new boat, some questions on 5.7 mercruiser

[idleRelaxation]

Re: new boat, some questions on 5.7 mercruiser

Actually we don't know, but I would guess the range is either 4200 - 4600 or 4400 - 4800. Hard to tell as we don't know how it was built . . .

completely understood, again sorry for the lack of info on my part, will try to gether as much as i can

thanks for the help so far though!

 

[Scott Danforth]

Re: new boat, some questions on 5.7 mercruiser

did you get the timing set yet? your timing could have been really really off (retarded) with the loose distributor and the engine will be a pooch

 

[idleRelaxation]

Re: new boat, some questions on 5.7 mercruiser

did you get the timing set yet? your timing could have been really really off (retarded) with the loose distributor and the engine will be a pooch

will be done by weekend, mechanic friend couldnt pass by and cant find a light gun, distributor was rather loose (easily turned by hand and slow leak of oil from being so loose), i have tightened it since then and waiting to correctly adjust

 

[idleRelaxation]

Re: new boat, some questions on 5.7 mercruiser

i also suspected something with throttle cables?

rpms dont just stop rising midway thru throttle and stay at 3.2k till WOT, but instead reach that RPM at WOT....idk if i explained myself clearly there, please let me know if anyone needs clarification

 

[QC]

Re: new boat, some questions on 5.7 mercruiser

i also suspected something with throttle cables

This is very easy to check. Engine off, put the control in throttle only. Push as far forward as you can, and then check if there is any remaining travel at the carb itself.

 

[idleRelaxation]

Re: new boat, some questions on 5.7 mercruiser

ok heres a pic of prop
View attachment 153112

pic of carb closed/WOT
View attachment 153114and View attachment 153115

and pic of where serial number should be, any hints on how to figure out the drive ratio short of opening it up? didnt find drive ratio printed anywhere
View attachment 153116

 

[QC]

Re: new boat, some questions on 5.7 mercruiser

Doesn't look like WOT to me, but I am a carb idiot.

For the ratio, put her in gear. Take your plugs out, and rotate the engine 10 times by hand. Count the number of times prop goes around.

 

[idleRelaxation]

Re: new boat, some questions on 5.7 mercruiser

Doesn't look like WOT to me, but I am a carb idiot.

For the ratio, put her in gear. Take your plugs out, and rotate the engine 10 times by hand. Count the number of times prop goes around.

doesnt look like WOT to me either, will look more into carb adjustment now...

will do, then what?

just ordered flame arrestor to replace current air cleaner for the safety comment

 

[QC]

Re: new boat, some questions on 5.7 mercruiser

will do, then what?

10/1.5 = Prop goes around 6.7 times

10/1.81 = Prop goes around 5.5 times etc.

 

[idleRelaxation]

Re: new boat, some questions on 5.7 mercruiser

10/1.5 = Prop goes around 6.7 times

10/1.81 = Prop goes around 5.5 times etc.

haha that went completely over my head, sorry been drinking, busy day at work

will post again with as close to accurate as i can drive ratio and try and do another sea trial this weekend after timing and possible carb adjustment depending on my findings and if anyone chimes in on the carb pics i posted, dont really know much as all my cars have been EFI :facepalm:

 

[Scott Danforth]

Re: new boat, some questions on 5.7 mercruiser

QC already posted. your carb is not opening fully. the pic looks like its only opening about 30%. take a bunch of pictures of the carb and linkage and post. something is awry.

 

[KyHeadhunter1]

Re: new boat, some questions on 5.7 mercruiser

Maybe its just my suspicious nature, but is anyone else getting the feeling the maybe the previous owner may have retarded the timing and backed off the throttle linkage on purpose to try to cover up something? Maybe bent pushrods or a dead cylinder? With a 23P prop, even if it has a 1.5 drive, this engine could easily be over reved in that light of a boat.

Is the upper drive covered in a white chaulky film on the outside?

If it were mine and I pulled the plugs out to spin the motor over to check the gear ratio, I think I would run a compression check too. If you don't have a compression tester, you can borrow one for free from an Autozone or Oreily auto parts if you leave a deposit. The results can give clues to not only the condition of the engine, but also it could give an idea as to how the engine is built.

 

[KyHeadhunter1]

Re: new boat, some questions on 5.7 mercruiser

I find two 5.7s available from Merc in 92 - 93; very possible it has a '92 in a '93 boat. Happens a lot. Anyway, the 5.7L was rated 235 at the propshaft and the 350 Magnum was rated 250.

QC, where did you find this info? I have an 87 350 mag in my boat and I would absolutely LOVE to find out as much info as possible about it, such as cam specs, cylinder head volume, and valve sizes without having to take it apart. My wrench time is limited to a couple hours a week and that's on a good week.

 

[John_S]

Re: new boat, some questions on 5.7 mercruiser

ok heres a pic of prop
pic of carb closed/WOT
and pic of where serial number should be, any hints on how to figure out the drive ratio short of opening it up? didnt find drive ratio printed anywhere

The picture is of the secondary air valve. It will not open until there is enough vacuum. The primaries are under the choke plate, which is closed. Move the throttle to wide open, and open the choke, and look at the primary butterflies. Then do the same for the air valve on the secondary side.

 

[John_S]

Re: new boat, some questions on 5.7 mercruiser

Maybe its just my suspicious nature, but is anyone else getting the feeling the maybe the previous owner may have retarded the timing and backed off the throttle linkage on purpose to try to cover up something? Maybe bent pushrods or a dead cylinder? With a 23P prop, even if it has a 1.5 drive, this engine could easily be over reved in that light of a boat.

Usually, retarding the ignition would cause the idle to be rough, which is not conducive to a sale. I have seen the opposite, where the timing was advanced to make it idle smoother.

Yea, should spin that 23P with any ratio alpha, in that light boat.

Once the simple things are checked,compression and a leak down test are in order.

 

[QC]

Re: new boat, some questions on 5.7 mercruiser

QC, where did you find this info? I have an 87 350 mag in my boat and I would absolutely LOVE to find out as much info as possible about it, such as cam specs, cylinder head volume, and valve sizes without having to take it apart.

What I have is much more limited than that, but if you PM me your email addy, I'd be glad to send it to you.

 

[idleRelaxation]

Re: new boat, some questions on 5.7 mercruiser

Maybe its just my suspicious nature, but is anyone else getting the feeling the maybe the previous owner may have retarded the timing and backed off the throttle linkage on purpose to try to cover up something? Maybe bent pushrods or a dead cylinder? With a 23P prop, even if it has a 1.5 drive, this engine could easily be over reved in that light of a boat.

Is the upper drive covered in a white chaulky film on the outside?

If it were mine and I pulled the plugs out to spin the motor over to check the gear ratio, I think I would run a compression check too. If you don't have a compression tester, you can borrow one for free from an Autozone or Oreily auto parts if you leave a deposit. The results can give clues to not only the condition of the engine, but also it could give an idea as to how the engine is built.

will be running compression check when i do timing, just for a baseline and peace of mind, though owner did state it had been recently rebuilt, which seals/hoses/gaskets/hardware seem to backup, but i guess you never really know about internals till you open it up, motor gives no other symptoms of low compression, turns very easily up till 3k with no hiccups or backfires or lag

 

[KyHeadhunter1]

Re: new boat, some questions on 5.7 mercruiser

Usually, retarding the ignition would cause the idle to be rough, which is not conducive to a sale. I have seen the opposite, where the timing was advanced to make it idle smoother.

Your right. Many years ago I bought a truck with a 350 in it that was full of bent pushrods and that's what had been done to it. Eventually found them because it cranked over really slow when restarting a warm engine.

 

[NHGuy]

Re: new boat, some questions on 5.7 mercruiser

Hi, Just noticed your thread. I have a similar motor in a 19' 6" boat. I don't know exact weight but I know the boat & trailer weighed 3250 when I got it a few years ago. So maybe the boat weighs 2500 or 2600 I'd guess.
I have a 23 pitch Michigan wheel 3 blade aluminum prop and can spin my old pre vortec 350 to 4700 RPM at 58 mph on a pitot speedometer. My drive is a 1.47 ratio Alpha 1. And my motor only has the factory Rochester 750 on top. As far as I know it's all stock. I can tell you the idle is better and it pulls out of the hole better with the timing where it belongs. I'd definitely wait til you have the timing right before running it again.
I got a car GPS this winter so maybe I can report a gps speed if I ever get the boat in the water this year. Been too busy to boat!

When you get that motor set up right be very careful how you hit waves, your boat can launch right out of the water if you hit em with too much speed. If your boat gets air you need to pull back the throttle while the prop is out of the water. Then once the prop is just about to bite bring the throttle back on. Also if you are going to intentionally get it out of the water don't hit waves at an angle, the boat can come down crooked or sideways.
I think you have a 60 to 65 mph boat there.

 

[idleRelaxation]

Re: new boat, some questions on 5.7 mercruiser

i was able to source a timing light gun, anyone help me with wiring this thing up? ill post pic of distributor wires in a bit for reference