Struggeling with tuning pilot circuit

chee_dee

Member
Feb 26, 2019
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South Africa
I am in the process of tuning, or rather trying to tune a Blaster.

Leak Test done, Compression test done.

I am at the Air adjustment screw currently but I can't seem to grasp the tuning method.

Problem is, on the one bike when I seem to get the highest idling speed set with adjusting the screw, the transition from idle to 1/4 throttle seems really bad and weak. When I on the other hand, I adjust the screw till the transition from idle to 1/4 throttle seems best, I end up 2 turns (anti-clocks) to where the idle was highest (1.7 turns out from closed).

Which is right?

Then on a different bike I cant seem to distinguish between idle going up or down when I do adjust. Will the tuning be easier when a tacho of some sorts is used?

Any advice would be appreciated. I really want to complete this idle adjust step so I can go onto plug chopping.
 
turn the idle screw up some so it's idling higher than normal
then adjust the airscrew to find highest idle.
>>>> allow 10-15 seconds between each 1/4 to 1/2 turn for the engine to catch up to the new setting. it won't respond instantly.
after you find high idle with the airscrew, turn the idle back down to the normal range, and fine tune the airscrew with 1/8 turns either way until it revs clean to 1/2 throttle. and it may require even more fine tuning once you ride it, or as temps and/or elevations change.

there is no correct setting, it's whatever each individual setup wants, the 1/2 to 2 turns is only the recommended range.
a little over or under that might just be what your bike wants, although anything over 2-1/2+ and I'd suspect an airleak.

anything over 2 turns out suggests you need a richer pilot, under 1/2 turn suggests leaner,
but I've never found the stock carb to want anything but the 32.5 pilot, from bone stock to piped and ported engines.
 
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Thanks @Awk08 . I will try again later today.

Yesterday I started from 1.5 turns out. I turned it in and at about 1/2 a turn left to go, the idle went down and bike started dying. This is good.

Now when I start turning it the other way (out/anti-clocks) the idle picks up around 2 turns out but it stays high until the screw is fully turned out. This suggests higher pilot. Not? But why? I do wait around 10 secs between adjustments for engine to catch up.

Also, when the screw is around 3 turns out the transition between 1/4 and 1/2 throttle seems better than when it is 1.5 turns out. This does suggest I need a richer Pilot Jet. But somehow this is not making sense, yet.
Leak test was done and passed btw.

I will play around more later this afternoon.
 
getting it to highest idle is kinda of just a starting point to find that sweet spot that starts/idles easily, and revs clean to 1/2 throttle.
none of this is written in stone.
your adding air to the circuit when turning the screw out more turns, not fuel.
the 3 turns out suggests a smaller pilot (not needed)
if it runs good at 3 turns out, run it.


"the idle picks up around 2 turns out but it stays high"
sounds like 2 turns is it, then fine tune with slight adjustments to get the revs clean, then possibly again in action, and during temp or elevation changes