Idling problem

Mikuni's are the ones that have:

MIKUNI ... written on them!

 

Then I guess mine are Hitachi's, unless the words are worn off, lol.

 

You can also look at the Carb "Tops"

Mikuni's are round.
Hitachi's have a little "Ramp" on them.

 

what model of hitachis generally found on XJ bikes are the HSC32's. best if you buy a rebuild kit, replace some of the rusted bolts with STAINLESS steel ones, which last almost forever.

 

No clue what solved the problem, but the RPM hang is gone. I just went out, fired it up, let it warm up and gave it a little rev, no hang...gave it more rev, no hang...gave it one hell of a rev (to like 7000rpm lol) and the RPM just plummeted to idle. Now I just need to get my license next week, adjust the rear brake pedal so the rear brakes actually work, get new tires, and bleed the front brakes, and she's finished!

 

After a good ride you may find it hanging again. If it does reach in and turn the idle speed knob dow (out) until it settles down. May take a try or two. Probably only a half turn will get it.

 

The problem did happen when I rode it about 2 weeks ago (just up and down my driveway), but that was when it was really bad. It didn't do it while I was actually moving, just when I was sitting on the bike revving it. To get the idle to drop back down, I just put it in gear and let the clutch out a little. The drag from the drivetrain was enough to get the idle to drop back down.

 

Find a spot where the Throttles work perfectly.
Move the Bars Left and Right and make sure the Cable isn't getting tugged.

Then, SECURE the Cable Sheath firmly in the Mount.
Cut a 2" Length of Duct Tape and lay it on over the Sheath and "Iron-it" on with a Blade from a Screwdriver.

Then, take a longer section of Tape and wrap it around the Frame Bar over the Tape you Ironed-on.

The Throttles ought to Open and Shut and NOT "Race" if you have to maneuver the Bike.

 

here's another scenario I got for ya...

when doing a running vac sync, (no air leaks already checked), and the motor gets warm (too hot to touch headers) my throttle increases steadily. when I use a long screwdriver to push down on the screws the idle drops back down (from 2.5k down to 1.2k rpms). it's almost as if the cable is pulling the throttle but that's not the case since there is always slack. somehow the throttle shaft is ever-so-slightly rotating as the bike gets warm. any thoughts?

btw: carbs were overhauled and all rubber was replaced including throttle shaft seals

 

Yes but you don't want to hear it.

You didn't get the carbs all dead lined-up on the rack when you reinstalled them and the linkages are not in a "straight line" anymore.

 

so tear down, remove all throttle springs, push, shove, twist, put throttle springs back on, then put carb rack together? kinda counter-productive when I did it the first time i suppose...

obviously its something carb related so at this point they're off the bike and I'm just staring at them. i know these things are precise engine components but jeez for 30 year old motorcycles the XJ's can be a pain in the butt. either you love it or hate it

 

Loosen the Enrichment Cable Mount.
Pull the Cable Sheath down insuring that the Lifting Forks ALL allow the Enrichment Plungers to seat.

 

I had the same problem. It took 2 years to figure out that the carb mixture was off. Here's my recommended order of operations:

Adjust valves
Bench sync carbs
Adjust mixture (12mm colortune works for the xj550)
Vacuum sync carbs
Adjust mixture

After getting my mixture under control, idle is much better and no rpm hangups

 

1.) valve clearance - check
2.) bench sync - check (using paperclips)
3.) adjust mixture - ?? here I thought the first thing would be to bench sync, then...
4.) vacuum sync, then
5.) adjust mixture with colortune

I've gotten steps 1, 2, 4 (#3 in my case) done. I know that my mixture is rich on all plugs so I could turn in the screws slightly i suppose (pretty sure all mixture screws are out 2.5 turns). my plan of attack is to hopefully get colortuning before the motor gets too hot because by then the throttle is hanging/increasing too high (near 4krpm).

for those who have been following my "checking cylinder compression transistions to no start" thread, I'm happy to say compression readings this morning were 125~135 psi across the board after re-torqueing the head. aparently the first time I assembled the upper engine rebuild I failed to properly torque each acorn nut near the center of the head once this small crack in the head disappears (its at a bad location where an anchor bolt on the corner is located for the valve cover), I'll be smooth sailing . trouble is the small crack is "more-of-a chip" since the entire threaded portion to hold the bolt securing the valve cover has broken. the J-B weld doesn't seem to be holding it since tension is too great for the valve cover

also the troubled battery issue was discovered to hold low cranking amps. AutoZone manager had a hell of a time believing me since they could not test it thoroughly; although it did hold 13.1 volts just low cranking ampherage power which was weird. new battery starts bike right up

 

what I don't understand is how can the idle increase after the bike is hot?

upon a cold start this morning the bike idles great around 1000rpm hardly any choke. hop on it and 3 minutes later after a short blip down the road the idle hangs too high 3~4k. if it were the linkages not in a straight line wouldn't that be present upon cold start as well? I've checked the choke cable and plungers are bottomed down on the rack

only abnormality I currently also have is a leaky valve cover near one exhaust port from taking the cover off so many times lately. plus paper gaskets suck and can't take re-installations numerous times

 

Can you bring that high idle down with the idle speed adjustment screw? If yes do that and ride it for a bit and see how it behaves. If it's starting with little choke and it's not pretty warm where you live then your idle mix is probably a bit rich.

 

idle speed adjustment screw doesn't help. I can turn out and turn out without any change.

and I know the mix is a bit rich by plug colors. temps this morning is already in high 80's with like 100% humidity ugh, great Ohio weather lol

 

I think you've got a throttle blade or more open too far.

I would take the carbs off and bench synch again unsing a business card or 3x5 card. I just compared one to my box of paperclips and the card was half as thick as the thinest paperclip I have. That little difference is likely enough to get atleast one carb to come up off idle and that will bring the rest along. Also, have your idle speed knob touching the throttle lever with threads each way for adjustment on the bike.

 

Because the relationship between the not-quite-lined-up carbs is changing enough when the assembly gets hot to create a bind.

Since you probably don't have access to an actual surface plate for re-aligning the carbs, the best thing to use is a carpenter's level (or a pair of them) because the carbs have to be truly aligned not just "eyeballed" when tightening them back up on the rack.

You did use the "clear tube method" to set the floats, right? If so, then I vote carbs not straight on rack. (Sorry.)

 

well no fortunate news... even after a carb disassembly this afternoon

took off the two mounting brackets as well as the enrichment rod so it was just 4 carbs connected by linkage and fuel rods. re-straightened the entire rack with a level and t-square hanging off dad's saw bench. re-bench synced as well this time with business card strips and all looked well. fired it up and went a half mile down the road. sounded good and its only hanging around 2.5k or so and then I remembered the idle adjustment screw back in the garage. turned it down and whew a nice idle once again around 1300 or so.

shut it off, hooked up manometer tubes on all four nipples; ready for running vac-sync. about 3 minutes into running time with manometers hooked up the idle begins to increase again. i'm lost. checked for random leaks with propane and no change. it still likes to increase the idle up towards 3 or 4k and I don't know what else has changed before this hanging idle issue occured... also I try to give it a blip and the throttle increases obviously to 5-6k then drops down to 4~4.5k