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jumping ...missing and backfiring

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Lobo:
Hi Billy,

The backfiring, lumpy, popping, plug blow-out are all suggesting (to me) a timing issue, and due that 4000 RPM threshold, perhaps a problem with the advance / retard unit... which is possibly 'stuck' in the advanced range? Check it's working properly, is smooth turning, the springs in good fettle, and most importantly of all, it's set up to the correct timing marks. And obviously, if one set of points is mis-set, that too will show up as a pair of mis-behaving cylinders.
(Ballpark, the advance retard kicks in @ 1100 RPM, and is fully advanced by 2500RPM.)

Apologies if you're familiar with setting up, but just to re-affirm, the static & strobe timing marks (low idle) are the 'F' mark, whilst above 2500 RPM or so the strobe should be illuminating at the two marks 23.5-26.5 degrees ahead of those F marks.

Er.... enjoy your Sunday!

Simon

billy192:
ok so had a busy sunday  8) advance is working fine,.
decided to check my coils so watched a utube vid

and i have 4.9 on the primary (ohm contacts on the yellow and black/white)
the vid said after switching to 2K on the multimeter keep the contact on the yellow wire and the other in the plug cap and you should have a reading of around 10. i get nothing :-\

then on to the other coil and  4.8 primary and nil again from the secondary

i put the plug on the head and spun on the starter and there is a tiny spark you can barely see it (inside the garage).

has anyone tested there coils like this?

Billy

ka-ja:
Hi,
    Try the 2nd test again in one HT lead with the meter set to 20K with both plug caps off the plugs on duel output coil, as 2K is too low for 2nd circuit, and "lesser" meters will not automatically shift upscale and will show no reading---Ken

billy192:
thanks Ken, i am sure i did try on 2K,20K,200K,as i remember the dot moving across each time i changed it, but i will re test next Fri (work away all week). fingers crossed

Billy

JamesH:
Billy, you need to break it down a bit and isolate the plug caps from the coils. Remove the plug caps and meter across the pair of HT leads on each coil (so 1&4 and 2&3). Should get 15 kOhms from memory. Then meter across each plug cap and if they are resistor caps you should get 5 kOhms. So total of 25 kOhms impedance across each coil with the plug caps fitted. This assumes you're running non resistor plug caps.

But this is based on 750 experience....maybe someone on here can validate correct for the 500/550?

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