Twin starts but won't run

[Bill Thomas]

Hello John, Sorry you wasted your time, No two vin's are the same, I think Tims special has very long inlet manifolds. I remember years ago a USA article on Ram Stacks, I think it works out if the length from the inlet valve to the end of the carb bellmouth on mk2 cams is 14 inches you get a mild supercharge. I wonder what your petrol is made of ??. Some time ago on the Forum, A bloke from AUS told us about special spark plugs that cost a lot and were very hard, I had to try them, What a pain that was, the silly thing was, The bike was fine before. Is that why we run these old bikes, Something to play with ??. All The Best, Bill.

 

[Howard]

Hello John, Sorry you wasted your time, No two vin's are the same, I think Tims special has very long inlet manifolds. I remember years ago a USA article on Ram Stacks, I think it works out if the length from the inlet valve to the end of the carb bellmouth on mk2 cams is 14 inches you get a mild supercharge. I wonder what your petrol is made of ??. Some time ago on the Forum, A bloke from AUS told us about special spark plugs that cost a lot and were very hard, I had to try them, What a pain that was, the silly thing was, The bike was fine before. Is that why we run these old bikes, Something to play with ??. All The Best, Bill.

I remember the ram stacks thing. I worked the exhaust length out at 34" and the inlet (as you say) 14" - if I'd used them both on the comet, the bellmouth would have been further back than the end of the exhaust.

And, yes that's why we have old bikes - modern bikes have no soul, and don't need us tinkerers - but they're good for blowing off steam when you've tried 39 different timing positions on the Vin, without success, and want to kick something.

H

 

[timetraveller]

Don't forget chaps that tuned length inlet tracts only work at certain revs. I find that with MkIIs correctly timed one has significant blow back from the carburettor bell mouth until the engine gets to 4,000 rpm, then it disappears.

 

[Tom Gaynor]

Interestingly, the Petty Manx gives optimum performance at 34 degrees BTDC (13.8:1 cr, on avgas) with both Lucas 2MTT mag, and super duper electronic PVL system. The only difference I can see is that the mag won't spark NGK 10 face-discharge plugs, and the PVL will.