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Old 05-08-2022, 08:45 PM   #1
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Default Engine wont go above 2200RPM

Hey Everyone..

Its been a rocky start to the boating season.. First day after winter storage, the engine wont go above 2200RPM. Its an 1996 LHX 4.3 Mercruiser.. Alpha 1 gen 2, 1.8Gear.

We were wakeboarding/kneeboarding fine today, up until I added some extra passengers towards the end of the day and discovered it was moving very slow. Now, without extra passengers it wont get on plane with 1 person in the boat. When I floor it (WOT) or try increasing gradually it will not go above 2200RPM. Things that changed recently is a new battery, filled the fuel with 60L. Did a slight shift cable adjustment to "fix the stuck in reverse issue" when returning to neutral.

When I have the throttle down about 1-2 inches down I get the expected speed.. If increasing I get a rattle from the engine (struggling) and doesnt go any faster.. RPMs remain the same.. Gauges show oil pressure ok , battery Voltage fine and temperature 175F.

Spark plugs/oil hasnt been changed in 2 years .. I say I did under 50 hours in the last 2 years.

Any help or advice would be very much appreciated.. Thanks :-)
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Old 05-08-2022, 11:06 PM   #2
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Is the boats speed also not increasing? If yes I would suspect either the carburetor is not fully opening, choke is stuck partially closed or blockage in the exhaust.
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Old 05-08-2022, 11:50 PM   #3
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Thanks mmwjr,

Correct the boats speed does not increase.

I do remember putting in a good bit of starbrite fog when I winterised it.. Perhaps its messing with the choke? However was fine for 2 hours before it started giving issues, I would have expected the choke to cause issues from the get go?

What do you recommend I try? The boat is on trailer at the moment, is there anything I can do to try fix it in my yard?

Thanks again!
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Old 05-09-2022, 12:35 AM   #4
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Pull the spark plugs to see if they fouled out from all that fogging oil.
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Old 05-14-2022, 03:00 PM   #5
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Thanks mmwjr

Set out on the adventure today..

Pulled the spark plugs.. Pic attached.. They didnt look damaged at all, just a little black perhaps from carbon?

Took the flame arrester off to make sure the choke valve was moveable and I could see it was black all around the outside.. Pic attached with my finger marks in silver. Cleaned it up however think i might try to blast it with hot water to thoroughly clean it.. Any tips here?

I picked up new plugs, oil and oil filter.. I put the old plugs back in to get the engine up to temperature to change the oil. I noticed at operating temp (170F) the starboard manifold was hot to touch and the port side STONE COLD. Could this be a thermostat issue?

I can also see at the back of the alpha outdrive, spurts of water are coming out the middle which I think I have never seen before.. I also hear the putput sounds of the engine which I didnt hear previously. Video Here (Watch your ears if you have speakers/headphones on loud)

I did some research online and indications point to the flaps in the Y Joint exhaust ?
I dont want to sway your thought process or the converstation in any way, just curious to learn myself and would love your advice.

Many thanks again!
Attached Thumbnails
FlameArrestor.jpg   20220514_105153-forum.jpg  
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Old 05-14-2022, 04:45 PM   #6
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Yes clean the flame arrestor in some soapy water and let dry. How did you measure the temp on the starboard exhaust; IR sensor? I have been suspecting you may have a flapper broken off blocking the exhaust at the bottom of the y-pipe. Regarding the choke verify it’s closed with the engine off and cold then start the engine to verify it fully open in a few minutes.

I could not get the video to play for me.
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Old 05-14-2022, 04:50 PM   #7
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Thanks again mmwjr.. I'll clean the arrestor shortly.

I measured the engine temperature using the gauge on the dash..
I was touching the manifolds when looking around and discovered the port side was stone cold with my hand on top of it.. Touching the starboard side was the usual hot I would expect.

I think my choke flap is open wide all the time but will check it shortly..

I guess Ill have to take off the rubber hose connecting to the Y joints and probably take off the outdrive too to discover the flaps?.. Wish me luck :-)

Will report back my findings..

Thanks again for all your help on this!
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Old 05-14-2022, 05:38 PM   #8
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Quote:
I noticed at operating temp (170F) the starboard manifold was hot to touch and the port side STONE COLD. Could this be a thermostat issue?
Ever had an impeller fail? Could be chunks of rubber plugging up the ports in the thermostat housing.
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Old 05-14-2022, 06:34 PM   #9
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Itís not uncommon to have one side of the exhaust hotter than the other. I prefer readings with an IR sensor when checking exhaust component temperatures. Typically when impeller vanes break off they get stuck in the power steering cooler which is before the water getting to the thermostat housing.

You can call me Mike and keep the beer cold for me.
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Old 05-14-2022, 07:43 PM   #10
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I had a Volvo Penta carbureted 4.3 that wouldnít get up to temp (different problem I know) that had a bunch of impeller bits stuck in the thermostat housing ports, some of them were really stuffed into some really tiny holes, which was why I suggested it.
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Old 05-15-2022, 12:03 AM   #11
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Quote:
Originally Posted by wiigelec View Post
Ever had an impeller fail? Could be chunks of rubber plugging up the ports in the thermostat housing.
Never had an impeller fail on me.. but I think Ill have to pull the outdrive out to inspect the exhaust and will report my findings..

Thanks for the suggestion :-)
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Old 05-19-2022, 08:48 PM   #12
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Is it possible to take off the manifold boots without removing the top riser part of the manifold? I have all the ring clasps either extremely loose or off and its impossible to move.. The rubber is SOLID.. Is there some mechanic touch or sacrifice I need to make in order to get it off cleanly. Their isnít much room around the engine and behind the boot to manoeuvre.

I love a challenge however Iím beginning to think it would be easier to take off the outdrive and shove a snake camera up the Y joint from the gimbal housing.. ?

Thanks :-)
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20220519_205834.jpg  
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Outdrive: Alpha1 Gen2 with 1.8gear
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Old 05-20-2022, 01:39 AM   #13
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I typically unbolt the rise so I can rotate it to break it free from the rubber hose. Be sure to first drain the exhaust manifold to prevent water from getting into the exhaust passage. You can pull the drive but might not be able to remove any broken flapper and if the flapper has broken off you’ll still need to pull the exhaust hose.
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Old 05-20-2022, 09:18 AM   #14
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Thanks Mike..

Do I need new gaskets for the rise when putting it back or can I get away with re-using the old ones?
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Old 05-20-2022, 12:11 PM   #15
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Quote:
Originally Posted by fester View Post
Thanks Mike..

Do I need new gaskets for the rise when putting it back or can I get away with re-using the old ones?
I would get new ones instead of risking a water to exhaust leak that could damage the engine.
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Old 05-22-2022, 10:44 AM   #16
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Thanks Mike,

I pulled both risers and boots.. The flaps are intact and in very good condition.. Like new.. Both fold without any issues or obstructions.. Put it back with new gaskets like you suggested.

When firing the engine back up with the muffs, looking at the back of the boat, water eventually comes on the port side from the transome however its just smoke/exhaust and no water at all coming from the starboard side. No water coming out the prop either.

I took the thermostat housing off as I was curious how it worked and replaced the thermostat with a new one while I was there.. Everything looked clear with no obstruction. Stuck the old thermostat in boiling water and opened just fine. Also checked the pipes from the thermostat to the bottom of the manifolds.. All clear there too with no gunk. I did a quick drain using the drain plugs at the bottom of the manifolds, water did come out both sides. Very hot from the starboard side and cold/lukewarm from the port.

I did some IR thermal readings when the engine got up to temperature @ 80c:
Port side top of rise 25c
Port side top of manifold 27c
Port side side of manifold 26c
Port side side of rise 26c
Port side top of engine beside rise 20c

Starboard side top of rise 84c
Starboard side top of manifold 90c
Starboard side side of manifold 91c
Starboard side side of rise 91c
Starboard side top of engine beside rise 36c

Thermostat housing 48c at joint on engine, 59c at bowside. Bottom of engine at block 59c/64c.

My Dr Watson gut feeling: I wonder if its the impeller thats gone? perhaps its not getting enough flow to push to the other side of the engine / manifolds? The muffs are ok and pressure is good from the tap. Trying to find a bucket big enough to fit the outdrive is difficult.

Next steps? Pull the outdrive and replace the impeller? or anything else I can do before trying that?

Haven't done an oil change or spark plugs yet.. Will get round to that after cooling is sorted :-)

Thanks again
Attached Thumbnails
2022-05-22 11_41_12-20220521_205934.jpg ‎- Photos.jpg   2022-05-22 11_41_45-2022-05-22 11_35_47-20220521_205924.jpg ‎- Photos.png ‎- Photos.jpg   20220521_112611.jpg   20220521_113955.jpg   20220521_173753.jpg  

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Old 05-22-2022, 11:41 AM   #17
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The Starboard temperatures are not normal and too high. Looking at the picture of the side of the thermostat housing it appears you have the design with popit valves and I bet itís not working properly. If the impeller was bad the engine and port exhaust would be high as well. Try removing the hoses that go to the port and starboard exhaust and compare the water flow. Also is the boat sitting level?
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Old 05-22-2022, 01:08 PM   #18
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Quote:
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Also is the boat sitting level?
I think you may have a point here.. It is on a slight incline however dropped the jockeywheel to compensate.. I'll move the boat later today on more level ground and retry..
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Old 05-22-2022, 01:13 PM   #19
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I dont think it has popit valves? Cooling system drawing attached but no mention in the inventory listing.
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Old 05-22-2022, 01:34 PM   #20
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Quote:
Originally Posted by fester View Post
I dont think it has popit valves? Cooling system drawing attached but no mention in the inventory listing.
In post #16 first picture, what is the the exhaust hoses port? Iím seeing what looks like a round pice of metal. Not see this before.
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