Scooterotica

my mates holed his piston on his mugello 186 28mm dellotro
with a snail exhaust
what should his jetting be i run the same set up but with a
pm pipe with a 122 mainjet he had in a 108 should
his have a bigger main than mine
thanks

holed mine ... 118 main jet... 28mm dellorto.. sterling exhaust

conflicting advice being given on main jets, i find, some people say as low as 110, others in the high 120's ..

would be intersted to know of anyone with a 28mm delly and performance exhaust as to what jets.... as the pistons don't come cheap!

The many scooters that ive had to rejet with blown engines are quite often weak on the needle/needlejet and it can be that weak that it dosnt make any differance as to what mainjet you put in, as the mainjet has to run through the needle/needlejet.   My brother back in the early eighties, built a water cooled small framed Vespa. A steel lined aluminium barrel & 2 piece billet head, Water in through the barrel and out of the head then through a thermostaticly controlled electric pump to a radiator. He was convinced he had a problem with the cooling system as he had jetted up the 26mm Power jetted Amal on the mainjet by five sizes then blanked off the powerjet and up jetted again , and convinced himself it was rich and could not be getting hot because of it being weak...I helped him with an old trick that the racers used to use Prior to Dyno's....I Took the mainjet out lifted the needle to its richest position then fired the scoot up. With no mainjet It ran exactly as it had with the mainjet fitted, this was because the needle and needlejet were restricting the flow of fuel from the mainjet, he'd had a 106 needle jet in so we fitted a 108 that was far too rich, much over 1/4 throttle it cut out, we then fitted a 107, better just under half throttle bogged down not perfect. so we adjusted the needle down one notch, it now ran to near half throttle then bogged down, now put the same mainjet back in, still rich. Three sizes down from where he had started and the jetting was getting better, un-blanked the powerjet (before anyone says they dont make a 26 Amal with a powerjet.. I know, but my brother made it run a powerjet and also made his own chromed brass slides for it as well as making lots of other one offs for this scooter) after about three hours work, it was no longer over heating and we had actually down jetted the mainjet, but now it was metering more fuel from half throttle upwards  because of the needle and needle jet and had cured the overheating....

interesting stuff J1MS......

so, what needle/setting/jet would anyone suggest for a dellorto 28 phbh?

lammydave wrote:interesting stuff J1MS......

so, what needle/setting/jet would anyone suggest for a dellorto 28 phbh?

One thats capable of flowing more fuel than the mainjet.......There is a mathematical formula (that I have memorised) but if you get the. dellorto A GUIDE 1.1 and on page 18 you will find the maths necessary to do your own calculations.....Hope this helps....

[quote="J1MS if you get the. dellorto A GUIDE 1.1 and on page 18 you will find the maths necessary to do your own calculations.....Hope this helps....[/quote]

where might one get such a guide?

Will scan it and post it on here weekend If I can get time..

Full title;
Dellorto Carburettors
Dellorto superperformance
A GUIDE1.1
to the choice, setting and
use of tapered-needle
motorcycle carburettors.

Have a go at

55 pilot
AV266 atomiser
X7 needle (or slightly richer on an X13) 2nd clip
118 main reduce to 115 if too rich and 4 stroking

Should get you into the ballpark

You can download the Dellorto guide here:

http://www.thisoldtractor.com/gtbender/ ... rburettors

Stringy wrote:You can download the Dellorto guide here:

http://www.thisoldtractor.com/gtbender/ ... rburettors

Thanx for that, It saves me scanning my copy.....