know what else to try. I'll have a conversation with Griz and then get back with you. Thanks again.
 
Thanks xj. I've replaced all the wear out parts except the diaphragms (which I've checked on both sets and patched). I don't think will need any parts.
Did you replace the float needle and seat? What with? Set float height using a ruler? Did you adjust the pilot metering screws? Replace the screws? What with? Got carb cleaner coming out all the little holes at the front? Check for throttle shaft leak? Throttle shaft centered right? My experience with mine is if you just follow the book it just works. Unless you've gotten crappy parts. Which are mostly documented here.

Didn't mean to volunteer anybody :) Right after I posted I realized I volunteered youse guys. Then I realized they're technically not volunteered until they take the initiative with a step forward. But I strongly suggest you take Griz up on his offer. Think he would get a kick out of it, else he wouldn't have...volunteered. And no doubt the scoot will benefit.
 
yes sir, done all the above. You may have seen my other thread when I first started trying to fix this issue. The only non new part on the original set are the diaphragms. I have:

  • New pilots and mains (45 & 137.5 running uni foams and straight through baffle exhausts)
  • new float needle and seat
  • new fuel screws and orings - 3 turns out
  • new fuel tee
  • stock needles and slides
  • choke plungers checked and cleaned
  • diaphragms checked and patched (one pin hole in one of them) - thumb test looks good
  • float levels set at 27mm
  • throttle shaft seals replaced with new OEM ones
  • All passages cleaned out, poked with properly sized guitar wire, blown out with carb cleaner & compressor air, checked for proper flow...all looking good

Bought a 2nd set of carbs - cleaned, poked, sprayed, replaced shaft seals as well with oem yamaha, yada yada. Exact same problem...

Spraying directly on the shaft end seal with starter fluid through a straw does affect the idle even after replacing both carbs shaft seals. Not as much as before seal replacement but will get a little bit of a burble out of it. I just can't see how two different sets of carbs, fully cleaned with new seals, etc can have the exact same problem. Surely no one, not even me, can have that crappy of luck. I get no response spraying around the boots (new as well btw) or the boot to head junction.

I've thought about grabbing a newer set of CVK's but before I do, I really need to determine if I am just the unluckiest person on the planet or there is some issue besides the carbs contributing to the problem. I've read of electrical issues causing idle problems. At this point, I just need to eliminate something definitively you know? For my own sanity. If I could just get a set of known working carbs to try, that would be ideal. Or someone try mine. Either way, it would narrow it down.

I have reached out to Griz. Unfortunately, he's 2.5 hours away from me.

Like I mentioned, I'll pay shipping both ways. I might even throw in some cash. I've done about hald a dozen engines before and never had this much trouble. I'm getting desperate....
 
I've been back and forth on my '77 swapping carbs. I'm going to readjust the cam chain and valves......vacation first. If that don't work I'll be swapping out the TCI black box. Fortunatly I've two others to ride on in the meantime but I'm starting to look beyond a carb issue. Eventually I'm gonna find what the problem is......glad this boat is big enough for the both of us......lol
 
Thnx xjwmx I'll be sure to find some extra duties for you...... Clear something up for me? Fast idle?
Always fast no matter how far you unscrew the idle stop screw, it just keeps racing? did you try running it with the throttle cable off?
Or hanging idle, it will idle but once revved it does not want to slow down, unless you drag it down with some clutch release then it will idle?
Has timing been checked with a light is it getting advance retard as it should?
anything unusual about starting, kick back anything like that?
Doing some traveling starting Friday or I'd take a look. I have a fully rebuilt set of BS34's going on Period Piece but haven't run them yet.
 
Are all the brass parts genuine Mikuni?

Got them from 650 Central so I do believe they are genuine.

gggGary:
Ok, it starts just fine. Will normal idle until it gets warmed up. Blip throttle, idle goes high, like 3k rpm and stays there. If I back off the idle adjuster to force it down, the idle WILL drop. But, as is obvious, with the idle adjuster backed out, it won't stay idling as it's set too low now. So, turn the idle adjuster back in for normal idle, and up it will go again to 3kish. Carbs are perfectly synced with a manometer. I've checked the cable for binding. It's brand new and run without any sharp bends. I've tried to force the throttle plates closed by hand to check if they are not fully closing. No effect. This is why I need someone else to try. I'm out of ideas and maybe I've just been fooling with them for too long and am missing something...

I haven't checked the advance since this is an 80 model and I can't adjust it. I don't have a strobe at the moment or I would at least take a look. Mine's broke and I need to get another just haven't gotten around to it...
 
...I haven't checked the advance since this is an 80 model and I can't adjust it. I don't have a strobe at the moment or I would at least take a look. Mine's broke and I need to get another just haven't gotten around to it...

That's the direction I'd pursue. A couple degrees retardation can help stabilize a touchy idle...
 
I haven't checked the advance since this is an 80 model and I can't adjust it.

A couple degrees retardation can help stabilize a touchy idle...

If the brass parts are genuine there will be a little Mikuni symbol on them. He sometimes sells parts from Mike's. I had some trouble with Mile's float valves. Worked ok for mos. Then rubber tip swelled and jammed up totally from something in gas. Original float valves, actually never heard of a problem with them. No need for you to have replaced probably.

Regarding changing the timing. You can take the pickup off the stator. I think I slotted the blank screws with a Dremel and just screwed them out. How to do it is here somewhere. Next there are two kinds of pickups, ones that are slotted on the top and ones that just have a hole on top. Once you've replaced the screws, on the slotted ones you can change the timing by the position of the screw in the slot. In the ones with just a hole, you can change the timing if you Dremel the hole into a slot. To retard the timing you'd dremel to the right, so that you can move top of the pickup in the direction of rotation (CCW).

As a last resort, in a matter of days I'm going to be going through my carbs. While they're off I could put yours on and see how they do. I can't send anything by UPS here though. THe nearest UPS office is 35 mi. away.

P.S. I think the pilot screws you can get nowdays are significantly different from the originals,, I think I remember LittleBill going on about them. My carbs still have the plugs over the screws and I wouldn't dare touch the screws for fear of killing them. So instead of turning the screws out I richened the mixture a hair by raising the floats about a half mm. from normal. On a different bike with the same carbs the screw was stuck and destroyed it getting it to move. Luckily had a friend with a donor carb I got a screw out of. Donor carb was screwed in some way -- excellent mechanic but said that carb simply would not work. I'd guess metal in a passageway. Also -- I would not suggest the guitar string thing. It is much harder than the carb metal and there is a bad risk of enlarging the very tiny holes. If I had to do that, I'd use copper from a stranded copper wire.
 
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damn I really feel for you dude.
I had exactly the same issue with my carbs and spent an unspeakable amount of hours troubleshooting the carbs . They were off and on more times than a pair of rabbits .

i found a lot of issues in my travels and as I had a fully electronic ignition and advance system I knew it couldn't be an ignition timing fault fortunately .

Here is what I did to cure my hanging idle which is invariably due to either a small air leak on the inlet somewhere or the throttles not fully returning . I am not exactly sure which solved the issue as I did several things at once .

1. Apply Liquid Threebond gasket cement to either side of the inlet rubber gasket to totally eliminate an air leak at the cylinders. Glue and forget.
2. Remove both the choke assemblies flat them on some wet n dry and apply Threebond to both sides of the choke body gaskets before refitting.
3. Eliminate any side to side movement of the throttle shafts by adjusting the white plastic shaft shims either side of the throttle butterflys
4. Re-centre the throttle butterflys by the snap throttle method . Loosen butterfly screws snap throttles several times to centre the discs then retighten.
5. Make sure that you can see no light around either butterfly disc and they have a perfect seal when fully closed. ie back out stop screws fully.
6. Either renew the throttle return springs or increase the spring tension by turning them clockwise 360 at one end or add an additional return spring somewhere on the throttle shafts
7. Carry out a diaphram/slide test ie 15-20 seconds for slide to fall with finger blocking top vent. Apply a smear of vasoline around the diaphrams to improve seal if necessary.
All of those are aimed at eliminating any tiny air leaks that is often all that is needed to give a hanging idle issue ie an idle that stays high when throttle blipped and slow to return on deacceleration.
couple of vids that may help.
 
I like peanuts post...
I haven't had to do anything as drastic as some of the measures he took on 7 or 8 sets of 34's I've done. I DO have the luxury of not going forward on a set that's really F'd up but HAVE brought back some pretty grotty looking carbs as much out of stubbornness as anything.
Are you using GENUINE Yamaha (mikuni) throttle shaft seals? Nothing else will work well, they need to be installed with the C facing out, flat side facing in. I see some fleabay(g) is selling screws and seals in a kit, looks like mcmaster carr or some other square o-rings in the kit, those will NOT work (yeah, I tried them ONCE years back).
The "snap the throttle shut to center butterflies" no light around the butterflies IS a big deal, skip this step and you will never get good throttle action. (Thanks to 5twins for this valuable advice)
Note the two throttle return springs for left and right carbs are different lengths they will cause problems if installed on the wrong carb.
One other arcane gotcha is the order of assembly of the jet needle stack in the piston. if the needle is forced sideways it can hang the piston keeping it from dropping fully. When assembled correctly the needle should have a bit of wiggle room so it can self center in the needle jet at the venturi floor. One time i tried two shim washers on the needles and found the spring above bound up the needle causing an "unfixable" hanging idle, only room for one shim washer in there. Also the plastic "pill" installed on the needle has a little tang that must be aligned with a hole in the piston when installed.
 
From what I can tell, the butterfly's are opening and closing properly. I followed the advice to do the "snap" process to center them and I did that on both sets. But, maybe another set of eyes more familiar with them can see something I'm not.

The slides and needles I didn't mess with. They seem to operate smoothly. Jets are genuine Mikuni. They have the little Mikuni stamp on them. And the shaft seals I ordered from the dealer. I'll get a new timing light this weekend and take a look. Doesn't seem like this could be it but worth checking just in case.

As a last resort, in a matter of days I'm going to be going through my carbs. While they're off I could put yours on and see how they do. I can't send anything by UPS here though. THe nearest UPS office is 35 mi. away.

Thanks xjwmx. I may do just that.
 
From what I can tell, the butterfly's are opening and closing properly. I followed the advice to do the "snap" process to center them and I did that on both sets. But, maybe another set of eyes more familiar with them can see something I'm not.

The slides and needles I didn't mess with. They seem to operate smoothly. .
.

did you do the slide drop test with both slides ? how many seconds did each of yours take to drop
 
I did indeed. Both sets. They drop nice and slow. I did inspect the diaphragms closely and a couple did have a pin hole in them which I patched. Griz is sending me a right side carb to try with a good slide in it. I'm going to put new shaft seals on it and new jets and see what that does. If i still have an issue, I'm going to go through the ignition system. Another member about an hour away from is gonna see about putting my carbs on a friends bike as well.

We will get this thing figured out come hell or high water!

Thanks everyone. I truly appreciate all the help on this.

PS. I found a bike I've always wanted since I was a teenager and going to pick it up today. It's a 11k miles 1989 ZX-7. Never got to own one as a youth but excited I finally get to have a bike I've always wanted before prices start to get too crazy.
 
guess thats why the XS is going on the back burner then eh !;):)

modern stuff just doesn't do anything for me . Good luck ...show us a pic when you get th ZX-7
 
No backburner. I'm still working hard to get the XS going. Just can't turn down a good deal tho haha
 
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