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Mercruiser 4.3 maxes at at 2200RPMs at WOT - Help please.

R

Rafael Anthony Acevedo

New member
Hey guys - took the boat out for the first time this season today and as the title says, she was not very responsive and I couldn't get past 2200 RPMs at WOT. To put it in perspective, at the end of last season, I had her up to near 50 hauling butt and she ran like a top. Took it out of winterization in May and changed oil/filter, fuel filter, drive lube, and replaced the trim pump. Just got around to taking her out today for the first time this season.

Took it out, water was calm, and when I got past the no-wake zone and tried to open her up, she wouldn't go past about 2200 RPMs and about 10 knots. Even though the throttle seems to go through the full range of motion, from about 3/4 to WOT, there is not change in engine whine, RPM, or speed. While at the max throttle of 2200 RPMs, all gauges seemed to read normal. Temp was about 175-180, oil pressure was 55-60, and volts were 13v. Again - just couldn't get it to open up and run like I know she can.

The boat is a 2008 Bayliner F-18 Flight with 4.3l carburated Mercruiser . When I got it back home today and put it on muffs, it idled fine, but when I put it up to about 1200 rpms, it seemed to surge every now and again to 14-1500 and then back down to 1200. Only I can think of is that the throttle cable is bad/misadjusted. In hindsight, now that I think of it, - even last season, though it did seem to go to full throttle at 4k plus RPMs, there did seem to be a little slop in the throttle lever - meaning I would have to move it a little to get it to change. I assumed that was normal, but now maybe not. Ay thoughts as to whether this could be a cable, etc? Thanks!
 
One thing to check when an issue such as this occurs is,

when on the water and this happens, you need to try to determine if it is fuel related or ignition related.

I doubt very much it has anything to do with the cable.


To determine if it is a fuel issue you can move the throttle/shift control back and forth very quickly (like pumping a gas peddle in a car).

When you have reached your max rpms/speed pump the throttle several times very quickly, this forces the accelerator circuit to force more gas through the carb. (assuming you are not running out of fuel). If the motor picks up speed/rpms then it is a fuel issue.

If not then it may be a ignition issue.

One thing that is common when a motor does not go above 2200 rpms +/- is the timing advance is not working whether it is mechanical or electronic.

The motor will only go so far under load and then the timing needs to be advanced to achieve max performance.

If it is not a fuel issue (lack of or possible water in the fuel) then you will need a timing light to see if the timing is advancing past the initial setting. Typically the initial setting is approximately 4-6 degrees before top dead center (BTDC)
Total advance would be around 28 to 30 degrees BTDC including initial so that would be 4 + 24 - 26 degrees = 28 - 30 degrees total.

The exact total is not important here as much as determining if it is advancing at all. If the timing is advancing past initial UNDER LOAD, then you have another issue. If it does not then your timing control module/ignition amplifier is bad.
 
Thanks Jack - I'll check the timing. I have a light. I have hear one thing to check is also the fuel syphon valve. Is there a way to test WOT while on the muffs? I ask because I have heard that you should not go above 12-1400 RPMs on the muffs. I know it will need to be in gear and not in neutral, but is it safe to attempt to test to WOT on the muffs? I would assume that is how the shop would have to do it if I took it in - correct?
 
You can run a motor until it blows up on the muffs..............that said you can rev the motor up to red line if need be but only momentarily!!!! not for any prolong period of time!!!! It is only to not over rev the motor.. Running at 1200 or so only is a MYTH (bullsh!t)...............I rev the sh!t out of motors but never exceed red line (5000 rpms is my preferred red line)

And NO you can not check WOT on the muffs..........No load on the prop it will rev to the moon.

You can see if the timing does advance. Start the motor, at idle see what you can see..........the timing may be moving around due to ignition control module. Once you can see the timing slowly increase rpms and watch the timing mark, it should continue to move counter clockwise about 2 inches from where it started. if you don't have a degreed timing light or any other way to see exactly how much the ~ 2 inches or so is good enough to see if it is advancing. Maybe youtube "checking timing advance"

If it does not move at least that far then I would suggest the timing control module is bad.

There is a specific procedure to establish base timing........(you either connect two wires that are hanging there or connect one wire that is hanging there to ground) Depends on your set up but I believe you should have one wire hanging there.....I forget if you need to establish the jumper to ground before or after the motor is started. This puts the ignition control module in base timing mode and this is how to set base timing per spec. (typically 4-6 BTDC. Check the motor decal for specifics.;
 
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kghost said:
You can run a motor until it blows up on the muffs..............that said you can rev the motor up to red line if need be but only momentarily!!!! not for any prolong period of time!!!! It is only to not over rev the motor.. Running at 1200 or so only is a MYTH (bullsh!t)...............I rev the sh!t out of motors but never exceed red line (5000 rpms is my preferred red line)

And NO you can not check WOT on the muffs..........No load on the prop it will rev to the moon.

You can see if the timing does advance. Start the motor, at idle see what you can see..........the timing may be moving around due to ignition control module. Once you can see the timing slowly increase rpms and watch the timing mark, it should continue to move counter clockwise about 2 inches from where it started. if you don't have a degreed timing light or any other way to see exactly how much the ~ 2 inches or so is good enough to see if it is advancing. Maybe youtube "checking timing advance"

If it does not move at least that far then I would suggest the timing control module is bad.

There is a specific procedure to establish base timing........(you either connect two wires that are hanging there or connect one wire that is hanging there to ground) Depends on your set up but I believe you should have one wire hanging there.....I forget if you need to establish the jumper to ground before or after the motor is started. This puts the ignition control module in base timing mode and this is how to set base timing per spec. (typically 4-6 BTDC. Check the motor decal for specifics.;
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Thanks! It looks like I might have found the problem. I pulled the top part of the exhaust and found the flappers were toast. Problem now is that I am missing one of the flaps. I looked down the y pipe with my inspection camera and found one of the pieces but the other is still missing. I have no idea where it went. If I pull the outdrive will I be able to see where the exhaust collector exits (ypipe)? Is it also possible that piece made it down to the leg? The problem is that I am new to boat repair so don't know the exhaust flow and I really need to know where this piece went. I don't want to take he chance of ruining the motor. Thanks!
 
The exhaust flappers do often break off, and yes if you pull the outdrive you can retrieve the pieces.

No you have not found your problem..............The exhaust flappers have no affect on performance they only keep most of the back flush water from reaching the exhaust manifolds........If you think they may be clogging the exhaust from exiting the boat I am not sure they would do that. Not enough to cause no more than 2200 rpms. Maybe a few hundred rpms near the top end......
 
kghost said:
The exhaust flappers do often break off, and yes if you pull the outdrive you can retrieve the pieces.

No you have not found your problem..............The exhaust flappers have no affect on performance they only keep most of the back flush water from reaching the exhaust manifolds........If you think they may be clogging the exhaust from exiting the boat I am not sure they would do that. Not enough to cause no more than 2200 rpms. Maybe a few hundred rpms near the top end......
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Thanks Ghost. Been a busy couple of days. Pulled the stern drive and found this :
image.jpg

The he exhaust was extremely blocked. Yesterday I did the following:
- Pulled stern drive and conducted inspection. All boots are good, gimbal bearing is good.
- Re-greased gimbal bearing
- Replaced exhaust shutters and re-installed exhaust elbows
- Replaced anti-siphon valve
- Replaced fuel-filter/separator. Fuel that came out of old one was perfectly clean.
- Conducted compression test - all cylinders at 180psi
- Re-installed plugs and wires
- Replaced impeller.

Today im going to re-install the stern drive and run her on muffs to see how she does and then I'll take her out tomorrow for optest. At this point, I'm not sure what else to check. Everything checked out fine with the exception of the exhaust shutter stuck in the drive.
 
Still not fixed. "@&&! Actually out on her as we speak. Throttled down and she got to 2200 quickly and then crawled to 3k. As soon as I throttled down, she will now only go to 2200. Frustrated does not seem to cover it! Any thoughts?
 
Occasionally on the first run on the lake after winter, the secondary intakes on my 4BBL carb will be gummed shut from hardened winterizing spray. This causes poor performance but not sure if it caused the boat to bog at less than 2500 rpm. Also it tends to self correct as soon as the engine warms up a bit.
 
Rafael Anthony Acevedo said:
Still not fixed. "@&&! Actually out on her as we speak. Throttled down and she got to 2200 quickly and then crawled to 3k. As soon as I throttled down, she will now only go to 2200. Frustrated does not seem to cover it! Any thoughts?
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Ayuh,.... My guess is, the carb is fulla crap,....

Pull it, clean 'it, 'n rebuild it,....

The hi-speed jets are plugged,....
 
I got to tell ya, my 2008 4.3 carbed VP was doing this same BS to me this year. Ran fine end of last year and winterized it. First time out this year was an embarrassing joke. Same as the OP.

6 new spark plugs, removed and cleaned the cap, rotor, and plug wires with ignition wire dryer. Checked resistance on the wires and they were just fine. Slapped it back together and it runs like new.
 
Hah! My boat does the same thing to me every freakin' year! Put her away in the Fall in perfect shape, but all hell breaks loose each Spring. That's why I sold the SOB.

Jeff
 
fastjeff said:
Hah! My boat does the same thing to me every freakin' year! Put her away in the Fall in perfect shape, but all hell breaks loose each Spring. That's why I sold the SOB.

Jeff
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I have had my 1987 boat since 1995.

Every year I put it away and every year I get it ready for use each summer.

I have never had an issue....................NEVER........in 20 years........

Guess you did not do something correct either before, during or after..............
 
Wanna work on mine for me?

Jeff

PS: Just came from it. Brand new port engine battery--that only runs that engine, has a maintainer charger on it, and had its Perko switch OFf--was dead flat. Dammed if I know why. Was fine 2 weeks ago. See what I mean?
 
Remove the battery + from battery..........connect a AMP meter in line from cable to battery...(fully charged battery)

The amp meter reading should be NO MORE THEN .07 amps.................

If the reading is any higher start disconnecting stuff until you find out what is drawing the current.....

You may be surprised what you find..........

I had a radio that was drawing .2 amps when OFF...........killed a battery in less than 24 hrs when not in use...........

Also found a alternator once drawing over .2 amps as the root cause..........
 
..."I had a radio that was drawing .2 amps when OFF...........killed a battery in less than 24 hrs when not in use..........."

Yeah! Mine does that as well. And with a charger on it (which MUST be no good).

Thanks!

Jeff
 
I suspect there is an internal transistor in the radio that when you power it off it is supposed to kill all power to the radio........well it does not........and keeps the radio powered on when it appears to be off. A inline ON/OFF switch can fix the issue if you so choose but all memory will be lost.

Best answer is to replace the head unit!
 
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