Carb-Related Problem

Alright XJ Wizards. I've got a bit of a problem that's been vexing me. As you may know, I've been working on the wife's '82 XJ650 Maxim. I recently did some carb work and reinstalled, synched, and colortuned her bike. Since then, I've noticed a rather pronounced miss and stumble between off-idle and 2500 Rpm when its cold and warm. It seems to go away after about ten or fifteen minutes of riding, though. So, here are the clues I can provide.

I went ahead and slid the YICS blockoff tool into the gallery and hooked my manometer up. Here's what I'm reading:



And here's what the four plugs look like:


Plug One


Plug Two


Plug Three


Plug Four

To me, one and two look lean while three looks too rich. Four is pretty close to what I imagine would be a correct air/fuel mixture.

Finally, here's a short video I took of each cylinder with the colortune plug installed. Unfortunately, the first segment, cylinder one, didn't come out very well. I can tell you that it wasn't very different than cylinder two, though.

[video=320,270]http://www.currentobservations.us/videos/colortune.avi[/video]

So, what do the experts think? Which dirrection do you think I should go first to figure out why the bike stumbles when it's cold?

 

You can do a better job on the Sync.
I like to see them columns of mercury dancin' like the Rockettes!

One and Two are "Critically Lean"
Enrich both 1 & 2 ... 3-Degrees and monitor plug color.

Three is OK. Safe. On the Rich side.

Four is Lean. But not "Critically" Lean.
I'd give 4 a degree of Richness ... just because

Givend that you have 3 Plugs too Lean it shouldn't come as a surprise to not have Out-of-the-hole acceleration.

You don''t have enough Fuel happening to support the bike running good until you are nearly at W-O-T and are runninng on Main Jet supply.

Further ... you NEED the extra Pilot Fuel to sustain ignition just off idle and to supliment the main jet feed at speed.

I wrote this up the other day, but i forget what thread.

Search: Colortune
Author; Rickcomatic

 

This could be a dumb question but could the diaphram have a leak in it (if yours have them) It looks like #1's really out of whack.I have 2 diaphrams with wear spots in them and mine wants to stumble too. Expensive to replace them. $90.00 U.S each.

 

Coat those wear spots on the Diaphragms with a layer of "Liquid Electrical Tape"

Use masking tape to secure the rubber on to a suitable frame to get it smooth.
I fabricated such a device by cutting the spout off a small funnel and spread-out the rubber diaphragm to the contour of the funnel with masking tape.

Even though the Liquid Electrical Tape comes with a brush-on applicator ... I used an Artist Brush and just painted the new rubber layer right on, It dries fast allowing you to apply a coat to the opposite side shortly after doing the one side.

The Diaphragms I treated are still in the game after two seasons of being repaired.

 

OUTSTANDING!
I've heard horror stories about what guys have used as coatings, gas disolves them and coats everything causing a mess.
Now I'll can give her a good tuning.
Wasn't sure if the diaphrams would be a problem if I colourtuned.
Thanks for the hope I had lost Rickcomatic.

 

OUTSTANDING!
I've heard horror stories about what guys have used as coatings, gas disolves them and coats everything causing a mess.
Now I'll can give her a good tuning.
Wasn't sure if the diaphrams would be a problem if I colourtuned.
Thanks for the hope I had lost Rickcomatic.

 

UPDATE: As per Rick's suggestions, I re-synched the carbs. Couldn't quite get the Rockettes but did manage to get 'em pretty close. Then I colortuned them and set them all so they were showing the recommended bunsen blue color. By then it was getting on to my bed time, so I shut the lights off and went in.

This morning, I fired her up and rode in to work. The stumbling was still there, but not quite as bad. On lunch, I grabbed a spark plug socket (gotta like working at a parts store ) and checked the four plugs. All of them were equally white. That's good and bad. Good in that I got the carbs equalized. Bad in that they're all still too lean. Using my specially made screwdriver (ask me about it some time...), I gave all the idle mixture screws a generous 1/4 turn out. As lunch was almost done, I buttoned her back up and waited ‘til after work to test her out.

On the way home, I noticed that it ran much easier and was way more responsive on the throttle with the choke off. Before it seemed to be a bit sluggish when cold or hot. However, while motoring down the road, I could still feel that slight hiccup and miss, but it was nowhere near as bad as before. I'm talking a HUGE improvement! I'm planning on pulling the plugs at lunch again tomorrow to check them and adjust as needed. I think I'm closing in on that fabled "dime's-width" adjustment that Rick speaks of.

Cheers for now...

 

Yes you are.
You're darn close right now.

Begin treating the Mixture Screws individually, now.
Just look at the Plugs and make a larger or smaller adjustment depending on what the Plug Read says to do.

Once you arrive at the point where you are "Tanning" the Plugs. Leave it!
You should be idling like it don't want to ever stop.

Getting ou-of-the -hole ... Fast!
And putting-on good power immediately coming off-idle.

Zooming ... in other words!

 

it might be a good idea check the sync a couple of times an the better you get the mix the steadier the sync will be an the mix will change the sync some also,,,,looks like she responding at least,,,,an be careful this is very addicting Dan

 

Addicting is true.

Once you do find the spot where your Bike is running better you could have ever imagined ... you can easily become a chronic tweaker. Tweaking one or two carbs at a time to get the whole rack perfectly matched in both Sync and the Pilot Mixtures.

I don't think its a bad thing!
It definitely separates you from those who don't have the patience to do ultra fine tuning.

As the Pilot Mixtures get closer to the optimum ratio of air and fuel to provide a rock solid and steady idle ... you will be able to Sync the four Carbs and get them looking like they are all hooked-up to the same manifold. Perfectly balanced.

The Pilot Mixtures will be so close to perfection that each of the four Plugs will mirror the other three in coloration.

This is where you will be doing the finest tuning of all.
One, maybe two ... will present a little darker of lighter than the others.

You'll find yourself deciding to get them to be matched in coloration; too.
This is where they are within the width of a Dime apart.

You'll be so wrapped-up in striving for perfection that you'll be looking for other bikes to tune-up.
I drove-up to New Hampshire to re-tune a Bike for a nice person who came to my Carb Clinic.

We were both still experimenting with the Colortune Plug back then.
Once I knew where the sweet spot was ... it became a Mission to sweet-spot any bike that might happen along.

The enjoyment is in the way the Bike Idles and takes-off after being Dialed-in just right.
The Idle is rock steady as an Atomic Clock and the off the line acceleration good enough for track day.

But, you still like to play with the Engine even if there is no reason too.
Just because you KNOW how and find it to be a lot of fun tweaking-up the four cylinder for Maximum Performance.

 

You guys are killing me, I've got to get my bike fixed, but I have the problem with the Idle mix screw being stripped on my 85' XJ700X...

Like this: http://xjbikes.com/Forums/viewtopic/t=5273.html

I'm new to this stuff, but I love it. The more I learn, the more I want to know. Thank to guys like yourselves this is much easier... I just wish I had more time to work on it... Good luck on your micro-tuning! =)