What is the fastest way to correctly set the mixture screws?

I have a colortune plug and a manometer. The colortune gets it running but not perfect. There's plenty of turns of the screws between rich and lean. I tried to get the highest vac reading on the gauges and then resync. I can get a smooth idle at 1100 rpm but then there's a stumble if I get rolling in 1st(or any gear) @ 1000rpm or so and go full throttle. It clears up around 2000 rpm and up.
I don't know if these bikes are supposed to idle like a sewing machine or if there is supposed to be a slight "lope" to it like a v8 at a cruse night that pounds on your chest as it idles past. The starter button side runs evenly through the pipes. The other side has a heart beat pattern mixed in.
I got it where 2 plugs were ever so slightly tan, one had a black spot developing on the side and one plain white. Adjust, short ride, cool down, and inspection is taking a long time. Day to day changes in the weather probably doesn't make this easier. Are there any tricks to this?

 

Q1- - did you check and adjust your valves?

Q2- - "There's plenty of turns of the screws between rich and lean. I tried to get the highest vac reading on the gauges and then resync." ???
If you are using a Manometer and a colortune, you should be dialed in alot closer than "plenty of turns".
You should be tweaking for the bunsen blue, or just richer, then adjusting the sync just a little. A red hair.
Your final tweak would be off the plug read.

My bikes lope a little, but you are looking for a smooth idle, and really good low end manners.
Skip your cool down, get gloves and a short piece of fuel line (to help twitter the plugs in and out) and write down notes as you tweak. You sound like you're close. Do small tweaks.

 

Re: What is the fastest way to correctly set the mixture scr

Jim, there is no quick fix to carb issues. It takes time & patience. When you started with your mixture screws did you turn them in till they softly bottom? Also you need to count the turns to bottom so you know where they were at when you started. Write those turn counts down. Next back each screw out 2.5 to 3 turns out, depends if your screws are course thread or fine, 2.5 fine, 3 course. Fire it up & see how it runs. If & when all is well should idle like a sewing machine, no lope. Take RPMs up to about 4k & shut her off. Pull plugs & check insulator color. You are looking for a nice even carmel tan on each insulator. If any plug is white, means running lean, back that mixture screw out about the thickness of a nickle. If you have a plug that is dark, turn that mixture screw in the thickness of a nickle. If you have one that is a nice carmel tan it is good. After ajusting screws put the plugs back in, fire it up, run RPMs up to 4k again & kill engine. Pull plugs you adjusted & repeat. Once you have the carmel tan on all insulators you are ready to synch & ride. You will be amazed at the difference. Good luck & if you have any problems be sure & ask. Also, lst us know how this works out for you.
Gregg

 

So run it up to 4k and switch to off or let it come back to idle then shut it off?

 

Switch it off while holding the rpm at 4k.

 

+1. A tight valve could be throwing the whole thing off too. Check and adjust valves and check compression FIRST. Then commence carb tuning.

 

Re: What is the fastest way to correctly set the mixture scr

I checked the valves 1200 miles ago and they were all on the tight side of the limits. I think I'll go out there and mess with it for a while and see what happens.

 

When you guys instruct him to run it up to 4k then kill it, are you talking about doing a plug chop where you ride the bike in a certain gear up to 4k then kill it and coast to a stop or are you talking about idling it up to 4k while it's parked?

 

Re: What is the fastest way to correctly set the mixture scr

Getting close. The plugs on the right side are good to go. The plugs on the left look like they were black and pieces of the black are chipping off to reveal pure white. Theres popping in the pipes at 5k rpm but I cant isolate it as far as left or right side. My neiphiew was controlling the throttle, I was trying to listen, and the bike was bugging the neighbors. After 5 reads it sure runs lots better. Thanks a bunch.
http://s89.photobucket.com/albums/k230/ ... ure050.flv

 

Good question.
You see, if you floor it, you are using the main fuel circuit, as well as the pilot circuit.
If you baby it, barely twisting the wrist a couple MM's , you are mostly using the pilot circuit, which is what you are adjusting.

My concern is that the "burn" should be longer than 20 seconds.

 

You can go to the AutoParts Store and buy a Pack of Champions and take them to a place where you can do some "Chop Runs" and get it done in under an hour.
(Or bring gloves to be able to handle HOT Plugs)

You can start a "Daily Check" for a few days and Tweak them in according to the way you ride.
(Replace an overly Rich looking Plug with one from a Hole thats OK)

 

Newb question here: why do you run it to 4k and do a plug chop if the mixture screws are only adjusting the pilot circuit? What's adjustable in the main fuel circuit? (The main jet sizes?)

 

The Pilot Mixture not only Keeps the Bike running at Idle ... But, you must also adjust it for Supplemental Richness.

Supplemental Richness is needed to provide fuel for the brief moment that the Bike is brought Off-Idle.

Not enough Supplement ... Backfire or Stalling-Out

Too Much: Bogging-Out or Hesitation getting out-of-the-hole.

 

I just want to get the bike running like it was intended. Rode my 1988 yz125 tonight and it feels 4X as fast as the xj650. 20 years from now someone is going to find a nearly 50 year old bike with less than 10k miles on it.

 

Re: What is the fastest way to correctly set the mixture scr

I was tough on the bike in the last post. I let my brother ride it tonight and it sounds like its running great compared to other old bikes I hear. I still plan on having it in 20 years. Thanks for all the help.

 

If you have a carb sync tool and you've adjusted the valve shims, it should be a quick job syncing the carbs. If you don't have a carb sync tool, you have to take carbs off the bike and bench sync them, which is remarkable accurate. There's a good article on it at:
http://xj650.blogspot.com/2009/04/how-t ... carbs.html

thx,
baz