Author Topic: BSA C15G  (Read 548 times)

0 Members and 1 Guest are viewing this topic.

Gary

  • Star
  • *
  • Posts: 7
    • View Profile
BSA C15G
« on: 12 April, 2017, 09:36:48 »
Hi.

After a couple of years ownership and riding my lovely C15G, I decided to address the slight hesitation on throttle take up, and mild mid range lumpiness at 1/3 throttle.

I decided to take a look at the carb first and found everything to be clear but now cannot find out which carb the bike should actually have and what the jetting should be. The carb I have is a 375/034 with a 1 1/16" bore, 140 main jet, 105 needle jet, 25 pilot and a 5 slot needle on 2nd from top slot with a "B" marking. The slide only has the markings "375" and "1". Probably should be a 3.5

I cannot find any information on the C15G model at all. The "G" was the last made in 66/67 only, but I don't understand the lack of information on them. I even found a website that specialised on the C15 but still no mention of the G model.

So my question is: does anyone know what carb this model should have and what the internal specs should be?

Thanks,
Gary.

JulianS

  • Empire Star
  • *****
  • Posts: 549
  • A10
    • View Profile
Re: BSA C15G
« Reply #1 on: 12 April, 2017, 10:30:22 »
photo below is from the 1967 BSA data book and shows the carb settings for the C15G - the same as for previous season bikes.

The production run was only about 2400 machines and no parts book was issued.

The factory issued an unillustrated parts service bulletin for the Sportsman version, GC14, which was just an update of the previous seasons book. They may have issued a bulletin for the standard model but so far I have not found one.


JulianS

  • Empire Star
  • *****
  • Posts: 549
  • A10
    • View Profile
Re: BSA C15G
« Reply #2 on: 12 April, 2017, 10:36:33 »
GC14 for the Sportsman is below some of the info may be of use.

Gary

  • Star
  • *
  • Posts: 7
    • View Profile
Re: BSA C15G
« Reply #3 on: 12 April, 2017, 11:09:49 »
Hi Julian.

Thanks for the carb settings and part number updates. Very useful.

Interesting that I have the correct carb body number but the bore is a different size. I thought the number would correlate to a set size for the bore.  Is that explainable? Is it important?

Thanks,
Gary.

JulianS

  • Empire Star
  • *****
  • Posts: 549
  • A10
    • View Profile
Re: BSA C15G
« Reply #4 on: 12 April, 2017, 12:02:13 »
375/34 is a unique identification for a carb.

 The 375 was the smallest monobloc and was made with bore from 21/32 to 7/8 bore. So 1 1/16 would not have been a standard size bore for the 375.

1 1/16 bore would have been a 376, the next body size up, and probably a bit to big for a standard C15.

Are your sure of the measurement?

Some C15 scramblers and US spec models had a 1 1/16 bore 376 - one number listed being 376/304.

Below are monobloc dimensions from Amal lists.
« Last Edit: 12 April, 2017, 12:04:53 by JulianS »

Gary

  • Star
  • *
  • Posts: 7
    • View Profile
Re: BSA C15G
« Reply #5 on: 12 April, 2017, 12:10:29 »
"Are you sure of the measurement?"

I've been pondering this for the last hour and it may be (fairly certain actually) that I have made a silly error. I couldn't understand how I had the correct slide but it still fits the bigger bore. Yes, you've guessed it. I am measuring the bore for the slide, whereas I should be measuring the bore for the inlet/outlet. Silly me!
I will be in the shed this afternoon so I'll measure the correct bore while I'm there. I expect it will be 7/8".

Gary.



Gary

  • Star
  • *
  • Posts: 7
    • View Profile
Re: BSA C15G
« Reply #6 on: 12 April, 2017, 12:13:29 »
Forgot to say that after your first reply Julian, I set the needle into the correct (3rd) slot and the hesitation I mentioned earlier has all but gone.

Gary

  • Star
  • *
  • Posts: 7
    • View Profile
Re: BSA C15G
« Reply #7 on: 16 April, 2017, 17:01:10 »
A quick update to this topic.

The bore of the carb is indeed 7/8".

I have also managed to fashion (bodge) an air tight rubber tube between the carb and air filter mounting. This has caused the tickover to settle down to a steady little thump, no longer going up and down like a yo-yo.

Thanks again Julian for your help.

Gary.

TIGER

  • Star
  • *
  • Posts: 42
    • View Profile
Re: BSA C15G
« Reply #8 on: 17 April, 2017, 03:32:48 »
I was interested to know how you made a joining piece from carb. to filter.
I have a similar problem with my c15.
Just getting close to completing.
I hove a difference in dia. Of 6mm
Also will have a few good spares !
Regards
            Tim

Gary

  • Star
  • *
  • Posts: 7
    • View Profile
Re: BSA C15G
« Reply #9 on: 17 April, 2017, 08:35:52 »
Hi Tim.

I bought one of the attached from B&Q. I cut it to the required length but still couldn't get the thing in the tiny gap between the carb and air filter flange. I then cut it along its length, wrapped it around the carb and flange, and used a couple of pieces of insulating tape across the cut I'd made. I then used the jubilee clips as you would normally. The clips are way too big for the air filter flange so can't be done up too tight without slipping off. Tight enough for a good seal though.

Told you it was a bodge!!

Hoping to think of something better at some point but at least this has helped me to get it running properly.

Good luck,
Gary.


Gary

  • Star
  • *
  • Posts: 7
    • View Profile
Re: BSA C15G
« Reply #10 on: 17 April, 2017, 08:37:48 »
One of the attachments went missing, so here it is.

Gary.

TIGER

  • Star
  • *
  • Posts: 42
    • View Profile
Re: BSA C15G
« Reply #11 on: 17 April, 2017, 23:02:28 »
Thanks for that Gary.
I will fashion something similar.
Tim