Need to find that perfect balance

Hi everyone,
I'm currently riding a 1985 XJ700 with about 43000 miles. I've recently cleaned the carbs (twice) and done some adjustments with the pilor air screws, yet, I can't seem to find the right balance using the idle adjustment screw. If I turn the idle screw pretty far to the right, the bike will idle well with no enrichment open. However, it seems to produce copious white smoke from both exhausts, and the RPMs will tend to stick if I rev the engine. The RPMs quickly drop once I let off the clutch, but it seems like I have to give it more gas than should be needed to get the bike moving. However, if I turn the idle screw a fair amount to the left (CCW), the bike requires about 1/4 enrichment though seems to idle better, does not produce any white smoke from the exhausts, and seems to move forward better.

Does it sound like I need to do a bench sync on the carbs? Ive checked the diaphragms and done a clunk test which seemed to be normal. Air screws are currently at 3 1/8 turns.

Also, a likely unrelated question. As of recently, my headlight and the lights for the tachometer/speedometer seem to be wonky. They will sometimes turn on, but almost always die within a few minutes of the bike being on. Or sometimes they won't turn on at all. I'm a complete stranger to most of the electrical working of the bike. Does this sound like a battery issue, bulb issue, or a fuse?

Thanks everyone! This forum is great.

 

The lights sound like a dirty connection. Chase the wires following the diagram in your manual (you have a manual right?) and clean and connectors, switches and/or grounds.

For the carbs it sounds like your pilot mix is too lean. Thus it gets better when adding fuel from the enrichment circuit. Either the pilot screws need to come out more or you've got an ait leak someplace.

Others should be along shortly.....

 

back the pilot screws out 1/4 turn more
no need to pull the carbs for a bench sync at this point just sync them while running
then tweek the screws and see what you can get

 

Everything needs to be properly adjusted to run properly. By turning one adjustment, you are just compensating for another adjustment out of whack.
AND, it's not a once and done thing if you really want it dialed in.

First you should check your float levels.
You'll need to sync, then get the idle adjusted so you can ride it without dying.
Then start adjusting the pilot screws with either a colortune or plug chops.
I prefer to put new plugs in and take it for a nice swift run and then check the plugs. Adjust each hole toward a nice tan color on the plug. Then you should resync and if it was way off (and if you have time), clean the plugs and do it again.
If you have to make significant adjustments to the pilot screws, that will push the sync out of adjustment a bit so you need to go back and re-sync, then ride, more plug chops, more tweaks until you are happy...then JUST RIDE!
The pilot screw affects the mixture during idling and running up to ...2000 rpm, then the main jets start kicking in SO you can get a somewhat decent read at idle(to start with anyway). If it sits and purrrs and doesn't start missing, you probably aren't that far off.
Too rich, and you'll start having a hanging idle when you let off the throttle.

 

You have to get the Bike to IDLE without depending on the IDLE Adjustment Rod to Open the Throttles.

Without benefit of a ColorTune Plug; adjust the Pilot Mixture Screws to provide the Highest rpm before being adjusted too Rich and causing a misfire.

As you Turn the Pilot Screws Out ... the rpm's will rise.
This technique is called "Tuning By Ear"
This is “Real Old School Tuning”
By “Ear”

Start 2.5 ~ 3 Turns OUT from bottom on all 4 Carbs
(For 750 Bikes I’d set them at just between 2-3/4 & 3 … closer to 3)
Put two drops of light Oil in each Pilot Mixture Hole'

Important:
Make yourself a screwdriver that fits the slot on the Pilot Mixture Screw with Precision.
Even if yours are loose and won’t bind … you want to be able to “Feel” the Screw moving.
If they aren’t loose an ill-fitting screwdriver will destroy the slot, causing a big problem!

Above the Starter Motor ... Under Carbs 2 & 3 is the Idle Adjustment Rod.
It has a Thumb Wheel on the end.

Turn it Clockwise a tiny bit at a time until the engine is running steadily.
Don't exceed 1,200 rpm’s (1,050 if you can get it. 950 if the Tuning permits)

While the Engine’s running.
Begin some Tweaking.

Turn the Pilot Mixture Screw for #-1 OUT ... real S-L-O-W-L-Y.
Listen for the RPM's to INCREASE.
The revs should rise as you give it more Fuel and Air at the Pilot Screw.
>>This is Pilot Mixture for Idling.

When the revs rise here’s what to do...
Keep the RPM's at 1,100 by reaching under the Carbs and lowering the Idle Adjustment Knob.
Stay close to 1,000 rpm’s at all times.

"Tweak" >>OUT<< ... the #-1 Pilot Mixture Screw listening to the Engine and Exhaust note VERY Carefully.

**>>Keep turning the SCREW ~> OUT >>IF<< the RPM's continue to rise.

At some point ... The RPM's ~~> will NOT continue to rise.
Remember this Point. You have to come back to it.
At THIS point:
>>>||| MICROSCOPICALLY continue the Turning OUT...

UNTIL <~~

The Mixture gets TOO RICH and the Bike:
Coughs
Misfires
Burps
Runs rough
Etc.

>> STOP <<

THEN <~~ Get ready to make a CRITICAL Adjustment.
Pretend you are about to move THE SECOND HAND on a STOPWATCH!
One FULL Turn would be 60 Seconds ... right?
OK.


Turn that Pilot Screw ~~> IN <~~

Two (2) Seconds ... maybe Three (3) (Seconds***, small, a (my-nute amount)
Don't go beyond four.

Run fans to keep the bike cool.
Throttle it up and let it idle.

Adjust the IDLE rpm's with the Idle Adjustment ROD.
1,100 Max

Tweak #-2
Just exactly like #-1

(If the rev's exceed 2,000 ... back-off the IDLE SPEED ROD More)

Then finish-up doing #-3 -&- #-4.

When you are done ... TWEAKING ... you will need to Road Test for THROTTLE RESPONSE.

IF...

You are Idling, say, at a Red Light and when the light turns green and you take-off ... (Getting “Out-of-the-hole”) … and, …

The Bike ~> BACKFIRES a little bit before the Power comes on:
Your LEAN
The Pilot Screws need to be:
Tweaked OUT
Two (2) Seconds. ((Degrees))
Chart where you are at from this moment on … +2 Degrees

IF...

You are at the light and take-off...
The Bike ~> HESITATES for the slightest bit before the Power comes on:
Your RICH
The Pilot Screws need to be:
Tweaked IN
Two (2) Seconds.
>>>(Almost not turning the screw at all. A nudge!)<<<

Fine-tuning will be complete when you have Tweaked-Out the Backfire or the Hesitation during Further Road Testing.

All further Tweaking is to be done in increments of:

Two Seconds at a time.
Go find a closed Industrial Park and do it all in one sitting.
Have somebody put the tools you need in a sack and follow you over there in the car.
Don’t forget a Flashlight.

Backfire = Lean = OUT

Hesitation = Rich = IN

Go for it!

Get Tweaked
Watch your Plugs and treat each Cylinder individually.
Read the Color of the Plug on the Center Electrode’s Ceramic Collar.
Too Dark (Beyond chocolate brown) Tweak IN: 2-Degrees

Too Clean: (Clean or no coloration) Tweak OUT: 2-Degrees
As you Tweak individual Carbs for the right Mixture … Watch the Plugs coloration at the Center Electrode Ceramic Collar.

CLEAN: BAD. Too Lean. Tweak Screw OUT for MORE Fuel.
Although the Bike will run superbly Lean like that … it’s a dangerous condition that can HARM the Bike permanently.

Light Tan: Lean but OK.
This is a Power setting.
The Mixture is burning Fast making big power. You’ll have fast acceleration with the Plugs a light tan. You must monitor the situation and keep an eye on the Oil Level. If your Oil starts disappearing and you don’t have a leak … you are still too Lean.

Light Brown: Normal. Nirvana.

Dark Brown: Rich.
Most people like to have them at the Dark Brown Mixture setting.
The Engine makes good smooth power and cruises really nicely, staying cooler than the Lean settings.
If I am tuning someone’s bike for them … I set them closer to Dark Brown so they are insured against Ring and Valve damage.

 

One other thing I didn't mention> Have you checked your valve clearances? If they are too tight, you will be wasting your time tuning (sorry)

Rick FORGOT to mention "bring a lunch" :lol:

Great write up BTW Rick!

 

The hanging idle can also be caused by an intake leak. I like to check them by spraying a SMALL amount of starting fluid around the carburetor holders and the butterfly shaft seals.

 

This article is EXTREMELY USEFUL!!! I'm not really able to adjust the floats, but I don't think the bike needs it. I'm pretty certain, almost 100% that I need to be messing with the mixture screws, and compensate with the idle mixture. Thanks so much!! I'm [] this close to it running really good!

 

You'll know "You got it" ... when you press the Start Button and the Engine fires-up immediately.
Immediately.
You hardly hear the Starter grinding at all.

Then, you get to NUDGE the Mixture Screws to get on the edge of Fine Tuning.
Possessed by the romantic obsession to achieve perfection.
Addicted to finding the ultimate state of Tuned.

There's no cure.
Just "Tweaker's Anonymous"
Meetings.

"Hello. My name is snowbrdr88. And, ... I'm a Tweaker!"

"I can't stop. Look, I just bought a 4-Pack of BOSCH Platinum Fusion Iridium Spark Plugs for 40-Bucks. Please, help me!"