5 replies to this topic

[dabomb]

Does any one know how many turns the mixture screw has to be out??
Cheers

[sr34]

from the 2002 manual


Slow Jet And Air Screw
The air screw meters air that is mixed with fuel metered by
the slow jet. .
Turning the air screw clockwis e, enriches the mixture:
counterclockwise leans the mixture.
Turn the air screw in until it lightly seats, then back it out to
specified position.
Air screw opening: 1 turn out
After warming up the engine, connect the tachometer and
slowly turn the air screw in or out until the engine revs up
smoothly .
Adjust the idle speed by turning the throttle stop screw.
Install the jet needle into the throttl e valve.
Install the thrott le valve spring and cable setting plate onto
the carburetor top cover, then connect the throttle cable to
the throttle valve whil e compressing the throttle va lve
spring.
Installation
Install the carburetor in the reverse order of removal.
Install the throttle valve while aligning ~ groove ~h the guide
in the carbureto r body.
Idle speed: 1.300 '" 100 min" (rpm)

[fastducs]

FYI montesa changed carbs in 2001 from Dellorto PHBH series to PHBL series. But as far as air screw goes, it is tunable for each specific bike to match conditions of the day, such as altitude, temperature, humidity, pressure. I'd start with 1.5 turns out from fully seated, and go from there, assuming that your jetting is pretty close to begin with. Keep in mind that the air screw has the most effect from closed throttle to about 1/8 open. The rest has to be done with jets and needle.

[samandkimberly]

I've been trying to adjust the mixture screw on my 2000 315 and finding it has very little impact at all. Fortunately the bike ticks over pretty well regardless of the setting, but I'm curious if anyone else has experienced this? My gut feeling is that the passageway must be plugged up, but is this were so I wouldn't think it would want to idle.

Sam

[Wherry]

PHBH. Mixture screw adjusts air. Around 1.5 turns out.
PHBL. Mixture screw adjusts fuel. Around 3.5 turns out.
It'll say on the side of the carb which one it is but if that's difficult to see the PHBH has the mixture screw towards the back (air-box side), PHBL has screw engine side.

[samandkimberly]

Thanks, everyone. I have the earlier PHBH carb, and understand relatively well how it works; I'm just surprised at how little effect it has on idle/off idle operation. From about 1/4 turn open on to 2-3 turns open it acts very similar, the exception being that it needs to be warmed up a little for the idle to be good at 2.5 + turns. I finally settled around 2 turns out.

It's really not a problem, in that the the bike runs well over a wide range. I'm going to remind myself that the enemy of "good" is "better" and leave it alone.

Sam