New everything and still zero spark

check the plug threads! yes, in the head! carbon isnt particularly conductive.

check that the head is "continuous" with the rest of the engine! its only contact with the rest of the engine electrically is through the cylinder STUDS. the cylinder has a fibre base gasket correct? thats not conductive!

im sure we tried new plugs ?

that can cause complete loss of spark... but replacing EVERYTHING should have resulted in SOMETHING that worked.... unless, as i said...heads not earthing. where are you holding the plug to check for spark?

multimeter will soon tell you if its the magneto not working, narrowing the field down somewhat.

can play a part in intermittents...but...id be far more suspicious of seals etc when its erratic...what may feel like spark, simply isnt...unless you have a data logger saying that it definitely is the spark missing at times... seals or crankcase gasket are my suspicions. or a dirty carb.

cus yes, im getting the same splutters on one particular engine...and so far ive been too lazy to dig into it. i got others that are running fine, so why bother :giggle:
 
im sure we tried new plugs ?

I have tried using 3 new NGK Spark plugs in 3 different heat ranges: BP6HS, BP7HS, BP8HS
I have always used BP8HS plugs. The 6 and 7 heat range plugs made no difference to the spark miss.

I have had crankshaft seals completely fail and also partially fail.
My current situation most definitely "feels" like a spark/ignition problem, but i cannot say 100% for sure that it 'is' an ignition system problem.

I have connected a wire to the spark plug and attached it to an couple of engine case bolts to bypass the potential insulator issues of carbon on the spark plug threads - the problem still remains.

Why would the spark miss become present at 3,300 rpm and progressively get worse as rpms are reduced?
The miss is present at higher rpms but it's barely noticeable, and the hotter the engine gets, the more the spark miss is reduced. When the engine gets stinking hot, the spark miss almost goes away.
Logic would say that it should be an air/fuel ratio issue being a temperature moderated problem, but would 3 different engines all have identical problems, including one engine that ran perfectly when it was previously pulled out of the bike and reinstalled to try and cure the problem?
 
All these things remind me of my 1997 merc 9.9 outboard motor (2 stroke). A few years ago it started knocking really hard at around 3000 rpm. If you were cruising along at that speed every once and a whole it would kick really hard, puffing out a big cloud of smoke, jerking the tiller handle and often even stalling the motor. Then one day last year I was driving it to the marina and when I let off the gas, it stopped cold and wouldn't start. I managed to get it running by turning the idle speed screw in all the way with some scissors and revving the cr*p outta it. Ever since then it starts right up when cold, then once it's somewhat warm the idle becomes nonexistent. If you hold it WOT it will slowly clean out and rev happily, but it has no power under load and is really slow to accelerate(at times it refuses to pull a tube faster than walking speed). I've got it to idle by leaning the idle by one turn. And if I pull the mechanical advance at idle it'll run great.
So far I've checked for a sheared flywheel key which would cause the ignition retard (from the knocking) and that was good, if I remove one spark plug to test the individual cylinders if I remove the bottom plug it runs absolutely no different than with both in. And if I remove the top plug it barely runs at all; I need to pull the mech. Advance and throttle butterfly just to get it to start. Switched coils, the botom cylinder's still bad. Plugs are the same. Top crank seal is good (can't easily check the bottom one). Only one carb so that isn't the problem. Only one trigger coil so that isn't the problem. I'm assuming the stator is one big coil and doesn't have a coil for each cylinder. That leaves the CDI (or switchbox as the fancypants manual would say). I'll be replacing that in the spring. It's a $150 part so it better fix it:(
 
And one time it would randomly shock me through the boat (aluminum), and only run with the engine cover off. When I put it on it would die. The cover was pulling my good cyl's spark plug wire out of it's hole in the coil:giggle: but the other problems still remain...
 
you should have a kill switch sometimes the switch goes bad or it may ground on to your frame take the black and blue wire off the coil wires that may do it or take cover off magneto make sure shaft that turns magnets is"nt bent
 
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