Boat not getting up on plane all of a sudden. Help!

[knapp870]

Hey everyone, I have browsed on here quite a bit over the last 2 yrs but have never posted. This year I took my boat out (21' 91 bayliner with a 4.3 Mercruiser V6) for the first time and everything was great, started, ran hard, etc. However, the second time I took it out, I can no longer to get it to come up on plane unless I am the only one in the boat.

WOT is only reaching about 2800 RPMs, when it should be at 4300+. Running in neutral it revs fine, though I know this doesn't mean much. It does not seem to be running rough and idles fine.

So far I have replaced the water separating fuel filter, checked the gas tank vent, checked the anti siphon valve for any corrosion or blockage, checked distributor cap and rotor, pulled spark arrestor off and tried running without it, attached a vacuum/pressure guage to fuel supply and tested, however so far only with muffs on, but will be taking it out to test tonight. Following these instructions (http://forums.iboats.com/showthread.php?t=283363) I received a reading of 4 almost 5 in. of Mercruy as far as resistance goes which seems a little high, but not too sure. When I pinched the line before the guage the pump was able to provide 10+ in. of Hg of vacuum.

I have never had any issues with this boat in the year and a half or so that I have owned it now. Any ideas? Next steps? I don't understand why this would suddenly start. Also, this boat is trailered and used on local lakes.

Thanks in advance for your help!!!

 

[Don S]

Re: Boat not getting up on plane all of a sudden. Help!

Hook up a remote fuel tank (6 gallon outboard tank) directly to the engines fuel filter and give it a try.
It sounds like you have a restriction in the fuel system with 4-5 inches of vacuum. Clogged screen on the pickup tube, plugged antisiphon valve, or ...........

 

[knapp870]

Re: Boat not getting up on plane all of a sudden. Help!

Hook up a remote fuel tank (6 gallon outboard tank) directly to the engines fuel filter and give it a try.
It sounds like you have a restriction in the fuel system with 4-5 inches of vacuum. Clogged screen on the pickup tube, plugged antisiphon valve, or ...........

I checked the antisiphon valve, but planned on also running on a remote tank tonight as well. I will get some concrete tests tonight on the lake under load and bring the results back tomorrow. Thanks!

 

[knapp870]

Re: Boat not getting up on plane all of a sudden. Help!

Hook up a remote fuel tank (6 gallon outboard tank) directly to the engines fuel filter and give it a try.
It sounds like you have a restriction in the fuel system with 4-5 inches of vacuum. Clogged screen on the pickup tube, plugged antisiphon valve, or ...........

so I took it out on the lake tonight. It was only showing about 1 inch of vacuum during WOT and idle.

When I clamped the hose it would not build vacuum during regular idle, but if I idled up to like 1000 rpm, then it would build 9+ in. Within 10 seconds. Is this a concern?

I also ran off of a separate fuel tank with new fuel and this had no affect either. I don't think it appears to be anything on the supply side and must be engine side.

Thoughts? What should I move to next or should I just take it to a local marine mechanic? Anything i could have done winterizing it to affect this? I changed gear lube, oil, fuel filter and filled it all up with marine "antifreeze".
Any help is greatly appreciated!!

 

[knapp870]

Re: Boat not getting up on plane all of a sudden. Help!

I'm guessing this vacuum advance line that I found only attached to the carb and not the distributor wouldn't cause this issue? Seems like most everyone agrees that boats don't need the vac advance

 

[Howard Sterndrive]

Re: Boat not getting up on plane all of a sudden. Help!

I'm guessing this vacuum advance line that I found only attached to the carb and not the distributor wouldn't cause this issue? Seems like most everyone agrees that boats don't need the vac advance

it's not a case of need
a vacuum advance on the distributor indicates the distributor is not marine.
an automotive distributor is a safety issue in a boat and a red flag that other equipment may be automotive

If you have a vaccum line running to nowhere off the carb, I suspect you have a non-marine carb.

Otherwise, I doubt it's a vacuum line - maybe a picture would help... don't suppose this line is clear/yellow?

 

[jimh1626]

Re: Boat not getting up on plane all of a sudden. Help!

If you messed with the distributor and unplugged the spark plug wires check to make sure you connected them back right. I changed my dist cap last week and went out Monday and couldn't get on plane unless everyone was up front. Boat only ran 24 mph and it is a 21' with a 5.7 and will do 45 plus. It also only hit 3200 rpm and should be 4200 - 4600. When we got to the beach I checked the plug wires and found 2 hooked up wrong. Switched them and it ran perfect. The cap has numbers for right and left hand rotation and it is easy to read the inside number on the top of the dist when it should be the outside numbers. Worth a shot I guess.

 

[knapp870]

Re: Boat not getting up on plane all of a sudden. Help!

No, I can certainly get a picture of it, but I'm pretty positive its red or maybe orange (I'm color blind). However, I believe this line was disconnected all of last year as well with no issues. There is both a vacuum port on the carb that this is connected to and a connection on the distributor that it looks like it was connected to at some time. This is the first indication I have that this is a non-marine motor, but I am finding that it has an electric fuel pump, which did not come with my year of boat(looks like mallory 9-35432).

I have not pulled off all of the plug wires or messed with the distributor other than taking the cap off to check how the rotor looked.

What should be the next step in troubleshooting? Could these symptoms indicate a bad pump? Carb needing rebuilt? But, like I said it was working correctly last year before I put it away for the winter.

 

[knapp870]

Re: Boat not getting up on plane all of a sudden. Help!

it's not a case of need
a vacuum advance on the distributor indicates the distributor is not marine.
an automotive distributor is a safety issue in a boat and a red flag that other equipment may be automotive

If you have a vaccum line running to nowhere off the carb, I suspect you have a non-marine carb.

Otherwise, I doubt it's a vacuum line - maybe a picture would help... don't suppose this line is clear/yellow?

You were right. It was not a vacuum line. It was a yellowish line off the back of the carb. The distributor cap is 100% mercury marine. However, it is an electronic fuel pump.

Next steps? Thinking maybe rebuild carb? I'd rather not though.

 

[Howard Sterndrive]

Re: Boat not getting up on plane all of a sudden. Help!

that yellow line was a safety feature of the original mechanical fuel pump. Seeing as someone replaced it with electric, they just disconnected it.

next steps.... I'd check engine compression first...and do a visual on plugs/ look for water in cylinders etc during comp test. then check that the timing is advancing properly... not sure what distributor you have, but if it has weights and springs, I'd be looking at those for rust and gunk or broken spring.

do you trailer the boat? I might weigh it. is it sitting any lower in the water than usual?
did it sit in the lake for a while between the 1st and 2nd outing where the hull could take on water?

any exhaust leaks on the motor?

I'd be looking at the electric fuel pump after that.... check supply pressure to the carb - should be around 4 to 8 psi...

could also look down the carb throat while someone else drives... see if it's lean or rich....

and backfiring under accel? - that usually says lean condition (pointing at fuel supply)

 

[knapp870]

Re: Boat not getting up on plane all of a sudden. Help!

that yellow line was a safety feature of the original mechanical fuel pump. Seeing as someone replaced it with electric, they just disconnected it.

next steps.... I'd check engine compression first...and do a visual on plugs/ look for water in cylinders etc during comp test. then check that the timing is advancing properly... not sure what distributor you have, but if it has weights and springs, I'd be looking at those for rust and gunk or broken spring.

do you trailer the boat? I might weigh it. is it sitting any lower in the water than usual?
did it sit in the lake for a while between the 1st and 2nd outing where the hull could take on water?

any exhaust leaks on the motor?

I'd be looking at the electric fuel pump after that.... check supply pressure to the carb - should be around 4 to 8 psi...

could also look down the carb throat while someone else drives... see if it's lean or rich....

and backfiring under accel? - that usually says lean condition (pointing at fuel supply)

Thanks Howard! That now makes sense as to the mystery line. I definitely plan on taking the distributor apart next and checking it over more thoroughly. Also, probably buying a new rotor and cap.

I do trailer the boat but it has not sat in the water for any length of the time as I pull it out and tow it home every outing. Also, if weight was a factor wouldn't the engine still get to the proper RPMs but just not move as fast?

There is one exhaust leak down by the Y that ticks, but that is all I have found. I have been thinking about pulling them apart and making sure that the flappers didn't break off and fall down inside. However, wouldn't you notice a sound change?

I have watched down the carb throat, as has my buddy while we accellerated. He seemed to think the streams faultered at higher RPMs, however when I watched I thought they were plenty strong, just more dispersed.

It hasn't backfired under accel or anything like that. I just simply won't get up and go. Everything idles correctly, responds to throttle, but will not get up on plane or over about 3000 RPM, when it should plane out and get up to about 4300. This is really starting to frustrate me.

As for checking pump psi, do you just make a T fitting between the pump and the steel line attached to the carb? Also, I promised pics earlier, but don't think they are now needed.

 

[Howard Sterndrive]

Re: Boat not getting up on plane all of a sudden. Help!

wouldn't the engine still get to the proper RPMs but just not move as fast?

that isn't possible... rpm = speed in a boat - there is no torque converter - it is direct drive
speed and rpm are almost linear once on plane

doesn't sound like weight is the issue though

There is one exhaust leak down by the Y that ticks, but that is all I have found. I have been thinking about pulling them apart and making sure that the flappers didn't break off and fall down inside.

that is good thinking. definite possibility

 

[knapp870]

Re: Boat not getting up on plane all of a sudden. Help!

Well, I just wanted to give everyone an update as to what fixed the boat, as I know it is frustrating for people to search these forums and not have the actual fix posted. Hopefully this can help someone in the future.

I checked the pressure from the fuel pump and it was between 7 and 9. So that ruled out that possibility. Checked the distributor/rotor and it was all fine. It did not have weights and springs, so that was not an issue and it looked ok. We then took out a few spark plugs and low and behold this is what we found....Some retarded mechanic had installed the wrong plugs and a piston and came up and broke one of them. We went and got the CORRECT spark plugs(plug on right) and it now runs better than it ever has since I owned it. This is why I like working and maintaining my own stuff.
We also took apart the exhaust and checked the flappers, which looked great. I'm guessing the ticking we thought was exhaust was actually the cylinder not firing. We brought the piston up to the top and stuck a magnet inside to get any fragments out as well. YAYYY

 

[QC]

Re: Boat not getting up on plane all of a sudden. Help!

The fragment(s) was still in there? And it/they matched up to the missing piece? Wow, you got VERY lucky! Odd only one would hit, and odd it would decide to hit after running well for a while. I'd sure like to see those pistons with a borescope, I guess just for curiosity. Sorry if I am making you nervous, just seems weird.

 

[knapp870]

Re: Boat not getting up on plane all of a sudden. Help!

The fragment(s) was still in there? And it/they matched up to the missing piece? Wow, you got VERY lucky! Odd only one would hit, and odd it would decide to hit after running well for a while. I'd sure like to see those pistons with a borescope, I guess just for curiosity. Sorry if I am making you nervous, just seems weird.

We got some crushed up pieces out. We did see that another one looked like it had hit but did not break it. I'm not sure why after a year it decided to break. They were some NGK not even a cross referenced.