Carbs & Primary Oil Seal

E

Evan

Full member
Location
Texas
Is it best to put carbs on before mounting engine. Last time I put carbs on after I put engine on frame & it took time. Then the mixture on the Del lortos right now is set for Ross Pistons which is on 17580 & running beautifully. I was told this is the max bore. These are coming off & going on 15538. This Gt I'm doing has Alitalia Laverda 2nd size up bore & pistons which I put in back in 1988. Now I Rebuilt top only. (head was making a tapping sound) So starting point on carbs (which I am not going to do) is 1 & 1/2 out. (When I did that in 2019 it was so lean on the bored out Ross' I overheated it. Took a while to figure it out.) So how far back should I turn the mixture for the Laverda 2nd size up? One full turn? Then figure it out warmed up @ idle?
Then Grn Bk says Plate Oil Seal is 20 x 30 x 7. I guess he means Primary Plate.
& then going up sizes on the Cylinder Bores. 2nd size up would be 75cc more. Making the GT a 825cc. then the Ross max bore would be a 975cc...? Just wanted to know.
 

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I never even envisaged putting the engine back in with the carbs, but why not.
They're however not difficult to mount, just start them horizontally on a silicone lubed intake and wiggle.
I'm no good at maths but the capacity you give for overbores would need new sleeves and boring out the cases and cylinder block!
First oversize is +0.2mm, second + 0.4 etc.

Alitalia must really make the bike fly. :)
Never heard of them otherwise than as the Italian national airline.

Paul
 
you just have to calculate the quotient of the square of 80,4 and 80, all other factors like pi, stroke will be constant.
The quotient is 1,01 so it is 1% and 7,5 cc not 75 cc ☹️.
 
You can't set mixture on a motor based only on the bore size. Loads of factors are at play: compression ratio, cam profile, valve size, carb slide cutaway and more.

The normal route is to get it idling and picking up off idle and dropping quickly back to a smooth idle. If the mixture screws aren't giving the right result from 1-2 turns out (more turns out = richer) then change the pilot jets.
 
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