1 Step Forward, 8 Steps Back...Tuning The Carbs...AARRGGHH

Ok. I've read, searched, and tried many of the things suggested to correct colortuning problems, but nuthin yet. Here's the history. It was a basketcase 1985 XJ750 Maxim-X. I've rebuilt and customized it to the point of running it. the carbs were COMPLETELY stripped down, cleaned, blown, cleaned again, and rebuilt with new float needle assemblies. The diaphragms are good. The pilot screws were removed and the enrichment circuits were also cleaned using that hair-fine drill. I put them back together, did a bench synch plus set up the floats. I then set the floats using the wet process and had to readjust the floats...no big deal. I reinstalled the carbs into new rubber intakes. Started the bike up and adjusted the idle after it was warm. Not running too bad, then tried to colortune...#1 cylinder only gets blue with screw turned all the way in...goes yellow and runs rough after about 3.5 turns out. As well, the brand new exhaust pipes discolored a little but the #1 pipe turned golden to th first bend...is this normal?
#2 cylinder adjusted ok with the colortune at about the 2 turns out point.
#3 cylinder didn't change color very much but the engine sound changed while I turned the screw. As with the #1 cylinder, I reset it to 2.5 turns out.
#4 cylinder was similar to #3.

Any ideas would be helpful. What am I missing? Sorry for the long story.

 

Re: 1 Step Forward, 8 Steps Back...Tuning The Carbs...AARRGG

you could try the plug chop method. see the sheikh of tweek, rickcomatic for that.
i spent a fortune getting 4 into 1 pipes chromed for a honda cb750 that i restored and they discoloured the first day, i was gutted.
this time i went the jet hot ceramic sterling route, depends how original the bike needs to look, but i am glad i didn't go chrome again.

 

a few things that might make the carbs run rich at idle:

-blocked pilot air jet or passage
-incorrect (too large) or missing pilot jet, possibly mixed up with the main jet (Hitachi)
-float level is too high
-enrichment valve not closing

hope that helps...

 

Re: 1 Step Forward, 8 Steps Back...Tuning The Carbs...AARRGG

I'd synchonize carbs first, then attempt a colortune session. Its an iterative process to get it right.

 

Make sure the Pilot Mixture Screw's little O-ring didn't flop-over and fold.
If it did,, it acts as a cork preventing the Fuel from getting into the Cylinder.

Sometimes you find that the O-ring and Flat washer have mysteriously changed positions, too.

If you are getting a couple of the Holes to show you the BLUE ... the Other ones cant be far behind.

Do a shortcut to setting the other Pilot Mixture Screws:

On the onen you know is Burning Blue and is running Nice ...
Stick a Glass Barrel Fuse in the Hole and let it rest on top of the screw.
Scribe its depth on the Barrel
An Ignition File makes a nice clean exact line.

After getting the "Mark" established on your "Depth Gauge" adjust the ones you can't bring-in BLUE.
Use the LINE on the FUSE to set the DEPTH of the Pilot Mixture Screws you haven't set right.

Screw the Pilot Mixture Screw IN until the SCRIBED MARK lines-up with the Carb Body on the ones you haven't brought-in, yet.
It's BALLPARK ...
But, it's close.

It should get the bike Idling right along with the ones you set and got to read Blue.
After you set the depths ... go look for air leaks and vacuum breaks and cracks in the Intake Manifolds and such!

Check the Plugs frequently!
You might be Lean if there are air leaks!

 

OK...here's the scoops from today's trials...so depressing that I'd have to cheer up to commit suicide. I tried doing the depth gauge measure plus re-synching but it didn't help. The plugs are black with soot and colortuning is hardly possible as there is no consistent idle. I use the enrichment lever to keep the revs around 1400, but after a few sconds, the revs either go up or the engine stalls. Then I have a heck of a time restarting, sometimes wearing the brand new battery down to the point of putting the trickle charger on it while I go measure out rope to hang myself (joking folks). If I'm lucky, it'll start after a while and as I try to dial in a carb, the whole process of revs/no idle kicks in again. Looking for a bus to throw myself under, I see none, and decide to try working on my Maxim-X again. This time I find oil under the bike and follow the trail to my freshly chromed valve cover...why not, I think...must keep repeating...life is good, and so is this bike. I've quit for the night and am rethinking that I might have to pull my carbs again (only takes 15 or so minutes now) and re-examine all orifices and check for that little o-ring flip possibility that Rick has suggested. Oh yeah, did I forget to mention that my headlight isn't working? New headlight, wiring metered fine, signal lights working ok though and so does the brake light. I hear the roar of other bikes happily driving down the road...I think I'll go have a bath.

 

I checked on the MapQuest web site.
It's 685 Miles to Dartmouth, Nova Scotia, Canada

Slightly beyond my limit for making a house-call!
If you were closer by 485 Miles ... I'd come and help you tune it.

Guess we have to settle for the written word!

Did you remove any other Jets beside the Main Jet and the Pilot Jet?
On Mikuni's ... the Main AIR Jet and Piloot AIR Jet are external, I am pretty sure ... located on the left and right of the Intake Horn on the Carb Body.

Shoot Cleaner into the AIR Jets and make sure that the Passages are open.

You could always take them off ... and bring them down to the Carb Shoppe and we could go over them together!

I regret having no time off to visit lovely Nova Scotia ... although the ride over on The Cat ought to be fun!

 

johno, you shouldn't use the enrichment lever to up the revs, get the engine hot and use the idle screw. don't forget to have the fan blowing on the motor. good luck.

 

Re: 1 Step Forward, 8 Steps Back...Tuning The Carbs...AARRGG

How about your coils and TCI unit? Are they up to snuff? Check for any vacuum leaks? Just a thought. Good luck!!!!!

 

Re: 1 Step Forward, 8 Steps Back...Tuning The Carbs...AARRGG

I'm always impressed with how well folks on this site pitch in to help fellow XJ'rs. I checked the coils and TCI a la Chacal method and they were ok. Since my carbs removing technique has been perfected from constant practice, I pulled them again yesterday to tear them apart. What do you know...blocked air passages! Whatever this stuff is, (white granular stuff) it was in several passages in the carbs that wouldn't adjust properly. Since I've ordered the throttle shaft seals anyway, the carbs are being dismantled for cleaning again. I believe the colortuning will work out great after this is done. As I originally tore these apart and cleaned them last winter, I wonder if storing them in plastic on a shelf caused the corrosion blockage? Not being in gas may have allowed the buildup? This time, once reassembled, they will go on the bike and run-up right away..hopefully this will be the end of it! Am I missing anything else?...but riding it this weekend? :cry:

 

Re: 1 Step Forward, 8 Steps Back...Tuning The Carbs...AARRGG

like most mechanical things, they are better being used than stored.
i would say clean the carbs, get them on the bike & use them.