Another ignition problem

[Mgaudet1993]

Hey guys sorry for the essay in advance. I’ve done a bunch of research but haven’t found anything that quite resembles my situation. Let me preface my problem by saying I just did my first engine swap from a cracked 87 mercruiser 4.3lx to a 89 mercruiser 4.3 2 bbl full drop in. Got everything in, outdrive on, fires up extremely fast and sounded good but was idling at 3000rmp. Not knowing carbs I adjusted the electric choke instead of the idle screw, also while it was warm. Fired it up again, barely started then same thing. So I pulled back on the throttle seeing if it would slow down, and it cut out. As it often used to do with my last engine. After that couldn’t start it up for the rest of the day

next morning I adjusted the choke cold and put it back very close to what it was and still nothing. I know I’m still getting gas in the carb so I figured i wasn’t getting spark at the coil. Tested and got about 10.5v at the positive terminal on the coil so cleaned every ground and power I could find including the starter. That got the voltage up to 11.85. Turned over stronger than before but still no fire. I’ve don’t various coil tests according to information given in other posts on this site.

My question is knowing that information do you guys think it would be a carb issue or an ignition issue? I’m ready to bring the boat to a shop but they’re a month out minimum with everything going on. thanks in advance for any advice you have!!

 

[Mgaudet1993]

Sorry, forgot to post the engine serial number! The serial number given on the cover is 0c656245. Thanks!

 

[Mgaudet1993]

One last thing, if it matters. When I got the engine in running condition there was a 10” ground hanging off the grounding plate of the ignition module. I tried all those tests with and without it connected to the ground above the oil filter. Also the yellowish green line coming from the back of the carb was unattached but I put it back on throughout the tests. No idea what either of those two but it ran great without either of them before I touched the carb.

 

[Mgaudet1993]

Hey guys just wanted to let you know it turned out to be a bad ignition sensor. I figured it out when I replaced the cap and rotor and the magnet was hanging around inside the distributor

 

[nola mike]

That green line is the overflow line from your fuel pump. If the diaphragm in the pump ruptures, the fuel dumps into your carb and kills the engine, rather than dumping into your bilge. Hook it back up.