BritBike Forum logo
BritBike Sponsor BritBike Sponsor BritBike Sponsor
BritBike Sponsor

BritBike Sponsor

BritBike Sponsor
BritBike Sponsor BritBike Sponsor BritBike Sponsor
Jwood & co JRC Engineering dealers Jwood & co
Home | Sponsors, Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons, "OLD" BritBike Forum | DVD- Manuals & Parts books | BritBike Stickers & Decals
Upgrade to: Premium Membership | Premium Life Membership | Vendor Membership | Site Sponsor Membership
Member Spotlight
sbolton
sbolton
Flint, Michigan
Posts: 39
Joined: August 2006
Show All Member Profiles 
Shout Box
Search eBay for motorcycle parts in following countries
Australia, Canada, France, Holland, Italy, United Kingdom, USA
Random Gallery photo
Who's Online Now
55 registered members (Alan_nc), 242 guests, and 445 spiders.
Key: Admin, Global Mod, Mod
Newest Members
Gaspare, eberhard, Norman Woollons, LandoLando, MikeA
10256 Registered Users
Top Posters(30 Days)
Stuart 76
Lannis 63
Popular Topics(Views)
608,657 mail-order LSR
Forum Statistics
Forums34
Topics67,112
Posts651,269
Members10,256
Most Online3,995
Feb 13th, 2017
Like BritBike.com on Facebook

Previous Thread
Next Thread
Print Thread
Rate Thread
BSA A65 Big port valves #715081
11/14/17 6:27 pm
11/14/17 6:27 pm
Joined: Dec 2013
Posts: 9
France
P
pete Offline OP
BritBike Forum member
pete  Offline OP
BritBike Forum member
P
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

Support Your #1 BritBike Forum!

Check out British motorcycles for sale:
British Motorcycles on e-Bay UK, British motorcycles on e-Bay North America
Check out British motorcycles for sale:
British Motorcycles on e-Bay UK, British motorcycles on e-Bay North America
Re: BSA A65 Big port valves [Re: pete] #715091
11/14/17 7:37 pm
11/14/17 7:37 pm
Joined: Mar 2005
Posts: 10,130
Boston, Massachusetts
J
John Healy Offline
BritBike Forum member
John Healy  Offline
BritBike Forum member
J
Joined: Mar 2005
Posts: 10,130
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?


Re: BSA A65 Big port valves [Re: John Healy] #715165
11/15/17 5:36 am
11/15/17 5:36 am
Joined: Dec 2013
Posts: 9
France
P
pete Offline OP
BritBike Forum member
pete  Offline OP
BritBike Forum member
P
Joined: Dec 2013
Posts: 9
France
=> => => "a good all around mtorcycle".

Re: BSA A65 Big port valves [Re: NickL] #715234
11/15/17 5:53 pm
11/15/17 5:53 pm
Joined: Dec 2013
Posts: 9
France
P
pete Offline OP
BritBike Forum member
pete  Offline OP
BritBike Forum member
P
Joined: Dec 2013
Posts: 9
France
Thanks Nick for your reply.
What settings do you recommend => Throttle cutaway, main jet, pilot jet ??

Re: BSA A65 Big port valves [Re: pete] #717545
12/03/17 8:58 am
12/03/17 8:58 am
Joined: May 2013
Posts: 4,841
Rotherham - S. Yorkshire
Allan Gill Offline

BritBike Forum member
Allan Gill  Offline

BritBike Forum member
Joined: May 2013
Posts: 4,841
Rotherham - S. Yorkshire
Not sure what Nick has posted as it wasn’t on the thread,

For a good all round bike the standard head is fine, however the earlier 68-466 head is quite tractable (it has a 1,1/8” port tapering to 1,1/16, about 1/4” in is the taper) these work well with the change from 38mm valve to 40mm and I have 32mm carbs mounted to mine, although they do pull very well with 28mm and for standard road use will be more tractable still.

In comparison the bigger port head will seem flatter at certain points in the Rev range and will work well... but only within a smaller RPM window, the smaller port head will pull much stronger over a bigger window. Cam will make a difference also.


beerchug
Re: BSA A65 Big port valves [Re: pete] #717562
12/03/17 2:35 pm
12/03/17 2:35 pm
Joined: Mar 2011
Posts: 836
derby england
wak Offline
BritBike Forum member
wak  Offline
BritBike Forum member
Joined: Mar 2011
Posts: 836
derby england
the carbs should always be bigger than the port or at least the same size,


BSA lightning
BSA B50MX
TRIUMPH TR6C
BSA BUSHMAN
BSA Gold Star Daytona
BSA Gold Star Scrambler
BSA Rocket Gold Star
BSA C15S
BSA Cyclone
Triumph T120
Triumph T100 Daytona
Triumph 5TA Trials
Triumph T100 Scrambles
Cheney 560 TT
Re: BSA A65 Big port valves [Re: pete] #717620
12/04/17 12:46 am
12/04/17 12:46 am
Joined: May 2013
Posts: 4,841
Rotherham - S. Yorkshire
Allan Gill Offline

BritBike Forum member
Allan Gill  Offline

BritBike Forum member
Joined: May 2013
Posts: 4,841
Rotherham - S. Yorkshire
Thunrbolts have 1,1/8” ports (28.5mm) yet they still match them with 28mm carbs, so half an inch is neither here nor there,


beerchug
Re: BSA A65 Big port valves [Re: pete] #717781
12/05/17 2:36 pm
12/05/17 2:36 pm
Joined: Mar 2011
Posts: 836
derby england
wak Offline
BritBike Forum member
wak  Offline
BritBike Forum member
Joined: Mar 2011
Posts: 836
derby england
That wasn't a serious answer was it Allan , thunderbolts are single carb with a Y adapter which goes a lot smaller , having a smaller carb than the port drops the gas velocity


BSA lightning
BSA B50MX
TRIUMPH TR6C
BSA BUSHMAN
BSA Gold Star Daytona
BSA Gold Star Scrambler
BSA Rocket Gold Star
BSA C15S
BSA Cyclone
Triumph T120
Triumph T100 Daytona
Triumph 5TA Trials
Triumph T100 Scrambles
Cheney 560 TT
Re: BSA A65 Big port valves [Re: pete] #717816
12/05/17 6:42 pm
12/05/17 6:42 pm
Joined: Apr 2005
Posts: 1,644
Mississauga, Ontario.
A
Adam M. Offline
BritBike Forum member
Adam M.  Offline
BritBike Forum member
A
Joined: Apr 2005
Posts: 1,644
Mississauga, Ontario.
Khm, smaller ports give higher gas velocity, but less volume.


Moderated by  Allan Gill 


Home | Sponsors | Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons | "OLD" BritBike Forum | DVD- Manuals & Parts books | BritBike Stickers & Decals
Upgrade to: Premium Membership | Premium Life Membership | Vendor Membership | Site Sponsor Membership
Powered by UBB.threads™ PHP Forum Software 7.6.1.1