Compression rate - 8.5:1 (manual) -> 10 kg/cm2 (measured) 2

[jangg]

I should very much know if 10 kg/cm2 (145 psi) is about right compression in this cylinder(s). - A Norton Commando 850 '73 model restoration project. Both cylinders gives exactly the same reading (I have certain mixture and ignition problems with this Amal 932, 230 jetted carburated engine...).

Sincerely
jangg (norway)

 

[patprimmer]

cranking compression readings do not really mean that much, except as a comparison to a similar engine in good condition, as they are dependant on cranking speed, static compression and cam timing. Cam timing can have quite a significant effect

Regards
pat pprimmer@acay.com.au
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[PEW]

Janng,

The fact that both pressures are about the same is a good sign.

A 230 jet? Is that standard size? It sounds rather big.

 

[PEW]

Janng, my apology, your main jet is probably OK! Having checked, the original was a probably a 260 but some bikes ran too rich so a 230 was fitted.

 

[jangg]

Thanks for taking the time to answer me. - Yes, I've tried
to be systematic for about 3 weeks now. Checking and measuring (ignition as the main focus, then the carbs - 260 -> 230 jets, new airfilter ...). Spark plugs breaking down regards to sothing. - The electric system's a mess, but the engine was functioning six months ago... - I use a stroboscope lamp for ignition timing, but something has been real out of shape (maybe some short circuiting as the rpm increase beyond 2600 - 3000). Extra 12v coils, extra condensers, checking (the wiring is a mix from before and after 1970 as far as I can see - the coils should have been 6v behind a balast resistance - the former owner has been to slappy...).