SX200 noisy

[pg42]

I have an SX200 engine that keeps 'nipping up' in spite of being very carefully run in for up to 1000 miles before being DRIVEN. It has always sounded tinny and had a vibration even after 2 total rebuilds including the crankshaft. One of the engine mounting lugs has been welded at some stage and i always put the vibration down to that. I have pressure drop tested it including patiently warming the casing with no loss. I wonder if there is a heat crack somewhere that opens up when hot thus leaning the mixture right out. I think i read somewhere, years ago, that engine vibration can cause the fuel to aerate which causes fuel starvation. Any thoughts ??

[vegansydney]

What was the run out on the crank when you rebuilt it both times? Under 0.03mm? Of the last several 'off the shelf' cranks I've purchased, only 2 were within spec, the rest were out of true and (a very expensive) one was millimeters out.

Good luck!

[Adam_Winstone]

Ignition advancing at higher revs? Fairly common and only observed with a strobe.