2008 Mercruiser 4.3L Alpha One Performance Issues

[kwortman]

I have been experiencing some off an on issues the last couple of years with my boat. This spring I replaced the spark plugs, wires, distributor cap and rotor. Boat was giving me fits so one day I decided to check all my spark plug wires to make sure a good fit etc etc and as I did I found that the throttle cable was extremely loose so I tightened it up and goodness I could barely move the throttle it was so tight. Came back, looked in SELOC manual for the throttle cable and saw in the manual that after you tighten it you need to loosen a bit (in my case a half turn) so great I did and since then the issue is this.

a. Fire up the boat for first time of the day no issue starting, warm it up by going through a large no wake area and then get to open the throttle. Boat sputters and spurts then goes. This is the only time this behavior happens, just the first time I give it a nice throttle up each day. After that I can start and stop all day long with no sputters. I do experience at times (may 3-5 times this year out of 25 outings) that when I cut the engine off the engine sputters and spurts and then when it does shutoff a puff of air/smoke comes out the flame arrestor that smells like oil.

b. Boat seems sluggish. I am not getting much past 3500RPMs or 34MPH at full throttle. Previous owner (father-in-law) says should be able to get to 5200RPMs.

c. I've noticed that the trim at all the way down goes even slower RPMs and MPH wise. The readings I gave in b are with the trim at 3/4

Not sure if this is all one issue or several so appreciate any feedback. Having to be my own mechanic right now as all the mechanics with 100 miles are backed up so bad they don't call or email back. I am a novice mechanic at best having worked on cars with my dad growing up so spark plugs and things like that I can do. Rebuild of carb seems overwhelming to me as has been suggested. Not sure if those who answered previously think this is still the case or not.

 

[alldodge]

cut the engine off the engine sputters and spurts and then when it does shutoff a puff of air/smoke comes out the flame arrestor that smells like oil.

This is called dieseling, and when it does this the motor runs backwards briefly and can suck water into the motor. Dieseling is caused by incorrect timing, incorrect idle rpm, to rich a fuel mix and carbon build up inside combustion chamber from oil and/or to rich a fuel mix.

Having the issue with throttle up one time a day would tell me the choke needs to maybe checked, but over all the symptoms lean me to do a good cleaning of the carb and rebuild

b. Boat seems sluggish. I am not getting much past 3500RPMs or 34MPH at full throttle. Previous owner (father-in-law) says should be able to get to 5200RPMs.

Your motor max rpm would be 4800
To find out if the motor is healthy enough to run well, need to do a compression and leak down test. Make sure timing, distributor, wires and plugs are all good. Also when checking rpm, many boat tachs are not accurate thru the full range, may check with a hand held

c. I've noticed that the trim at all the way down goes even slower RPMs and MPH wise. The readings I gave in b are with the trim at 3/4

Trim is used to help take off (hole shot) and also to increase planning angle and reduce drag

Trim should be all the way down to take off. Once boat is coming up on plane (coming out of the water) trim is increased to lift the bow higher which reduces resistance and increases speed. Trim is ever so slightly increased until the speed starts reducing (for a given rpm) then back down just a touch.

The more/less rpm is used the more or less trim angle is needed. After doing it for a while it becomes second nature.

When the boat goes into a hard turn more throttle will be needed to keep same speed and then reduced when turn is done. Same can happen with trim, just pay attention to what the boat is doing

 

[kwortman]

Also when checking rpm, many boat tachs are not accurate thru the full range, may check with a hand held

So I saw something about this earlier can you recommend a digital tach. I was on amazon and there are a ton and the original one I looked at had a piece of tape or something that you had to put on something that goes around in the video. If this is the recommended one would i put the "tape" on the drive belt? Someone mentioned something about putting it on the #1 spark plug wire but the digital tachs were all a little overwhelming on amazon.

Thanks for any advise/recommendations. I did play a bit with the idle screw so it's completely possible I caused the dieseling effect on my own since I used the tach on the instrument panel.

 

[alldodge]

The photo tachs are very accurate but the tape or spot would be on the crankshaft pulley or vibration damper

I have an inductive tach so it clamps on a spark plug wire like this one
https://www.amazon.com/Electronic-S...er+tool&qid=1595276951&sr=8-6&tag=googhydr-20

This would be another
https://www.jbtools.com/electronic-...GZrMaTwXXa4XBUuU3tUB60g9MbihCofhoCs6AQAvD_BwE

 

[kwortman]

Awesome thanks so much. I'll see if this solves the dieseling problem. You aren't the first to mention the carb so I am guessing I will need a carb rebuild which means I will have to wait for a mechanic to call me back or wait till after the season. I watched a video on rebuilding a carb yesterday and it looks a little above my skill level

 

[alldodge]

Carb rebuild is not that hard if your mechanically inclined
Just follow the instructions and it should work out, and if you get into a hard spot ask here

 

[kwortman]

This would be another
https://www.jbtools.com/electronic-...GZrMaTwXXa4XBUuU3tUB60g9MbihCofhoCs6AQAvD_BwE

I set this to 4:6 correct?

 

[alldodge]

I set this to 4:6 correct?

I haven't seen the instruction manual on this one so don't know what your asking

 

[kwortman]

4 represents the stroke and 6 represents the cylinders for a RPM via Ignition Coil wire. There is also a description for four stroke engines using 4:1 for conventional auto engines, 2:1 for engines with DIS ignition. The description for just 4 stroke says for measuring RPM on engines with spark plug wires. I am assuming I could do either 4:1 and use SP wire or 4:6 using the ignition coil since I have a distributor.

 

[alldodge]

Agree, figuring your using the coil wire, otherwise if just one plug wire of a 6 cylinder it would be 4:1

 

[kwortman]

Agree, figuring your using the coil wire, otherwise if just one plug wire of a 6 cylinder it would be 4:1

Thank you you have been very helpful and I really appreciate it. Tackling the carb rebuilld this weekend then will use this tool once its back on, unless I try it out before I take the carb off just to see how off the RPM gauge on the boat is

 

[kwortman]

Okay carbs been rebuilt and put back on. Boat fired up fine, Idle'd fine, forward gear at idle fine. Try to accelerate and boat dies. Thoughts?

 

[Rick Stephens]

Okay carbs been rebuilt and put back on. Boat fired up fine, Idle'd fine, forward gear at idle fine. Try to accelerate and boat dies. Thoughts?

Power valve or needles still blocked. Running out of fuel when the carb plates are open.

 

[kwortman]

Power valve or needles still blocked. Running out of fuel when the carb plates are open.

i don’t get it, I dipped everything I could rinsed sprayed with simple green rinsed again and dried over night. Used compressed air on everything I could that had some sort of tiny hole in it (jets, Venturi, etc) Everything is new except jets (I have three due it being a tks engine) and even those I blew out and put against a white background to make sure I could see through them. I guess I’ll take it back off and start over again and double check everything. This is really frustrating because the carb looked nice and clean I didn’t even really need to dip it but I did anyways

 

[alldodge]

When the throttle goes forward, is there a squirt of gas going down the carb?

 

[kwortman]

When the throttle goes forward, is there a squirt of gas going down the carb?

not sure was in the boat by myself when the adjustments were made and I tried it. Will have to wait until I have someone with me to be able to stay back in the engine compartment and not have to drive the boat too. No one was put this morning early
so wasn’t too worried about being alone but wasn’t comfortable doing it so will wait until I have help hopefully next weekend

 

[alldodge]

Disconnect the throttle linkage at the carb. Start the motor and let idle a minute. Turn OFF the motor and go and open the carb throttle plate and see if it starts to squirt fuel down the carb and does it from start to at least 3/4 open. Your looking for a steady stream

 

[nola mike]

alldodge , how about a malfunctioning TKS module? I don't know enough about these to troubleshoot...
Also op, did you adjust the idle mixture after the carb rebuild?

 

[kwortman]

When the throttle goes forward, is there a squirt of gas going down the carb?

Sorry I am somewhat repeating what I said last night, I didnt see that there was a page 2 to this thread and thought maybe I didnt post last night. I am not sure about the gas squirt, I will check this weekend when I have help. When I made my adjustments yesterday to the idle speed and idle mixture I was alone, so I was adjusting and driving the boat. It was early in the morning so I wasn't worried about other boat traffic. It seems to me I've gone from a rich (spark plugs are coated in black and just changed in may) to lean. I've ordered new spark plugs, but given that the boat fired up, idled and runs at forward at idle, I dont think this is going to help anything but perhaps I am wrong. Somebody told me to check the anti syphon valve but I am not sure I have one. I dont remember seeing one. Any chance I didn't get the idle mixture adjusted right? I will have help this weekend and bought a tool that will allow me to adjust it easier as it is at an angle right now to adjust and not confident I did it right with everything I was trying to do alone.

 

[Furbird]

Watched a youtube video and maybe the pump rod is in the wrong spot? It should have three holes and supposedly you're supposed to start in the hole closest to the carb. Mine hesitates some on my brand new carb and it was shipped in the middle position. Was actually going to post this anyway to verify this information but if both of us have a similar issue, kill two birds with one... thread?

https://youtu.be/6tLeTT4rNSI?t=213