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#688490 - 03/18/17 7:25 am A good Gold Star  
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John Alexander Online content
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John Alexander  Online Content
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Kent, England
My Goldie Pulls 6000 revs on half throttle, and will accelerate to 6,500 to 6,800 revs on full throttle to approx 112 to 118 MPH. Engine no. GS DBD 5684 First listed engine no for 1961. Inlet port opened to same size as GP carb, no inlet port step, in theory, should lose power.
Goldie John.

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BSA Gold Star forum This board is dedicated to BSA Gold Star motorcycles.

#688716 - 03/20/17 4:37 am Re: A good Gold Star [Re: John Alexander]  
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Kerry W Online content
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Kerry W  Online Content
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Middle East,
Measure it. Then you'll know.


No generalisation is wholly true, not even this one.
Oliver Wendell Holmes
#688766 - 03/20/17 3:24 pm Re: A good Gold Star [Re: John Alexander]  
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John Alexander Online content
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John Alexander  Online Content
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Kent, England
Have done, exactly inch and a half.
Goldie John.

#688767 - 03/20/17 4:02 pm Re: A good Gold Star [Re: John Alexander]  
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Kerry W Online content
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Middle East,
Not the inlet hole size, the hp. It'd be interesting to see what it makes at the rear wheel, especially if you had (as most dyne's usually do) an exhaust gas sensor, so you can really see what the mixture is doing.


No generalisation is wholly true, not even this one.
Oliver Wendell Holmes
#688780 - 03/20/17 7:37 pm Re: A good Gold Star [Re: John Alexander]  
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Andy Higham Online content
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I fail to see how removing a step in the inlet port will reduce power (or putting a step in it increase power).
Possibly if the carb is badly worn and not atomising the fuel correctly, the turbulence may help mix the fuel/air. Normally you need a clean straight port from the bellmouth to the valve


1955 BSA B31 400cc "Stargazer"
1962 Greeves 200cc "Blue Meanie"
1962/67 Greeves 350cc
1967 Greeves 360cc Challenger
1984 Suzuki GSX1100 EFE "Sorcerers Apprentice"
Modified Nu-Trak GM500cc sprint/LSR bike "Deofol"
2003 Aprilia RSV Mille "Lo Stregone"
#688782 - 03/20/17 7:46 pm Re: A good Gold Star [Re: John Alexander]  
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kommando Online content
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Joined: Dec 2004
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Scotland
I believe John is referring to a section in Roland Pikes memoirs where he detailed some tests on Gold Star engines, one test showed a power increase when a larger carb was used on an unchanged inlet port. This is the section from Chapter 26

One of the strangest occurrences to do with carburettors was when one day Reg Wilkes sent an apprentice from the test shop into our,
main shop for a 1 3/32 GP carburettor and he misread the size and gave Reg: a 1 3/16th carburettor and they immediately got quite a
jump in power. They reported this to me and I went to the shop and the test was repeated and there was no doubt it was quite a gain in
power. I suggested to Reg to open the port to match, immediately we lost what we had gained plus a bit more, so we made a thin
sleeve and pressed it in and the power was back. We repeated this on other engines always with the same results. A number of private
owners of DBD Gold Star noticed the carb being bigger than the port and opened up the port thinking to gain power, but not having a
dyno were not aware of the results. Later on we fitted a venturi behind the carb and picked up even more power. The smallest diameter
of the venturi could be 80% of area of the carburettor. We tested this on several engines and it always worked and seemed to improve
carburation. The venturi had to have the classic included angles of 22 degree in and 7 degree out.


It is counterintuitive but it is in the memoirs which are a very good read.

#688801 - 03/20/17 9:29 pm Re: A good Gold Star [Re: kommando]  
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Andy Higham Online content
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Bolton Lancs UK
That shouldn't happen, I guess the poxy GP carb has something to do with it. Yes I know they look good but as a precision instrument for a road bike they are sh1te


1955 BSA B31 400cc "Stargazer"
1962 Greeves 200cc "Blue Meanie"
1962/67 Greeves 350cc
1967 Greeves 360cc Challenger
1984 Suzuki GSX1100 EFE "Sorcerers Apprentice"
Modified Nu-Trak GM500cc sprint/LSR bike "Deofol"
2003 Aprilia RSV Mille "Lo Stregone"
#688809 - 03/20/17 10:09 pm Re: A good Gold Star [Re: John Alexander]  
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Boomer Online content
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Orygone
Well, in 1954 when Roland Pike was developing the Gold Star engine I don't think he cared sh1te about developing something for the road. He was developing race engines for Daytona and other venues. I don't think Mikuni was making carbs then.


Bill B...


Boomer
#688810 - 03/20/17 10:38 pm Re: A good Gold Star [Re: Boomer]  
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triton thrasher Online content
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Originally Posted by Boomer
I don't think Mikuni was making carbs then.


Bill B...



Strange thing to think and very wrong.


Amateur Loctite enthusiast.
#688811 - 03/20/17 10:40 pm Re: A good Gold Star [Re: Andy Higham]  
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triton thrasher Online content
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scotland
Originally Posted by Andy Higham
I fail to see how removing a step in the inlet port will reduce power (or putting a step in it increase power).


Your failing to see has little effect on a dynamometer reading 60 years ago.


Amateur Loctite enthusiast.
#688814 - 03/20/17 11:05 pm Re: A good Gold Star [Re: John Alexander]  
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geordie Offline
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Blue Mountains, Sydney Austral...
If A/F readings were available from Mr Pike the changes in power may be more easily understood


58 goldstar
74 commando
70 Thunderbolt
81 Darmah
#688822 - 03/21/17 12:13 am Re: A good Gold Star [Re: geordie]  
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[Linked Image]


heavens
turnips, and watermelons, and the elegant commando
and other stuff, unclassifiable
#688826 - 03/21/17 12:53 am Re: A good Gold Star [Re: triton thrasher]  
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Boomer Online content
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Orygone
Originally Posted by triton thrasher
Originally Posted by Boomer
I don't think Mikuni was making carbs then.


Bill B...



Strange thing to think and very wrong.




That was meant to be tongue in cheek......


Bill B...


Boomer
#688873 - 03/21/17 6:04 pm Re: A good Gold Star [Re: John Alexander]  
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John Alexander Online content
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Really good feedback guys, what got me wondering about the size of the inlet tract from the carburettor to the cylinder head is that on most DBD Goldies i have looked at, they all seem to have a step as standard. In the book by A.Golland on page 21, ''Technical Advances,'' it does say just that they discovered a slight increase in power by the inlet port being slightly undersize to the diameter of the inch and a half GP, the cylinder head inlet port diameter 1 and seven sixteenths . Don't know if there is any thing special about my Goldie, what it's subsequent history is, but for some reason, i have heard people say that a good year for the Gold Star was 1961. My engine no. is 5684, the first listed no. for 1961. I know, but everybody would like their bike to be ''special''. PS. It has revved through 2nd and 3rd gears on one mad occasion, out accelerating a 650 Bonny, which turned out to be a 750 trident , my mistake, it had a Bonny tank, revs- 8,000, yes i know, but it survived, amazingly.
Goldie John.

#688944 - 03/22/17 4:12 am Re: A good Gold Star [Re: Andy Higham]  
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Jerry Roy Online content
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Denver CO
Originally Posted by Andy Higham
I fail to see how removing a step in the inlet port will reduce power (or putting a step in it increase power).
Possibly if the carb is badly worn and not atomising the fuel correctly, the turbulence may help mix the fuel/air. Normally you need a clean straight port from the bellmouth to the valve


Here is some reading that may give a clue as to why the phenomena happened. The step may not be the important part.

http://www.mototuneusa.com/think_fast.htm

CZ

p.s. There are 4 parts, if you are up to it.

#689078 - 03/23/17 8:29 am Re: A good Gold Star [Re: John Alexander]  
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John Alexander Online content
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Kent, England
I'm surprised you Goldie guys were not aware of this information, in 1956 theBSA competition shop reduced the inlet tract to1 7/16 to provide a small 'turbulence lip' said to improve performance, that is why i wondered as my Goldie does not have one.
Goldie John.

#689142 - 03/23/17 9:09 pm Re: A good Gold Star [Re: John Alexander]  
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Boomer Online content
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Orygone
Originally Posted by John Alexander
I'm surprised you Goldie guys were not aware of this information, in 1956 theBSA competition shop reduced the inlet tract to1 7/16 to provide a small 'turbulence lip' said to improve performance, that is why i wondered as my Goldie does not have one.
Goldie John.




You're referring to one Goldie guy, aren't you?



Bill B...


Boomer
#689223 - 03/24/17 4:27 pm Re: A good Gold Star [Re: John Alexander]  
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John Alexander Online content
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Kent, England
H.mmm- who knows.
Goldie John.


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