1995 Gen V 7.4 Ignition

[hutsonb12]

Hey there. I purchased a known seized 1995 Bayliner 2250 with a Gen V 7.4 Bravo 3. Thunderbolt V(i think) ignition. Pulled the motor and rebuilt with .040 bore. Loved every second of it and used this forum for a lot of good info on my first go at a boat build. I finally got the fresh motor broken in after fighting the distributor and old dirty carb. Ran it for 20 minutes and didn't have time to set the idle before dark.
The next day I swapped the carb out for a known good 750.... coughed for a split second once the bowls filled up and then nothing...
I am getting spark from the coil to the distributor but not out to the plugs. Checked with my timing light. I then went ahead and bought a new cap, sensor, and rotor since they were about the only thing untouched from the rebuild. Still nothing. Getting frustrated and hoping to get some additional input on it.

Thanks in advance!!
Brandon

 

[alldodge]

getting spark from the coil to the distributor but not out to the plugs

This comment says its the cap and/or rotor, its the only 2 pieces between them

Suggest run thru the TBV trouble shooting chart

 

[hutsonb12]

That's the frustrating part! I thought the same thing.... that's why I replaced the cap and rotor. Is there a ground I missed??

 

[alldodge]

That's the frustrating part! I thought the same thing.... that's why I replaced the cap and rotor. Is there a ground I missed??

Ground normally comes thru the dizzy, but also can use an extra wire in the newer modules. That said, if you get spark out of the coil, then you don't have a ground issue

 

[Scott Danforth]

as all-dodge indicated, if you have spark out of the coil, only things left are the rotor, cap, and wires.

if it ran before you swapped carbs, go back to the carb.

if your "known good carb" sat for any length of time, then it needs to be gone thru.

 

[Fun Times]

Ensure your battery volts and cold cranking amps are up to specification as should either specification be low it could show signs of no spark at the plugs while cranking.

Pull some plug wires off the spark plugs and use some (other?) spark plugs to check for spark and colors.

Pull out some spark plugs to make sure they are not fuel fouled from the new carb......As Scott mentioned, try the original carb as you may have compromised the spark plugs, fuel flow, air flow settings, etc..

Where you able to set the ignition base timing while it was running okay?...Distributor assembly hold down bolt tight.

Make sure there are 8 (not 6)metal tangs on the rotor that pass-through the mercruiser distributor sensor.

Is the engine in the boat now or still on the engine stand?

Crank the engine over at night looking for a light show and listening for a sparking type noise.....Maybe the plug wires are going to ground someplace.

 

[hutsonb12]

Thank you for the responses!
Battery is GTG
I didn't mess with timing during break in.... just got her up to temp. My next step was getting idle set and base timing. I currently have the purple/white wire connected to ground to set base.
I will check the tab count on the new rotor.
Motor is in the boat.

I am trying to post a picture and thumbnail, but it isn't working for some reason.

 

[Scott Danforth]

you need to have 3 posts under your belt and your pictures must be about 400k in size (re-size them)

you now have 3 post

 

[hutsonb12]

I finally had a little time to look at this again. I connected a spark tester to one of the distributor outputs. I am seeing a spark. My next thought is the short. I had the cap distributor off and was re positioning the rotor and I can hear the coil firing when I spin it. Loud spark pop. Make sense that the short draws enough of the voltage away from the plug wires not to trigger the timing light? or ignite the fuel for that matter....