Pilot Jet Size 17.5mm Carb?

[mkksat]

I have a 2T Zuma sport 70bbk with a Technigas Silent pro exhaust. It’s currently running stock carb upjetted to 85 main & stock pilot, stock airbox snorkel removed. It runs great with that setup.
I have a 17.5mm carb I want to use, but having tuning issues. I tried with 89 main. The mid to high throttle was great, but low not so much. I have a 38 for pilot…. is this the correct size? Seems low to me but that’s why I’m here asking for advise, lol.

[RyanWiltshire]

38 is a standard size pilot that usually comes standard OEM out of the box. have you tried putting in a W7 needle? what needle you got and long as you're idling fine and you're not running too rich or too lean on the pilot, you should be fine, it might be needle related, but always change one thing at a time, try first with lowering the pilot and see how it acts, gets worse? go back and then up a pilot, is it running worse still or better or no change really? you need to work out where exactly in the circuit it's playing up, it goes off from the pilot to the needle then main, so take your time!

[mkksat13]

To tell you the truth I never did anything with the needle in the 17.5mm carb. In my stock Zuma carb I raised the clip up one notch. I’ll look into the W7 though.

[RyanWiltshire]

Jun 28, 2023 12:28:21 GMT -5 mkksat13 said:

To tell you the truth I never did anything with the needle in the 17.5mm carb. In my stock Zuma carb I raised the clip up one notch. I’ll look into the W7 though.

W7 is quite the norm usually for dellorto carbs, I have always used W7 in my dells with a 38 pilot and 92 main. with this weather in the uk right now I am constantly changing needle clip and main jets etc, it's such a pain but a massive con to 2strokes I guess. let us know how the needle change goes, personally I would  go with the needle change first and see how your bike behaves, as I think you're getting issues from possibly needle>main or your pilot is too rich and bogging you down, is it going burrrrrrrrr on the crossover to the main or is it spluttering and spitting and then all of sudden just takes off? 

[mkksat13]

It feels rich to me at idle, tons of smoke. If I raise the clip, that lowers the needle, so it leans the pilot circuit, correct? My air screw has zero effect on the idle as it sits now. I can close it completely and no change.

[Zino]

the needle does very little to the idle circuit
The needle does the most from 1/4 to 3/4 throttle
do you have a manual choke ,or auto choke ?
could it be stuck ?

[Zino]

you  just might need to go to a smaller pilot jet
the 38 might be to big since you cannot get any control of it with the air screw between 1 and 3 turns out 
I dropped down from a 38 to a 34 on current scoot with my 17.5 dellorto

[seacoastzuma]

Jun 28, 2023 11:31:05 GMT -5 RyanWiltshire said:

38 is a standard size pilot that usually comes standard OEM out of the box. have you tried putting in a W7 needle? what needle you got and long as you're idling fine and you're not running too rich or too lean on the pilot, you should be fine, it might be needle related, but always change one thing at a time, try first with lowering the pilot and see how it acts, gets worse? go back and then up a pilot, is it running worse still or better or no change really? you need to work out where exactly in the circuit it's playing up, it goes off from the pilot to the needle then main, so take your time!

I'm running nearly the same setup as you, albeit with a malossi 72cc kit and some airbox mods. Ryan makes some great points with changing the needle, as when using the stock needle on my 17.5 del carb, In couldn't get my low/midrange dialed, and was running something like a 118 main jet with the stock pipe. I swapped the needle from my OEM zuma carb and now am running a 92 main and I've fixed the flat mid range and peaky top end. The stock pilot has been good, so the needle swap is a free experiment worth trying.