not planing with 3.0 mercruiser

[benjjordan]

I have a 87 Mark Twain 17ft with a 3.0 mercruiser 130 horse and has hardly any hole shot. I had 2 normal sized (170lbs) adults in the boat and was trying to pull up my friend (210lb) on a wakeboard. When I got on it, he got up but I couldn't break a plane (speedo doesn't work, but was probably going 10-15 mph). Engine seems to be running fine, so im wondering if this has anything to do with the prop. It just had a new one put on (14 3/8 x 17). It feels like the boat is just too heavy and the engine is working too hard to get on plane. Any help would be appreciated.

 

[steelespike]

Re: not planing with 3.0 mercruiser

imo it should be able to get up fairly easy with a 17 and probably over rev with only the driver aboard as it approaches close to 40 mph.First thing I would check is that it is running on all cylinders.Second that the throttle plates in the carb are opening all the way.Is the bottom clean and smooth?Is the motor in excellent tune with good compression?Is there a possibility the foam under the floor is water logged usually from being stored for long periods with water standing in it.

 

[benjjordan]

Re: not planing with 3.0 mercruiser

well i have heard about the water logged foam.. im thinking that might be the cause because the trailer tires look underinflated but i checked the psi and it is right at 40 where it is supposed to be. How much weight could the water logged foam add? How do I tell if it is waterlogged?

 

[benjjordan]

Re: not planing with 3.0 mercruiser

sorry and also how do I check compression and if it is running on all cylinders?

 

[steelespike]

Re: not planing with 3.0 mercruiser

First be sure all wires are firmly on the plugs and in the distributor.Not rubbing on the hot manifold or against something.Look at the idling motor should be smooth if it has a weak cylinder it will have a noticeable bob a 4 cylinder is easy to notice.
Try not to be too rough on the wires twist and pull.
To check all cylinders loosen all plug wires at the destributor leave them in place so you don't lose track where they go.Start the motor and using insulated pliers pull off one wire at a time each time you should hear the spark snap and as you remove the wire the motor idle will noticably change. If one doesn't change that one is dead for some reason could be spark bad plug or the compression.You pull them at the distributor end because if the spark strays it will usually stay at the distributor instead of jumpinhg to you.OUCH!
Water probably wouldn't kill the speed that bad but would slow the hole shot.
Could add a couple of hundred lbs right near the stern where it would have the most affect.Might appear too low at the stern.
As far as compression goes buy or rent a compression tester pull the plugs,pull and carefully ground the distributor end of the coil wire.Test the compression on each cylinder through about 3 or 4 compressin strokes.You could also listen for a weak cylinder.leave in the plugs ground the coil wire.Crank the motor and listen for an uneven cranking speed.
the weak cylinder(s) starter will speed up.Of course if it has generally low conpression this won't tell you anything.If one cylinder is weak you can put a couple of squirts of oil in; if the pressure comes up you have bad rings if it remains flat you have a bad valve(s)

 

[benjjordan]

Re: not planing with 3.0 mercruiser

okay well with just me in the boat i can get on plane, but it does take a minute. Once on plane, the boat probably goes about 35 or so. Even if it is water at the stern, a couple hundred pounds (at most) shouldn't affect it that much, should it? How do i go about checking for the water logged foam? My floor feels pretty solid, but my bench seat behind the captains chairs has some rot and I am in the middle of replacing it now.

 

[steelespike]

Re: not planing with 3.0 mercruiser

To check for water you can sometimes carefully hole saw a hole near the stern in the floor surface only and examine the foam I haven't actually seen any but they say
its like a hard wet sponge. Gotta run.
Back again,I really think your problem is elsewhere.
Most likely with the motor.With a 17" pitch I think the motor would be wound pretty tight.
And with a 17 is should pop up pretty easily.Is your tach working?

 

[benjjordan]

Re: not planing with 3.0 mercruiser

okay ill try that.. thank you so much for your help

 

[JimS123]

Re: not planing with 3.0 mercruiser

A 3.0 liter with a 17" prop on a 17' boat should over-rev and jump out of the water like crazy. Even if you add 4 more people (or have a waterlogged hull)...IMHO.

Sounds like you have an engine problem. Best to have a mechanic troubleshoot it.

 

[rs1lollie]

Re: not planing with 3.0 mercruiser

I have a 1990 18' maxum with a 3.0L alpha 1 out drive I'm running with a 14x20 4 blade prop, I'm on plain with in about 5 sec top speed is 42mph @ 4800rpm's with 2 adults. sounds like you have motor problems.

 

[nitrosteve]

Re: not planing with 3.0 mercruiser

Here is a thought make sure your 2 buddy's are in the bow of the boat when you attempt any water sports. This added 400# on the bow will settle the front down and help you plain out much faster once your on plain they can move back. I am 265# and my 1986 MTB 175 would pull me up skiing with a 19p prop and 3 people in the boat.