A10 won't start.

[Klaus]

Hi Ewen,
I had a simmilar problem with a running bike. On day to another it won't start, only a few bangs. Before it was an easy starter, five kicks without ignition on, and then first kick.
They drive me mad, it only could be the carb, but wtf. I checked all jets if blocked but nothing. Only a few bangs sometimes.
Then I forgot to fit the airneedle, and it starts as usual. As I would  screw in the needle it stalled.
The first solution was to run a fine wire from a cable into the pilotjet to get a run, but it was not satisfied.
I changed to an other carbbody and all was fine.
What was wrong?
I gues it was haircrack in the carbbody that allowed fuel to pass  by the pilotjet.

good luck and heers
Klaus

[Ewen]

Right, I will take the car off and look for this small hole. I blew compressed air down a very small hole (maybe 10 amp fuse wire size) running horizontally which was situated right at the mouth of the car. I take it your hole runs vertically?

[Ewen]

I blew compressed air into a very small hole (about 10 amp fuse wire size)  which ran horizontally and was situated right at the mouth of the car. But your hole sounds like it must run vertically.... is that correct?

[Ewen]

This hole Trevinoz.... it sounds like it runs vertically. Is that correct?

[Ewen]

Thank you Klaus and others. I am going to try with the air screw out. I put in brand new plugs..... got just the odd pop. I bent the electrode of another plug right out... about 5mm gap and the spark is jumping that.

[RDfella]

Jumping 5mm in air doesn't mean it'll jump 20 thou under compression. Do you have resistor-type plug caps? Shouldn't use them on a magneto as they raise the internal voltage and can cause breakdown.
Take the cap off the pluglead and see how far it jumps. Hopefully a blue spark min 6mm, preferably more. And what are your plug gaps? Most plugs come pre-gapped at .025" (moderns around .040") . We need under .020"

[Ewen]

Okay thanks.... I will take the cap right off. I had it off actually to check that the leads had real copper wire (I thought of the suppressor issue)  I don't think it can be a resistor cap... it is just a slim rubber affair.

[Ewen]

I set the new plugs at 19 thou.

[trevinoz]

Ewen, the hole is vertical and is drilled into the pilot adjustment chamber. It is a very small hole and is hard to see but trust me, it is there.
Your symptoms are typical of not having a pilot feed.

[Ewen]

I stripped the carb down, again, must be the cleanest monobloc in the southern hemisphere now. I put some fine wire down the tiny hole (it was in fact the hole I mentioned earlier... I remembered its location totally incorrectly) I could see the wire quite clearly through the pilot screw hole. I'm pretty sure that hole must have been clear because it is  in line with the pilot jet hole which I blew through several times. Engine still won't run. There's a pretty good spark but I think the mag is now the most likely.

[Swarfcut]

 Ewen. After that mechanical disaster, worth checking camshaft and crank pinion keys and keyways are still intact. Sparks and valves, cranks and pistons all in the right time and place are what you need. Even a drippy carb should give enough vapour to get it to fire. Plug leads get swapped, a mistake we all make.

 Swarfy.

[Ewen]

What a good point.... it stopped rotating in a big hurry. I will check that woodruff key on the crankshaft tomorrow.

[Ewen]

I checked that the brass section in the slip ring was in line with the correct pickup so I know that the leads are right.

[chaterlea25]

Hi All,
I have had a weird non starting problem with my SR  (and Guzzi single) on occasion 
The bike can be running fine but after stopping for a coffee or petrol will not fire up again
Take out the plugs and they look absolutely fine and spark in air no problem
Fitting new plugs and all is well  for another year or xxx miles
I am convinced its a result of ethanol in the petrol putting some sort of coating on the plugs

John

[Ewen]

Interesting John but I have brand new plugs.