C15 Cough and Stall

[Gary]

Hi all.

I've had my 1966 BSA C15 for a few years now. It suffers with cough and stall syndrome at low rpm. I've read on several forums that this is common on these bikes, but I've never managed to find out the cause, and better still, the cure.

It's only a problem when having to stop in traffic, but with the type of riding I do, that's quite often. Tickover is a bit random as well. Tends to fluctuate up and down.

As far as I know the bike is running everything standard.

Maybe someone on here will know more about this apparently common fault, and would be good enough to enlighten me🙂

Cheers,
Gary.

[B Murphy]

Hi Gary

I hope you find some answers, I have given up on C15's after years of having them doing just this. I'm happy with my B31 that would tick over all day long without the cough and stall.

[ChrisG]

1966 has the points in side cover so it's not the dreaded cam flapping about in the distributor. As it's low rpm and tickover is random, it's likely the pilot system in the carb. Is it a monobloc or concentric? If the former, then remove the pilot jet and thoroughly clean the circuit out with carb cleaner. If its an early concentric then I suggest a new replacement as you cant get at the jet. However, in both types, there are two tiny holes, in the bottom of the main choke bore, one each side of the forward/front of the throttle slide. Clean these out with strands of copper wire and carb cleaner.   

[Gary]

Hi guys. Apologies for my lack of response. I'm new to this forum and had assumed I would be notified of responses via email as do similar forums. I'm sure there's a button somewhere on here to choose for this to happen!

Well, £500 later and a lot has changed, but not the dreaded cough and stall. Despite the original carb looking and measuring up well, and the little holes in the throat being clear, I decided to go for a new carb. With standard jetting this improved the mid range and top end noticeably, but not the bottom end.

I also fitted a regulator rectifier and electronic ignition. The EI has also improved the mid range and top end even more than the new carb did. The original auto advance unit was cream crackered, so no surprise things have improved........but not the bottom end!

I've been through a number of pilot jet changes, some weaker and some richer. They all made a difference, and the richer ones did slightly improve the problem, but not enough to be called a cure. I also tried different cutaways on the slides, and again, the richer ones improved things a little, but not much at all.

Something of note is that the inlet port has been severely roughed up. Maybe an attempt by a previous owner to cure this very problem? Well it didn't work!

Like Mr Murphy, I am considering moving on to something else. I wonder if the C15s big brother, the B40 had similar issues?

Apologies again for the late response. I have just found the tick box for replies🙂


Gary.

[Whiskey69]

Hi Guys
Relativity new to Brit Bikes, but had plenty of Japs and land rovers, so not bad with the spanners
Quickly learning the in and outs of BSA bike happiness!
I have a B25 Star-fire, would not idle and snatches at low revs, went well flat out though, then cough and stall at any traffic lights, went through the carb and ignition system lots of times trying different things.

First thing is the carb, clean the pilot circuit and do it again, drill an access hole opposite the air screw, makes cleaning easier, slight improvement then i purchase a card rebuild kit, instantly a lot better, then ignition, i still have points, gap a par manual, new plug, lead and cap, check both advance/retard springs are there, guessed the timing then set up with timing light with high revs, so full advance, you will see the difference of the advance while doing this as the revs climb

Now the fine tuning, i originally i set the timing dead on the timing marks but the idle, low rpms and starting to feel better setting the timing about 2mm retarded from the marks, anymore and top end rev will suffer, then fine tune the carb, the air screw was making a big difference so i raised the needle (gave it more fuel), played with the with this setup it will idle fine and no cough and stall☺
But.......
It only likes these settings when the engine is hot, below five miles and she still plays up and i have not got a choke/air starter
So i put up with the cold running for the good times and only do decent journeys
Makes you wonder, what did they do back in the day?
Whiskey

[OVERTHEHILL]

I have a 1960 C15, everything is standard, I set the timing as per the original BSA handbook that would have been supplied with the bike, I fitted a new carb 5 years ago when I got the bike.  I don't have any problems with stalling but I don't set the tickover very slow, I have seen B31's ticking over like steam engines the C15 wont do that. Tickover is still slow enough to engage 1st gear with out a crunch.  I was around bikes when these were new and I don't remember a problem with stalling so I am surprised that this is happening now.

[Gary]

"I was around bikes when these were new and I don't remember a problem with stalling so I am surprised that this is happening now."

Fuel has changed a lot over the years, and especially ethanol seems to be causing much trouble for classic machines. Maybe this is a part of the problem, and maybe we will see an increase in running issues as ethanol makes its way into all grades of fuel in ever increasing amounts?

[OVERTHEHILL]

Yes modern fuel does not help, I use the Esso super grade if I use the ordinary unleaded it does not run as well. A bit of pinking and less power.

[Gary]

I also use Esso Premium grade. Officially it is now E5, but it often comes in as E0. Unfortunately there is no way of telling when that is going to happen. It's just pot luck.

[AdrianS]

My B40 ticks over very evenly at a low rpm. The engine was completely rebuilt including a rebore and piston. The carb is also new and I had the lollipop distributor rebushed . The tick over was a little erratic before the distributor was rebushed. I use standard unleaded petrol and with the amount of work done to the engine, fuel system, and ignition ( still on 6v points), I would say the bike is as close to new as you could get.
For the symptoms the OP gets, I would say there is something not right somewhere.

[Gary]

"For the symptoms the OP gets, I would say there is something not right somewhere."
I think you might have hit the nail on the head!

[B Murphy]

Not sure what the issue is with modern fuel and ethanol in classic motors, could someone enlighten me please? the B31 runs great, so does the two Bantams and all the other 60's bikes Iv'e had, Also a 1934 Austin 10 ran great.

The only bikes I have had issue's with was the C15's with the same problem as the OP has and I remedied that by selling the heaps of s**t and will never get another one even if someone gave me one for nowt. Just saying 

[AdrianS]

"For the symptoms the OP gets, I would say there is something not right somewhere."
I think you might have hit the nail on the head!

I was on Mastermind answering questions on the Bleeding Obvious!

[AdrianS]

To be constructive, my previous post was a bit tongue in cheek. My B40 runs and ticks over perfectly and I just use standard unleaded fuel. As yet I don't appear to have had any ethanol related issues with any of my 3 BSA bikes; the only issue I had was with my old mgb where all the rubber petrol pipes split..
The problems described by the OP could be caused by a multitude of causes so very difficult to diagnose, only suggestions as to where to look can be given.
If I had that bike, and was unaware of any history, then I would systematically go through each system thoroughly ( ignition, fuel) and then check the engine (valves, clearances, compression ) until the problem is resolved. It doesn't take much to cause a problem but finding it can be very time consuming.
I wish I could be more constructive and give a diagnosis.

[Gary]

"my previous post was a bit tongue in cheek."
Ditto🙂

The fuel and ignition have been done to death. I experimented with the old carb and old ignition in many ways to no avail. It now has a new carb and new electronic ignition which have also been heavily experimented with to no avail.

The compression has been tested and is good. From memory it is somewhere around 130psi.

The valves and clearances I haven't checked. I surprise myself by admitting the clearances haven't been checked as it's quite simple to do. My only excuse is that I had spent many months messing with the fuel and ignition and I reached a point where I'd had enough. Checking the valve condition is obviously a bit more involved. I will check clearances at my next opportunity, and then the valves after that.

Did anyone have any thoughts on the roughness of my inlet port? I posted a picture earlier in this thread.