Starting trouble

[tippi11]

Hello engine experts,

I have problems to start my g3 engine (magneto ignition, no automatic advance, timing set as per manual) fitted with a Amal 376/5 carb. Never had this engine running before, but compression is good, valves operation, fuel supply, spark from magneto all ok.

Apart from numerous kick-start attempts with “nothing happening”, the engine occasionally makes a loud “bang” and a gas cloud comes out the inlet side (something like an external combustion). The most obvious thing on inspection: the inlet side of the carb. is fairly wet (petrol).

I am a bit lost at this stage because as far as I understand the Amal carb, one should be able to start the engine (pilot jet for idling) even if the set-up/tuning hasnt been completed or optimised.

Your hints where to look at are very much appreciated...

Thank you very much!
Regards, Peter

[dave16mct]

Are you sure it is timed on the compression stroke? It sounds like it might be 180 degrees out.
Dave.

[SPRIDDLER]

I am a bit lost at this stage because as far as I understand the Amal carb, one should be able to start the engine (pilot jet for idling) even if the set-up/tuning hasnt been completed or optimised.

In principle that is correct as long as the other parts of the carb are not seriously the wrong ones or have been incorrectly fitted (which is unlikely). However, it won't help if you are holding the throttle open more than perhaps a quarter open when trying to start. Strictly speaking it's not necessary to open the throttle at all for the engine to start and run for at least a few revolutions when the kick start is operated.
As Dave has said, your description of the symptoms suggests that the engine is timed 180 deg wrongly and the sparking plug is firing when the inlet valve is still open.

[tippi11]

Good morning,
I will check ignition timing later today - thank you; keep you informed about the progress ...
Regards, Peter

[tippi11]

Hello there,
some news (and even more help required) - it is now timed on the compression stroke, the "bang" from the inlet side I mentioned earlier did not happen anymore
But: I hear and feel that the engine wants to start but during numerous kicking it only runs for 2-3 revs (for two or three times out of 15 attempts or so). What would you suggest for the Initial carb settings? For example for the pilot jet adj screw, how many turns from fully screwed in? Would you use the air valve, or keep it fully open (no function)?
And more general: Are these engines very sensitive regarding ignition timing/firing (my Enfield engine, for example, at least runs/idles even when timing isnt perfect)?
As I said already, I never had this engine running - can you think of a foolproof procedure to get this done???
Thank you!
Regards, Peter

[Pharisee]

Sounds a bit like not enough fuel to keep it running... Are you 'tickling' the carburettor until the float bowl is flooded?

[tippi11]

Hello Pharisee,
Yes, I did...
Thank you, Peter

[raffles]

Hello Peter
with the 376 carb the pilot jet is crucial for starting, so first of all remove the pilot jet and make sure there is nothing
(dirt ,water,or other muck in the jet) you can usually blow through the jet once removed. If all ok refit the jet and nut
remove the air adjuster screw, check for muck and that it is not bent,if ok screw in until just tight then back off (undo)
one and one half turns, petrol on and give it a kick. Unless you have greater problems this should work.
Tony

[tippi11]

Hello Tony,
Thank you - I will follow your instructions, will see what happens (tomorrow).
Peter

[SPRIDDLER]

It does sound like fuel shortage. As Tony said, the pilot jet and its airways in the carb body are tiny. Make sure they are completely clear.
Have a look at the spark plug after several kicks. It should be getting wet with fuel.
It's always a good plan to fit a new plug - it may spark regularly outside the cylinder but not when under compression. The insulator on the central electrode on modern plugs is not glazed and minute scratches will cause tracking or failure to spark consistently when under compression. Only clean them with a rag or a soft (non-wire) brush.