Idling problem

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

 

It might just be getting too hot on you while you're trying to sync. Once it starts to get too hot, it WILL "race."

Set up a couple of those window-type "box" fans to blow air across the motor; be sure it's warmed up when you start. As soon as it starts to act "independently" shut it down and let it cool for a few minutes before continuing.

Once you DO get a good sync, you may find that you do need to turn the "master knob" down a bit once the bike is warmed up fully. That's OK; as long as it then keeps returning to idle after that.

Mixtures at 2 1/2 turns out to start, right?

 

that's true. mid 90's this afternoon in mid-west Ohio. tomorrow won't be much better from the weather forecast

yep. screws set out 2.5 but since one of the plugs was clean white I turned it out to 3.0 for a starting point to do running vac-sync. thanks

 

okay, got running vac-sync outta the way. great equal balance across all four so then I checked the plug color for ColorTuning. 3 outta 4 either needed richness/lean adjustments. did so without any problems either turning out or in less than a half turn. jumped on with my helmet for a cruise. came back 5 miles later with great acceleration and hardly any bogginess/hesitation from the carbs

haven't checked plug colors yet but when I returned to the garage the idle eventually lowered to 1100 or so rpms. it took some time and even after a few blips with the throttle it took awhile to slowly fall. left if sit there running and within 5 minutes later the idle started increasing again slowly up to 3k like it was racing. fed up with it and shut it off even after turning the idle adjustment screw out. grant it, the temperature is still hot this evening but nobody should have this kind of situation no matter where the location is. i just don't understand how the idle can creep like that...

 

AIR!

The Engine is getting AIR from some place.
Do the Starting Fluid or Propane Gas Trick.

See it you can find where there is a leak introducing AIR into the System.

Candidates Include:
Manifold -to- Head Seats.
(The O-rings Leak -- Dangerous to fix. Seal the Edges.)
Manifolds
(Loose clamps, Sliced-thru rubber at clamp, Splits.)
Throttle Shaft Seals:
(Drip some Engine Oil on the Hinges. Listen.)
Tight Cable