No power after 3000 RPM

Good Sport

Cadet
Joined
Jun 8, 2003
Messages
22
I am trying to help a friend fix his boat. It is a 1976 Bayliner with a Volvo 280 OD w/ GMC 350 CID 225hp engine.<br /><br />Suddenly this engine will not power the boat past 3000 RPM. It will rev to 4400 RPM with no load. But it dogs out @ 3000 RPM when pushing the boat. We have changed the fuel pump & filters. We have tried fuel from a seperate source. So far, no luck.<br /><br />Please help.
 

Good Sport

Cadet
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Jun 8, 2003
Messages
22
Re: No power after 3000 RPM

Coil has not been changed. Could it be the culprit? I thought coils either worked or didn't work.
 

oldboat1

Fleet Admiral
Joined
Apr 3, 2002
Messages
9,612
Re: No power after 3000 RPM

If the motor is running smoothly, would want to rule out hull issues (trim tabs not working, hull needs serious scraping/cleaning).
 

Yepblaze

Lieutenant Commander
Joined
Jun 1, 2001
Messages
1,686
Re: No power after 3000 RPM

Make sure someone has not kinked the fuel line where it makes it's final turn towards the big fuel filter nut.
 

cobra 3.0

Lieutenant Commander
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Jul 31, 2003
Messages
1,797
Re: No power after 3000 RPM

Coils sometimes give out at higher rpms before they fail.
 

orion208

Petty Officer 2nd Class
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Jun 20, 2003
Messages
134
Re: No power after 3000 RPM

Mine did the exact same thing at 3000 rpms turned out to be a spun prop hub works great now since I installed a new one.Now I am back to 5000 rpms no problems.Just a thought.
 

liquidasset

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Joined
Aug 23, 2003
Messages
21
Re: No power after 3000 RPM

How do you check if your prop hub is spun? Ive never pulled my prop off. Do you need any special tools to pull it off?
 

Boomyal

Supreme Mariner
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Aug 16, 2003
Messages
12,072
Re: No power after 3000 RPM

you haven't said how the motor runs when you try to push it past 3k rpm on the thottle?
 

liquidasset

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Aug 23, 2003
Messages
21
Re: No power after 3000 RPM

I just went and checked my prop. The only thing holding the nut on was the cotter pin. The nut had backed almost completely off. I hope this fixes my power issues. Why would this limit my RPMs like that? Im going to put her in the water and test it this afternoon.
 

Good Sport

Cadet
Joined
Jun 8, 2003
Messages
22
Re: No power after 3000 RPM

Broomayl, it just doesn't go any faster despite more throttle. It's not a spun prop & I don't think it's the coil. Like I mentioned, it goes 4,400 RPM with no load. And this is a sudden, not gradual, problem. It was running fine last time out.
 

Mikedg

Petty Officer 2nd Class
Joined
Sep 3, 2002
Messages
131
Re: No power after 3000 RPM

If the ignition advance is sticking the engine will run fine at low to mid RPM and show a distinct lack of power above 3000. Check the ignition advance at 3,000. It should be somewhere between 28-32 degrees, but I can't recall the exact spec for your engine. Maybe someone else will provide the spec.
 

Boomyal

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Aug 16, 2003
Messages
12,072
Re: No power after 3000 RPM

MGD, I've got the graph for that disributor and it shows a 'total' advance of 38 deg at 3000 rpm.<br />The distributor itself has a final centrifugal advance of 30 deg and that tops out at 2800 rpm. after 2800 the distrib goes flat to redline. there is a 2 deg discrepency because the distrib spec for that engine show an initial advance of 8 deg but the tune specs show an initial of 10 deg btdc. It probablly counts for little however.<br /><br />GS, you can extrapolate 38 deg on your damper or pulley, making a white chalk mark on the pulley, measuring the stamped 0-10deg marking dimension. that should get you close enough to determine of the distrib advance is free. make sure you check your initial. it it was off by much you'd have a poor idle anyway.<br /><br />If you had an inadequate fuel delivery at rpm under load, the engine would run fine up to a certain butterfly opening then go lean when you pushed the throttle past that point. it would not be running smooth at maximum throttle under that scenario. you are correct that you don't have a prop problem, 'cause then you'd have the rpm but wouldn't be going anywhere.<br /><br />Also check that you didn't lose a throttle cable adjustment and that your butterflies are wide open at full throttle.<br /><br />other than these issues I'm at a loss unless you grew an 1/8 of an inch of fur on the underside that you are unaware of.
 

Boomyal

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Aug 16, 2003
Messages
12,072
Re: No power after 3000 RPM

ps, GS, did you check the screen/filter at the bottom of the pickup tube in the fuel tank. That could be partially plugged, delivering enough fuel to run at 3000 rpm under load but no more. but once again if that were the case when you pushed the throttle past that point the motor would lean out and fall flat.
 

liquidasset

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Joined
Aug 23, 2003
Messages
21
Re: No power after 3000 RPM

I took my boat out to test some theories to solve the bogging problem. I finally got the boat to accelerate. Heres what happened. At the point where it started bogging I manually closed the butterflies and held them closed. As soon as I did this she took off. Got all the up to 4400RPM and 43MPH(per the GPS). Why would I get better performance with them closed instead of open? I havent rebuilt the carb yet. I have the kit but if Im going to have the carb apart I might as well try and fix what is causing the problem.
 

Boomyal

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Aug 16, 2003
Messages
12,072
Re: No power after 3000 RPM

Who's problem are we trying to solve here, Goodsport's or Liquidassets?
 

Boatin Bob

Lieutenant Commander
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Sep 24, 2001
Messages
1,858
Re: No power after 3000 RPM

Liquid...do you mean you closed your choke and it took off? If so that would really mean you have a lean condition, could be carb adjustment or rebuild time?
 

Roger030

Recruit
Joined
Aug 25, 2003
Messages
2
Re: No power after 3000 RPM

Mine does that too. If I hold the secondaries closed it takes off but not too full speed. I rebuilt the carb and no change. I looked for leaks and no luck, Im going to try a different prop and go to electronic ign.
 

liquidasset

Cadet
Joined
Aug 23, 2003
Messages
21
Re: No power after 3000 RPM

Does it matter? We both have the same problem. Maybe my findings will help him. It happens when I hold the butterflies on the secondary barrels closed. I tried doing that with the choke but nothing happened.
 

liquidasset

Cadet
Joined
Aug 23, 2003
Messages
21
Re: No power after 3000 RPM

Rebuilt the carb today. Runs like a champ. We think it was the float adjustment. It was pretty far off, probably not letting enough fuel into the bowl.
 
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