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Thunderbolt IV Wiring Question

WaitUpGuys

WaitUpGuys

Contributing Member
Hello folks! Just bought a 1993 Maxum 1900SR with 4.3L + Alpha One gen 2 and I'm going over general maintenance to make sure everything is in order since i don't know the history of how well it was taken care of. My next thing to do is check the timing at idle. Boat idles in nuetral fine at 650 RPM. So from what I've read about the Thunderbolt IV ignition, I don't have to use a jumper to check timing, just hook up the timing light, point and shot. However , i did find a purple and a Black (possibly gray) wire that is zip tied to the carb and not connected to anything. The end of the black (possibly gray) wire has a ring looking connector. The purple one has a plastic end that looks like it should snap to another connector. Long story story short, what do those do? I suspect the black/gray is the tachometer...? No idea what the purple one is. I'll try and post a photo when i get home. Thanks!
 
Correct on checking the timing....also a good idea to measure the timing advance as well (vs RPM) to make that function is working.

If the wiring was done using the color standards, purple is +12VDC from the ignition switch and black is 'ground' so, being as its at the carb, my first guess would be for an electric choke coil....best to check the manual to see what's in that area.
 
makomark said:
Correct on checking the timing....also a good idea to measure the timing advance as well (vs RPM) to make that function is working.

If the wiring was done using the color standards, purple is +12VDC from the ignition switch and black is 'ground' so, being as its at the carb, my first guess would be for an electric choke coil....best to check the manual to see what's in that area.
Click to expand...


Thanks Mako. Regarding the total advance...the graph show it should be 22 degrees for my engine at 2500RPM. Sounds dumb, but is that 2500 RPM in neutral or is that in gear? I'm going to the lake this weekend, so i'm gonna hold off on doing the timing check on muffs.
 
you can do it in neutral but I would NOT do it on the muffs - most hoses won't give the pump enough water....

make sure you read the 'graphs' correctly - most factory service pubs do NOT include the initial timing value in the chart....
 
makomark said:
you can do it in neutral but I would NOT do it on the muffs - most hoses won't give the pump enough water....

make sure you read the 'graphs' correctly - most factory service pubs do NOT include the initial timing value in the chart....
Click to expand...

Yep, thanks for the reminder. Yep, graph show min of 12 max of 16 at 2500 RPM then add the 8 degree from base. So i took 14+8=22. I'll wait till this weekend when i'm in the water to test the advance. Thanks again.
 
Finally got a chance to check the timing on the motor. It appears that the distributor have been untouched since the factory paint show no wear. The timing at idle was 8 degree ATDC. Have anyone seeing that before? I adjusted it to 8 degree BTDC. Come to think of it, after the adjustment, the idle RPM went from 650 to 900. I adjusted the idle back to 650, but now as i'm typing, i realized i should have rechecked the timing again to see if it's still sitting at 8 degree BTDC. Dang it!
 
Assuming it is factory paint and was 'untouched' one could draw the conclusion the timing chain has stretched a bit....but not knowing the history of the engine, it hard to say.....the timing - idle speed interaction is normal.....check the rpm on the advance curve to see when the advance starts should give you an indication of the criticality of rechecking the timing.....
 
makomark said:
Assuming it is factory paint and was 'untouched' one could draw the conclusion the timing chain has stretched a bit....but not knowing the history of the engine, it hard to say.....the timing - idle speed interaction is normal.....check the rpm on the advance curve to see when the advance starts should give you an indication of the criticality of rechecking the timing.....
Click to expand...


Good idea. I guess the important thing at this point is to set the total timing. as long as the engine starts up, idle timing seems less important.
 
Finally got a chance to check the total advance. Didn't have timing tape so I measured the distance of what 10 degrees would be and traced that on the harmonic balancer from the original line. When I was running at 2500 RPM and 3500 RPM, I just made sure that my new line is at the 12 degree BTDC mark. That would put the original line at 22 degrees. Glad that is over! Thanks for the help everyone.

https://photos.app.goo.gl/C3sX6y69V6IGnNE93


 
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