87 mercury 3.0 not going past 3000 rpm under load

[thejeep007]

Hey guys always read things on here and always found my answer. I just got a 87 sebring regal cuddy with a mercury 3.0. Got her running with a new fuel pump and carb rebuild. Took her on the lake for a test run yesterday and would only do about 20mph @ 3000rpm. With out a load the engine goes no problem and now signs of misfire Had a 13.75 x 21p prop. Switched to a 14 x 19 with minimal improvement. Then went to my old 13.75 x 15. Engine could rev right up but prop "lost its bite" lost acceleration and engine revs spiked. Hub was fine and showed no damage when I took it out of the prop. The out drive has obviously been changed and thought maybe with the wrong gears. My grand 15 pitch prop idea didn't pan out. Thanks guys. Always appreciate the help

 

[NHGuy]

Re: 87 mercury 3.0 not going past 3000 rpm under load

So the 15 broke loose. Did you try taking off easy? Just roll on the power and allow the prop to do it's thing. Did you put the drive all the way down for takeoff? Once you get on plane you can bump the trim up a bit to get some more speed by raising the bow, just don't raise it so much that it causes porpoising or slipping.

 

[thejeep007]

Re: 87 mercury 3.0 not going past 3000 rpm under load

Rolled it on as slow I could go. Didn't even get close to plane before breaking loose. Moved the trim around with no change. The motor also seemed to get really hot with the 19 prop. Thinking just from working the engine at wot only at 3000 rpm. I remember lean condition ups temp but a complete carb rebuild and pump don't know how. It's not cutting out just not winding past 3000. I am hoping the advance for timing. I only know vacuum advance, any other thoughts?

 

[thejeep007]

Re: 87 mercury 3.0 not going past 3000 rpm under load

The weights in distributor seem fine. They move free. Goin on the lake now to see what happened with a good 19 prop. This thing is frustrating!!

 

[Don S]

Re: 87 mercury 3.0 not going past 3000 rpm under load

List of possible causes of low WOT (Wide Open Throttle) rpm.

In no particular order

Engine Won't Reach Operating RPM. Check

1. Fuel condition. Type and Octane possibly old fuel
2. Propeller pitch or diameter, damaged blades
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
5. Marine growth on hull and outdrive
6. Wrong gear ratio in outdrive
7. Restricted carburetor air intake (clogged flame arrestor)
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
9. Poor cylinder compression Compression Test
10. Carburetor defective, or wrong type.
11. Fuel pump pressure and vacuum
12. Boat overloaded, improperly loaded, or improperly trimmed.
13. Engine Overheating
14. Engine timing and ignition system operation
15. Remote control cables and linkage for proper travel to open throttle plates fully.

 

[jimbo_jwc]

Re: 87 mercury 3.0 not going past 3000 rpm under load

My 87 came with this 48-78118-a40-17p prop its a 3.0 L Mercruiser Alpha One outdrive

 

[thejeep007]

Re: 87 mercury 3.0 not going past 3000 rpm under load

Well I am on the lake right now. Getting up tp 3800 after messing with the distributor. But have a ping up high. Also pretty sluggish. I have looked at the adults only tread haha. Thamks

 

[thejeep007]

Re: 87 mercury 3.0 not going past 3000 rpm under load

Think this might turn into an over heating thread. Still waiting for my new temp gauge to get here but don't think a was water cooled engine should be getting this hot. About half hour after taking it out still can't touch the block mire then a second. Water foaming out of the bleeder idle in the water and flowing out on the muffs. Think all of this is from running hot? Way does that sound like impeller? I want to go back to an outboard!!

 

[thejeep007]

Re: 87 mercury 3.0 not going past 3000 rpm under load

Took a pic but my smart phone isn't smart enough to post it. All the fins are rough, 2 are half gone. Not as bad as I though it would of been for running so hot. I'll try to get the picture up. Thanks for any advise.

 

[thejeep007]

Re: 87 mercury 3.0 not going past 3000 rpm under load

Update.... Replaced the water pump and running so much cooler. Just brought it out on the lake engine holds at 3800 all day. It's a lot of boat for a little engine so 35 mph is fine with me. Gunna get 17 prop for it and as the old gas gets pushed out maybe I can get a little more. Thanks for all the help, I know ill need more with this stern drive.

 

[Bondo]

Re: 87 mercury 3.0 not going past 3000 rpm under load

All the fins are rough, 2 are half gone.

Ayuh,... Did ya find All the pieces,..??

They'll come back to haunt ya later...

When I change a beat impeller, I backflush from the T-stat housing back to the drive, while the lower is off...

 

[jimbo_jwc]

Re: 87 mercury 3.0 not going past 3000 rpm under load

My impeller scatered on drive with I/O in plastic 55gal drum first time I reved to 5,000 Rpm in neutral , and noticed how Quickly the tempature climbed . When I pulled the lower unit the vanes ended up in the bottom behind water intake grates , thermostat,and bypass hole to cool exhaust in thermostat housing . Found out best drum to test run in was one I cut down to fit my old OB 120hp with whale tail because I just bent back notched peices and these now direct water from Holes in bottom back to tank . Moved a couple of inches from under tank and I/O set level to test like on lake . I don't trust muffs as a good trial as forced water can hide all kind of water related issues . Besides horse likes her Galv water tank back and it was a lot of water to test .

 

[elkhunter338]

Re: 87 mercury 3.0 not going past 3000 rpm under load

I would add is your tach correct. Mine would not rev past 3,800 rpms but sounded like it was reving plenty. New tach indicated 4,600 rpms wot.
Changed my prop to get me at 4,200 rpms wot, boy I go through alot less gas cruising at 20mph now. i was running around 4k before at 20mph now down around 3.2k.