T5 jetting.. it's good but it's not right(!)

Hi all,

so threw the second hand Malossi kit on my Mk1 t5 (24mm del, simonini, mod head, timing 14deg - otherwise standard).

I’ve been trying different main jets to try and get it running right… but it’s being a bit of a bitch in a band between 3 and 4K revs when it misses quite badly… then cleans out to run nicely around 5 and above.

This is when running a 122 main as recommended to me (i think 120 is standard for this kit?), it is a little better when i switch to a 118 (and completely chokes up wiuth a 126 - no accel) but i’m concerned that the plug looks a little light after a bit of a run.

So it sounds like it’s flooding at lower revs… any idea why it would be doing this with the recommended jet that i think comes with the kit? Is there a way i can change some of the other jets to eliminate this?

It’s great at 6K!! just getting there cleanly is the problem!

Thanks v much.


ok so i’ve checked out all my jets now and the bike is currently holding:

Idle jet 50/100
Main stack - 120 air, BE4 mixer, 118 main
Mix screw is set at 1 1/2 turns out from closed.

Does anyone know if these settings and jettings could be causing the missing problems that i referred to earlier in this post?

What would people recommend running with for a t5 172 kit, simonini pipe? Would a 26mm carb give much improvement in the power?

Thanks v much.


The mixer tube on a standard T5 carb is BE4

How many turns on your mixture screw? Your idle jet is probably a 55/160. And your main jet stack is probably a 160 air, BE3 mixer, and whatever main you’re using. Check it out as I’d be curious to know. Good luck…Also be sure all of the jets are free from any crud, give 'em a good blast of carb cleaner.

Thanks… i’ll check this out and get back.

Also… another question!!

I was looking at the listing on the Sip site for the Malossi T5 172 cylinder kit… can anyone tell me what the two small metal pins are for in the photo? i’m a bit confused here as i bought mine second hand and am wondering if i’m missing something!



have you had any luck with the kit yet

HI Gaz,

unfortunately not!

I’ve gone back to my standard T5 piston and barrell (hence the search for a cheap unmodified head that you will see in another post!).

The kit was just rattling around too much for me… it seems that the piston was moving around on the gudgeon pin a lot and making a really bad noise.
The bike ran alright… but i just couldn’t ride it every day when it sounded like that.

Several people have said that the Malossi’s are just naturally noisy but this was a little ridiculous. I bough tit second hand so might wait till i can fork the cash for a new one and try that out. I’m still keen to kit the bike though cause i am certainly missing the low end torque now that the original setup is back in place.

Haven’t got a T5 head have you?!! ;D ;D

Cheers for now