mags...or carbs

[Guy Wilson]

I've just rebuilt / put together a 1958 A10 on a budget with my son.. supposed to be a joint effort although I did most of the work and enjoyed all of it.. However now complete, Its hard to start although does run well once started.. I have good compression - equal on both cylinders. and the static timing is good..
I've tried a couple of carbs although they don't seem to make much of a difference, so I focused on the Mag..the spark was there although not super bright on the original mag so I switched to a spare mag I had that produces very bright sparks.. still the same issue.. hard to start..

I bought and EasyCap from Brightspark and fitted to the original mag.. It doesn't produce as bright a spark as the one I switched to, so maybe it wasn't the old capacitor that was at fault in the original mag..
both mags were tested on the bench. Both produce pretty much identical spark strengths on the bench as when fitted to the bike..

I'm temped to go back to look at the carb now.. although as I've posted on the Ignition thread, I still suspect the mag..
Any ideas anyone?
Many thanks!
Guy
 

[limeyrob]

Can you describe the hard starting a bit more:
Is its a lot of kicks then it runs, or something else?  With mags the key is plenty of fuel, a couple of slow kicks then one really fast one.
How is it if you bump start it?
Once its running and hot does it restart easier?
How is the idle?
How much do you tickle it? Do you hold the tickler down until petrol come out?
Where do you set the choke?
Is it manual or auto A-R?
Sorry for all the questions, but 2000 miles away I'm trying to build a better picture.

[muskrat]

G'day Guy.
I agree with Rob, more info is needed.
If manual A&R are you moving the lever in the fight direction? If auto are you re-checking the timing after the nut is done up (they can creep) and setting the timing with the auto wedged in the full advance position?
Cheers

[KiwiGF]

Are you flooding the carb with the tickler? and starting on (say) quarter throttle?

They do vary but that’s how mine starts best.

[Guy Wilson]

Rob, Kiwi, thank you..

The mag has an auto advance and is set correctly. I will re-check again when refitting the mag..

What strikes a chord is Rob's point.. it does take a lot of kicks before it starts, sometime more than I have in me.. once running its runs pretty evenly. and again is fairly easy to start once its been running. I have NKK BP6 plugs which my other A10 likes and always starts first or second kick on 1/4 throttle when I start it cold , its not fussy once hot..

I haven't tried bump starting as it feels like that's not a solution at this point..

The carb is tickled until fuel overflows, although checking the plugs after many kicks, they are dryer than I would expect.. maybe I should be looking at the carb now or elsewhere...?

Valve gaps are set as per spec.. Piston rings are new and the compression is good and equal in both cylinders..

thank you both,

Guy

Can you describe the hard starting a bit more:
Is its a lot of kicks then it runs, or something else?  With mags the key is plenty of fuel, a couple of slow kicks then one really fast one.
How is it if you bump start it?
Once its running and hot does it restart easier?
How is the idle?
How much do you tickle it? Do you hold the tickler down until petrol come out?
Where do you set the choke?
Is it manual or auto A-R?
Sorry for all the questions, but 2000 miles away I'm trying to build a better picture.

[limeyrob]

Hmmm.  If its a lot of kicks I'm thinking it's less likely to be the spark as the first few kicks will be the best.
The problem with the carb is that it could be flooding or it could be weak.  It may need a lot of kicks to get enough fuel or to clear the flooding and from bitter experience its not always obvious which one you have.
Do some tests:
Try starting with with no tickling and no choke.  It shouldn't start, but if it does then its getting petrol while its parked - perhaps a leaky tap.
Try with lots of fuel - tickle and full choke.  If its this then there's a blocked idle circuit, I know you tried another carb but there's a slim chance both have the same problem.
Try your normal starting regime then after a few (ie normal for an A10) kicks open the throttle fully and kick a few more times, if it spits after a few kicks its probably getting flooded.
Of course it could still be the mag/spark, but we have to start somewhere

[Guy Wilson]

yes..I'm leaning towards a fuel issue.. I don't have a choke on either bike.. its not particularly cold here and at 6000ft absl, things tend to run rich anyway.. a weak carb could explain the apparent dryer plugs.. I will start there and the idle jet..
Guy

[Radlan2]

Swop carbs with your easy starter?

[Swarfcut]

 From inexperience and a previous association with Lambretta 2 strokes, choke and quarter  throttle to start I learned that my AMAL carb prefers an almost closed throttle, full choke and a good tickle when cold. So you may need a choke just for the inital start up, to help draw fuel through the idle circuit when cold. Checking the plugs after a futile kicking session should tell you if fuel is absent or there is too much and the plugs are wringing wet.

 Another test would be to forget the fuel system, try it with a shot od Start Yer B**tard. If it fires for a couple of seconds you know the ignition system is producing sparks in the right place.

 You could also  try oiling the bores, after a rebuild and with too much fuel  you will wash the bores of the film of oil that helps seal newly installed rings, and with low compression it won't fire.

 Swarfy

[Guy Wilson]

thank you all, I have enough to occupy my weekend now! I'll update on the progress !
Guy

[chaterlea25]

Hi Guy,
You don't say what carb is fitted?
If it's a monobloc, check if the jet block is loose in the main body,
Loosen the big nut on the get holder and see if the jet block will move easily.
No cure except replacement

John

[limeyrob]

Swarfcut, interesting you should mention the need for a choke. My Matchless has a Monobloc and came with no choke. Pig to start, would fire but not run. Fitted a choke and its transformed it, as you say it seems to be unable to pull fuel through without it.

[Guy Wilson]

not being able to pull the fuel through seems to be best clue so far...my easy start A10 has a mono bloc 376 5 . The one on the bike thats refusing to start is a mono bloc 389 B which used to be on the other bike and was a really easy starter when fitted on that bike.. I know it's an odd carb (Spanish Amal - maybe off a 2 stroke) but it worked well other than running rich. I'll swap them over and see what happens..



Guy

[Rex]

Swarfcut, interesting you should mention the need for a choke. My Matchless has a Monobloc and came with no choke. Pig to start, would fire but not run. Fitted a choke and its transformed it, as you say it seems to be unable to pull fuel through without it.

Funny you should say that, but all my bikes have chokes and need them too if I want them to start easily, but it's amazing how often on the Net someone will state that "yer don't need those chokes, take 'em off".
Sorry, in my experience you do.

[Worty]

When my GF was rebuilt, it was really hard to start, so I bought a new carb.  Ever since then it's been excellent at starting (apart from a couple of maggie failures).

My start method is always with the choke fully off because if the lever screw is loose enough to move it, it keeps moving to 'choke on' on a ride.  My solution was to make sure it was fully off and tighten the screw so it can't move.  Occasionally kicks me back, but always starts first or second kick regardless of temp.  I tickle it up until a bit of petrol starts to appear, than a good swing or two usually does the trick.

Always did wonder why 'choke on' is with spring pressure and 'choke off' is against it - perhaps there's no other way of arranging it on these carbs.  Mine always runs a tad rich with the dark side of tan on the plugs.