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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
big TT carbs
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<blockquote data-quote="davidd" data-source="post: 54709" data-attributes="member: 1177"><p>I did not make the casting, although I wish I did. I do not have an original to compare it to, but I would not be surprised if it were done by a pattern maker and the shrinkage seems to be well accounted for. All the internals are Amal MK2. The cap on top was made so the spring could nest up inside and allow the throttle valve to to clear the bore. I will try to take some more detailed photos. </p><p></p><p>Glyn Johnson has an original on his Flash and I do have some photos. I will hunt them down.</p><p></p><p>Bill, this was prior to tuning and when I put it on the dyno I had to raise the bowl immediately. But, the very next run (on the single racer) was 42 bhp. Because it was MK2 I did not have a single tuning item to change out. I was hoping just to see what it did with the 28" long 2" pipe. We were all quite impressed, but had nowhere to go. This is also with a standard size head, not the big port. I put the 32mm 10TT9 on it and got 40, which was quite heartening, but by the time we put the straight through silencer on it was 37. I did many runs with different lengths and 28" open pipe made the most power at 7,000. So, it is very easy to get power from a straight pipe, but the minute you put any absorber silencer on it you loose quite a few hp. So, the racing silencer requirement works heavily against the Vincent. </p><p></p><p>The port velocity is very low with this set up leading to speculation that a smaller pipe with a megaphone would provide more power and it certainly did on Lindsay Kyle's bike. But, this is the stage of tuning that is wildly expensive. You have to make several custom exhaust systems that will probably not work and spend hours on the dyno. When you are done with the exhaust, you need to tune the intake length for the exhaust you have ended up with it there is a reversion issue, which there usually is, and so it is exactly the sam tuning on the intake as you do on the exhaust. It is a little cheaper to lengthen and shorten manifolds, but there is still hours of dyno time involved. Then you have to make sure there are no drivability issues. Usually, you give up somewhere in this process and just go racing!</p><p></p><p>To return to the carb, I will say that although testing was limited, I was using jets in the 300 plus range, so whatever issues were present in the original which required huge jets seems to have been dealt with. John Renwick said he tried to use the best of both the TT and MK2 when making it.</p><p></p><p>David</p></blockquote><p></p>
[QUOTE="davidd, post: 54709, member: 1177"] I did not make the casting, although I wish I did. I do not have an original to compare it to, but I would not be surprised if it were done by a pattern maker and the shrinkage seems to be well accounted for. All the internals are Amal MK2. The cap on top was made so the spring could nest up inside and allow the throttle valve to to clear the bore. I will try to take some more detailed photos. Glyn Johnson has an original on his Flash and I do have some photos. I will hunt them down. Bill, this was prior to tuning and when I put it on the dyno I had to raise the bowl immediately. But, the very next run (on the single racer) was 42 bhp. Because it was MK2 I did not have a single tuning item to change out. I was hoping just to see what it did with the 28" long 2" pipe. We were all quite impressed, but had nowhere to go. This is also with a standard size head, not the big port. I put the 32mm 10TT9 on it and got 40, which was quite heartening, but by the time we put the straight through silencer on it was 37. I did many runs with different lengths and 28" open pipe made the most power at 7,000. So, it is very easy to get power from a straight pipe, but the minute you put any absorber silencer on it you loose quite a few hp. So, the racing silencer requirement works heavily against the Vincent. The port velocity is very low with this set up leading to speculation that a smaller pipe with a megaphone would provide more power and it certainly did on Lindsay Kyle's bike. But, this is the stage of tuning that is wildly expensive. You have to make several custom exhaust systems that will probably not work and spend hours on the dyno. When you are done with the exhaust, you need to tune the intake length for the exhaust you have ended up with it there is a reversion issue, which there usually is, and so it is exactly the sam tuning on the intake as you do on the exhaust. It is a little cheaper to lengthen and shorten manifolds, but there is still hours of dyno time involved. Then you have to make sure there are no drivability issues. Usually, you give up somewhere in this process and just go racing! To return to the carb, I will say that although testing was limited, I was using jets in the 300 plus range, so whatever issues were present in the original which required huge jets seems to have been dealt with. John Renwick said he tried to use the best of both the TT and MK2 when making it. David [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
big TT carbs
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