A10 won't start.

[Ewen]

Hi guys. I have done the ignition timing, valve timing checked , tappet clearances, points gap. I removed all the carb jets, and float cover, float needle, throttle slide while the carb was still on the bike and blew out with compressed air but the beast won't start. My best guess is that a small passage within the carb body must be blocked... how likely is that? I have never heard anyone mention that being a problem. Presumably could only affect slow speed because higher speed controlled by needle and slide. Spark seems reasonable.... its yellowy white.... not actually blue. Any ideas?

[Chris A10]

have you tryed to start it with Deo or brakecleaner yet ?
if that doesn't give atleast a little rumble I would look for the ignition.

cheers

Chris

[BSA_54A10]

I repair small engines for a living ( when I am allowed to )
SOP for no start once you have confirmed you have a spark
1) a SHORT shot of carb cleaner down the plug holes.
Should get 1 or 2 bangs from the engine.
If not swap leads & repeat
If still no bang then valves timing or spark timing is wrong

If it goes bang then repeat down the carby
Engine goes bang ( usually get a few ) then valve timing is OK & problem is in the carb
Does not go bang then problem is valve timing or valve lash , which is sort of the same thing .
Good idea to use either a fresh plug or warmed plug with the above to aviod a bad plug allowing the spark to leak down the insulator nose .

[Ewen]

Thanks guys. Update... I took the carb of and stripped it down fully. I think idle jet may have been blocked but I stupidly didn't look through it before blasting compressed Air through so not positive on that point. Even took the jet block out and cleaned everything very  thoroughly.  Will now fire a couple of times most times when I kick her over but will not start up. So I think timing is okay.... I was pretty careful. Have 25 idle, 240 main, 106 needle and number 4 slide. Right plug slightly damp but left not noticeable.... 3 times that has been the case. The bike was running. Could be hard to start when hot. Spark is yellow, white. Not blue. How telling is that?

[Ewen]

When I say it was running that was almost a year ago. I took a while to get back to it because  it jammed up.... a piece of aluminium casting from around a timing cover screw broke free and jammed in the timing gears.... luckily while I was starting it. The previous owner had glued it in place... (Einstein)  Think I changed the throttle slide to a 4... is that correct?

[groily]

Isn't a # 4 slide too big a cutaway for a GF and therefore weak? 3 1/2 more like? Can make the difference  . . . (Needle on middle groove?)
Try putting a hand over the carb mouth with filter off (if fitted) and see if it stays running.
Spark colour - hard to say - but a blueish tinge is nice certainly. However, if there are good ones, it should run, and it does seem from what you say there are sparks under compression. So I think it's weak mixture.

PS you can mod the slide easily if you think you need to, no need to buy another

[Ewen]

I have a 31/2. It must be what I took off. I must have read somewhere that it should be a 4. Needle is in 3rd notch down... so pretty rich you would think. I tried giving it choke to figure out if it needed to be richer but it didn't seem to like that particularly. Tickling help a bit. Fires but won't run.

[trevinoz]

Have you cleaned the pilot orifices in the body?
Usually if the engine will fire after tickling and won't run there is a blockage in the pilot circuit.
Check that the small hole above the mixture adjuster is clear, it is hard to see but it is there.

[Ewen]

I think I got everything. I took out the jet block and cleaned the 2 channels there. I will look for this small hole.
Thanks

[Ewen]

Dead as the dodo when I wind the twist grip round a bit.

[Ewen]

Hi Trevinoz
Is this small hole accessible from ootside of the cab?

[RDfella]

This doesn't sound like carb to me, especially as choke apparently makes it worse. Take a plug cap off its lead and tell us how far the spark will jump when kicked over. Around 10mm would be good.

[Ewen]

Thanks. I too was moving towards the mag as a more likely culprit because of a lack of any change with the choke experiment. I attached an air filter last night to richen things up a bit and don't know if it even fired. Must get my hands on a can of ether before I resort to taking the mag out. Will try the lead test. Thanks.

[trevinoz]

The small hole is in the inlet tract forward of the jet block. Awkward to get at but possible with a fine wire.

[trevinoz]

 Ewen, the small hole to which I am referring is in the inlet about 5/16" forward of the small hole in the jet block.