Lark IV Ignition Mystery

[mstahl1171]

I'm stumped on this on. I keep loosing spark on the #1 cylinder. I have replaced plugs, plug wires, coils, condenser's and points. I have used a spark tester and get good hot spark with a 7/16" gap. Motor will run fine for a few hours and then drop the top plug. I checked for spark and have none. Removed the flywheel and the the coil is cracked and burnt. This is the second set of coils. The previous owner said he had the same problem. Any ideas??....Im not sure what else to check....ugh!!!

 

[lindy46]

Re: Lark IV Ignition Mystery

Sounds like you may have a short somewhere. Possibly something is not wired properly, or bad or wrong ignition switch. Maybe 12 volts getting back to the coil and frying it. Do you have a wiring diagram? I'd probably check the black kill wires and make sure they are connected properly to the "M" terminals of the ignition switch.

 

[mstahl1171]

Re: Lark IV Ignition Mystery

Checked the wiring....yes...I have wiring diagrams. Checked the key switch...replaced over the summer....the old one checked fine but went ahead and replaced just incase. Also found a NOS wiring harness from a local dealer...that too has been replaced...the only thing that has not been replaced is the flywheel.

 

[bktheking]

Re: Lark IV Ignition Mystery

So you replaced the coils and removed the flywheel and they are cracked? Motor overheating perhaps?

 

[mstahl1171]

Re: Lark IV Ignition Mystery

Engine is not overheating...pumps water just fine...can put my hand on the engine block while running...even after WOT run....wires are not burnt...just the coil for #1 cyl. I have replaced before....works fine for a few hours....good spark...smooth running...and then the cylinder drops off. Today a crippled my way back to port on one cyl...removed the flywheel and found the coil cracked and burnt on the top. I had an old one that i just installed and spark returned.

The previous owner said he had the same problem...could never get it fixed from the dealer. I too have tried and at my wits end. When i first replaced the entire ignition system back in March...I was able to run several weeks with no problems...Ran like a new motor...then it would start acting up. I checked for spark with a spark tester and all checked out..changed plugs and ran good again for a few weeks...then back to its old ways...changed coils, points, wires, condensers and again ran like a champ.....now 2 months later its back to loosing spark on # 1 cyl.

Checked the wires on the coil to make sure they were not rubbing the flyweel shaft...all check good. I will test run tomorrow after work and see if it too comes back fried.

 

[F_R]

Re: Lark IV Ignition Mystery

Cracked and burnt coil strongly suggests that 12 volts is being applied to the black mag wire. You will have to figure out how that is happening. We can't diagnose it from here. It USUALLY happens when somebody tries to use the wrong kind of ignition switch, but hopefully you aren't doing that----are you?

Could the black mag wire be being used as a ground for some accessory or running lights or something? That should not be done. NOTHING gets connected to the "M" terminals on the key switch but the two black mag wires. Well, a tachometer if you are lucky enough to have one.

 

[bktheking]

Re: Lark IV Ignition Mystery

12V being applied usually accompanies a sizzle, smoke and a pop, usually everything else melts, points, wiring, it's not pretty.

 

[mstahl1171]

Re: Lark IV Ignition Mystery

No luck F_R...I checked everything as you suggested and all connections are wired as per factory wiring diagram. My accessories come off the Electrical Junction Box into a fuse block, then to accessories. My next step is to remove the harness from the engine to the JB and check for any fraided wiring.

Yes...I do have a tach...found one on ebay a few months ago but never hooked up. Will do after I get the ignition figured out.

 

[lindy46]

Re: Lark IV Ignition Mystery

I'd be looking for a frayed black kill wire that's shorting out to 12 volts somewhere. Or just disconnect the black kill wire from the set of points and run the motor without it for awhile and see what happens. You'll have to choke the motor to stop it.

 

[mstahl1171]

Re: Lark IV Ignition Mystery

Mystery Solved!!! You guys where right one the money......found dry rotted wiring in the harness from the engine to the junction box. will bring home wire and heat shrink from my workplace and make a new harness....oh joy!....lol

Thank you all for your insight

 

[mstahl1171]

Re: Lark IV Ignition Mystery

Wiring harness is now complete. Getting ready to head out for a test run and make sure everything is okay. Wish me luck!

 

[asdasc]

Re: Lark IV Ignition Mystery

good luck with it!

When they run nice, they are a joy to have, and seem to run for many years.

 

[mstahl1171]

Re: Lark IV Ignition Mystery

Success!!! Was able to run for almost 5 hrs till I finally ran out of gas....

Anyways...the wife is so happy to have the whaler back in tip top form we are going to dinner tonight by boat....yeppie!!! Thanks again guys....peace at last!...lol

 

[lindy46]

Re: Lark IV Ignition Mystery

Great! Glad you got it fixed. Wiring problems can be the most vexing to diagnose.