Mercruiser 5.7L 350 270HP poor top speed **but good idle and good acceleration**

[ericlepine26]

Hey guy's. Im new here. What a great forum this his. Here is my problem. Just bought a 23 foot Conquest 230 made by Power Play. Kind of a small Baja. Equiped with a 1989 Mercruiser (350) 5.7L 270 HP with Alpha one 19 pitch propeller. The boat iddle perfect. It as a descent acceleration for its size and weight. Here is my probleme. It stop at 3800 rpm (wot) and i can't go over 36 mph. Original w.o.t is 4400-4800. I think im suppose to get at least 48 mph easily. Rochester 4bb is the carb's set up. (original) The boat as been sit for 3 years at a friend house. I bought it from them like that. They said the boat always did those performance but im pretty sure there is a few horsepower missing.

I was thinking about bad fuel pump psi ? Maybe the carb's need a rebuilt ? Im not to sure, but as i said. The iddle is pretty good and the 0-36 mph is pretty smooth. Im just stuck at 3800rmp and 36 mph wich is not fast enough for this kind of boat.

Thank's for your time...and help

Eric

 

[abrx7]

Re: Mercruiser 5.7L 350 270HP poor top speed **but good idle and good acceleration**

What size prop do you have on it?

 

[Failproof]

Re: Mercruiser 5.7L 350 270HP poor top speed **but good idle and good acceleration**

Could be secondarys on the carb? Can you tell when they open? Could be overpropped as well. Need just a little more info.

 

[QC]

Re: Mercruiser 5.7L 350 270HP poor top speed **but good idle and good acceleration**

How are you confirming your speed? Your numbers seem to be reasonably accurate, but we need to confirm them. I agree 36 is too slow. Altitude?

Be aware, in 1989 horsepower was measured at the flywheel and that is probably around a 230 - 240 horse if rated today. Also, I don't believe there was a 270, top Alpha rated small block was a 260 at the time. That's just for reference.

 

[ericlepine26]

Re: Mercruiser 5.7L 350 270HP poor top speed **but good idle and good acceleration**

the prop is 14.5x19...wich is good for this boat...euh i think

 

[ericlepine26]

Re: Mercruiser 5.7L 350 270HP poor top speed **but good idle and good acceleration**

my speedometre gauge is pretty accurate since i was running aside from a friend boat of mine. And yes, its a 270hp..wich Mercruiser did sometime in 1989....i know most of them are 260 but this one said 270.

 

[ericlepine26]

Re: Mercruiser 5.7L 350 270HP poor top speed **but good idle and good acceleration**

here is my info !

 

[abrx7]

Re: Mercruiser 5.7L 350 270HP poor top speed **but good idle and good acceleration**

Could be secondarys on the carb? Can you tell when they open? Could be overpropped as well. Need just a little more info.

If it were the secondary's he would have horrible acceleration.

 

[ericlepine26]

Re: Mercruiser 5.7L 350 270HP poor top speed **but good idle and good acceleration**

I change the distributor and the rotor. Im changing this week end the spark plug. I put new gas in it. The only thing left to change is the fuel filter. Overall i guess it might be the pressure on the fuel pump. But as i said. Im not sure. The acceleration is good but i still think it could be faster the get it out of the hole....i think it miss a bit of ''guts''....ahhhh...pleasure of old powerboat )))

 

[Failproof]

Re: Mercruiser 5.7L 350 270HP poor top speed **but good idle and good acceleration**

If it were the secondary's he would have horrible acceleration.

not necessarily true. He could have less than ideal acceleration and **** poor top end, but amazing mid rpm throttle response. Partially cloged secondary jet, impropper linkage, bad diaphram (if used) it could also be timing. Just asked if he could tell when secondarys opened!!!

 

[ericlepine26]

Re: Mercruiser 5.7L 350 270HP poor top speed **but good idle and good acceleration**

should i consider a 250$ rebuilt ?

 

[Failproof]

Re: Mercruiser 5.7L 350 270HP poor top speed **but good idle and good acceleration**

should i consider a 250$ rebuilt ?

Rebuilt what? You said you replaced the distributor, did you check the timing? And before you throw any money at a carb or pump you NEED to have new plugs, gapped propperly, new rotor, new cap, and wires that you KNOW are good. Then set timing. Test run, then start worring about fuel.

 

[ericlepine26]

Re: Mercruiser 5.7L 350 270HP poor top speed **but good idle and good acceleration**

no. Didnt check the timing....wich i will do. I did replace the cap and rotor. Not the coil and wires. Will put the new spark plug this week. Yes, might be the timing...wich i didnt think since it was running smooth.

 

[QC]

Re: Mercruiser 5.7L 350 270HP poor top speed **but good idle and good acceleration**

here is my info !

Yeah, I just took another look at 88 and 89 and I was looking only at the SeaRay ratings. There was indeed a 350 Magnum rated at 270. At the crank, so around 240 at the propshaft.

Here is a low WOT diagnostic list. I think your numbers make sense, so I don't doubt them. Sounds weak to me, but you need to eliminate the hull based issues as well.

http://forums.iboats.com/showthread.php?t=295070

 

[ericlepine26]

Re: Mercruiser 5.7L 350 270HP poor top speed **but good idle and good acceleration**

I call at a Marina were the do mecanics....and the guy told me he is 99% sure its the wrong propeller.....Can a Mercruiser 350 5.7 270hp 23 foots boat run a 17 pitch propeller ? It seems a bit small

 

[QC]

Re: Mercruiser 5.7L 350 270HP poor top speed **but good idle and good acceleration**

A prop will make it run higher RPM, but you need to check everything in the link I sent first ^^^^^^ You are not going to pick up 800 RPM with a 2" pitch change. There is something wrong with this boat. Could be the prop itself, the bottom, the drive, the engine, over loaded, full bilge. Some will say soaked foam (I doubt with a 23 footer). We can all guess at this, even the mechanic, but a 17 inch, as the proper pitch would indicate about a 433 MPH top speed. Maybe, but I think this boat was faster, and I don;t think the 2 inch pitch change will magically fix a 600 - 800 RPM problem Needs to be diagnosed.