Losing Power - After two hours

[Kconleyk]

Everyone,

This is from another thread because I thought it was a prop issue, but below is my experience on my latest trip out. New boat owner, 1999 Bayliner Trophy, 21' cuddy cabin. Bought it to take my 9 year old daughter out.

First two trips boat ran great, but were short trips. Last trip, boat ran great for two hours but on the way back started losing power and over revving then jumping back to right rpms. Wrote it off to I spun the prop, bought a new prop and took it out yesterday.

So update, bought and replaced the prop, launched today and ultra high tide after storms to make sure i didn't spin a prop from shallow water. First time launching just me and my daughter (9) and she did great helping tie the boat up and hold it while I ran to get truck.

So first two hours boat ran perfect, got on plane quicker than ever, hit higher speeds than previous normally at 28.2 at max was up at 30.9. Crushing speed at 4,200 Rpms at 28.4 mph.

We rode out did some site seeing and rove for about 2 hours. Turned around to hide back, never had the boat turned off, we floated on neautrel for about five minutes while she grabbed us drinks and a snack.

Heading back, same thing as last weekend (last weekend we thought it was a spun prop, but worked perfect for two hours then did this as well), started in got up on plane and the boat kept losing power, then reviving real high then going back to correct Rpms and mph, then drop down and up again. Kept losing Rpms then over revving then holding tight for a few then the same over and over again.

I'm lost, it ran so good with the new prop I thought I had fixed it.

Took us a long time to get back to the ramp.

Fresh gas, new prop, under 2,000 Rpms it seems to run fine, only when you add throttle and only after about two hours of running perfectly.

All gauges show oil temp, battery, etc as good.

Any ideas?

 

[dubs283]

need more info, what engine/drive package? serial numbers can help, have you done any troubleshooting aside from changing prop?

 

[Kconleyk]

need more info, what engine/drive package? serial numbers can help, have you done any troubleshooting aside from changing prop?

See attached, as far as trouble shooting I haven't done much else it was just me and my daughter out there yesterday so couldn't do much, and as the boat lost power she was getting nervous so I just headed back in.

 

[dubs283]

4.3 carb, guessing alpha drive

when over revved what is rpm? is this in gear or neutral?

loosing power usually indicates a fuel supply issue, can't say for the over rev other than possibly fuel pump/system "catching up" and engine responding to it

 

[Kconleyk]

4.3 carb, guessing alpha drive

when over revved what is rpm? is this in gear or neutral?

loosing power usually indicates a fuel supply issue, can't say for the over rev other than possibly fuel pump/system "catching up" and engine responding to it

Yes Alpha One drive sorry

It's weird we will be on plane cruising along, and it will lose power and drop to like 1,200 rpms then catch power again, and rev way up to 5,000 then settle back at where it started around 4,000.

Or it loses power completely, and goes to zero, and then the gauge needle actually goes the wrong way, and goes backward from 6,000 rpm side but then settles back at 4,200 or 4,000

 

[dubs283]

strange issue for sure, at this point it sounds like either fuel or ignition, tachometers can be wonky if they are getting an intermittent signal.

at this point i'd recommend a full tune up, including fuel filter(s). check to make sure the ignition sensor in the distributor is the latest style, oem fully potted (no exposed circuitry)

it'd be good to see what the fuel pressure is when the issue arises as well

 

[Kconleyk]

strange issue for sure, at this point it sounds like either fuel or ignition, tachometers can be wonky if they are getting an intermittent signal.

at this point i'd recommend a full tune up, including fuel filter(s). check to make sure the ignition sensor in the distributor is the latest style, oem fully potted (no exposed circuitry)

it'd be good to see what the fuel pressure is when the issue arises as well

Is there anything to change for fuel filters beside by the Fuel water seperator filter?

How would I tell the fuel pressure?

 

[Stinnett21]

Yes Alpha One drive sorry

It's weird we will be on plane cruising along, and it will lose power and drop to like 1,200 rpms then catch power again, and rev way up to 5,000 then settle back at where it started around 4,000.

Or it loses power completely, and goes to zero, and then the gauge needle actually goes the wrong way, and goes backward from 6,000 rpm side but then settles back at 4,200 or 4,000

You mean it revs to 5000 without advancing the throttle to WOT? When this occurs does the speed advance along with it or is it just revving? A video would certainly help.

 

[poconojoe]

At first I was going to ask if you changed the hub also when you changed the prop. But the low Rpm's, I think ruled that out...I think....
It's not a bad idea to check it though. Mark the hub and see if it moves after a good run.

If not, fuel or spark, maybe...

As stated, do a full tune-up. You can't go wrong with that. It's probably due anyway.

 

[Kconleyk]

At first I was going to ask if you changed the hub also when you changed the prop. But the low Rpm's, I think ruled that out...I think....
It's not a bad idea to check it though. Mark the hub and see if it moves after a good run.

If not, fuel or spark, maybe...

As stated, do a full tune-up. You can't go wrong with that. It's probably due anyway.

I (my neighbor who is a retired fireman and now a boat captain) changed the hub when we changed the prop. I would think a Spun Prop would do that all the time, not working perfectly for two hours and then stop.

I called some places to get time frames and quotes on a tune up waiting to hear now.

 

[Kconleyk]

You mean it revs to 5000 without advancing the throttle to WOT? When this occurs does the speed advance along with it or is it just revving? A video would certainly help.

Yes I will be crusing at whateve speed, say 28 mphs, it will lose complete power and drop to 1,200 rpms or so, then rev real high, all with out power then randomly kick back in and start accelerating again. All with out moving the throttle.

 

[Kconleyk]

You mean it revs to 5000 without advancing the throttle to WOT? When this occurs does the speed advance along with it or is it just revving? A video would certainly help.

Since it was just me and my daughter yesterday and a little choppy, I was more worried about getting back in, didn't think to take a video. I will try and get out this weekend if it doesn't go in for a tune up and get a video.

 

[Stinnett21]

To those who know more than I could this be a bad coupler? I was thinking the drop wouldn't indicate coupler but what if it was triggering an overheat when it revved?

 

[nola mike]

Or it loses power completely, and goes to zero, and then the gauge needle actually goes the wrong way, and goes backward from 6,000 rpm side but then settles back at 4,200 or 4,000

I mean, this is an electrical problem. I'm not sure if how you're explaining it is actually what's occurring--unless you have 2 separate issues. Just to be perfectly clear: the boat is in gear, under power. Then the rpms increase without speed increasing, but you're still in gear. You aren't touching the throttle when all of this is occurring. Also, when the rpms increase on the tach, can you actually hear the engine speed increasing?

 

[Kconleyk]

I mean, this is an electrical problem. I'm not sure if how you're explaining it is actually what's occurring--unless you have 2 separate issues. Just to be perfectly clear: the boat is in gear, under power. Then the rpms increase without speed increasing, but you're still in gear. You aren't touching the throttle when all of this is occurring. Also, when the rpms increase on the tach, can you actually hear the engine speed increasing?

I am in gear on plane just cruising along, not touching the throttle, the boat loses power and we slow way down quickly, the boat with me not touching the throttle revs back up, passed the crushing Rpms I was at, I can hear the boat rev, then it goes back to 4200 Rpms but doesn't seem to have the same power. So I put the boat in neutral and give it a second then put it back in gear and it starts going again, sometimes for five minutes before this happens, sometimes 30 seconds.

Again only after about two hours of driving, always runs perfectly when I first drop it in the water.

 

[Kconleyk]

Anyone else have any other thoughts, struggling to find a mechanic available my area any time soon to look at it

 

[nola mike]

You need to determine whether it's an engine problem or a drivetrain problem. When you say "didn't have the same power" at 4200 rpm what does that mean? Is your speed actually decreased? As someone mentioned above, a video would probably be helpful

 

[Kconleyk]

You need to determine whether it's an engine problem or a drivetrain problem. When you say "didn't have the same power" at 4200 rpm what does that mean? Is your speed actually decreased? As someone mentioned above, a video would probably be helpful

I replied with the below, only posting again to make sure you saw it, when I say didn't have the same power, the boat loses power, slows down completely from on plane to a stop, it then gains a little power but nothing compared to what it had and starts moving forward again, maybe 1/4 power at best. At that point I touch the throttle and put it back in neutrel and let it sit for a minute.


I am in gear on plane just cruising along, not touching the throttle, the boat loses power and we slow way down quickly, the boat with me not touching the throttle revs back up, passed the crushing Rpms I was at, I can hear the boat rev, then it goes back to 4200 Rpms but doesn't seem to have the same power. So I put the boat in neutral and give it a second then put it back in gear and it starts going again, sometimes for five minutes before this happens, sometimes 30 seconds.

Again only after about two hours of driving, always runs perfectly when I first drop it in the water.

 

[nola mike]

, passed the crushing Rpms I was at, I can hear the boat rev, then it goes back to 4200 Rpms but doesn't seem to have the same power. S

Yeah, saw that. "Doesn't seem to have the same power" doesn't answer the question. At 4200 rpm (or 3k, or 3500 or whatever) when acting normally, what is your speed. At those same rpms when acting abnormally, what is your speed. If you're doing 35 mph @4200 normally, but only 20 mph @4200 when acting up, that tells me you have a drivetrain problem. If the speeds are the same, you have something else going on. Your description probably has most people thinking drivetrain, but I'm guessing that isn't actually the problem.

 

[Kconleyk]

Yeah, saw that. "Doesn't seem to have the same power" doesn't answer the question. At 4200 rpm (or 3k, or 3500 or whatever) when acting normally, what is your speed. At those same rpms when acting abnormally, what is your speed. If you're doing 35 mph @4200 normally, but only 20 mph @4200 when acting up, that tells me you have a drivetrain problem. If the speeds are the same, you have something else going on. Your description probably has most people thinking drivetrain, but I'm guessing that isn't actually the problem.

I appreciate the response, and it's hard to answer, it is never the same speed I can tell you that much.

4,200 rpms cruising at 29ish MPH, the boat loses power, and slows ways down to all but a dead stop. It then revs back up and boat starts to go forward again (i haven't touched the throttle) but it won't get anywhere close to 29mph again, maybe 11 tops.

Again for two hours it works perfectly, accelerates perfectly, does everything perfectly, then this problem starts. If I turn the boat off and sit for a minute, will work again briefly and then start doing the exact same thing.