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Amateur Manx 40M preparation

This is a discussion on Amateur Manx 40M preparation within the Vintage Motorcycle Racing forums, part of the Caferacer.net Forums category; Originally Posted by Mike 40M Test start accomplished. It'a a lovely engine (thanks Molnar), really smooth. Only air in tyres and petrol in tank (not ...

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Thread: Amateur Manx 40M preparation

  1. #101
    Senior Member Cyorg's Avatar
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    Quote Originally Posted by Mike 40M View Post
    Test start accomplished. It'a a lovely engine (thanks Molnar), really smooth. Only air in tyres and petrol in tank (not the opposite). It's a very easy starting machine. As an old racer explained it, compression ratio should be where it gives lot of power and is easy to start. In the old days when engine was off when the flag was dropped. Seems the float bowl change worked. Now load everything in the van. Practise on track sunday
    Looks very nice. It inspires me to head out to the garage and do something with the shrapnel laying under the bench.
    I’m assuming there are modern bits lurking inside that mag. Wonder if they help with the starting, although nothing wrong with a old one in proper working condition (other than price). Good luck at the track. Perhaps a smidgin of R40 just to add to the religious experience.
    "Non urinat in ventum"

  2. #102
    Senior Member Mike 40M's Avatar
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    Track test done. On the positive side it's nice handling and fairly comfortable to ride. I am a bit more used to the TTI gearbox but still don't like it. On the negative side it still was ok when warming it up but still power for a couple of seconds and died a couple of seconds. So my guess that it was a float bowl problem was wrong. Luckily a Velocette racing friend appeared. He had time to help me trying to figure out what reason it has to behave as it does. After a while, we found that when I put a finger close to the intake, it got soaked with petrol. Much. Explained the 5 MPG fuel consumption. Our guess is that in the fight between intake sucking in and exhaust blowing out, the silencer won and made the carb work the opposite way.
    Some of you probably has a better explanation to it. As carb, engine and exhaust pipe is a proven combination by other racers, the most likely culprit is the silencer.
    Next to do will be either to buy or build a new silencer. I think the way to go is a less tapered cone, followed by a revese cone and after that a large diameter stinger. Lots of calculations though to get it right.

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