600cc Comet Carbie?

Normski

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Non-VOC Member
600cc Comet Carby?

Hello fellow enthusiasts. I'm new to this so go easy on me.

I converted my Comet to a 600 using one of 'our Terry's ' kits a couple of years ago. It goes well, although its a pig to start with a BTH ignition. I'm using a 36mm Dellorto pumper carby at the minute, although Terry did recommend a 38mm. After seeking advice from Dave D I'm at 24degree ignition timing. I had a 47 tooth rear sprocket made by a legendary Vincent owner Brendan ONeal in Geelong. Am I on the right track?
David's advice(and his help and advice has been enormously helpful to me too) of 24degree timing has given you good running, but this lower figure for advance may be giving you your starting problems, would it be worthwhile timing the ignition to say 30 degrees and see if the starting improves? If it did you'd know you need to find a means of having less advance/retard in order to keep the 24 degrees for running and still have decent starting.
 

Robert Watson

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VOC Member
I might ask what plus you run with the BT-H ignition.
I run NGK 7's on my Harley inspired ignition and it starts on half a prod. With the BT-H on another bike it was a bearcat to start on 7's, and on 6's became a one prod starter.
 

Black Flash

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VOC Member
Hello Greg
I'm using a standard rebuilt crank. I had loads of problems and went through 5 different silencers destroying most of them trying to get the noise down to be able to pass the MOT in Germany.
I finally built one myself. The engine easily spins to 6200 then slows down to 6400.
The Comet is geared to 110 mph at 6500 and feels rockets hip fast. Boy she really flies compared to a standard one.
I had loads of problems with the silencer as any change affected the carburation massively, I completely underestimated the effect of a race cam in a 4 stroke single
. With open pipe the engine spun to 6700 with earbleeding noise.
Bernd
 

vibrac

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VOC Member
Silencers and tests:
I was once volunteered as a noise tester at a race meeting, during testing a very very noisy NSU sports max came to be tested, we checked the stroke and found the correct revs the reading was to be taken at. The rider increased the revs the noise increased then as the correct measuring rev band came near all went quiet and at the measuring point it was legal at 105 Db. I of course asked the question and the rider showed me that under the crankcase at right angles to the main exhaust was a branch pipe sealed off with a brazed on disc. he had found by experiment just the length that cancelled out the sound waves. I belive helmholtz chamber is the key to further reading. If you cant join em beat them.
 

davidd

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VOC Member

Bernd did build a lovely Helmholz chamber for his Comet! I believe he used it to pass the test.

Bernd Exhaust.jpg


Bernd Ex 002.jpg


David
 

Black Flash

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VOC Member
Hello David,
Thank you for posting the pictures. I have no laptop at the moment so I can not get hold of my pictures.
I was on my last test ride before the MOT when I ruined my engine.
I got the noise down from 110 db with a Gold star silencer to 86 db with my self made silencer. Measured at 4000 rpm static. That is how the test goes in Germany depending on the standard rpm for the original bike.
When the engine is under load its a different story though.
But I think we are digressing .
I wish Harry all the best with his Vincent.
From my personal experience I would completely disassemble the engine and check everything. An easily solvable problem can bust your bank account if you break the engine.
Also with not so many specialists left, it could take years to get the engine back.
 

ericg

Well Known and Active Forum User
VOC Member
Hello David,
Thank you for posting the pictures. I have no laptop at the moment so I can not get hold of my pictures.
I was on my last test ride before the MOT when I ruined my engine.
I got the noise down from 110 db with a Gold star silencer to 86 db with my self made silencer. Measured at 4000 rpm static. That is how the test goes in Germany depending on the standard rpm for the original bike.
When the engine is under load its a different story though.
But I think we are digressing .
I wish Harry all the best with his Vincent.
From my personal experience I would completely disassemble the engine and check everything. An easily solvable problem can bust your bank account if you break the engine.
Also with not so many specialists left, it could take years to get the engine back.
Talking about specialists left, Is Bob Dunn still running its business?
 
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