3000 rpm idle

[GaryS-NJ]

for those of you who have been following my various posts on bringing my bike to life, it's still not running right. I bought this '95 katana 750 not running and with the carbs stuck (throttle shafts seized and sliders stuck).


I got the carbs apart and together and had trouble getting all four cylinders to fire (carb body passage to the pilot jets and also the pilots them selves re-clogging).. But whenever I've had all four firing, I'd had a high idle (3000-4500 rpms). Early on, I think I alleviated the high idle briefly by replacing a float o-ring but perhaps I just coincidentally lost a cylinder firing. Chokes are OK, throttle cable slack, butterflies snapping closed to the bench sync position, carbs now vacuum synced (well close), no air leaks detected with WD-40, or carb cleaner. Mix screws set at 2.5 turns out and I've tried the floats set at 14.6mm and down towards the 13.6mm.


Oh, and at the get go, I was soaking and hammering on the throttle shafts and actual butterfly plates so I've done my best to make sure the plates are all pretty flat and sealing symmetrically in the carb bodies. Bench sync looks very good. and opening the throttle and letting them snap back, they are snapping right back to the bench sync spot (first orifice). And through all of this, after the initial super clean and chem dips, I've sprayed out the whole pilot (and choke) circuits..


I'm about to pull the intake boot O-rings but just don't believe they could be leaking that bad and consistently to produce the high idle weather the bike is cold or warm.. moreover, it rev's pretty strongly and I would think an intake air leak would upset that somewhere..


Folks are saying pilot clogged, starving for fuel, running lean, high idle but when I had the pilots clogged, the cyclinders were not firing.. And mix screws are traditionally set for highest idle.


one curious finding yesterday though when doing my vacuum sync yesterday, I saw a different affect from pulling off the sync caps. pulling cap #1 and the idle goes even higher, pull any caps 3-4 will drop the idle.. That is telling me air leak somewhere, right? And thanks again and in advance to all that have shared and tried to help me. I hope I can pay it forward to others (because you probably won't ever need my help)

[GaryS-NJ]

intake boots

the intake boots came off easy enough (first time ever) which makes sense since the bike only has 9000 miles on it. the orings were definitely squared up very flatish but not cracked or obviously leaking. I ordered new orings but could see a stain on the bottom of each intake manifold as if excess fuel was flooding in in addition to the atomized mixture.. I know I've sprayed the intake boots with wd-40 to make it easier installing the carb set so it could be the wd-40 or perhaps fuel staining. Has anyone else noticed this moist stain.. (and yes, smelled a little like gas but after rocking the carbs to remove them I think I had some fuel coming out the carb outlets..

[arsenic]

I don't care if the bike only has 9000 miles. That screw has been there for around 27 years. The only reason it came off easy is if someone messed with it previously or you're way stronger than any full grown man I've ever met.

See what I did there? I made a post with zero useful information.

[GaryS-NJ]

someone was in there

not absolutely ZERO useful info.. the orings may have been in there for 27 years (holy crap, this is my latest year bike) and taken a nice set, and the screws came out without impact probably because someone was in there and didn't crank them back on (I did try the first tighten check and was able to get most of them to take a little move). And I should also expect someone was in there because I had to snug up the oil lines after a leak and those bolts were very loose.


But could an intake o-ring leave me with a constant 3000 rpm idle and not affect reving?? (I haven't tried it under load). will know by Friday/Saturday..

I don't care if the bike only has 9000 miles. That screw has been there for around 27 years. The only reason it came off easy is if someone messed with it previously or you're way stronger than any full grown man I've ever met.

See what I did there? I made a post with zero useful information.

[Kreylyn]

Air or vacuum leaks generally = bouncy or hanging idle. Could also be out of sync carbs or mounting hardware for the carb boots catching on the throttle assembly of the carbs.

You can do some simple tests to check for vacuum /air leaks with a spray bottle and rubbing alcohol.

Krey

[GaryS-NJ]

only 21 years old

hey wait, my bike is only 21 years old.


Yes I didn't think the intake O-rings could produce a solid high idle. And I did look for a vacuum leak (several times) using wd-40, carb cleaner, and propane.. I shot the intake manifolds (both sides), the throttle shafts, the sync caps, and the carb caps, and the airbox to carb attachment. It looks like someone had bonded the intake runner to the airbox and that may be leaking a little but I'm sure that's not causing the high idle. and yes, I checked throttle linkage and also verified the cable in slack condition. And I have them synced pretty close (as I got them real close, the idle rpm increased).


The one glaring thing here is that while the bench sync had the butterflies all lined up on the first carb body orifice, and the throttle will snap closed to the same place repeatedly, if while idling at 3000 rpm, I push on the main throttle cam as if to close the throttle, the idle will go down. I can only guess that this is forcing all butterflies closed as compared to the bench sync or the final sync and could this be a red herring I don't know.

[mmiltonp]

idle adjust screw maybe?

[92xjunker]

Sticking throttle cable or bound up cable or misadjusted cable.

[GaryS-NJ]

nope!

Each time I install the carbs, I bring the idle adjuster just into contact and then one full turn in and then each time she fires, and idles way high, I know I can turn it one full turn out and there is no more.. as for the throttle cable sticking or hung up, again no, I check to see twisting the throttle open and letting go to snap back, she is snapping back to home (Ive done this on the bench to verify all four butterflies are snapping back to the same first bench sync carb body orifice. and then installed, I'm looking down and pushing on the throttle cable sideways to verify there is play and it's not pulling on the throttle cam (if I push hard enough I then get the cable to engage the cam).


Tonight I installed the new intake manifold O-rings and she did same (in fact, she is idling at 4000 rpm. all cylinders are hot. Tomorrow, I'm going to recheck and tweek the vacuum sync and then pop the carbs off to adjust the mix screws from 2.5 turns into 2 turns.


I really feel like I bent or twisted something in the throttle shafts/butterfly plates when I was happering on them to free them up (when I got the bike, the throttle shafts and sliders were frozen). I think this because at the 4000 rpm idle, I can push on the main throttle cam (or either of the 1/2 or 3/4 cams) and slow down the idle to 1000 rpms. hard to believe that starting the bike at bench sync (the plates are pretty dam closed) that the bike would idle at 4000 rpms there.


does anyone know if you need to turn the idle screw up to open up the butterflies enough to line up the four butterflies to the first carb body orifice? and then to run the bike at a regular idle, you would drop the idle screw back down./. this is a basic question that anyone who has done a bench sync could answer. HELP!!! because if this is the case, then I need to loosen the throttle shaft nuts to see if I can get the shafts to rotate to a more closed position with the spring closing the throttle. I hate to completely tear down the carbs (or at least pull the plate screws, separate the carbs, and pull the throttle shafts).. Is there a trick to hold the throttle shafts in a certain position when locking down the shaft nuts?? I was able to loosen one of the nuts when I was trying to unstick the throttle shafts (and later tighten it back up) but I don't think I ever loosened the other shaft nut.

[ZookRick]

Did you remove the butterfly plates from the shaft when you were freeing them up? Did you orient them the proper way up when reinstalling? Did they get bent or anything? Those plates have to seal quite well to stop the engine vacuum from pulling air through. Did you make sure they seated well before tightening the plates screws? Did you use new screws?

[GaryS-NJ]

I didn't remove the plates. I actually hammered on the plates and on the throttle shaft cams to unstuck them.. Later I tapped and twisted the plates trying to get them flat as possible.. Right now they seem pretty flat and the bench synch snaps the throttle back to the first orifice without any idle screw actuation. Should they snap more closed than that?? I'm thinking I might be pulling those butterflies to try and flatten them more and recenter them

[GaryS-NJ]

I tried running it with a nanometer backing off the idle screw all the way off and sync screws to let the butterflies close all the way and the idle dropped to about 1500 rpm but I'm sure that's because 1/2 and 3/4 were so missmatched. So I synced them up (& yes, I checked the nanometer calibration all four tubes on one port) and the idle went back up to 3700 rpm. I carefully pulled the carbs back to turn the mix screws in to 2 turns (not believing 2.5 turns could be way too rich and causing high idle) and I looked into the intake manifoldswithout turning the carbs to the side and again I saw the intake runners wet with fuel. Hard to believe atomized mix could wet them that much and so before I pull those butterflies out I'm thinking something is just dumping fuel in. I have had the floats set to the lowest bowl level (& to the highest) but now they are are at 14.6mm).. Ideas?

[GaryS-NJ]

I after leaving only the choke circuit as suspect or perhaps the throttle plates not closing up right, I bought a junkyard set of carbs and cobbled some of my parts into them.. runs right now.. thanks all!