88 Supra TS6M Hard start when hot.

I have a 1988 Supra Comp TS6M with the 351 Windsor.
It will run fine for 15 - 20 min through our no wake zone and when we get out on to the main lake we run around at 25 - 30 mph for 10 minutes or so. Once we stop and get a skier in the water it will crank and crank what seems like forever. Usually takes cranking 3 separate times for 10 - 20 seconds to start.

The coil gets extremely hot and i think that is the issue but don't know exactly what I need to trouble shoot.

The boat was converted to electronic ignition by the previous owner.
The ignition module has 1904 on it. It also has a purple and black wire that come out of the distributor. The purple wire connects to the positive side of the coil and a pink wire connects to the positive side also and runs back to the resistor.
The black wire connects to the negative side of the distributor and also has a grey wire that runs into the wire loom I assume to the gauge.
The coil has #903 on it and says use with external resistor.

The distributor is a prestolite.

If anyone has any ideas or suggestions i would appreciate it.
I cant find the part number or any information on the ignition module itself except for that 1904 number. I have searched it and came up with nothing.

Thanks again.

How old is the carb ? Has it been rebuilt?

Carb is brand new last season from skidim. Carb seems to run and function fine.... Had this same issue with the last carb except the old one would puke fuel .

Is it a external mounted coil ?

If so research of the coil is internally resisted or externally resisted .

These boats came with points and condensers , they used a ballast resistor to keep the coil cool and spark hot !

I once made the mistake and found using my volt meter the coil maintains 8-10 volts once running and any more than that it would overheat and cause misfires / hard starts . Ect . Take a pic of the mentioned wiring and you ignition .


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Have you tried using recreational fuel? The fuel without ethanol?




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Yes it is a external mounted coil. It is the one that skidim sells it says " 12V use with external resistor 903"

The resistor is externally mounted at the back of the engine and it has a circle with 700 on the side of it.

Lively, I saw a post somewhere that said you bought all of your parts from napa, do you still have part numbers ?

I haven't been on for a few days, i have been chasing other little problems with the boat.

Took the boat out today. I put a 2 inch piece of rubber to lift the coil up from the intake manifold because the mount was transfering heat. The boat ran great for 3 hours. It wasn't until I was trying to get my 7 year old daughter wakeboarding that it started giving me problems. We probably tried 30 times to get her up. It was a lot of idling and slow pulls.

Lifted the dog house and the coil was finger burning hot. Checked the resistor and it was just as hot. Took a a rag dropped it in the lake and set it on the coil and the boat ran a lot better after a minute. Every time it would miss or start running / idling crappy i would dip the rag and soak the coil and it would run better. So im almost positive something is going on with the coil and resistor.

Any ideas?
Thanks for your help.

I have not tried recreational fuel, actually i have never heard of it.

here are some links to images of the coil and the resistor. couldn't figure out how to link them so they came up in the thread.
the purple wire comes out of the distributor and goes to positive side of coil. The pink wire connects to the positive side of the coil also and goes back to the resistor.
The black wire comes from distributor and connects to the negative side of the distributor. The grey wire connects to the negative side also and goes back to the tach.

https://ibb.co/kjFpTF
https://ibb.co/i5Uuvv
https://ibb.co/ndSgav
https://ibb.co/iTw7Fv

Bump to the top

Still trying to figure this thing out.
So I bought a new coil and ballast resister from Napa Auto parts. The lady at the counter didn't know what ballast resister went with the coil.
The coil I got was the Echlin IC12, I grabbed 2 ballast resisters that she thought went with it.
One meters out at 1.9 Ohms and the other at .8 Ohms. I hooked the 1.9 ohm up and it would not start the motor. I then threw the .8 ohm resistor in and it fired up.
The original resister metered out at .6 ohms before I unhooked it. Before removing the resistor the readings from the orange wire from the choke hooked to the terminal was 11.28 vdc in and 6.65 vdc on the other terminal out to the coil.
With the new resistor installed it metered out at 11.03 vdc and 7.75vdc out.

With the old coil hooked up to the old resister at the coil terminals I read 6.64vdc from the + terminal to a ground bolt.
From the positive terminal to the negative terminal it read 5.11 vdc.
From the negative terminal to a ground bolt it was 1.5vdc.

with the old coil hooked up and the new resister the readings are now 7.75vdc from the positive terminal to ground bolt.
from the positive terminal to the negative terminal it reads 6.09vdc.
and from the negative terminal to ground bolt it reads 1.64vdc.

all of the readings above are with the key in the on position.

The old coil metered out at 1.2 Primary and 9.5 secondary.
The new coil meters out at 1.3 Primary and 9.1 secondary.

I currently still have the old coil on and haven't swapped out for the new one yet. I haven't put it in the water yet but was wondering if anyone had any info.
Thanks.