So... I'm at a loss...

First I'd like to thank mwhite for loaning me his colortune!

Ok, so I can get nice colour on all plugs, sync is right on, runs real nice! Except for one thing... Idle adjust is all the way off and she idles at 1200-1300 rpm (my tach jumps a little on my ace well at idle)

I've checked for air leaks and can't find any.

Valves are in spec.

#1 carb won't fire unless the pilot is 5 turns out, but I do get a nice adjust range between 4.5 - 5.5 turns.
#2&3 both like to be 4 turns out, and #4 likes to be just under 3 turns

I've even gone as far as letting #3 carb have less vac that the other 3, hoping that closing the other butterflies (having #3 open a touch more than the rest) would bring the idle down, no dice.

I'm at a loss guys. Where should I be looking, I can't think of anything that would possess this bike like it is.

 

It definitely sounds like a vacuum leak somewhere. If it's not external it can still be internal. Somehow air is getting past the butterflys or it would idle down and die with the screw backed clear off. (you knew that... ). Have you had the carbs apart?

I ran into the same issue with a set of Webbers (on a car) and the butterflys had been switched from carb to carb when the owner had pulled everything apart. The short story was that the butterflys had just been dropped in the slots and tightened down and were leaking all the way around on all but one carb. They need to be centered and seated with the shaft held closed before they are tightened. Big vacuum leak but not to the outside.

Of course it would be a lot easier fix if it was a boot or something like that.

 

I did have them apart last weekend and went through them. I was very precise when I put the rack back together... I guess I could pull it off tomorrow again and check the butterflies at least.

One thing I did think of, I was running it for quite some time today, and I didn't have a fan on it. I'm not sure if this would matter, but would it overheating, make it run with high idle?

Can't do anymore today, battery died from running at idle too much. Horrible that I drained the bat from full to dead just from colortune and syncing lol.

 

NP dude, glad to meet another XJ dude!

I'd keep an eye out for another rack of carbs if it were me... If you have the wiggly throttle shaft on the one perhaps that is resulting in butterfly variance at idle? I had a similar gremlin on my 750 Rack, and only when i used my old 650 rack did it finally start running ok (minus today of course hahaha).

PS: the bike didn't sound that bad to me at all, but I know the perfectionists we XJ folk tend to be sometimes

 

Ya I could give zdenos a call and see if they have anything half decent. Didn't want to put that much more into it, but, if I have to.

I'll pull the rack tomorrow and see if its something simple first.

 

ohohohoh just thought of a question I wanted to ask Rick and fitz. What sort of vacuum numbers should I be seeing? I think I'm running around 19 mmHg when it was running good.

 

can you reach in and push the throttle lever down? is there any slack in the cable?

 

X2, check the throttle cable adjustment

 

I had the same problem after a carb rebuild on my XS11. Turned out one of the butterflies didn't seat right when I tightened them down and was off by just a fraction of a hair so they were hanging open. I just loosened the screws, hit the linkage to make sure they seated and re-tightened them.

 

I do have slack in the cable, and i did try to do that (butterfly fitment) last weekend, but it'll recheck tomorrow.

thanx for suggestions guys.

 

I pulled the carbs today, it wasn't so much the butterflies sitting akward as it was the sync screws wouldn't let the butterflies close all the way.

I basically had to set it so all plates were open except for #3, then adjust 4 to it so they were both closed, then 1 and 2 as close as i could to 3 and 4. It was impossible to get all 4 completely 100% closed, i had to have 1 and 2 open just the slightest bit so 3 and 4 wouldn't open a touch.

She does idle much better now (lower) after mulitple colortunes and sync adjustment. Still idles 1100-1200 but way better than before.

I'm basically keeping it the way it is and just ride it till I sell it for a new machine. Which will probably be quite a few years.

Thanx for all the input guys!

 

KrS14 check with Tom at N.C.K cycle salvage for a set of carbs 519 268 2523. Did I see your bike at Turkey Point today?

 

on your sync screws there's two sizes of springs, it matters which one is on top

 

Another cause could be the rubber plugs that cover the vacuum tubes. they my feel snug but if they have gotten hard and you have taken them off to do a vacuum sync they could be leaking, drawing in air, I had that happen with mine. It was a real pain in the a*s to try an get the carbs set up properly. Once I replaced the caps no problem. And it was nice to you to day Lostboy.

 

Oh my I missed these couple posts here lol.

I should go see Tom, haven't had a chat with him for a while.

It very well could have been me at TP, I did go down there for a quick cruise one day, can't remember the day tho. Went from there to Long point on front/lakeshore rd, was nice! had to watch some of those 90 degree curves tho lol.

 

Oh my, THIS I didn't know! They all looked the same to me so I didn't think anything about it. Is one thicker? which goes where?

 

take a look at this
schmuckaholic's fine write-up has some fine pictures. thicker spring under the screw head

 

Crap... I may have those backwards, i'll have to check tomorrow.

 

Checked this morning and i've got them on the right way, yay!

 

Did you sync all the carbs to #3? The screw to raise idle is on that carb you have to sync in proper order if you don't the screw will not work. If you use the paper clip to bench sync on #3 and bring the rest to that level. The reason your air screws are all over the place is because butterfly is slammed shut on#3. I know this sounds strange when your syncing you do not want to move the idle adjustment screw at all the reason the idle goes up is your opening up the butterflies on the other carbs. I have done the same thing long ago. You are going to pull your hair out until you bench sync them again then you can fine tune with vac gauges they should be very close. Hope this helps a bit