Idle mixture screw

[breakwellmz]

For anyone wanting to adjust that difficult to get at idle mixture screw on the left-hand carb,i`ve found just the thing.
One of those double-ended driver bits that come with electric screwdrivers and drills.
A flat bit,anything between a .6x4mm to .8x5mm. By marking one of the hexagonal flats with paint or tape,it is easy to keep note of how many revolutions it has been turned.
I found mine to be set at SIX turns out(Manual says 2 1/2)-No wonder i have always felt it has run rich!

[Nils D]

You call it "Idle mixture screw". Don't you think it is the one that usually is called "Pilot screw"? It does not adjust the idle, but how the engine runs at lower revs.
Anyhow, I have made my version of screwdriver to adjust that screw http://www.mzriders.com/viewtopic.php?f=3&t=3288&start=15#p18562
(There I call it mixture-screw.)
And my bike does not run smooth at lower revs if it's at just 2 1/2 turns.

[billr]

I found mine to be set at SIX turns out(Manual says 2 1/2)-No wonder i have always felt it has run rich!

And my bike does not run smooth at lower revs if it's at just 2 1/2 turns.

I agree with Nils on this one. Just completed a round of maintenance, decided to "adjust" the pilot screw from 5 turns out (and running very smooth) to 3 out (hey, that's just about where the manual says, right ), just to see...
One ride to and from work...
rough idle, poor transition, surging at low revs, POP-POP-POW on decel...

Guess where the pilot screw is now...won't be messing with a good thing anymore...
Bill R

[Bill Jurgenson]

the "recommended" position for that screw is to get the required CO2 reading at idle.
It is too lean.
It is not to achieve a well running engine.

[DoubleTapper]

I live in Israel and ride a Yamaha 1997 XTZ660 3yf as my daily driver.

My bike is not idling well. It started out with what was diagnosed as the carburetor sucking air through the throttle shaft (part number 5Y1-14572-00) this resulted in the engine climbing to high RPS and not going back down to idle speeds once the bike was warmed up. The part (plate stay, 2 rubber gaskets) was replaced on both ends. I reassembled the carb, started the bike and sprayed the carb down with starting fluid. It didn't start revving so it looked like I had fixed the problem.

Now I can't seem to the bike to idle normally. It seems to start out ok, then after it warms up, the rpm's climb and drop and aren't consistent. I checked my valves, they are ok.

I've tried adjusting everything I can think of and even changed the needle settings.

Please give me the full list of what to check, how to adjust, what ever you can think of. Page 20 http://www.yamaha-motor.com.mx/Manual_P ... 2_1998.pdf

[pwillikers]

I just rebuilt my carbs and adjusted the pilot screw to 2.5 turns out. I am now experiencing dramatic pop pop pows on deceleration. Isn't this caused by unburnt fuel, resulting from a rich idle mixture, finding its way into the exhaust? Based on your recommendations, I'm going to enrichen it to see if that alleviates the backfiring, but it seems counter intuitive. I"ll report back.

[basser23]

So you've got the pilot at 2.5 and it pops alot? What happens when you decelerate and hold
the throttle just slightly open allowing more air in? Think you'll find is doesn't pop nearly as much...think that pilot screw allows a bit more air into the circuit..maybe wrong, but when
I do the above with the throttle,mine pops a bunch less...I will adjust to 5 turns and see what happens.
This can also be caused by an exhaust leak in the pipes..dont ask how I know:)