idle screw well in, mixture screw does not a lot

[tonydevon]

Hi, just wondering if this is a sign of maybe my carb needing a bigger pilot jet?? or maybe the nut holding the bars is buggered

198 Mugello small block, 28mm dellorto, PM tuning pipe, no filter, 18 degrees timing, NGK BR8ES.

it starts pretty much first kick, 99% of the time.

only way I could get it to idle was with the idle screw all the way in.

I have tried the mixture screw, was told 1.5-2 turns out, have been well either side of this and nowt appears to happen

AV266 with X7 needle, 2nd groove from top. 55 pilot, 118 main, 40 slide

choke is going fully off and theres some slack in the outer cable housing to proove this. putting the choke on kills it, so its not lean.

all manifolds are sealed and tight, head is correctly torqued down.

given the engine a few little revs (just blips to about 1/3rd throttle) and its boggy, but this is a newly built motor, and its my first 2 stroke, so no idea if they will improve running with same carb settings as the top end beds in? or if the setup is just wrong

[goldeneye]

i"d drop the pilot jet to a 50 , or even a 48.

[sideout]

AV266 could be a bit rich. As there is a fair bit of bleed in the stages of carb progression, try dropping the needle a clip position or give a AV264 a go, however you may need to be a bit careful with the latter without a filter
Some people prefer an AS266 with that set up as it get leaner quicker. (The needle engagement is different than a AV atomiser)

[tonydevon]

ok thanks guys,time for some online retail therapy

suppose it actually makes more sense to make it smaller, less fuel,so leaner, and wont need the slide to be so open

will look into alternate diffusers and needles.

I obviously wont be ragging it,as it needs running in, but will it rev up if the jetting is right, or will that improve as it runs in

[nelson pk]

In my opinion i would not try an AS266 with an X7needle it will be way too lean in the mid range!
Try the 50 or 48 pilot to get it ticking over. If you've just built the engine dont worry too much about an over rich tick over as long as it will tickover.
In my opinion if you go down to a 48 pilot and it still seems way too rich on tickover try a 45 slide before leaning the atomiser/needle combo. Again if it comes back down to tickover pretty quick you will be safe.
A lot of people dont bother changing slides because they are more expensive than jets and just change the atomiser but remember the bleed hole between your needle and atomiser has to be big enough to supply more fuel at higher revs when in mid range postions.
As long as it revs up and comes back to idle (without "hanging up") quickly your safe.
If you change the slide also re check the needle setting as it may want a richer needle position after this change but it will lean off the rich tickover.
Take it out and dont worry if its a little bit spluttery at very low speeds. Doesn't hurt to be a little rich at slow speeds.
Run it for 300 miles getting a feel of it as long as its rideable and then start fine jetting after the running in process.
When you jet it, jet it for when "its on the pipe" or in the powerband. Again a bit of splutter wont matter at very low revs. This way it will not go pop.
The biggest danger point in my opinion is when you run at full throttle to get your speed up and then roll the throttle off to cruise in the mid range for long periods of time so check this out when your doing your jetting.

[Darrell Taylor]

if its newly built and your only revving it to 3 k it may be nothing more than oiled up from the build oil ,id fully warm it up and give it a good clear out with some 3/4 to almost full throttle blips then when clear see how it is ,quite often what appears as rich jetting upon starting can clear by the time you ride it to the end of your street and run really well ,if not then as nelson said,and id start bigger on the main jet 125/128 better to start with a full thottle too rich splutter and work down than start with a small jet and a seized top end

what squish clearance was it set to in the end?

[tonydevon]

Thanks. i will up the main. i have a 125 so will fit that. as it is is just goes BLAAAAARRRGGGHHHH if you open it up.

squish set at 1.2 mm

just noticed today i got needle clip in 2nd from bottom not from top. will change that.
placed an order with wasp performance last night for other diffusers and x13 needle. aling with 50 pilot. will look into the alternative slide. i have a spare 40 so mightopen it up to experiment. believe the sizing is related to the height of the gut out 40 - 4mm 45 is 4.5mm

[nelson pk]

Yes your right tony about the size of the cut away in the slide and yes you can mod a 40 to 45.

[tonydevon]

new jets and bits should be here tomoro, it was suggested to me today by someone that maybe my timing setup of 18 degrees is possibly affecting the idle, and I should go to 16 degrees

I was under the impression that 18 was a safe setting so I went with it, could he be right?

[nelson pk]

I would say doubtful Tony........as in my mind if the timing is more advanced (18 degrees instead of 16 degrees) it should in theory help the tickover.
If you retard back to 16 degrees it will be safer at higher revs but if anything it will make the tickover slightly worse.
As Darrell said its definitely good practice to warm the engine up for a few mins by giving a quick try up the road before you make any carb adjustments.