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Engine Speed #786952 10/12/19 11:58 pm
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nert Offline OP
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Quick question. 1966 650 BSA Lighting. 60 mph at about 4,000 RPM seem about correct? After all, I am reading stock Smith gauges on a vibrating sanding machine, so a bit of "margin" must be considered?

thank you


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Re: Engine Speed [Re: nert] #786954 10/13/19 12:30 am
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Lannis Online Content
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Depends on the gearing (my A65 with a 21/47 sprocket set is about 3700 RPM at 60), but yours sounds right for a 19 tooth front. Bike should be happy and "eager" at that speed!

Lannis


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Re: Engine Speed [Re: nert] #786972 10/13/19 11:52 am
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I would agree with Lannis. 19/47 would be 'standard'. I found that 20/47 is the best compromise for normal riding here in NJ. PRT

Re: Engine Speed [Re: nert] #786987 10/13/19 3:50 pm
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Allan Gill Offline
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19:47 would be stock for a late firebird but 19:42 might be right for 66’ or 20:47, the lower 20:47 gearing came about when the ports went to 30mm


beerchug
Re: Engine Speed [Re: nert] #787015 10/13/19 10:32 pm
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nert Offline OP
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The bike has the standard 389/228 and 689/228 Monoblock carbs. I do not know what the port size is for that carburetor. Please reply if you know. I believe the bike is pretty standard from birth. Does have EV forged pistons and gapless rings I installed. I replaced bearings, and bushings. EV serviced the valves and springs. I also installed an SRM oil pump. Alternator is original, I am running with points, but I did change to the newer point set and auto advance. 19" wheels. Does not leak oil from engine or primary. I get a few drips from the chain oiler/ breather after long spirited rides. I am used to a lower RPM at speed and the 4,000 from the BSA scares me a little. I feel the same "tension" on my 73, 850 Norton Commando as well. But the Norton is silky smooth. Up to 3,500 rpm the BSA has a comfortable balance of rhythm in sync with the exhaust tone. As speed increases, I am reminded of something more similar to riding a paint mixer from the local hardware store. However, getting above 4,000 the frequency seems to become less "repulsive", but more concerning. Either way, I love to ride my BSA. ITs my go to for the biggest smile on my face. I guess I will need to count how many teeth I have drive and driven.

Thank you for your reply's.


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Re: Engine Speed [Re: nert] #787031 Yesterday at 02:38 AM
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htown Online Content
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That Commando engine is vibrating just as much at 4K, you just don't feel it because the iso's are doing their job.


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Re: Engine Speed [Re: nert] #787044 Yesterday at 12:03 PM
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Allan Gill Offline
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Without looking in the AMAL book saying 389 covers a multitude of carb sizes, however in the earlier models with 389 carbs used were 1 1/8". As no 1 1/8" carbs were ever made as 689 (the opposite handed variant) its most likely your carbs are 1 5/32".

Whether the port size correctly matches the carb or not is a different kettle of fish, so yes the only real way of knowing is counting the teeth. 47t rear drums almost all have bolt on sprockets (earlier fixed sprockets are easy to spot with 47t) most fixed sprockets were 42t with the steel (chromed or painted) back plate (aluminium with bolt on sprockets) the chain runs very close to the back plate. Good luck counting the front sprocket.


beerchug
Re: Engine Speed [Re: nert] #787048 Yesterday at 01:18 PM
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gavin eisler Offline
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from the porklips site
389/228 BSA 650cc 1966; A65 Lightning & Hornet 1 5/32" 25 3 270 0.11 3
689/228 BSA 650cc 1966; A65 Lightning & Hornet 1 5/32" 25 3 270 0.11 3

a handy ref for old AMAL carbs
http://porklips.org/~mason/moto/amal_specs.html

Alan says
"As no 1 1/8" carbs were ever made as 689 (the opposite handed variant) its most likely your carbs are 1 5/32"
Not true if the porklips side is correct A50 wasps had inch and 1/8th LH monos as did a few others.

Last edited by gavin eisler; Yesterday at 01:23 PM.

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Re: Engine Speed [Re: nert] #787052 Yesterday at 02:27 PM
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nert Offline OP
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Good info there. Thank you.
That makes them 29.3688 mm bore


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Re: Engine Speed [Re: nert] #787053 Yesterday at 02:28 PM
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Allan Gill Offline
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I stand corrected, although in 65 only right hand 389s were fitted.

Side note, just noticed on the AMAL website that they will no longer be making 689 carbs due to lack of demand.

Attached Files Capture.JPG

beerchug

Moderated by  Allan Gill, Jon W. Whitley 

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