1975 Norton 850 Mark 3 will not start :(

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thackero

thackero

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During the last 12 months my 75 Norton E/S was getting more and more difficult to start. I made the decision to finally fix my front cylinder stud that had dropped out many miles ago due to a stripped thread. Carbs (new in 2015) were also rebuilt and now its all back together however it will not start. Sprayed starting fluid in the carbs . Gas is evident as plugs are getting wet. There is a spark but it looks weak . New battery. I am running a Boyer and my thoughts are maybe under pressure the spark in the cylinders is too weak. Now I am backtracking to try to source the problem . My question for the forum is it possible to install the pushrods incorrectly ? i.e exhaust should be the shorter ones inlet the long pushrods. Could I have mixed them up ? - maybe although I pulled the rocker covers last night and all valves are showing that they close and all have the correct clearances 6 thou inlet 8 exhaust. I will check the timing tonight but I suspect Boyer could be faulty. I am running 6 Volt coils (new in 2015). Any suggestions ?
Thanks
 
Certainly sounds ignition related. Re "weak spark," check all your wiring connections related to the ignition system, including the Boyer sensor under the point cover. Did you change anything that would have affected the ignition timing? Of course, the Boyer itself could be bad but the wiring/connections could easily be the problem.
 
You can't mix up the pushrods, the head will never fit.

So many things to check and double-check.

If you pulled the timing cover off, you could have installed the rotor slightly off time...
 
It seems unlikely that ignition should be that much off. First check would be to look at rotor position and timing mark at the alternator rotor / degree plate inside the inspection plug. If approximately correct and sparks are sufficient, you should get some popping and banging at least. Assuming the timing is ~ok and since your engine is "dead", I bet connections to the Boyer stator plate are bad, or there is a broken lead between the Boyer module and the stator plate. For correct timing, use a strobe lamp as described in the workshop manual.

For troubleshooting, please read
http://www.boyerbransden.com/faultfinding.html
http://vintagebikemagazine.com/technical-articles/boyer-trouble-shooting/

-Knut
 
Last edited:
Check the charge on the battery.
Make sure it is fully charged....
 
There is always the POSSIBILITY that swapping the ignition stator leads will fire it up.
 
Do you have good compression? Check ignition system ground/earth and try running a live wire direct from the battery to the ignition system eliminating possible kill and ignition switch issues.
 
Last edited:
Try bypassing ign/kill switches with a direct line battery negative to boyer. Also confirm you've got good ground on engine and at boyer.
 
Thanks for all your suggestions. Battery (new) is fully charged. Starter is rotating the correct way ( I cleaned the 4 brushes). Checked kill switch and earth points. Checked wiring. Plenty of compression.Dried out plugs (new). I will change out the boyer tommorow and provide an update. I am thinking electrical as the spark on both plugs seems weak.
 
When you get it sorted, let us know.
I'm interested in where this winds up.
 
thackero said:
Thanks for all your suggestions. Battery (new) is fully charged. Starter is rotating the correct way ( I cleaned the 4 brushes). Checked kill switch and earth points. Checked wiring. Plenty of compression.Dried out plugs (new). I will change out the boyer tommorow and provide an update. I am thinking electrical as the spark on both plugs seems weak.
Click to expand...
No, the two little wires to the Boyer ignition (not the starter) can sometimes get "confused". Try swapping them.
 
Just because the battery is new and "fully charged" doesn't mean it can deliver full load. The Boyer ignition will not work correctly
without full voltage and if the starter is sucking all of the goodness from the battery then the Boyer will not fire. Have the battery
load tested at your local battery shop. Without a good fully charged battery you are risking a back fire which will wreck the sprag
gear.
 
lazyeye6 said:
Just because the battery is new and "fully charged" doesn't mean it can deliver full load. The Boyer ignition will not work correctly
without full voltage and if the starter is sucking all of the goodness from the battery then the Boyer will not fire. Have the battery
load tested at your local battery shop. Without a good fully charged battery you are risking a back fire which will wreck the sprag
gear.
Click to expand...
EXACTLY CORRECT.
 
I also tried kickstarting only for half an hour so that should eliminate starter taking charge from the battery (although it wore me out phsically )
 
My Boyer & Lucas 6V coils always delivered a small, but blue spark while kickover testing. Not the big fat thunderbolt we see on modern vehicles. Started reliably.
ANY sign of life at all? Pops? Backfires? Kickbacks?
Or NOTHING in the way of firing?
 
Is there any utility in using one of those spark tester, variable gap gizmos to assess the actual spark power?

1975 Norton 850 Mark 3 will not start :(
 
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