Mikuni mixture settings

Apologies in advance if this seems obvious (I'm sure it's been asked before ad infinitum) but after poking around the forums, I can't seem to find anything concrete to go on.

When I first got the X, it would barely run on full choke, if at all, on two cylinders. Got the carbs off, they were gummed up nine ways to Sunday, with at least one pilot jet clogged. Got them apart, soaked everything and got the jets open, set the float levels, and reassembled. One or two of the float levels were borderline, I thought, but I decided to chance it.

Bike started, idled and ran fine. Thing was, it started having a hydrolock problem. Pulled the carbs again ("twenty minutes" my dying ass!) and lowered the float levels, along with replacing the float needles just to be paranoid. Funny thing about those levels, though -- seemed like they kept changing. First measurement would be spot on, second would be lower, third might be different again... anyway, where they're at now is somewhere around the lockwasher on the bowl. If anything, they're a bit low.

So now, the bike has issues with stumbling on low RPMs. I've tried playing with the mixture screws (anywhere from 1.0 to 3.0 out) and tweaking the idle rod. As it sits, it seems like it wants to idle with choke on, and revs nicely. Turn choke off, and it dies. Yes, it seems like it wants more fuel. Right now, I'm not even sure where I've got the mixture screws at.

I've also changed the plugs, checked the air filter, and did a one-gauge sync (the right two cylinders were a bit high) to bring everything in line. Not having a cursed colortune plug (although I may be forced to get one) I'm at a loss as to how to proceed from here.

 

Run the bike up to 5,500 rmps for 20 seconds and then hit the Kill Switch.
Pull the Plugs. Keep them in order 1,2,3 4
Examine them for coloration.
Look for one that is a deep tan or light Brown.

When you have found the Pluug with the right coloration ...
(Tan or light to med brown on the center ceramic)
Duplicate the Pilot Mixture Screw setting of that Plug on the others.

Insert a Glass Barrel-type Fuse in the top of the Pilot Mixture Screw Housing for the Plug with the best Coloration and rest it upon the TOP of the Pilot Mixture Screw.

Scribe or Mark a line on the Depth of the Fuse as it rests on the TOP of the Pilot Mixture Screw.
Using the scribes Fuse ... set the other three Pilot Mixture Screws to the SAME Depth as the one you selected for best Sparl Plug coloration.

Once you have all four Pilot Mixture Screws set to match the depth of the one you selected as best ... begin several rounds of Plug Chops.

Once you set them all to the same depth and begin the Plug Chops treat each Cylinder independently and adjust the Screw to Lean or Enrich the Mixture as needed.

At this point ... the Pilot Mixture Screw will only need to be moved a minuscule amount to correct for Rich or Lean.
Minuscule.
Tiny tweak either way.
Don't move the Screw beyond the width of a Nickel either way while correcting the Mixtures during the resetting of them after reading the Plugs.

Fine-tuning is just that.
Fine.
You can very easily go from too Lean to too Rich within a quarter turn.
Think in Degrees.
Not Fractions.
Get a baseline for tuning using the Depth Guage Fuse technique and begin Tweaking your bike until you have it right on the money,

Clean Plugs are TOO LEAN.
Tweak them for a deep tan or brown.

 

Update.

I set the screws to 3.0 turns out, started the bike, and let it idle on choke while I did other things. When I heard the engine suddenly rev, I went over, turned off the choke, and ran the plug chop. All four plugs, without exception, were sooty black -- rich mixture. I wonder if this also helped expose a flaw in my previous testing, in that the engine wasn't warm enough. (The hot coolant lines convinced me otherwise... but I digress.)

It'll be a day or two before I can take another swipe at it, but I've turned the screws back in to 2.5 out, and I'll redo the chop and see what happens.

 

If you plan on getting the Mixtures right ... you got to get yourself out of the FRACTIONS mind-set.
There's nothing about fine tuning moving the Pilot Mixture Screws a whole One-Half a turn.

The optimum setting is going to be found within a window appreciably less than a half a turn.

You have to get the Pilot Mixture Screws to a point where moving them in or out the width of a Compact Disc is going to change the Mixture from a little too Lean to just-right.

Turning the Pilot Screws a whole half a turn could have gone past where you needed to be.

 

Let me at least get it close, Rick. 3 turns out is past factory spec by anywhere from 1/2 to a full turn. I think I'd rather start lean than rich.

Yes, I realize factory spec is a bit on the lean side, but it's a good starting point.

More as it happens.

 

Update.

I couldn't shake the idea that the float levels were low, so a week or two ago I pulled the carbs again, and raised them a tad. This time I marked the target level on the edge of the float bowl, and brought them at or near this level. Reset the screw settings to about 2 turns out, and while the bike still didn't want to idle on its own, the bogging largely went away, with a small spot at about 1500rpm.

I had knocked most of the carbon off the plugs after the last chop, but everything was still pretty dark. Last week, I think it was, I rode the thing down to work and back, which is at least 30 minutes plus each way at 5000. I pulled the plugs last night, and all the carbon had been burned off, with a dark brown ring around the top edge of the insulator. So, I figure I'm close.

Today, I spent a bit of time with the bike again, trying to get the thing to idle on its own -- I thought it might be a good idea to do this before throwing my newly acquired 12mm colortune at it. Now, I realize the butterflies have to be open at least a little bit at idle, I'm also thinking that too much would be bad as well.

Where I'm at now is: I've cranked open on the idle adjustment screw a bunch, and it kinda sorta wants to idle warm at just under 1000. I'm thinking maybe edge the mixture screws open a hair at a time while simultaneously backing off the idle adjustment screw to ensure the carb is actually running off the idle circuit and not the main jet... am I right?

I also keep thinking that, despite my seeming ability to document disassembly procedures... I do NOT know what the hell I'm doing.

 

schmuck or well I guess any of you with an 85 X I have a yamaha factory manual that I recieved with my 85 when I bought it this spring. No tthat it will help in this situation as it is truely trial and error. But if you need anything from the book I will have to grab it from my bud's garage were the bike is at. I can scan and email some pages your way just send a pm with your email and info you need and I will try to get it out in a timely manner.

P.S. hang in there once you have it down right these X's run dang strong and smooth.

Ken

 

You're on the right track.
From where you are with the Plugs showing a brown rather than being black; you aren't far from being dialed right in.

Keep in mind ...
The amount you have to move the Pilot Mixture Screws to GET Dialed-in is going to be very, very SLIGHT!

Once you find the Mixture that "Browns" the Plugs and not fouls them ... the ideal Mixture is not far away.

Might be the width of a Nickel
Maybe the width of a Dime (or half a dime).

You'll hear it and feel it when you get it in!
The Bike will Idle like an Atomic Clock. Even at 950 or 1K. Steady!
Not a miss.

The Bike will accelerate, getting out-of-the-hole, seamlessly!
Raring to go. No bogging-out. No hesitation. Instant power on.

If you tweak it LEAN it will be powerful and fast with a high performance burn that you need to monitor --> regularly!
If you tweak it RICH it will be smooth as velvet. A slower burn that makes cruising long distances pure joy. A cooler burn; too. Safe.

 

I had a friend help me, and he insisted on messing with the carb synchronizing screws (why use the meters?, uncessary of course). Does this change procedure at all?

 

Keep your friend away from your bike- - start over with a running sync.
I've heard people say they can tune by ear. . . NOT the sync screws !!

And Welcome to XJBikes !!

 

Thank you... for both the info and the welcome!

 

I'm thinking I may have a problem related to this topic. When I let off the throttle and pull in the clutch the engine still revs high and slowly comes down. I don't think I can lower the idle screw any more without it eventually dieing. Anybody ? I'm 2 turns out on the idle screws and the carbs are very clean now. Haven't done much with the float levels. Cruises very nice.
Marty

 

How did the Diaphragm Pistons drop after the cleaning?

The Bores for the Diaphragm Pistons need to be scrubbed and polished.
Aluma-oxidation coats the Bores and reduces the tolerance causing binding.

If it's not the Diaphragms sticking ... you have to look for air leaks.

But, Pistons failing the "Clunk Test" is becoming more prevalent.

 

In reference to Schmuckaholic`s comment about inconsistent fuel levels when checking float levels, I had that problem when doing my hitachis off the bike with a gravity fed clear fuel line running to them. Erratic levels, then while sitting there thinking bad thoughts about the damn things an air bubble or 2 went up the plastic line, a-ha so i slowly rocked the whole rack from side to side like they were going through some nice bends. Did that for each adjustment after that and got consistent readings, well it worked for me.

 

Bushy, I just got this mental picture of you doing simulated knee scrapers with the rack in your hands. :lol:

 

Diaphragms are good and the pistons were clean. I buffed them a little with a cloth to get off any superficial stuff, but I didn't polish down the bores. Is a 3m green pad acceptable for such a task ? I usually work with a worn one cause they are softer.
I wouldn't be surprised if there was an air leak somewhere. The intake boots are getting tattered. Where's a good place to buy new intake boots ? Another project for later today.
Thanks !
Marty

 

i just used a coarse paper towel and Mothers Mag Polish on mine the other night...like a mirror now