Let's discuss vacuum sync'ing.

The bike being discussed has Mikuni carbs. I recommended an initial pilot mixture screw setting of 2.75 turns "out" (from bottomed) as a good starting point.

That doesn't apply to Hitachis. I believe the recommended spec for Hitachis is 2.5 turns, at least on the "early" ones.

 

After the fiasco of the Yamaha-supplied, EGA Testing Machines blew-over; Dealerships all but abandoned the sniffer. They usually were "Present" at the Dealerships for some time. Eventually most (if not all) became coat-racks, bulletin boards or a skeleton in the corner. Today, I'd say anyone who has one would let you haul it out for them.

Most Bikes had EGA Test Bungs.
If yours aren't seized; consider yourself lucky!

Tuning pretty-much got handed-over to the Tech with your W/O.
The era of Customer Satisfaction to end the come-backs of more tuning
evolved.

There seemed to be a consensus that if the Pilot Air Screws (Mixture screw)
were set to whatever kept the Customer from needing to come back for a lost time tweak be used.

This got determined by Off-idle response, ... (most cases).

This Preset, intended to make people smile, ... usually did the trick.

"Between 2.75 -and- 3.0 Turns OUT.
(Closer to 3.0 splitting the distance between (a) & (b).

 

ABSOLUTELY true. There are Yamaha tech bulletins to that effect. ("Tweak 'em rich until the customer is happy.") Not bad advice, actually.

BUT this is another reason to not trust the "as found" pilot screw settings for anything other than maybe reference at some point, even if they were capped.

If the carbs are properly serviced, the pilot screws will have been out and their o-rings replaced.

So ya gotta start somewhere. The factory was really cagey about "admitting" to even the very existence of the pilot screws; and only published specs for some bikes (mainly the pre-YICS 650s.)

The 2.75 turns to start recommendation comes from my personal experience with Mikunis and on multiple bikes.

Oh, and I have a copy of the Yamaha EGA manual for our era bikes. It is quite honestly, a ring-tailed hoot to read through. They were very afraid of the EPA.

 

Now y'all have me intigued. I am currently going through the above mentioned steps but was not aware of the Pilot Screw step. I have my carb rack off right now and can't seem to locate these Pilot Screws. I know that they haven't been messed with or serviced because *cough cough* I'm the original owner.
Where are they and should I mess with them since I know they were last set at the factory?

 

Follow the arrow for the mixture screw:



and after a bit of cleaning:

 

Would you PLEASE POST THIS I would LOVE TO READ THAT. 8O

 

There is a chance ... but, thanks to the many great "Tuning Tips" from our Forum's Wizard's, a slim chance your Pilot Air Screws will be Plugged.

If they're still in there, ... call the FBI and ask one of their Top Agent's, "What's the best drill size, for yanking-out the EPA Plugs on Mic and Hi-tots?"
Don't be surprised if he tells you and warns you about how close the Top of the Air Screw is to the Bottom of the Plug.

If you need to drill; don't lean into it.
Cause no harm to the very closely underlying Screw Head.
They need to be removed for you to get those Felonious Air Screws pulled, O-rings removed, and top-end flushed before the FED's bust-down your door, and Tazer you; then hall you away for testimony before an EPA Regional Sub-committee.


Clean the Hole.
Oil a M6x0,5 *Bottom Tap* -- Chase the Threads.

If you are lucky enough to get a Chewed-up Air Screw ... OUT, great.
Don't put-it back in.
Toss it.
Get new ones from Len.

Put the old ones out with the Recycling.

 

You are 100% correct in your thinking You are syncing which means to make the same( sync your watches on the count of 3 its 0500 we all set our watches to 0500 right) The slight differences (this is what is known as tolerances) compression, valves clearances, etc whatever is why we sync the carbs we are trying to get all the cylinders to perform the exact same as much as we can this makes for a balance of power and a smooth running engine. We bench sync to get the carbs close enough for the engine to run so we can tune it out thats all Bench syncing should get it within the paramaters that the cylinder should at least fire . If your gages have weird readings just switch them to a different cylinder if the reading matches the previous readings your gages are good dont toss them. Start the process with carb #3 its the kingpin all the other carbs sync to it

 

PS the clunk test has no effect on the carb sync if the slides do not work correctly thats a performance problem has nothing to do with carb syncing

 

Absolutely you should check them out and replace the o-rings if you are having poor fuel milage and performance problems

 

Ahhh okay! I do remember seeing those screw heads now, so mine must not be capped. Thankfully. I'll have to check them out when I get back home this evening.
Thanks for the pics! Like they say, "A picture is worth a thousand words."

 

Don't try to move them until you buy or make a Special Tool Screwdriver.
The Screwdriver Tip MUST fit the Air Screw's SLOT with NO side-to-side free play.

I bought New Ones.
I'd like a set with External Tweak Knurl.

If you find one that has a look of being Hacked-at; evoke Rule No.1!
"Don't do anything that will make your Bad Situation, ... worse!"

Whatever you decide to do if you find yourself behind the Eight Ball with one or more of those Damaged or Seized Air Screws, ... (after discussing the matter with the New Pope, extensively) ... should NOT be without the aid of a DRILL PRESS!

My advice from now-on, ... If you ain't got a drill press; find a Machinist to bail you out.

 

Yeah today I've been contemplating what to do. I could have sworn I read somewhere that they were factory set and not to be messed with. Now I know that's just an invite to mess with them for most of you renegades on this site. What exactly am I going to gain by tightening them down, then backing them off 2.75~3 turns? If they are "stuck" wouldn't they be stuck at the proper setting as I know for a fact that they have never been turned by a tool?

 

You need to remove the Air Screws to replace the TINY O-ring seated at the Bottom of the Screw Port.
Removing them and Flushing the Pilot Passages is important after over 20 years of neglect.

After the Screws are OUT, ... make sure you will never have to fight to move those Screws again.

Chase the Bore with a M6x0,5 Bottom Tap
Flush clean.
Flush Passages by douching through the Pilot AIR Jet, flushing the Pilot FUEL Jet and Air Screw Port passages.

Prep the Air Screws for Fine-Tuning.
Anti-seize the Threads in the Hole.
Teflon-wrap the Threads on the Air Screw.
One Layer.

Preset for future Fine-tuning.
Darken One Wing of the Air Screw's two Slot Wings with a Magic Marker.
It makes the Observation of the Adjustments less confusing and less likely to lose track.

 

That's what they wanted you to believe, so as not to mess up their emissions. As we discussed above, the dealers were told to go ahead and mess with them to keep the customers happy (and about half of the dealers re-capped them.)

The very first time the motor had its valves adjusted, the original settings became invalid. But it doesn't matter, because you're going to be removing them anyway.

Before you REMOVE THEM to clean the passages and REPLACE the tiny o-rings, carefully turn them in until they gently bottom out, and record the original settings. For posterity.

If you're working with (early, pre-YICS) Hitachis the factory recommended setting is 2.5 turns out.

 

Okay I can do that Rick. Once I've followed those steps and have backed out the screws 2.75~3 turns. What is it I'm listening, feeling, tweaking for?
Or just back them out that amount and it's good?

 

"Off-Idle Performance"

You want to dial-in a STEADY reliable IDLE.
Plus, ... a smooth, uninterrupted ... "Transition" from IDLE to OFF-Idle.

When you open the Throttles to take-off, ...
NO Bogging-out or Stall
NO Hesitation in the least.

The Bike should IDLE without Hunt or, what I call "The Poppities".
You should Idle: "Rummmmmmmmmmmmmmmmm"
Not: "Rummmm-popity-pop, rummmm, pop, rummmm, poppity-poppity".

You'll hear it at 2.5
Maybe even stall.
As you add Richness, ... Idle will sound like a Sewing Machine.

The ColorTune Plug allows you to "Find" this accuracy, ... Visually.
The Plug shows you the Burn inside the Combustion Chamber.
Adjust OUT until you achieve: "Bunsen Burner Blue".
Perfect Idle.

Tweak the Screw a bit more Rich, ... until the Blue fades-away.
Utopia.

 

Utopia I shall seek!

 

Now THAT is my nomination for "tuning tip of the month"!