5.7 350 i/o

[Merc 2.5]

well there's probably a correct thread for this but I'm gonna ask it here mite get more views. I'm working on a 94 95 5.7 350 mercruiser. Issue is motor starts and runs fine , if u get on plane and back off and cruise slow if will run fine. Now if you try give it hell for say 30 sec or so maybe more it will run good then start to "run out of gas" is what I think. I haven't rode in the boat while doin this but was riding beside it. It will eventually die out and will not restart. Well after it cools off and lots lots of cranking ot will eventually start again if battery don't die 1st. Sounds like running out of fuel to me. The cap and rotor button look fairly new. ( boat new to him but had receipts of work done) I did check the cap and button it has the 4 barrel Rochester carb. Would this be a power valve issue in this thing? Just rebuild carb? I plan on backing it in water and leave on trailer and try to get the issue to pop up so I can watch it. Any help is appreciated. Whatcha thinkin?? I want it out my yard!!! Haha.

[nitro_rat]

No power valve in a q-jet! They do have a pretty small float bowl that can get sucked dry if the fuel pump isn't up to snuff. Check the filters too. Maybe a combination of weak fuel pump and clogged filters. Trash in the tank can compound this. Is it a mechanical pump? If so check the oil. A ruptured diaphragm will let gas leak into the crankcase!

[Merc 2.5]

Ya its mechanical pump. I looked at carb diagram but I probably used wrong name or sumthin. But yes it still seems like its not keeping up just like outboard almost. Just takes a whole lot longer to restart from the mechanical pump i guess. I did check oil but did not smell it. I'll do that

[Merc 2.5]

Yep gas in oil. Gonna grab a pump always look over simple **** and jump into sumthin else. But that's y I posted here 1st. Thanks nitro

[Merc 2.5]

I guess its been bouy10 yr or more since I messed with old school sbc. Especially in a boat. Never cared for i/o

[nitro_rat]

They're a huge PITA in a boat. Last one I had to put a fuel pump in I sent my GF down in the hole to do it :D

[rgsauger]

Had the same thing happen in my old baja. Chit load of gas in my oil. Be sure to use a marine pump and not just auto zone stuff.

[FMP]

Drain the oil, pour a couple three quart cheapo in, run a few minutes , drain and filter. Use good high zinc oil.

[Merc 2.5]

I know a trick for holding the rod up in the block by running a long bolt in and it will touch rod and keep it from falling down until u get the pump in. Hopefully it won't b to bad , but sure is tight around motor on this one

[Merc 2.5]

Had the same thing happen in my old baja. Chit load of gas in my oil. Be sure to use a marine pump and not just auto zone stuff.

He sure had it planned to go to parts store and grab a pump. So I shouldn't let him huh?

[nitro_rat]

O'reilly's can order Sierra but they won't have it in stock...

[nitro_rat]

I know a trick for holding the rod up in the block by running a long bolt in and it will touch rod and keep it from falling down until u get the pump in. Hopefully it won't b to bad , but sure is tight around motor on this one

I stick my finger in there and hold the rod up and use a remote starter button or an assistant to bump the motor over until the rod is all the way up in there. Then I let the rod drop out, slather it on grease and stuff it back up there. It will stay long enough to get the pump bolted up.

If the pump cam has the rod pushed down it's a b!t€h to get the bolts started!

[KIRCHNER]

How is the marine pump diff? i know alternators, starters, distribs have marine versions.

[nitro_rat]

How is the marine pump diff? i know alternators, starters, distribs have marine versions.

A real marine pump has an all aluminum housing that's screwed or bolted together instead of the crimped steel lower body like a car. They're actually Carter's "high performance" mechanical pump I'm pretty sure. The Mercury version comes painted, Sierra's is bare.

Not just a corrosion issue, the higher volume pump keeps the bowl from going dry. A car doesn't usually experience full load/full throttle acceleration for long durations. A car engine in a boat thinks it is pulling a loaded trailer up hill all the time, fuel consumption is much greater!

[KIRCHNER]

yes, carter an old name not heard in a while. know it well. the old AFB 4 BBL.

[Merc 2.5]

This pos boat is cursed I say. So I can crank ,crank all day long won't start but as soon as u let off the key to stop cranking it fires up or tries to , its like there's no fire until u let off the key and it starts firing and motor starts. But will not start while cranking. Fuel is there. All that's good again

[Merc 2.5]

I wish I could post a short video but I'm to dumb to no how. Bout ready put few holes in and go for test ride.

Has anyone ever heard anything like this?

[nitro_rat]

I'd get out my meter and start testing voltage drops. Probably a corroded connection. What ignition system is on the boat?

[Merc 2.5]

Thunderbolt. Has separate coil. Not hei dist. It runs good but starting it is crazy. No telling how long he been trying run it like that

[Merc 2.5]

Well its fixed for now. Guy left plug in boat and went outta town. Got back and it was full of water. Got water drained ,new starter, new fuel pump, and got everything dried out in the sun and starts like it suppose to now

[nitro_rat]

Well its fixed for now. Guy left plug in boat and went outta town. Got back and it was full of water. Got water drained ,new starter, new fuel pump, and got everything dried out in the sun and starts like it suppose to now

yeah, bad connection at the starter will do that...

Make sure there's no condensation built up in the motor, run it up to temperature and check the bottom of the oil fill cap for white/tan sludge. May need to change the oil a few times to clear it up!

[Merc 2.5]

Well its back. Took bout 30 min of running under a load and when it happen it put a huge load on alternator and started squealing. I'm leaning toward ignition switch at moment. But go test it now BTW. Starter and all connections r good

[FMP]

Tighten the v belt or get a fresh one ? If it's loosing V because it's slipping ign will drop off.

[Merc 2.5]

Not slipping its tight. Only does it when the heavy draw is put on it from whatever it is??

[Merc 2.5]

So it was screwing up when I brought it back home after test. Just went to try start it and its fine like nothing was ever wrong so now won't b able to test til screws up again. Wtf? I hate this boat and I knew it would haunt me when he bought this pos. Been a nightmare since day 1

[FMP]

What could draw that much, trim pump standing on it bottomed out.

Battery crapping out

If a v belt squeals it's loose or glazed also pulley or the bearings in the alternator itself, bench test yet?

[Merc 2.5]

No bench test yet. I have 2 things I'm but to do ....


Bout to change it al to the hei distributor and get rid of the coil and crap, and test/change alternator. The problem seems to accur when it gets warm or when the batt run low enuff the ignition isn't up to par , but yet it cranks fine. ?? Hell idk

Battery and starter new and fuel pump

[nitro_rat]

Don't put a damn car distributor in it whatever you do. ����*♂️

[FMP]

Don't think that's roller cam , but make sure you're using the correct dist gear. Also you'll need to set up for advance curve spring weight, idle advance and total limit if needed. You think the ign is pulling that much to cause that drop, what's the v meter saying during this ?

Change the v belt and clean that pulley to steel in the groove.

[Merc 2.5]

Don't put a damn car distributor in it whatever you do. ����*♂️

I'll say I've done it b4 and sob ran real good. This was 10yr or so ago

[Merc 2.5]

Don't think that's roller cam , but make sure you're using the correct dist gear. Also you'll need to set up for advance curve spring weight, idle advance and total limit if needed. You think the ign is pulling that much to cause that drop, what's the v meter saying during this ?

I didn't have the meter on the river. By time I got it home pos was working fine. Yes. Its a nightmare. My sbc guru cousin just got here and we gonna try few things. It's in the ignition when it warms up under a load. I wanna say alternator, I wanna say coil I wanna say etc. But really it could be any of em and I'm guessing still. I'll figure it out one way or other. If u can think of something please speak up

[FMP]

New belt, clean clean pulley, 100% fresh battery swapped, check coil spec, bench test alt.

[nitro_rat]

I'll say I've done it b4 and sob ran real good. This was 10yr or so ago

Any more advice? Don't put a car motor in a boat!!!

[FMP]

Grab an extra spare belt , keep in boat

[Merc 2.5]

Any more advice? Don't put a car motor in a boat!!!

It don't have a car motor. But have ran quite a few with hei. Just not seeing what that issue is???? Gonna take it to water in morn and test everything while its screwing up. Good possibility it's the ignition module heating up and acting stupid. We will pin it down better tomorrow. Also checked alternator belt , retighten the belt. Motor sure does run good when its right tho

[nitro_rat]

Car motor HEI usually doesn't have a good advance curve for a marine application.

[Euroski]

Next time it doesn't start until U leave up on the key, check to see if there is spark while cranking?

[Merc 2.5]

Next time it doesn't start until U leave up on the key, check to see if there is spark while cranking?

Thats my next task this morning

[rgsauger]

An ignition won't put the kind of heavy load on the alternator you're talking about unless it's a dead short. Even then, the wires are small and it would probably pop a fuse or burn a wire. Look for anything with big wires going to it. Trim, starter, etc. Rubbed wires, possible shorts.

[rgsauger]

And that is a roller cam motor. They went to roller cams around 88 or 89.

[FMP]

89, time flies.

[nitro_rat]

87 in car motors, 96 in trucks. Somewhere around 89 they stopped drilling the fuel pump pushrod hole and the bosses for the roller lifter spider in truck applications that didn't have the roller cam. Not sure about the marine engines, I would think they followed the car motors.

[flabum1017]

Put a vacuum gauge on the fuel line before the motor, should be 4" of vacuum or less. If higher, check the anti-sphen valve and any filters before it. If they are good, remove the gas cap and see if the vacuum gets better, if so, blocked vent hose or fitting on the side of the boat (I've had mud doggers build nests in them)