Carb Tuning.

[Bill_on_a_bike]

Basicly, I'm pretty sure my 'ickle bike is running a bit rich, the mpg isn't anything like it should be, and occasionally the spark plug cokes up a bit.

I've read many websites and many books and have concluded that I need to adjust my throttle jet? Can this be done without completely dismantling the carb?

As the signature says, a bit green.

Cheers all

[Bill_on_a_bike]

Ok, on re-reading, haynes manual says "check float chamber level" yeah ok "Then run the engine until it's at operating temperature and adjust the pilot mixture screw" THen it gives a load of symptoms for over rich and stuff.

but as far as i can tell, this screw is inside the float chamber, do you really have to take the float chamber off, adjust the screw by quarter of a turn, put it all back together, and run it again!?

[Guest]

Ok, on re-reading, haynes manual says "check float chamber level" yeah ok "Then run the engine until it's at operating temperature and adjust the pilot mixture screw" THen it gives a load of symptoms for over rich and stuff.

but as far as i can tell, this screw is inside the float chamber, do you really have to take the float chamber off, adjust the screw by quarter of a turn, put it all back together, and run it again!?

 

the sr screw is on the underneath outside of the carb in a little recess no need to take carb apart ......

i am only giving this advice on its location not any advice regarding tuning

[Bill_on_a_bike]

Thank god for that, cheers Tim

That makes life alot easier. I've got this saturday off work, so i might have a little tinker then. And hey, if it all goes wrong I get monday off

[rollazuki]

OK, remove carb, remove float bowl, and clean out with proprietary brand carb cleaner(blow compressed air thru jets etc(carefull with eyes))

Position carb so float is just rested against its (sprung) stop and measure float height.

On some bikes it is set by using a transparent tube to measure petrol depth.

Follow manual for this one.

Refit carb, warm bike up.

The pilot screw is usually set approx 2 1/2 turns out from just bottomed. This is a good starting point.

letting bike tick over, turn anticlockwise(outwards) 1/4 turn. What did the engine do?

If it increased in revs, wait a mo and turn 1/4 turn again.

Do this until the revs fall slightly, then turn it a 1/4 turn back.

1/4 turn increments only ok, you could do 1/8 if you are really patient.

If it immediately starts to lower the revs on the first turn, go the other way. ie 1/4 turn in each time, until the revs start to fall, then 1/4 turn back out.

After you have done it, rev the bike and let it fall to tickover. If it hangs for a moment then settles its a little rich(1/4 turn in) or if it drops, falters , then picks back up to tickover, a little lean(you guessed it, 1/4 turn out)

You can always fall back on the factory setting if it all goes wrong.

When you are done, rub a good smear of grease round the airscrew threads to stop it corroding in place.

[Bill_on_a_bike]

Cheers rolla, that's kinda what i had in my head but I wasn't sure what the tests for rich and lean would be.

The manual mentions adjusting the throttle stop, "adjust idle jet to the highest possible stable tick-over speed speed, this speed can be altered with the throttle stop"

Yeah the clear tube idea is mentioned in the book aswell, sounds like alot less faff aslong as you've got level ground.