new to me 312... first twin engine boat questions
 

I just got a 03 312 with twin 496 mags. My previous boat was a 94 252ls with a single 454 mag mpi. I have some questions about driving a twin engine boat because I have never driven or owned one until now. First, is it normal to have to throttle one engine up a little more than the other while cruising? My port engine was always lagging a few hundred rpm unless I moved the throttle up a little more than the starboard side. Oil pressure was pretty close to the same on both engines it did vary slightly on each side from time to time. Also the port engine showed that it was running slightly hotter than the starboard but both engines were between 150 and below 180 degrees on the gauges. My 252 used to hop on plane immediately with no tabs and just easing into the throttle, this 312 seems like it puts the bow way up and doesn't plane nearly as quickly. Is there something I am doing wrong when trying to get on plane? I put tabs down a bit and outdrives down all the way of course? Also my steering wheel position seemed to change constantly depending on how the boat was trimmed? So far im thinking I liked driving a single engine boat much better lol. Any advice is greatly appreciated! Thanks!

Great boat with great power package. Your throttles arr prob just outta sync a bit you can adjust them some but you may need new cables. Steering wheel wander is just the play in the cable. If you keep boat for a while invest in full hydro steering best upgrade to a stock boat and will make handling so much nicer and safer. Gauge sifferences most likely sender differences as long as you are within operating parameters no worry. Lastly bow rise like tou describe is typical of a stepped hull formula. Down tabs down drives. Ease onto plane you will feel the boat pick up speed. At this time bring up tabs the adjust drives. Use tabs to level nose of boat. Prob mot needed unless you are in chop. Tabs are much less drag than running drives in. Enjoy thats a nice ride

I had a 312 before I got my 353, first, the 312 Formula is a heavy boat, it's going to take a lot to get it to plane out, it's like that with most of them, second, a twin engine boat is totally different than a single engine, the engines aren't going to act the same, the water, oil and rpms will be slightly different in them, there's no way to get them exactly the same, as long as the gauges are reading correctly and both are running well they're fine, it's like two separate woman, have you ever met two of them the same, you'll get used to it, it's a great boat.

And you will never have 2 at the same time......

El dude, what is the boat propped with?

Lol... Thanks everyone for the info! The boat has full latham hydraulic steering already from factory, and is propped with 28 pitch bravos. So should I try to adjust throttle cables? Having the throttles out of sync drives me nuts! I may look into having props blueprinted as they do have a few small nicks in them. and the silent thunder is coming off....

My first question is what are the RPMs at WOT? They should be close if not the same. If they are more than 200-300 RPMs apart, I would say there is a problem.

I would also run the boat with a good quality electric tach and verify the gauges are reading correctly, if they are then you can adjust the cables so the throttles are in synch

So for the most part anyone with a twin engine boat, the throttles are in the same location without having to compensate one engine or the other?

I would look into finding a set of 26s to try. My Pops' 312 with 6.2s came with them new and the boat always jumped on plane quick. He sent them out a few years ago to BBlades to get a few more RPM out so hes around 5100-5200 WOT. Its a heavy boat but sticks to the water no porpoising and now with the way they are cupped you can get a lot of trim out of it. I have seen 70 gps a few times when the planets align but hes good for 68mph on the usual. At least there are some numbers you can compare to with the 496s.

As far as setting the cable and what not, the proper way is to either have a Merc scan tool and read the TPS to see if both engines match at a certain throttle location. If they do not adjust cables accordingly to match. If you dont have access to a scan tool but do have a multimeter/fluke meter you can read the tps voltage between the two wires while they are still connected. The tps shows different voltage depending on the resistance (location) of the sensor. If they are both the same and your throttles are off then you have to look further. However if you do indeed see a different voltage at a certain throttle position you diagnosed the cable needs to be adjusted and you can just adjust to make both readings match at the same location.

I know that is not as easy as adjusting and trying but at least you are not running in the dark and actually know what is going on.