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#332886 - 09/11/10 2:33 am A65 jet questions  
Joined: Apr 2009
Posts: 22
TomWengler Offline
BritBike Forum member
TomWengler  Offline
BritBike Forum member

Joined: Apr 2009
Posts: 22
Chattanooga, TN USA
71 BSA A65 Lightning. manual sales main jet should be a 220 and needle jet a 105.

My needle jets are 106.
Just replaced jets that were 200's with the correct 220's.

Question is this - should I replace needle jet with 105? What does a larger needle jet do exactly - more fuel I assume but want to be sure. Will a 106 be ok to use?

Assume 200's give me less fuel in the mix - again, totally new at this so am not sure.

The bike ran great under 45-50 mph but over that, where I suspect the main jet comes into play, and the bike lost power and ran inconsistently (a steady hand and the bike seemed to lose power and speed so I was constantly accelerating - losing speed, then more throttle over and over again). Hoping jets are the issue and that 220's will solve this.

Thoughts and thanks in advance for sharing your wisdom with a neophyte.

*Will not be able to test until issue with a stripped stud is resolved but while bike is down I am going through these odd bits.

Semper Gumby, in his first email to me, started with "welcome to the madness" - I had no clue what he meant by that but now I fully understand. I have come to embrace the illness that has come with inheriting this motorcycle.


Tom Wengler
learning to love the BSA madness
71 BSA A65 Lightning
Chattanooga, Tennessee
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#332894 - 09/11/10 5:20 am Re: A65 jet questions [Re: TomWengler]  
Joined: Jan 2004
Posts: 3,513
DMadigan Online content
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DMadigan  Online Content
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Joined: Jan 2004
Posts: 3,513
ca, us
The range of effect for the pilot screw, slide cutaway, needle, needle jet and main jet are dependent upon the throttle position, not MPH. Do a search on AMAL tuning.

#332906 - 09/11/10 10:00 am Re: A65 jet questions [Re: TomWengler]  
Joined: May 2004
Posts: 3,547
BSA_WM20 Offline
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BSA_WM20  Offline
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Joined: May 2004
Posts: 3,547
Sydney Australia
Go here, Bushmans Concentric tips
Every thing that you wanted to know about amals explained very clearly.
It sound like you have both a timing & carby problem but best to correct them one at a time.
Modern fuels tend to be a bit on the lean side so usually you need to jet a bit bigger.
Needles & jets are a tune up replacement item and not really dear so but a new set ( well 2 sets actually ).
Buy a colour tune read the instructions and in particular check that both carbs are working properly. When you can see what is going on it all makes perfect sense. To do this properly you need to remove ( or pinch totally closed ) the balance tube between the carbs.
99.99999999999999999999 % of members who come in have one carb's idle circuit blocked and both sides are running on one carb at idle.
The fact that you can actually do that and ride the bike is a testiment to the robustness of the system


Bike Beesa
Trevor
#332929 - 09/11/10 1:56 pm Re: A65 jet questions [Re: TomWengler]  
Joined: Sep 2002
Posts: 7,812
Alex Offline
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Alex  Offline

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Joined: Sep 2002
Posts: 7,812
Seattle
Not sure where you're getting your info, but you should get a factory shop manual. The factory correct jets were already in there if you're running the stock 930 carbs. What you describe sounds like jetting for using 932's. That said, google reading spark plugs to get your jetting right.


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
#332976 - 09/11/10 8:26 pm Re: A65 jet questions [Re: Alex]  
Joined: Apr 2009
Posts: 22
TomWengler Offline
BritBike Forum member
TomWengler  Offline
BritBike Forum member

Joined: Apr 2009
Posts: 22
Chattanooga, TN USA
I'm running AMAL 930's stock. Brittish cycle supply parts manual indicates that I need 220's for main jet which I ordered and installed.

manual says .105's for needle jet but discovered mine are .106's. I guess I will leave them in there and see what happens.

I have a factory manual but the cover is missing - it refers to OIF Models and to previous year's back to 1963 so maybe this is not a factory manual after all. Perhaps it's too general so I will get the correct manual and will call Brit Cycle on Monday.


Tom Wengler
learning to love the BSA madness
71 BSA A65 Lightning
Chattanooga, Tennessee
#332977 - 09/11/10 8:28 pm Re: A65 jet questions [Re: BSA_WM20]  
Joined: Apr 2009
Posts: 22
TomWengler Offline
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TomWengler  Offline
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Posts: 22
Chattanooga, TN USA
Bushman's Concentric tips is a great resource. thanks for sending that source over.


Tom Wengler
learning to love the BSA madness
71 BSA A65 Lightning
Chattanooga, Tennessee
#332988 - 09/11/10 9:26 pm Re: A65 jet questions [Re: TomWengler]  
Joined: Oct 2001
Posts: 1,059
Shane in Oz Online content
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Shane in Oz  Online Content
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Joined: Oct 2001
Posts: 1,059
Sydney, Oz
The 1971 parts book on Kim's CD (well worth having, especially if you have a few models) says 220 main, 3 slide, .105 pilot jet and needle in slot 1 for a Lightning. 230 main for Thunderbolt and Firebird.

That does seem over-jetted, because the 1970 book lists 180 mains, 3 slide and .106 pilot jets, and I would have thought that the 1970s breathed a bit more freely.

45 - 50 mph with a constant throttle opening would be just getting onto the needle.
Replacing the needles and jets would be a good move.
It's possible that the needle clip is in the wrong slot so it's running rich on the needle. The clip should be in the top slot.
Also, check for air leaks and warping of the carb mounting flange.

If possible, it's very useful to have somebody really experienced to give you a hand with carb setup. I thought my T140 was running reasonably well until Steve (Retired Fireman) went through my carbs and found all sorts of gremlins.

#333006 - 09/11/10 10:43 pm Re: A65 jet questions [Re: TomWengler]  
Joined: Aug 2005
Posts: 1,145
bodine031 Offline
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bodine031  Offline
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Posts: 1,145
melbourne florida
go to the GABMA web site tech section under AMAL's

#333066 - 09/12/10 8:38 am Re: A65 jet questions [Re: TomWengler]  
Joined: Oct 2008
Posts: 4,860
DavidP Offline
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DavidP  Offline

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Joined: Oct 2008
Posts: 4,860
Gnashville
It would seem that BSA was confused as well.
I just looked. My factory shop manual calls for 200 main, 106 needle jets. My factory parts catalog specifies 220 main, 105 needle jets.
They both agree on #1 needle grove and a number 3 slide.

I can't comment on which is correct, as I was using 107 needle jets and 200 mains with the needle in the center groove. Mine is 0.060" over with non-stock exhaust.
I have since switched to Mikunis.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
#333112 - 09/12/10 4:59 pm Re: A65 jet questions [Re: TomWengler]  
Joined: Aug 2001
Posts: 3,871
Mr Mike Offline
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Mr Mike  Offline
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Joined: Aug 2001
Posts: 3,871
Cape Carteret, NC
FWIIW, I spent a lot of time getting my A65L jetted right. It is a 66 with concentrics. After about a dozen changes with test rides and plug checks alongside the road, I ended up with .106 needles in position #2, a #3 slide and a 190 main jet. It should be noted that the 66 A65L originally came with monoblocs, but the PO has installed concentrics and they were clapped out, so I installed new 930 concentrics and started with the 68 setup and went from there. A couple of things that I noticed is to use NEW needles and needle jets. Old jets are often worn and bigger because of the wear. I found that manual setups were in general a bit too rich so I moved from 2.5 to 3 on the slide. Once I got it right I had eliminated the stutter I had been experiencing when a rolled onto the throttle at 55-60 mph. It also elimintated the slight hesitation I had when I cracked the throttle just a tad.

I have been happy with my setup but it took several days of testing to get through it. I don't know what the differences in head design are from 66 thru later years. Sometimes a single change is hardly noticeable until you check the plug.

Mr Mike


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