Jetting a dellorto SI 24 or 26 carb for Polini 208cc engine

I am building a P200 engine with Polini 208 cc barrel, piston, head etc. I bought the unit complete and the casings have been ported already. It is the steel barrel version with a piston with two rings.  I have just purchased a serie pro gas flowed race crank and countless other new parts. Bearings, seals, in fact everything I could need to do a full rebuild. The barrell has been cleaned and rings gapped correctly. Everything that needs replacing is being replace, even the engine mountings!

The engine came with a dellorto SI 26-26mm carb and I also have a dellorto SI 24-24mm carb. I do NOT want to be putting PHBH car or anything like that on the bike. I would prefer to use one the carburrettors I have already.

I am planning to fit a fast flow fuel tap, and also the DRT float chamber with 5.2mm float to whichever carburretor I choose to use on the engine.

My questions are as follows:

1.  Am I better to use the 24mm carburettor rather than the 26mm carb? Some people in the UK say the 24mm is a better choice. I have no idea why?

2. How should I jet the carburrettor for a polini 208cc ported engine? I have heard many different views on this. I need to know the size of idle jet, air corrector, mixer and main jet - at least as a starting point to work from.





i've read that the 26-26 is more difficult to get tuned in optimally. if you are going with the DRT chamber, DRT float and DRT spacer i would think the 24-24 would be fine.

Hi I have a great bit of info on the carbie tunning it is not on dellorto but it give you simple tips to how it works and how to get it tuned to the engine it won’t tell you the jet size but it will tell you if you need to go up or down in size

If you want it let me know and i will email it to you it is a bit big to put on the forum

it has always worked for me no mater witch carbie i hapened to use

Regards Clayton

I'd be keen on this info as well.

Can you PM me with your email address?