Will not reach top speed

[WorldOfJohnboy]

OK, here's the history of what I have done with my boat (1988 Raven Cuddy Cabin 18', Mercruiser 3.0L w/ Alpha One o/d):

-2 weeks ago took the boat out on a lake and it ran beautifully at about 35mph @ 4300 RPMs. (Added new gas to boat, filled it up)

-Gear Lube must have leaked out and at least the upper gears were completely shot. Got towed back to launch and back home.

-Swapped in a used Alpha One o/d, new lube and grease, same gear ratio (1.98).

-Took boat out on lake and it started no problems and would accel. to about 18mph and 2300 RPMs then when pushed from about 1/2 throttle to WOT, it would maintain the speed and just kind of "sputter."

-Bought a new prop (same pitch: 19) as I suspected a spun prop hub and I needed a new one anyway. No change in speed or RPM performance.

-Bought four new plugs and cables/wires for the plugs as they seemed old, though generally weren't bad. Engine starts much easier and purrs at idle and low throttle, still seems to top off at 18MPH @ 2300. (Putting the throttle down any more than that just makes it sputter and no speed change.)

-My brother in law and I were looking at the plugs, etc. and basically I took the throttle and held it (throttle only, not in gear) put it at about 1/4 throttle. When he removes the 1st and 4th plug cable from the plugs, it starts to stall the engine. There is little (if any) change in the sound of the engine if he removes the two middle plug cables. We even took the boat on the lake and he did the same thing with the throttle at 100%. We noticed a slight change in the noise when one of the middle plug caps was removed, but the other one makes no difference.

All 4 plugs are firing as they are all nicely dry and my brother actually checked each one. The distributor cap is fine, the air filter on top of the carb is fine. We are puzzled as to what else this could be... is the cylander(s) starving for fuel? Any ideas on what this could be or what we could do to possibly get this going?

Please note that nothing was done to the engine since my outdrive was replaced and when it ran fine. Any help is much appreciated!

 

[searay3]

Re: Will not reach top speed

Compression test to start...

 

[Bigdave196]

Re: Will not reach top speed

I would pull the out drive back off and see if you can go thru it. if the only thing you have changed is the outdrive when thats where I would start looking.

IMHO it may be good to have someone who is familiar with them to go thru them and look for something that could be binding or causing serious friction at upper rpms.


put on a set of muffs and see if you can duplicate it out of the water with minimal resistance on the prop and motor.

 

[searay3]

Re: Will not reach top speed

The outdrive issue had to be dealt with and it sounds like you did. The reason I mention the compression test is the fact that you can pull either of the two center plug wires with little to no effect. You are basically taking 25% of the engine out of the equation when you do this. They should have just as much effect as when you pull one of the outer plug wires. I would rule out the engine in this case first. You had a look at the ujoints/gimbal etc when you pulled the drive and swapped. Not a bad idea to run it without the drive, but without a load the engine will spin up to redline on two cylinders...tells you little or nothing...

 

[WorldOfJohnboy]

Re: Will not reach top speed

OK, I can't compression test as #1 I don't know what that means and #2 I likely don't have the tools. I was hoping that I could try something simple to diagnose the situation so that when I get back home, I can just take it to the shop and say "The problem is: ________" If I can fix it myself, all the better.

I can 100% guarantee that there is nothing wrong with the outdrive. I took it off the old boat, drained it and even opened up to look at the gears, gimble, u-joints, etc. This is definately an engine issue...

 

[searay3]

Re: Will not reach top speed

The only things you can do to try a quick fix is check your fuel delivery. with little or no tools, it's gonna be tough. Replace the fuel filters, at least one in the fuel line between or at the pump, one just inside the carb where the fuel line enters and the anti siphon valve. It is where the fuel line enters the tank. Should be clean and no debris. Other than that, you will have to dig deeper into the engine and see whats up..

 

[Maclin]

Re: Will not reach top speed

That 2300 rpm "limit" is about where a points system drops off if the points are not installed correctly regarding spring tension and gap/dwell setting.

This statement of yours is interesting regarding where it fits in the chronology....:".........(Added new gas to boat, filled it up)......."

Also, triple check the plug wire order on the cap in relation to the rotation of the rotor.

 

[WorldOfJohnboy]

Re: Will not reach top speed

The only things you can do to try a quick fix is check your fuel delivery. with little or no tools, it's gonna be tough. Replace the fuel filters, at least one in the fuel line between or at the pump, one just inside the carb where the fuel line enters and the anti siphon valve. It is where the fuel line enters the tank. Should be clean and no debris. Other than that, you will have to dig deeper into the engine and see whats up..

Let me just state: I am not a mechanic by any means, but my brother-in-law is pretty good... we first thought perhaps it was water-related fuel, but there is no water filter that we can see (I believe the manual states that not all engines have this filter in place...)

I do have a full toolbox, but I don't have a lot of the mechanical type of tools with me nor at home. I hope that we can figure out how to check the other filters. I do know that we had the line off the carb and I think he checked it for debris. I will let you know what results. I guess I am just going to deal with it for now and take it someplace when I get home.

 

[Maclin]

Re: Will not reach top speed

I guess I should expound on my mention of the gas fillup....It sounds like the boat had older gas in it. You added fresh gas and ran the boat and it was all agitating and keeping mixed, maybe the long sit after the fillup caused some separation or solvent action or other type of deterioration in the old/new fuel left in the tank.

 

[utadventure]

Re: Will not reach top speed

Just a stab at it here. Change the fuel filter. It is usually inexpensive and easy to do. Old fuel may have pushed garbage into the filter that is now restricting fuel flow at higher RPMs. Also, add some Seafoam to the fuel (maybe a high dose to the remaining fuel tank and then add fuel after it fills the float bowls/fuel injectors), let it set overnight, fill the tank with good fuel and test it again.

Dave

 

[WorldOfJohnboy]

Re: Will not reach top speed

That 2300 rpm "limit" is about where a points system drops off if the points are not installed correctly regarding spring tension and gap/dwell setting.

This statement of yours is interesting regarding where it fits in the chronology....:".........(Added new gas to boat, filled it up)......."

Also, triple check the plug wire order on the cap in relation to the rotation of the rotor.

Plug wire order is fine, we checked it when I replaced all the plugs and wires on the distributor cap.

I ran the boat for 2 hours (different speeds, started and stopped it, etc.) before the outdrive gear lubes died, so I highly doubt that it is bad gas. I will have to wait until I get home to remove the fuel and start over, or just use up the gas as is...

 

[WorldOfJohnboy]

Re: Will not reach top speed

Just a stab at it here. Change the fuel filter. It is usually inexpensive and easy to do. Old fuel may have pushed garbage into the filter that is now restricting fuel flow at higher RPMs. Also, add some Seafoam to the fuel (maybe a high dose to the remaining fuel tank and then add fuel after it fills the float bowls/fuel injectors), let it set overnight, fill the tank with good fuel and test it again.

Dave

We are going to check the fuel lines/filters soon, maybe tonight or tomorrow.

 

[Howard Sterndrive]

Re: Will not reach top speed

same gear ratio (1.98).

I'd double check that.

 

[WorldOfJohnboy]

Re: Will not reach top speed

I'd double check that.

I did before I bought it. Then checked again after installing. The number on the old drive (left side sticker) says "1.98" and the 'new' drive I installed says "1.98"

If this is at all related to the outdrive, then I think Michael Bolton is the greatest singer of all time...

 

[WorldOfJohnboy]

Re: Will not reach top speed

Just a stab at it here. Change the fuel filter. It is usually inexpensive and easy to do. Old fuel may have pushed garbage into the filter that is now restricting fuel flow at higher RPMs. Also, add some Seafoam to the fuel (maybe a high dose to the remaining fuel tank and then add fuel after it fills the float bowls/fuel injectors), let it set overnight, fill the tank with good fuel and test it again.

Dave

OK, here's the latest:

-Took off fuel lines at the pump and at the carb, no issues there. Took off the fuel filter and it was full of pure gas, no foreign objects or clogs, etc. Finally, with half a tank of fresh gas, dumped a whole can of Sea Foam in the tank and drove it around more. Runs EXACTLY as it did before all this was checked. Sorry folks, but I am 99% certain that this is not a fuel issue. I also checked it today, the "cutoff" seems to be closer to 2000 RPMs as to where it cuts off. It's rather sad as my Dad's 10HP Johnson moves his 12' row boat a lot faster than my freakin boat. I am guessing that the two middle pistons aren't working. Back to the marina/mechanic I suppose!

 

[wire2]

Re: Will not reach top speed

"I am guessing that the two middle pistons aren't working"

My first thought is the head gasket has blown out between cylinder 2 and 3. A compression test is in order. You can buy a tester for under $20, remove all 4 plugs, thread the adapter into 1 cylinder at a time, spin the engine over for a few seconds with the starter. The gauge should go to ~150 psi for each cylinder. If 1 or 2 are much lower, there's a mechanical problem. If not a head gasket, possibly a cam, lifter or rocker issue.

 

[WorldOfJohnboy]

Re: Will not reach top speed

Thanks Wire and Searay (and everyone for that matter that's contributed). I Think Wire hit the nail on the head either with the head gasket or something else related...

I went to AutoZone and bought a compression tester... put the device on Plug 1, cranked 4 times and it read 135. Ran it on #2, this time it didn't even register. #3 was the same as #2. #4 was the same as #1, ~135.

So basically, there is a problem with the gasket, cam, lifter or rocker. I am going to just drop it off at the local Mercruiser repair shop/marina as my vacation is over and I can have the boat in the shop for a week+ and not lose anythink. I wanted to take the boat on vacation so I could fish and possibly go tubing with, and I got to use it to fish with. (The tubing didn't work out as my nephews left early, they would have liked going slow anyway!)

I will update the post one more time once I take the boat in and they tell me what it was and what they have to do to fix so that everyone one here can use my post as a learning experience. I have no idea why two pistons stopped working, they were running fine 2 weeks ago!

 

[poppasmurff]

Re: Will not reach top speed

Well it sounds like there was a minor issue undiscovered in your engine already the way your center cylinders "popped" when the gears tore out of your upper drive. At the very least be glad it happened where you were around others for the assistance instead of out fishing with no other boats around. Good luck and hope they can repare it all for ya.

 

[WorldOfJohnboy]

Re: Will not reach top speed

Well it sounds like there was a minor issue undiscovered in your engine already the way your center cylinders "popped" when the gears tore out of your upper drive. At the very least be glad it happened where you were around others for the assistance instead of out fishing with no other boats around. Good luck and hope they can repare it all for ya.

Just out of curiousity, I was reading the repair manual and it looks like in order to check the head gasket for problems (as was stated as a possible cause for the problem) there are only a few simple steps according to it to remove the Valve Cover: Disconnect crankcase ventilation hose at valve cover, disconnect spark plug cables at plugs, remove any other accessory unit that might interfere w/valve cover unit (may only be the gas line/sight tube?), Rmove cover attaching fasteners and load spreaders if used, then rap the valve cover with a soft-faced mallet to break the gasket seal.

I have a 1988 Mercruiser Inline 4 cyl. 3.0L engine.... is it really that easy to remove the valve cover, and if so, will that show me the issue (and what should I be looking for)?

 

[poppasmurff]

Re: Will not reach top speed

That will only remove the valve cover, the valves are a part of the head and the head is mounted to the the top of the engine block. the "head" and "block" are seperated by the head gasket, and that is where you have to get to in order to see the problem. Also, keep in mind if you are going to remove the head, you are going to need a new head gasket, they are NOT reusable.