In relation to all four, or technically 5 engines that i've had, they all sounded a bit rattly, but i just thought they were poorly machined and assembled so accepted these rattles as normal.
I didn't realise that the engines were severely detonating and that's with 98 octane fuel!
The only modification i've made are that of grinding out the aluminium intake tube for a smoother turn radius at the elbow.
I'm sure the larger D-sized hole adds a bit more flow to the system, but i can't see it allowing such an increase in air flow that a massive increase in fuel flow would be required.
I know some may suggest the intake tube to cylinder or intake tube to carburettor might have air leaks for it to be requiring a No 84 main jet, but this is not the case as i've sprayed mineral turps all over the carburettor and intake tube when the engine is idling and the rpms do not change at all.
This suggests absence of air leaks.
I've read many times, how people have found their engines to run optimally on a No 72 or No 70 main jet - compared to my engines, i don't know how this is possible.
When i ordered my Dellorto SHA clone carburettor from Rock Solid Engines, it came with the standard No 76 main jet and a Rock Solid Engines "preferred" No 72 main jet.
For the life of me, i couldn't get the carburettor to run correctly - the engine ran poorly with the No 76 and even worse with the No 72 main jet.
In the end after about 2 days of frustration, i gave up on the Dellorto clone and went back to the standard NT carburettor which ran a lot better.
In hindsight, i should have tried experimenting with larger jet sizes.
Who knows, with a No 82 or 83 or 84 main jet, the Dellorto clone might have worked very well.
Having said that, the NT carburettor works perfectly with the No 84 main jet and the circlip installed on the highest setting (the needle sitting in the lowest possible position in relation to the needle barrel and the carburettor slide).
I have no reason to change carburettors as the NT works perfectly well with a No 84 main jet, not to mention a noticeably cooler cylinder head at cruise, providing a smoother and more powerful engine.
The fact that i've traveled 1200 kilometers (745 miles) on a partially damaged big end connecting rod bearing which is 400 - 500 kilometers (248 - 300 miles) longer than all 4 previous engines suggests that the No 84 main jet is playing a significant if not a complete part in the longevity of the engine.
I can't say if others have just been lucky or if there are manufacturing differences between Australian and American shipments of these engines.
People will just have to try it for themselves.
My suggestion, based on my own experiences - order three jet sizes (No 82, No 83, No 84) and experiment.
There are only two outcomes - either it will be operation success or operation failure, but if it's operation success, it will be the cheapest power up option you can get; not to mention a smoother, cooler running engine that has greater longevity.
Fabian