250-500cc Where do I start?

You can only try, one quarter turn will make a difference but weather its hitting that magic spot right on well that's only going to be known once tried.
Pj won't be affecting anything until your over half throttle, could trim your pj tube a fraction and get that to kick in earlier.
May just be on the cusp of kicking in when the hesitation starts.

Wake up juicy - trimming the tube make the pj work later

I would expect if it was rich enough to cause a hesitation (loading up) then you'd have many other rich symptoms too. If it's loaded up from being rich then also it wouldn't clear out immediately.

Generally a hesitation when you open the throttle indicates a lean mixture. When you open the throttle you allow in more air, that's all you're controlling. The amount of fuel drawn into the air stream does not increase at the same rate. This causes a momentary lean condition, that's why 4t carbs have an accelerator pump.
The hard part is determining at what throttle position the leanness is. Generally the lean area is just after where the throttle started before it was opened. Does that make sense??
It's all trial and error mate. If in doubt go richer first.....that's safe.

I dunno I just fitted my lectron and left it right lean.
Works fine for me.

What's a mik...a mik...ahhh nevermind

I think a 1/4 turn on the rod can make a significant difference. I did some 1/2 turns too, but now 1/4 t at a time. I'm fussy too and notice every stutter and blubber. People who say their 2t carb's perfectly must not be fussy. Anyway, every bike is different and just have to find that special setup.
My 165 likes and works best for me lean on the bottom and a lil rich on top. Starts 1 kick cold and idles a lil high, doesn't run away!, until warm, spooges a little if I do much putting around, pulls strong and clean off the botttom, then screams very strong on top Only issue is have to clear her throat after doing much putting, but I've adapted and it's just reflex now.

Don't forget when the PJ opens fuel mileage drops like an anchor.

1/4 turn can make a big difference especially when you get close to the sweet spot. Also you might want to check your compression after the red hot run, you might have killed your rings. I've experienced not being able to tune a Lectron properly until the squish band was done properly on a Honda CR250... the top end was fresh but the compression was 160 psi and no matter how we set the needle it had a dead spot or wouldn't idle. We cut the squish to get 225 psi and the Lectron tuned perfectly.

My 165 does same thing high idle on start up then settles once warm. 1 kick start every time. 38mm PJ 3/4 from seated, ms3 rod @ bout 49.5mm from memory. Wat u runnin Steve?
After leaning it out 1/4 turn the other week seems to have cleared up spooge n need to clear it's throat(within reason), seems very crisp!

I dunno I managed 100km to dry pretty much on mx track on 165 which was predominantly WOT so economy was pretty bloody good still. Reckon could go 130-140km on cruisy fireroads/open riding with stock wr tank!

I think u n Steve are right bout 1/4 turn making big difference especially as u say wen close to sweet spot. Jus seems odd I guess that it ran like a dog half a turn richer but now is borderline lean on top! I think that 1/4 turn back richer is gonna be 'it'!-hope so anyway. As it is now is more than adequate but if there's more to be had then I want it

Had a look at piston skirt n top thru exhaust yday n looks spot on! Can't really tell bout rings but bugger all blow by I could see n she's still runnin hard. Never took an initial comp reading so not much point checkin it now. Piston has bang on 50 hours on it so I'll run it for another 30-50 hours then pull it down. Cylinder really needed a Replate 2 top ends ago!:0

My 165 is set about the same as yours mate, 38mm, MS3 rod, @ 49mm, PJ 3/4. Didn't mess with the PJ hose. Installed white/green PV springs, so opening @ 6000rpm. F'ing ripper! tears the center knobs of every tire I've had so far I'm only about 70 kilos + gear, so easy to haul around.

My 165 has my modified rod in it, Its close to a MS3 just a tad richer from about mid to wfo, PJ tube is really short so the carb uses the rod to meter all its fuel untill its wound flat out then the pj works. Pulls like a train but is really smooth and long and not peaky at all, Not a drip of spooge /loading up even after 3 hours of playing trials rider and mixwd at 32.1 , took ages and was a labour of love to get it where it is but well worth all the effort.

Well I I did bout 3 hours Ridin today in nice wet sand across road from my place. Maybe I was a bit harsh on the 300 as the slight hesitation may jus be me not givin her enough wen changin gears in the sand n motor droppin off the pipe a bit. I taped a screwdriver to fork to adjust PJ whilst I was over there but got side tracked cuttin in new single n grass tracks n never adjusted anythin!!! Chased a few kangaroos round for a while then it was gettin dark. Not a trace of spooge even after slow Ridin in first gear, no loadin up, didn't get hot n nice strong idle too. Did cut in sum nice tracks tho! Love holidays!!!

I may still try a 1/4 richer n maybe even a 1/4 leaner on rod jus for shits n giggles. Run coupla tanks of 40:1 but can't be arsed mixing seperate fuel so will jus go back to 32:1 cos I'm lazy. Gotta take 165 over there tomoro or weekend should be a hoot!

johnny boy your silencer looks sweet. I think my 165 is bout as good as it gets after a 1/4 turn leaner rod adjustment the other week. Am very well satisfied it's close to perfection. Havnt noticed any spooge but I'm gonna try get it to by playin graham Jarvis' nuffy 3rd cousin log hoppin, practicing wheelie turns n stoppies n cuttin in tracks!

why go leaner for no reason? if it passed the test playing trials rider it should be good. i prefer to be a touch rich than touch lean tho..
glad its getting close!

Il try 1/4 richer first if worse I'll try 1/4 leaner than wher it is now. If neither as good I'll go back to wher it currently is. I gotta stop riding it n giv it a wash to be able to adjust first! Enjoying Ridin it ATM!

I'm talkin bout the 300 not the 165-she stays as she lays carb wise ATM very happy with it! Gotta pull me finger out n swap air filter out for clean one do can ride it. Ahh maybe tomoro

Ahh crap can't be bothered starting new thread or lookin for old one so postin here. Jus did 20km of grasstrack n single trail n noticed 165 was spitting coolant out overflow. Stopped let her cool for 10min then took rad cap off. Had pressure build up in there(not from bein hot). Couldn't see any coolant above fins. Started it n it's pumpin so high tailed it home. Can see coolant under exhaust manifold where pipe goes in. Havnt bothered to refill rads as I'm guessing this is head orings again? Letn exhaust gas in building pressure forcin coolant out overflow? Fricken dirtbikes always sumthn!

This was after I gave it a hose off. Whys it cumin out bottom of pipe? Is it jus left over coolant trickling down? Can't see any visible leaks around head or base of cylinder

Take the head off Shawry and it will reveal all!!!

Com'n mate, in your new found enthusiasm of being a member of the home mechanic, the bike's are testing you now

Testing my blood pressure!!! Grrrr