Futility of testing ignition coils?

C

cabarete_cub

New Member
Mine tested according to the manual, both primary and secondary.
Actually it was the only thing that passed resistance tests with flying colors.
My guess the problem is ohmmeter doesn't do a hundred tests a second
while varying amplitude (and then count the passes), so almost-shorts are
never discovered. Makes sense?

Engine was stalling on high rev, and I thought the carburetor, where
I just installed a new throttle cable and lost the needle W-shaped stopper
is the problem. Made some, got some wonderful tips from OLD CT and made
some more - to no avail.

So in retrospect I should've bought and test new coil first, then new CDI
and only then a new carb. Well, what's a hobbyist without a spare carb?
 
cabarete_cub said:
Mine tested according to the manual, both primary and secondary.
Actually it was the only thing that passed resistance tests with flying colors.
My guess the problem is ohmmeter doesn't do a hundred tests a second
while varying amplitude (and then count the passes), so almost-shorts are
never discovered. Makes sense?
Click to expand...
In a word 'no'. The coil sounds like it's ok.

A stall at high revs seems it's more likely a carb issue (since it's a CDI motor)..But I would go ahead and check the spark plug and see how it looks. The condition of it can tell a lot of what's going on.
 
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Initially the problem was
- stalling on high rev
- stalling on 3/4 to full close choke

I still think it was coil.
I put a new carb - same. New CDI - bit better. New coil - much, much better.
Now it works very well on high, but is almost impossible to start.

Spark plug is black as hell. Aside from idle, I have only one screw on my Keihin PD
clone. It is my first moto carb, so it is possible that I am missing something stupid, but
aside from the screw the only reason I can think of for mixture to be so rich is an air leak I introduced while
swapping the carbs.
 
Far be it for me to diagnose an engine, as there are lots of members here that have been-there and done-that.

However, according to my Clymers manual; your plug is carbon fouled caused by possibly too cold a plug, weak ignition, dirty air cleaner and/or too rich a fuel mixture. :39:

A normal plug should be gray or light tan. Another part of the Spark Plug guide mentions worn rings or valve adjust...
 
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I know black means rich mixture, but the spark is long and blue, I have no air cleaner installed now and I am cleaning the plug every 30 seconds.
Valves is a good idea, though, especially since I also think engine sounds a bit harsh. I see if I have tools to do it.
 
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