470 mercruiser help!!

[Tulkster]

So just picked up a 16'5 gerw with the 470 having a few problems first problem is when i put the boat in reverse it shuts off so i found out that the wire from the coil to the tack is killing it in reverse. i know there is a interrupter switch in the shifter when i disconnect the wire on the coil every thing is ok but i have no tack.. is it maybe because of the trim? does it have to be all the way up to put in reverse?.. and another problem is should i run high test gas or is reg ok because when i'm at 3/4 throttle to full it seems like there's no more power but the engine sounds like its working really hard.. could it be over propped? also after running for awhile at idle the oil pressure is almost at 0 but if i turn it off for a few minuets and restart its ok intill it gets hot,, could it just need a oil change?.. also for the size of the boat what should the top speed be? so far i can get it up to 42mph on the fish finder.. sorry about all the questions but some info will put me at ease.

 

[fmalott]

Re: 470 mercruiser help!!

first things first check compression

 

[Bamaman1]

Re: 470 mercruiser help!!

I have a 16 1/2 deep v hull bowrider with a 470. Before the engine blew, it would run about 50 mph--chine walking my relatively light hull. I could get all but 2' of the hull out of the water with a 23 pitch prop.

I still have all the motor parts (machined), lower unit and prop available for sale--unassembled. All 4 cylinder I/O's are a little slow coming out of the hole, but the 470 is pretty strong from mid-range on up to redline.

 

[stonyloam]

Re: 470 mercruiser help!!

So just picked up a 16'5 gerw with the 470 having a few problems first problem is when i put the boat in reverse it shuts off so i found out that the wire from the coil to the tack is killing it in reverse. i know there is a interrupter switch in the shifter when i disconnect the wire on the coil every thing is ok but i have no tack.. is it maybe because of the trim? does it have to be all the way up to put in reverse?.. and another problem is should i run high test gas or is reg ok because when i'm at 3/4 throttle to full it seems like there's no more power but the engine sounds like its working really hard.. could it be over propped? also after running for awhile at idle the oil pressure is almost at 0 but if i turn it off for a few minuets and restart its ok intill it gets hot,, could it just need a oil change?.. also for the size of the boat what should the top speed be? so far i can get it up to 42mph on the fish finder.. sorry about all the questions but some info will put me at ease.

The tach wire should not do anything, sounds more like an intermittent problem with the lower shift cable, the trim position should be a non-issue. Could be overpropped, what size is yours? Should say on the hub. Should be running a good straight 40w or 25w40 oil. Sounds like you may be running a little hot. A new impeller would probably be a good investment especially with a 470. I would think a 16.5 would do a little better, what rpm are you running at wot? It almost sounds like you are not trimmed properly at high speed.

 

[Tulkster]

Re: 470 mercruiser help!!

when i trim i start all the way down then work my way up till it starts bouncing on the water them trim it back down a little till it stops bouncing it runs at 150 degrees and doesn't get any hotter.. i dont know what rpm it is because with the tach wire is disconnected.. but when i take it out this weekend i'll hook it back up

 

[stonyloam]

Re: 470 mercruiser help!!

So far so good LOL. Come to think of it, if that tach wire were to short to ground, it would be a problem:redface:.

 

[Tulkster]

Re: 470 mercruiser help!!

only shuts the engine down when i put it in reverse

 

[stonyloam]

Re: 470 mercruiser help!!

only shuts the engine down when i put it in reverse

In that case you may need to adjust your shift cable. Start at page 87 here: http://www.perfprotech.com/store/app_themes/ppt/images/tech-specs/alpha-shift-adjust.pdf