1978 1400 tower bogs in gear (video)

Thought I got this "new to me" setup running good - new rectifier, new plugs, carbs rebuilt, water pump kit, LU oil, idles at 800 neutral, new fuel lines and bulb. It throttles up fine in neutral. I put it in the water for the first time and it bogs/dies near half-throttle. I checked spark with a timing light in gear and they are all firing. I read a bit about the idle screw being too lean and it bogs out in gear - so I tried tuning them out a bit at a time and throttling up... no difference.

I have to say when I put it in gear, I do feel some vibration in the hull, not sure how normal that is for these older engines or if there could be a problem in the gearcase... I kinda want to pull it out of the water and check for metal filings on the plug.

But is there anything else that could be checked while she's still in the water?

Here is a video - you can hear it "die" at that magic point, if I bring the throttle back quickly, it keeps going (you can hear it kick back in). At the end of the vid I goose it and it dies completely. I am new to mercs and large outboards... any help would be appreciated.
-Tom

Re: 1978 1400 tower bogs in gear (video)

When it does it, try squeezing the primer bulb. If it picks up then probably means you need to rebuild the fuel pump. Otherwise I'd guess that when you rebuilt the carbs you got the float level too low and at least one bowl is running out of gas.

Re: 1978 1400 tower bogs in gear (video)

The idle mixture screws have no effect at RPM faster than 1200. There is no dedicated mid range fuel jet or circuit in the carbs. If it is a carb issue, the carbs would need to have general dirt in the main nozzle. If she runs at high speed, the fuel pump is fine.

That motor has a distributor ignition, right?

Re: 1978 1400 tower bogs in gear (video)

Yup I had someone squeeze the bulb while accelerating, no effect. I also rebuilt the fuel pump with new diaphragm and put an inline fuel filter between pump and carbs, looks like a good flow (I'm guessing it would look somewhat empty if the carbs were starved). ... but yeah I could've messed up the float height. I remember blowing through each fuel intake while upsidedown/right side up and they seemed to be functioning properly. Maybe I should redo the carbs and fuel pump to ensure everything is clear.

Ah, I suppose the idle mixture issue with bogging is for hole shot... makes sense.

There is no distributor cap/pulley system... there is a coil(?) going to each spark plug wire; and those are wired to two switch boxes. Is that Thunderbolt ignition? Serial #4867256

Re: 1978 1400 tower bogs in gear (video)

Lot's of those "inline filters" leak air. To be on the safe side, try it without that and see what happens. Are you 100% sure your fuel tank is venting properly? Just throwing out ideas to keep your thread at the top! Good luck.

Re: 1978 1400 tower bogs in gear (video)

I got a seachoice one that has glass (seemed better quality than the plastic automotive ones), but yeah I could swap a hose and do a test. Gonna tinker around right now. Thanks for the ideas!

Re: 1978 1400 tower bogs in gear (video)

could be a spark/powerpack issue, a timing light would help determine sparkage while running in water.

Re: 1978 1400 tower bogs in gear (video)

Just to update - I took the fuel filter out and pulled the carbs, double checked the float heights, and replaced all zip tie connections with hose clamps, and tightened them on really good. Took it out last night... she finally screams at around 5100K. Now to move on to all the other issues

Thank you for the help!

Re: 1978 1400 tower bogs in gear (video)

Awesome! Thanks for the update.