rpms drop from 4200 to 3000

[a24rick]

When my 26' searay I/O 1989 5.7 Mercruiser rebuilt this year hits 4200 rpm it drops down to 3000 rpms .When I put it back in neutral the rpms are fine.Then when I take off again she will run fine for about 2 minutes then she will do the same thing again.She runs fine with no load. checked the Carb fuel filter (perfectly clean) Fuel filters are new.Is it the fuel pump? or carb?or??????? Help<br /> Rick

 

[cneste]

Re: rpms drop from 4200 to 3000

I have the same problem. This is an email from another boater. I will let you know the results by weeks end<br /><br />Yes, the problem was the spark plug wires. I also replaced the distributor cap and rotor. 6000rpms out of the water is reving it too high. this is because it does not have the water load on it. <br />hope this helps<br />dave<br />-----Original Message-----<br />From: Chuck & Diane Neste []<br />Sent: Sunday, June 19, 2005 10:27 AM<br />To: <br />Subject: Boat Question<br /><br /><br />Hello Dave,<br /> <br />I came acorss your message posted on a boat forum. Did you ever resolve your problem? I have a 1988 rebuilt 4.3L and took it out for the first time yesterday. I can get my boat past 2300 rpms but out of the water on the trailer with ear muffs, I can get 6000 rpms(briefly).I have a brand new electric fuel pump with all filters new. My carb was winterized last year and was also bought new June of last year.<br /> <br />Thanks<br />Chuck<br /> <br />Thanks<br />Chuck in Atlanta, GA<br /> <br />messgae posted on another forum<br /><br />My 1996 4.3L with 2bbl merc carb does not accelerate or come up to proper RPM's. this past weekend I could only get 3900 to 4000 RPMs versus the normal 4600 to 4800. When accelerating the motor lacks power. I replaced the plugs and cannister fuel/water filter, checked the Carb fuel filter (perfectly clean) and it still performed without power. Clymers says it could be the electric fuel pump or even the anti-siphon valve. any help would be appreciated in where I should look for the problem? thanks

 

[Don S]

Re: rpms drop from 4200 to 3000

Need some more info, Year, make (Mercruiser, Volvo, ????) model number????

 

[imported_scott_m]

Re: rpms drop from 4200 to 3000

The fact that it runs fine for a couple of minutes, then drops down indicates to me that it is pulling a vacum on the fuel system. Try removing the gas cap next time it happens. If it picks back up, you likely will have a plugged vent line.<br /><br />Actually, I JUST had this very thing happen on of all things, my weed whacker. 10 year old motor that would not get full RPM any longer. I figured the motor was just tired and was ready to trash it when I thought of the vacum thing, so loosened the gas cap, and she runs nearly good as new.

 

[cneste]

Re: rpms drop from 4200 to 3000

I have just changed the spark plug wires /plugs and installed a carb( due to epoxy lifting and leaking from fuel bowl / non related). <br /><br />The boat could not reach 2300 rpms before the plus and wire change. The old plugs all burned fine / light brown so I would assume the wires caused the lack of power. All is well now. I can run WOT @ 4200 RPMS<br />Chuck

 

[a24rick]

Re: rpms drop from 4200 to 3000

thanks cneste but my boat dose hit 4200 rpms then it cut out to 3000 rpms the spark plug wires and plugs are new

 

[a24rick]

Re: rpms drop from 4200 to 3000

macksea I will try removing the gas cap and checking the vent line.I will let you know thanks

 

[cneste]

Re: rpms drop from 4200 to 3000

I had a surge problem where it would run at WOT fine but then suddenly dropped to 2300 rpms. If I drove it a fe wmiles, I might get 3000 rpms out of it. Even though it was thouroughly tuned up last year, Something went wrong over the season.<br /><br />Good Luck

 

[a24rick]

Re: rpms drop from 4200 to 3000

when out to try gas vent line that was not it. got towed in !! Blown head gasit.will fix it ths weekend I hope that was the problem? Not coused by the problem.