Need help with 3.0 coil issue

[Slamnslash]

Thank you in advance for the help.

I have been having an issue with my coil overheating causing a miss. There are several threads that I have found and have come to this point because I cannot find the issue.
Let me start with the details.
Boat is a 1999 Maxem 1800SR
Motor was blown and a replacement was installed but ignition system was not carried over. This boat was originally built with the TKS style electronic ignition.
The donor motor had points.

Now the engine harness plugs into the boat harness and everything is working.
What I have done.
I added a Petronix ignition and flamethrower coil with an internal 3 ohm resistor. I am running the coil and igniter from 12vdc off of the choke wire.

Voltage at the coil was 13.5 running. I added a resistor and brought it down to 11.5.
With the original points and coil it would start to miss and die after about 20 minutes of running. Now it can run for about an hour and does not stall (yet) but starts to miss.

I am thinking I might have an issue with my tachometer and it causing the coil to heat up.
I notice that if I am using the trim, the draw in power will cause the coil to start missing shortly after the voltage has stabilized (draw doesn't seem to cause the miss but the continuing draw and recovery seem to have more of an effect.)

My questions are;

Should this tach run to the alternator or to the coil? Could the change from the newer style TKS ignition back to the old point style have caused a compatibility issue with the tachometer?

I plan on taking her out and leaving the tach disconnected and see what effect it has but can the tach be hooked up to the alternator? I am pretty sure looking at diagrams that the alternator has a tach terminal.

 

[TunaFish389]

What Petronix ignition are you running? Kit 1146A is a 3.0 Ohms coil and 91146A 0.6 Ohms coil. Both for the 3.0l conversion.

 

[Slamnslash]

1146A igniter and 40511 coil.

 

[Scott Danforth]

first, you went backwards with your donor motor. points ignition would put the motor as a pre 1991 motor. that means you stepped backwards in block technology

second, why did you not transfer the delco ignition over? it is about 50 years more advanced than the old prestolite distributor and a pertronix kit. did you at least put new bushings in the old points distributor?

tach gets connected to the coil negative

if you develop an ignition miss, I would look at the pertronix kit and the load on it (coil and ballast) as well as how much play you have in the distributor shaft

if you still have the other engine, go get the ignition from it.

 

[Slamnslash]

"why did you not transfer the delco ignition over?" Ignorance, lazyness. I thought points would be fine and they should be. They are a proven design and when maintained correctly should be very reliable.
"did you at least put new bushings in the old points distributor?" No, the motor was a late 80's boat that sat most of its life and rotted away. The motor is very sound and very low hour. I was not looking at a complete rebuild of the motor and still have no reason to believe that would be necessary. The shaft has little to no play and the advance is free and clean.

As far as the problem goes, I had the coil and ignition being powered from the choke power and have taped off the resistor wire per instruction. I have had an issue with the tach fluctuating going haywire so that was why I suspect it but it could be the coil causing the issue.

The way it sits now.
I have the igniter being powered directly off of the choke power (13.5vdc) and the coil being supplied from a 1.5ohm resistor with about 11.5-12vdc voltage. It is running off of the hose at idle speed letting it get warmed up. I am going to see if this works.

Plugs are stock and gaped to .040. Plugs, cap and rotor are new. Ignition and coil were installed last year. Maybe 10 hours on them.

This is a thread that has the exact same symptoms as me from a while back.
Edit to add the correct link
https://forums.iboats.com/forum/eng...4814-ignition-coil-overheating-mercruiser-140

Is 13.5 too high for this coil?

 

[Scott Danforth]

depends on the resistance of the coil, and the circuit firing it

most motors have alternator outputs in the 14.6 volt range. the coil doesnt care assuming the driver circuit (points or pertronix module) is set up properly for the coil resistance. the pertronix paperwork is very clear on coil resistance and wiring


since you kept the points ignition "because its a proven design and reliable" why would you muck it up with a pertronix conversion vs grabbing the Delco Voyager electronic ignition?

as a side note, every pertronix unit I have used, I ended up back with points as they all failed. however YMMV, and that was my experience.

hours mean nothing if there was lack of maintenance. a 30 year old boat should have between 1500 and 3000 hours if it was used at all. that is still low hours. if there is any wiggle at all at the top of the shaft, pull the dizzy and throw in some new bushings (available at napa)

as another side bar note, TKS stands for Turn Key Start. it refers to a fuel enriching solenoid in the carb wired to a thermal switch and has nothing to do with the ignition other than the power source.

 

[Slamnslash]

Update.

I have went over entire electrical. Cleaned every connection, added a ground to the block, installed a new ignition switch and ran a wire from the switch to the coil.

Took it out this morning and lasted about 45 minutes running Petronix igniter and flamethrower 3. ohm coil.

So I took the old points (still mounted to the plate) and re-installed them. Verified timing and found it retarded by quite a bit. With the timing light set to 0 the notch was below the scale on the block.
This doesn't sound right to me. It should have been closer to 6* BTDC.

I advanced the timing and adjusted idle down to 650-700. Had to keep advancing and lowing the idle to get below the mechanical advance range.

Took it out for over two hours and was running for about 2 hours prior so I am missing something or the igniter is not working correctly.

When I installed the Petronix I set the timing to 6*BTDC at idle rpm. I have had issues with my tach and I think I may have set the timing wrong and it was too far advanced.

Would this cause the Peteronix to have too much dwell or something and cause a problem?

Will running the Flamethrower 3 ohm coil cause the points to fail because of the higher voltage?

I want to get the Petronix to work but I need to learn how not to be so stupid.

I am planning on re-installing it and trying to set it up right again but want to take the kids out tomorrow for some swim time. Its freaking hot out and I think it should get us around for a little while tomorrow.