Author Topic: C12 difficult starting  (Read 374 times)

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Offline johnboyfully

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C12 difficult starting
« on: November 30, 2019, 12:52:27 pm »
Hi all. I was ecstatic a couple of Sundays ago when my C12 fired up for the first time in 10 months, following a strip down and tart up! (Ooooer missus!). However she's not keen at all at starting up. Today for example I tried for a good 20 minutes and all I got was a puff of smoke at one point and an encouraging few seconds of running before she cut out. Here's my resume of where I am.

1 When she has started I need the tick over quite high to keep her going, but she does run smoothly, doesn't dip or stutter
2 I can kick multiple times but there's no sense she will start, no coughing, spluttering, back firing...nothing. It's like the kick-start isn't turning the crank, but there is resistance and compression. Then for no determinable reason, even on "half" a kick, she fires up! I then adjust the tick over to keep her running and a couple of days ago she ran for a good 10 mins before cutting out
3 There is a spark at the plug
4 I've put new clutch plates in and adjusted the armature in the gearbox accordingly...I think! There's 3/16" of free play and when the clutch lever is pulled the plates separate. I would add that the arm is not as near the outer-casing of the gear box as it was, but there is still the recommended 3/16" free play. While running but still on the bike lift I tested the clutch and it appears to bite at the right time (just as the lever is almost released) and I can select gears and the clutch disengages when the lever is pulled
5 I'm using 6v Pazon ignition
6 I have a new Amal carburetor (I notice when tickling the carb fuel leaks out of the holes in the back of the carb rather than the tickler itself)

I'm nearly there, I feel, but this non starting is frustrating me. Do any of you master mechanics out there have any suggestions, checks or adjustments I can try to improve the situation, please?
As ever, thanks for any advice, cheers, JBF

Offline ROB KEMP

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Re: C12 difficult starting
« Reply #1 on: November 30, 2019, 03:18:06 pm »
is it a genuine amal carb ??

Offline johnboyfully

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Re: C12 difficult starting
« Reply #2 on: November 30, 2019, 03:33:36 pm »
It is and the bike used to start first or second kick previously JBF

Online Owen

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Re: C12 difficult starting
« Reply #3 on: November 30, 2019, 03:46:41 pm »
Had you left the battery connected and it run down a little. Was there old fuel in the carb. Did you tickle the carb prior to starting?
1940 C12 (350cc)
1945 C10 & C11
1953 C10 & C11
Anyone want a B20 in need of a lot of tlc

Offline camman3

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Re: C12 difficult starting
« Reply #4 on: November 30, 2019, 04:07:20 pm »
Always difficult to diagnose without all the history, but if the ignition system is unchanged and the battery is healthy, it sounds like primary jet wrong size or more likely it, or galleries are blocked, especially if you are using the same fuel from 10 months ago.
Whip the carb off,  strip and soak in thinners, before blowing compressed air through the tiny primary gallies and jet.
While there, check that is jetted correctly, correct slide, needle etc
Certainly sounds like fuel starvation to me....did you pull the plug after several un successful kicks to see if was wet or dry?
Graham
1957 C12
In sunny (sometimes) Christchurch, Dorset, UK

Offline ROB KEMP

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Re: C12 difficult starting
« Reply #5 on: November 30, 2019, 04:52:15 pm »
if its when its cold push a bung up the bellmouth and semi restrict the air see if it fires if so the carb is probably blocked

Offline rolariel

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Re: C12 difficult starting
« Reply #6 on: November 30, 2019, 10:37:11 pm »
I had a similar problem with an Enfield a while ago. Did all the usual checks and then, as a last resort, changed the plug for a new one and BINGO. I can only assume that the plug was, somehow, firing erratically. Worth a try?

Offline Ginge

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Re: C12 difficult starting
« Reply #7 on: December 01, 2019, 08:28:48 am »
Quote
It's like the kick-start isn't turning the crank

Well JBF, it might be clutch slip.  If the bike is still on the bike lift, just back off all clutch adjustment and that will rule that out.

Quote
need the tick over quite high to keep her going, but she does run smoothly, doesn't dip or stutter

This could be ignition timing.  Did you tinker with that on the rebuild?  Hard starting, coughs and spits.  It might run well occasionally but a bike running and revving on the table is going to respond differently when you load it up with road rolling resistance or transmission load.  Now that you know the gearbox selects ok, just do your tuning in neutral.

Valve timing?  Now it has run for ten minutes you might need to tweak and check valve clearances.

Quote
semi restrict the air see if it fires if so the carb is probably blocked

Rob’s idea can help.  Choke the air intake with your hand half over the carb intake hole and see if that sucks a bit more fuel through the pilot circuit.  Take the air filter off first and use your third hand.

Check the throttle cable run.  Make sure the slide isn’t hanging up or the cable jammed or too tight. That will introduce more air into the carb past the slide just when you don’t want it to.  It should start and idle just on the pilot when warm.

It is possible to start a bike just on the pilot as long as the slide is closed. 

Do the easy things first before pulling things to bits.



Ginge.

Offline Kiwipom

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Re: C12 difficult starting
« Reply #8 on: December 01, 2019, 08:52:31 am »
Bit left field but check there is some play on the clutch cable, with new builds the play can disappear and cause clutch slip during kick starting.

Simon

Online timsdad

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Re: C12 difficult starting
« Reply #9 on: December 01, 2019, 08:54:48 am »
I think you have more than one problem here, John, - one that's making the bike awkward to fire up and one that's causing it to stop running.

I'd agree with some comments but not others. Plugs are not what they used to be and often, with modern petrol, they'll get a coating up inside that shorts them out and weakens the spark. First, buy two new plugs, one to fit in the engine and one for a spare, and throw the old one in the bin even if it's quite new. Make sure the battery is charged right up to at least 12 and a half volts and check for a good spark with the new plug by turning with the kick start. The battery should hold its charge for a long time and may be damaged by going flat and being charged too fast.

The carb may need cleaning out if it's been standing 10  months but shouldn't be too bad. Its settings should be fine and the pilot jet, needle and needle jet will  be correct and the main jet will not affect starting and normal running. The needle clip needs to be in the middle groove but also doesn't affect starting or low down running. The slide will not affect starting and slow running if it has the wrong cut-away but check its number on the bottom to make sure its the right one or there abouts. It will run fine on any slide of about 3 or 4 for testing purposes.

To make sure the carb is clean, take it off and remove the slide, float chamber and air adjusting screw. Blow an aerosol carb cleaner into each of the four pilot holes in turn and make sure it comes out of the other three holes each time. There's the one that the screw threads into, the one the fuel sucks up out of the bottom of the float chamber, the one the air sucks in from the rear and the one the fuel mix goes into the manifold from that's the engine side of the slide. All these should show a good flow of carb cleaner because they're all connected up. - use fingers to block up some holes if needed. Then replace the adjusting screw all the way to the bottom and turn it back exactly one and a half turns.

When you've got the carb reassembled, and the slide back in, turn the throttle stop screw in far enough so it touches the base of the slide and then just starts to lift it slightly. Flood it up, one kick and it's away. If not, come back for more advice.

The carb can be fine tuned if it starts and runs well. I think a new plug and well charged battery, the old one may be knackered, will sort it out. I assume the clutch isn't slipping but you don't seem too sure about that - you should be able to tell easily if the engine is spanking over when you're trying to start the thing.


Ray
Just a motorcyclist.

Offline johnboyfully

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Re: C12 difficult starting
« Reply #10 on: December 01, 2019, 10:13:49 am »
Thank you all for your comments and suggestions, much appreciated. I’ll go through them in turn and see if any help. Personally I suspect the clutch set up, but I will carry the other checks and adjustments. I did put a new plug in to no avail and it does get wet with fuel. I realise it’s difficult to accurately diagnose without seeing the bike so thanks again. I’ll let you all know how I get on, cheers JBF

Offline BSAc11g

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Re: C12 difficult starting
« Reply #11 on: December 01, 2019, 11:17:56 pm »
Before I go and post my pet problems I like to get all the facts
Tart up ?
What exactly have you doe to the bike since it last ran properly ?

Now apart from the common problems caused by storage which have already been covered by others, what have you done that might have changed things ?

Do you have mice in your shed ?
have they been munching on the wiring loom ?
built a nest in the muffler ?

Are you hearing excessive blow-by ( ring/s stuck ) ?

I fix lawnmowers and when I get a won't start i\I use a procedure similar to this
1) shot of carb cleaner  ( it is easier on the mower than starting fluid ) down the plug hole, brand new warmed plug ( prevents deposits on the plug  & aids vapourization )  the attempt a start .
Fire up then stops = carb / fuel problem
confirms ignition & timing
Does not fire = Ignition / vale problem

2) same thing but spraying through the carb
Fires right up
Confirms valve operation and points the finger at the carb
Does not fire right up = valve problem
Bike Beesa
Trevor

Offline johnboyfully

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Re: C12 difficult starting
« Reply #12 on: December 02, 2019, 06:33:25 pm »
Thanks Trevor, I will definitely give your trouble shooting procedure a go. Just to clarify, by tart up I meant the frame etc was painted and the engine/gear box vapour blasted. New nuts and bolts etc I changed the head as the previous had a very visible broken fin. The valve seats and valves were re ground and I cleaned and polished the valves. It’s had a complete re-wire by a supremely competent fellow forum member (ex MOD RADAR electrical engineer) I did the static timing, valve clearances and Pazon electronic ignition set up. I put new clutch plates in and re set that. At strip down in January I ran the carb empty. I guess the fuel is a few months old as I got it for the garden machines in the Spring.
One more thing though...would it have a detrimental effect on the ability to turn the engine over by kickstart if the primary chain was too tight? But again, thanks for all the advice, JBF

Offline Tman

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Re: C12 difficult starting
« Reply #13 on: December 02, 2019, 06:48:01 pm »
I'm getting confused. So is the engine not starting or the clutch slipping, or even both? :-\

Offline johnboyfully

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Re: C12 difficult starting
« Reply #14 on: December 02, 2019, 10:59:25 pm »
It’s not starting but I can’t see why. I’m thinking clutch not turning the crank, but could well be wrong! I’ve not had chance to try the suggestions yet but hopefully by the weekend JBF