BSA Owners' Club Forum

The BSA Workshop => Singles => Topic started by: TIGER on 12 July, 2017, 18:59:42

Title: Trial run
Post by: TIGER on 12 July, 2017, 18:59:42
Just completed a few miles on the C15.
Running quite well.
Starts easy from cold BUT not when hot ?
Backfires on overrun.
Comments welcome
Regards
           Tim
Title: Re: Trial run
Post by: Bess on 13 July, 2017, 06:06:54
Hi Tiger,
            If my bike backfired through exhaust and difficult to start when hot, it could have be the mixture is too rich, adjust carburetter.

 However it could also be; mixture too lean and an electrical issue, then I check the spark quality when the engine is hot (I often electrocuted myself in the process so I get someone else to hold the plug these days), then adjust the carburetter.

Carburetter Tuning Guide:

http://amalcarb.co.uk/downloadfiles/amal/amal_tuning_guide.pdf

Best wishes...
Title: Re: Trial run
Post by: TIGER on 13 July, 2017, 16:53:39
Many thanks Bess.
My bike is stamped SS80 which should have 376 carb
However at present I only have 375 running a 180 main jet
So a bit of a lash up
Regards
            Tim
Title: Re: Trial run
Post by: STAR TWIN on 13 July, 2017, 16:56:00
Backfiring on the over-run when hot is frequently air getting into the exhaust where the pipe enters the cylinder head. Exhaust paste or even RTV should sort it.
Title: Re: Trial run
Post by: TIGER on 14 July, 2017, 13:59:23
Thanks for that I always though it was unusual not to have a gasket or other method
Tim
Title: Re: Trial run
Post by: TIGER on 20 July, 2017, 03:19:07
Deligated duties by management ( AKA ) wife prevented work on the C15
So back now.
Main concern backfiring on overrun
Purchased a copper ring to help seal exhaust joint at cylinder
Stripped and cleaned all bits copper ring is good fit in head
Applied gun gum to the seal and when tightening main engine bolt to secure front pipe BOLT SHEARED
BUGGER
Quickly cleaned up parts and awaiting for new pin
Updates later
Will I ever finish ?
Or at least get an MOT
TIM
Title: Re: Trial run
Post by: TIGER on 20 July, 2017, 19:54:26
No wonder it's not finished.
Tiger playing golf today.
Written by management.
Title: Re: Trial run
Post by: TIGERJ on 29 July, 2017, 22:26:03
Exhaust resealed.
Short road test today backfire improved
I am still using 375 carb. With 180 main
Can anyone help with needle positions and what effect on "flow"
After run plug is sooted up
May go back to 140 main with highest needle position ?
Advice welcome
Regards
           Tim
Title: Re: Trial run
Post by: Bess on 30 July, 2017, 07:41:01
Hi,
    Hope this helps:

http://amalcarb.co.uk/downloadfiles/amal/amal_tuning_guide.pdf

Best wishes...
Title: Re: Trial run
Post by: TIGERJ on 30 July, 2017, 19:21:21
Thanks Bess
I felt like I was on Blue Peter
But now it is very useful
Dropped the needle right down but too wet to road test
When grip is twisted to a fast tickover and let go
Engine all most stops but then races
I notice Amal sell three 375 carbs with increased bore sizes
So need to do a lot more fettling
Regards
Title: Re: Trial run
Post by: Bess on 30 July, 2017, 21:00:53
Hi,
     You're most welcome. I also use a colortune:

http://www.gunson.co.uk/product/G4074

They can be bought for less elsewhere.

Best wishes...
Title: Re: Trial run
Post by: MICKREEVES on 20 August, 2017, 07:27:19
My C15 SS has the needle fully down on the slots.
Mick
Title: Re: Trial run
Post by: MICKREEVES on 20 August, 2017, 14:32:01
My C15 starts cold first kick every time without fuel on, choke, or tickle.
The throttle stop is screwed up to a known position.
With engine hot, the stop can be lowered.
To start hot, it needs throttle open the right amount. Too little = nothing. Too much = kickback.
Mick