Got spark but no fire on top pot

[gusthewonderslug]

Hi all finally put my 68 lark x back on my boat after its birthday
Now she has spark on both plugs but is not firing on the top cylinder.
I've tried swapping plugs but still the same it will start first kick but runs like a bag of nails as the top pot won't fire.
Does anyone have any suggestion?
Gus

 

[Tim Frank]

Re: Got spark but no fire on top pot

Check compression.

 

[gusthewonderslug]

Re: Got spark but no fire on top pot

Without a compression tester it seems to have heaps !
I will have to get a gauge and test properly
Any other ideas?

 

[Tim Frank]

Re: Got spark but no fire on top pot

Without a compression tester it seems to have heaps !
I will have to get a gauge and test properly
Any other ideas?

How are you checking/evaluating spark?

 

[gusthewonderslug]

Re: Got spark but no fire on top pot

Pulling plug out and grounding on the side of the engine

 

[Tim Frank]

Re: Got spark but no fire on top pot

Not a reliable test.
You need an adjustable gap tester.
Spark should jump a minimum 1/4" gap.

Then check compression.

 

[geoffwga1]

Re: Got spark but no fire on top pot

It's a common problem Gus,I just overhauled two motors that did the same thing,you just have to be patient and work from the coils out.I had a good fat spark 1/2 inch long on one of them and it still wouldn't fire on the top pot.Assuming you have checked the coils and set the points and they are good the next candidate is the plug leads,usually the culprit and definitely so in my case.Even if you have a good fat spark on your tester if the lead is breaking down the spark will jump off sideways to ground somewhere along the way.It's a cheap fix to put new leads on,make sure it is the metallic core stuff and not the automotive carbon crud 'cos that won't work.If you local NAPA or omc guy doesn't have it almost any motor bike shop will.Finally be sure and check the plugs themselves,I had two new plugs fitted on one of mine and it took me hours before the penny dropped and I checked them and found one was duff.It's nearly always the little things,just work through them before you get out the straightjacket and call the guys in white coats.
Good Luck geoffwga1.

 

[bob johnson]

Re: Got spark but no fire on top pot

you have spark.....if the spark will jump a 7/16th" gap... and it is firing...then you dont have gas getting to that hole! use a spark tester...leave the plug in the cylinder head and attach the spark tester from the end of the plug to your spark plug wire.....if the motor is running and you are constantly seeing the spark jump.......while the motor runs.....then that hole isnt getting gas...bob

 

[gusthewonderslug]

Re: Got spark but no fire on top pot

Guys
Managed to get the flywheel off both coils had popped/ delaminated I had a pair of old ones on a spare engine that I fitted. I now have spark on both pots.
My issue is now it won't idle smoothly, it sounds like a blocked low speed jet, or the timing is out as it pops almost like a backfire, i have kitted the carb, once she is up an running it goes great, it just doesn't want to run slow.
Took it for its first run hoping I would clear twelfth but unfortunately in back to trying to find the problem.
No the plus side the selectric shift works a treat.
Any ideas ?
Gus

 

[Tim Frank]

Re: Got spark but no fire on top pot

Guys
Managed to get the flywheel off both coils had popped/ delaminated I had a pair of old ones on a spare engine that I fitted. I now have spark on both pots.
My issue is now it won't idle smoothly, it sounds like a blocked low speed jet, or the timing is out as it pops almost like a backfire, i have kitted the carb, once she is up an running it goes great, it just doesn't want to run slow.
Took it for its first run hoping I would clear twelfth but unfortunately in back to trying to find the problem.
No the plus side the selectric shift works a treat.
Any ideas ?
Gus

Without a compression tester it seems to have heaps !
I will have to get a gauge and test properly
Any other ideas?

Yes, get a gauge and test properly.....ideally one that has finer graduations than "heaps"....

 

[boobie]

Re: Got spark but no fire on top pot

Gus, you should stick to one post as it's less confusing. Or else answer the other one back to be polite.

 

[gusthewonderslug]

Re: Got spark but no fire on top pot

Guys
Opologies for my lack of decorum I'm new to forums.
I have managed to get the spark issues sorted out once i removed the flywheel.
The coils were delaminated and in hindsite I was lucky to get it running in the first place.
I have replaced the coils from my spare engine and now my issue appears to be idle circuit related.
I pulled the idle screw out and have sprayed the orifice out with cleaner carb.
I will hopefully test it this arvo if the weather breaks.
I appreciate all the help and advice that everyone has given to date.
Gus