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#715081 - 11/14/17 6:27 pm BSA A65 Big port valves  
Joined: Dec 2013
Posts: 9
pete Offline
BritBike Forum member
pete  Offline
BritBike Forum member

Joined: Dec 2013
Posts: 9
France
Hello to everyone,
Finishing actually the restoration of my BSA lightning, I'm waiting for the delivery of my head that had the following
modifications :

- Inlet port to 32 mm with 43.5 inlet valves

I have twin AMAL carbs 389 1' 1/8 (Main jet 220 / Throttle : 3 1/2 / Pilot jet : 106)

My questions :

Do I need to rebore my carbs to 32 mm to maximise the performance of my engine ?

Thanks

Pete

#715091 - 11/14/17 7:37 pm Re: BSA A65 Big port valves [Re: pete]  
Joined: Mar 2005
Posts: 9,965
John Healy Online content
John Healy  Online Content


Joined: Mar 2005
Posts: 9,965
Boston, Massachusetts
Quote
maximise the performance of my engine


What are you going to do with this engine? Are you looking for top speed, maximum acceleration, or a good all around motorcycle?


#715165 - 11/15/17 5:36 am Re: BSA A65 Big port valves [Re: John Healy]  
Joined: Dec 2013
Posts: 9
pete Offline
BritBike Forum member
pete  Offline
BritBike Forum member

Joined: Dec 2013
Posts: 9
France
=> => => "a good all around mtorcycle".

#715168 - 11/15/17 6:12 am Re: BSA A65 Big port valves [Re: pete]  
Joined: Jan 2014
Posts: 3,321
NickL Online content
BritBike Forum member
NickL  Online Content
BritBike Forum member

Joined: Jan 2014
Posts: 3,321
Aus
Bung a couple of 30mm concentrics on it. Any bigger and you'll have to mess about with it at lower RPM for small gains above 5k
The ports are a little big now but they'll be ok with the big valves.



#715234 - 11/15/17 5:53 pm Re: BSA A65 Big port valves [Re: NickL]  
Joined: Dec 2013
Posts: 9
pete Offline
BritBike Forum member
pete  Offline
BritBike Forum member

Joined: Dec 2013
Posts: 9
France
Thanks Nick for your reply.
What settings do you recommend => Throttle cutaway, main jet, pilot jet ??

#715283 - 11/15/17 10:27 pm Re: BSA A65 Big port valves [Re: pete]  
Joined: Jan 2014
Posts: 3,321
NickL Online content
BritBike Forum member
NickL  Online Content
BritBike Forum member

Joined: Jan 2014
Posts: 3,321
Aus
Kickoff with the standard settings, 200mj, 106nj, 3 slide, needle pos 1. and go from there.
That's if you use air filters, which i suggest you do.
It won't be far out but depending on exhaust, comp ratio etc may need some tweaking.
While the head and barrel are off, spend some time removing the sharp edges around the valve pockets on the piston crowns,
no need for mirror finishes but 'rounding off' the crowns helps the old heaps burn a little better without 'pinking'.




Moderated by  Allan Gill 


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