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Can't start B33 engine after renovation
#645861 03/26/16 5:24 pm
Joined: Aug 2015
Posts: 60
Owain Offline OP
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I was in the MC garage all day today trying to get my new renovated B33 to start and just couldn't bring it to life and I'm scratching my head to what it might be...

I have good compression (freshly bored with new pistons and rings).
The AMAL 298 carb is set up with the correct jets, needle position, etc and have set the pilot screw all the way in and then out 1 turn. The throttle screw is set so that it is jus very slightly lifting the throttle body.
The timing is set up correctly. Magdyno advance set to 11mm BTDC on compression stroke (I opened up the rocker covers too, to double check that the inlet valve had just closed and that it was the compression stroke).
I fitted a brand new spark plug (NGK B6HS) and tested to see if it sparks when I give it a kick...it does.

But it won't start, in fact, it won't even ignite even when starting fluid is sprayed into the carburetor. Not a single heart beat. Is there anything I've missed out here? The spark plug is sparking but perhaps it's simply not a strong enough spark? Magndyno renovation needed? Other than that I can't think of what the issue could be...


Owain
1969 - BSA Rocket 3
1950- BSA A10
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Re: Can't start B33 engine after renovation
Owain #645872 03/26/16 6:52 pm
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Posts: 32
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hi,

I had a similar issue with my B33 last autumn. Is showed up as a weak magdyno, renovation in the 90s.
There was a visible spark at the spark plug outside, but no firing. After some trial and error I had the impression, that the spark plug outside fired always in advanced and mostly in retard.

I got the explanation, that the magnetic field is weaker in retard than in advanced position.

Maybe you can check this by setting it in full advance to 11mm, just to see if it starts then.

Josef

Re: Can't start B33 engine after renovation
Josef2 #645928 03/27/16 6:01 am
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Did you put a sealant inside the petrol tank ?
If so dump the fuel in the carb and hook up another temporary tank ( I use an old plastic lawnmower one and was doing the before I became a lawnmower mechanic as it had a tap on it ).
And try a brand new fresh plug.
See how you go.

If you can get your hands on a colortune they are magic in this situation as you can see into the cylinder under compression and see if you are getting a spark. £ 30 is a lot cheaper than a £ 400 unnecessary mag rebuild.
OTOH if no spark then you are no longer guessing, off to the maggie man with no regrets.


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Re: Can't start B33 engine after renovation
Owain #645941 03/27/16 8:18 am
Joined: Nov 2013
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Maybe Check valve not sticking to guide thus staying open

Re: Can't start B33 engine after renovation
Owain #645944 03/27/16 9:11 am
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If everything else is set up properly I suspect the ignition system. Either not properly timed, or not providing enough spark. In my experience, typically the symptoms of a magneto in need of a new condenser is that it works when cold, and gives up when it gets hot.

I would double check the timing, points gap, plug gap. I have a collection of spark plugs I keep handy, all nice and clean and properly gapped.

Last edited by stubbicatt; 03/27/16 9:12 am.

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