SI26mm on the T5..... bugger!

Hi all,

I got a spaco 26mm to fit to my T5 after the old 24mm finally gave up the ghost. I’m having a world - o - pain trying to set it up to run right… anyone got the same combo?


T5 mk1
Malossi 172
Head mod by Chiselspeed
Spaco SI26mm
Sito Plus
Timing 14deg strobed
8 plug

The carb was supplied by the guys at Chiselspeed after a conversation on the phone. They fitted it with a 132 main (which seemed kinda big to me considering i was running a 122 with the 24mm dellorto), a 50/100 pilot jet and a small drill bit with intructions to open out the pilot jet a bit if it running too lean down low.

I’ve drilled out the pilot and the bike misses a lot and has no power at speed in top gear.

Any setup advice appreicated. I’m wondering if i shouldn’t have just got the standard 24mm…!


… and also… (keep forgetting things)

what do you reckon is a good safe squish clearance for this setup?

and, Gaz, you running standard timing or a bit advanced? Strobed? (my timing marks on the casings were way out …).


I all so see you use 8 plug shoud be ngk B9ES in T5

MY carb is 24G bored out to 26mm

The area of the bore of the SI 24, is 452 sq. mm, and the area of the jet 1.22 is 1.16 sq. mm. It gives a relation of 1/387. This is what you had.

I.D. 26 mm, 531 sq. mm, jet size 1.32 mm, 1.37 sq. mm, gives a relation of 1/388 and that should be about right.

The odd thing is that SPACO make thier 26 carb with a 25 mm bore, so with the same relation you need a 127 jet, nearest size being the 128 jet.

Try that.


I’ve a GTR with T5-engine. Have put on a Malossi 170 and suitable head. Run Sito+. I’m very satisfied. Run with standard reinforced clutch. Tried Cosa FLII, but didn’t work. Will change to 21 tooth for upgearing approx. 5%. It’s really strong uphill and runs good, and suitable for touring. Wondered about going for expansion exhaust, but runs good enough with this setup, strong from low rev. Runs OK with 24/24E. Started with 125 main, and it seems OK. Should probebly use 122, but the sparkplugs looks OK, so I keep driving with 125. Have bought a Spaco 26G from Chiselspeed, but haven’t tried it yet. See some have some problems with that carb. Maybe trying it next summer (season almost ended here 63,5degr. north).

Pondus I think you may find 21t not as much fun as 20t. I both my T5s with 20t and one is a reedvallve. Also you will lose some power uphills and this can be frustrating. 21T works well with a Taffspeed pipe and 172 but otherwise dont bother.

would start ok and idle ok as soon as you went to rev it it would splutter then die drilled out idle ok now timing set at 15

P.S T5 always B9ES or equivelent

ok 25mm spaco

Hi jonni i have T5 172 kit, tafspeed head, scorpion pipe, 26mm carb i allso got drill bit of chiselspeed they said try 125, 128 ,130 main found 125 to be the right one the other jets are

120 air
50/100 idle with the first bit drilled out from under side hope this helps Gary


OK this time I just guess, then for curiosity and my data base please let me know:

main 125
iddle 50/160

Thanks for all the feedback guys… i appreciate it. Gaz, i had a vague memory that you had the same setup so it’s good to get yr info.

I’m hearing what Diablo says about the design of the carb too… the bike was running so damn fine with the 24/24G… really gutsy. Might fiddle a little more then end up with a new standard carb in the end anyways!.. ah, the sickness is deep!

Gaz, last question… did you try running with the 50/100 pilot before you drilled it out? What was the ride like? Plug too light?

ALso, whats yr idle mix set to?


Hi Jonni. I don’t think this carb will be of any great benifit to you because am I right in saying it is based on a 24/24E? The T5 carb is different and makes power lower down(dont forget it was a sports scooter) You wiil only see a slight benifit(if any) top end if you change the exhaust for an expansion. A shop will always put a big main jet in so its not there fault if it blows up. I’d be very surprised if 128 is the biggest you’ll need. If you rev counter works do some back to back tests and see if your making more power wouldn’t be surprised if your not-sorry

Original von gaz7: MY carb is 24G bored out to 26mm