Logo

Mercruiser 50 weak spark wonbt start

ready2lake

New member
"i have an 83 ebbtide with a c

"i have an 83 ebbtide with a chevy 305. I just swapped motors because the one in it was cracked. the boat has the thunderbolt iv ignition system and i have replaced the distributor ignition sensor. it has a msd blaster coil, taylor wires, and new plugs. i also replaced the wire from the coil to dist. my problem is it has a very weak white spark, and has yet to try to fire. i have considered changing this over to an hei distributor but am unsure on how to make the shift assist module work with the hei. does anyone have any info on this? all my local boat shops are at a loss, and nobody has any info on checking the spark amplifier.. also, both motors ran before the swap, and i detailed every wire before i took the ignition system out."
 
Maybe you need to go back to a

Maybe you need to go back to a basic Merc system and see if you can get it running and tuned with that. Once thats done you can then start swapping in aftermarket parts and make sure it still runs.
Right now you have too many variables to nail down the problem in my view.
The shift interrupt switch on carbed engines is a NO unit that momentarily shorts the points or optic sensor out to kill the engine when you shift out of gear. I don't know if you can use this same idea with an hei ignition.
Rod
 
"Aaron:

I believe Rod has


"Aaron:

I believe Rod has the right idea, especially concerning the coil. Are you using a 12 volt coil that has a built in or external ballast resister?

I was reading some info. on changing TB ignition coils. The SELOC manual talked about how some coils will overheat the ignition aplifier and kill it. You may have done that.

Try this test procedure:

Tests for Thunderbolt Ignition: W/ignition key on AND BILGE WELL VENTILATED OF GAS FUMES!!!

#1 - Connect your voltmeter neg. lead to the engine ground and pos. lead to the white/red wire terminal at the dist. It should read 12 volts.

#2 - If 12 volts is present, remove the coil spark wire from the distributor and connect it to a spark gap tester to ground. Remove the white/green lead from the dist. terminal. Turn the ign. key to on and strike the white/green lead to ground. If there is spark, replace the ignition sensor in the dist.

#3 - If there is no spark, substitute a new coil and repeat test #2. Now if you get spark, install a new coil. NO SPARK, replace ign. amp.

#4 - In #2, if there is No voltage present, disconnect the white/red wire and check it again for 12 volts. If 12 volts is present, replace the ignition sensor inside the dist. cap. If no 12 volts present w/it disconnected--ignition amplifier is shot and must be replaced."
 
"hey guys, thanks for your hel

"hey guys, thanks for your help.. everyone i talked to around the okc area sent me in different directions.. i finally got her fired up after setting the timing for the hundredth time, had to set it about 8 to 10 degrees before top dead center. purs like a kitten now. everyone told me the i/o are just like car motors, and while the internals are similar, seems everything outside is different.. thanks for all your help..... headed2lake
rofl.gif
"
 
Back
Top