Gem JAP 600 – getting it to bloody well start – carb prob?

[vhgmcbuddy]

Further progress in that I’ve got the now-sparking mag back on, plug sparking like a goodun (thanks Neil for the new condenser).

I think I timed it up so the points just start to open as the piston is 3/8″ before TDC on the compression stroke. I’m now wondering did i REALLY check the full stroke sequence and set it right…. both the valves were closed and i backed it off from TDC. Or am I being stupid here…?

Anyway – i stuck the head back on and gave it a whirl.

First – the carb float was well up the needle, so it just p*ssed petrol out of the overflow holes. Managed to get the float set to the groove on the needle so that seems to have stopped that problem.

Flooded the chamber with the tickler til it just runs out the overflow hole and stopped.

Lifted the decompression lever (it snapped the thread on the solid steel rod, so have now mackled one together with a piece of garden wire for the time being) – this works, and means i can spin it. Without that, I could only just move it through a couple of cycles – so at least it’s well compressed!

Once, I managed to get a single fire – a sort of PFFTTTTT! – it shot a bit of white exhaust and that’s it.

If i take the plug out, it seems wet, but still sparks. I give it a good few turns with the plug out, try again. About the best I manage is that single soft fart…! Although a lot of the time i’m just cranking away with nowt happening.

I look at the carb – it’s the Amal 225/3 model. It seems to be missing a screw, one of the mixing chamberplug screws. On this parts diagram they are number 228
http://www.tractorbox.co.uk/forum/forum_posts.asp?TID=7831

So i wonder if that’s meaning that it’s dragging in excess air and not fuel?

I’ll stick some tape over that for a quick fix.

But is there a more logical process to setting up the carb. I’ve left the throttle stop screw (part 220) on the top as it was, presume that was set up vaguely.

With the main jet needle underneath, i’ve no idea where to set that…. while there is the little lock nut, there’s no spring, and it leaks if it is undone too much as it also seems to be missing the cork glands referred to in that previous post.

Is focusing on the carb the right thing at this point…. or is there something more in the logical process i should look at?

A soft fart still represents progress though, even if i do now have a sprained wrist from all the cranking (bless me Father for I have sinned).

[charlie]

I assume you are releasing the decompressor once you have the engine swinging over nicely??!!

[vhgmcbuddy]

Thanks Charlie – the soft fart fire has come at the first couple of turns of the handle, with the decompressor lifted. As soon as I drop it and try to continue to crank it just sort of bounces – does nowt. Then, despite that one fire, it does nothing again until i’ve taken out the plug and spun it over again, start over. Same result.

I need to cover over that blanking hole first and see if that makes any difference.

But its more the general systematic approach i ought to take to setting the carb that I am unfamiliar with. I was hoping that if i could get it to fire a bit, then at least that’s a positive sign and i can try different variables.

[charlie]

Have you tried a new plug?
With old plug cleaned and dried or new plug, try pouring a drop of petrol in plug hole replace plug and see if it will fire. This should help prove the ignition system is delivery a good spark at about the right time.
Does the magneto have an impulse unit on it, setting the timing for these is different, something I have not done.

[vhgmcbuddy]

Thanks Charlie – it’s not a brand new plug, but it’s sparking very well. The mag hasnt any form of impulse so it is theoretically simpler.

I may get a chance to have another go tomorrow, but i’m away for the weekend so probably wont get a chance to swear at it until Monday now….

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