Pilot Jets - Carb - tickover-idle circuit

So I’ve beng trying to get my idle circuit right, and have these three jets.
Looking at the photo you would think they are increasing size L to R
But actually they are
L 42.5 from rebuild kit
Mid 45 genuine Mikuni from Allensperformance
R 42.5 Original
No wonder it’s trial and error

Any thoughts

Always use real mikuni jets/parts!! I have seen bad things from aftermarket stuff.

Rejetting can get ridiculous some times. Try this. Take the smallest jet you have and drill it oversize. Keep doing this, and testing until you feel you have it correct. Even if you go too large you can start over with another jet. https://affordablegokarts.com/pages/how-to-drill-the-main-jets

At one time in my life, Id say sure yea drill them jets out. My opinion has changed over the years though. Use authentic Mikuni jets. Aftermarket jets are not sized right and they arent machined like the Mikunis are. Have you decided on a main jet yet?

Hi All, thought this needed a bit of Engineeing so I built this this test rig. A litre of water up in the air, some hose connected to the jet which is pushed into a bit of heatshrink. I did this to close all the air holes and just test the Small hole at the end. Then timed how long it took for 10ml of water to drain through the jet.
Really interesting
42.5 Original jet 16.1 ml/minute
42.5 Pattern from rebuild kit 12.7 ml/min
45.0 Mikuni 15.9 ml/ min

so actually when I thought I’d gone up a size from the original to the 45, I’d actually stayed the same!
Also i checked the consistency between jets which was good.

Specdog said:

Rejetting can get ridiculous some times. Try this. Take the smallest jet you have and drill it oversize. Keep doing this, and testing until you feel you have it correct. Even if you go too large you can start over with another jet. https://affordablegokarts.com/pages/how-to-drill-the-main-jets

Click to expand...

Hi, smallest drill I’ve got is 0.7mm and even that looks huge next to jet.

NewHavenMike said:

At one time in my life, Id say sure yea drill them jets out. My opinion has changed over the years though. Use authentic Mikuni jets. Aftermarket jets are not sized right and they arent machined like the Mikunis are. Have you decided on a main jet yet?

Click to expand...

Hi Mike, I’m sticking with the stock 125 mains for now. Have 127.5 in case, but having learnt the hard way just changing one thing at a time. You have to get slick at getting the carbs on and off though. I’m down to about 30 mins.