Max RPMs at 3000

[Scottshipm]

Engine: Mercruiser 5.7 thunderbolt iv, alpha 1 drive, MSD ignition<br />Boat: 1985 Formula cruiser 21'<br /><br />I lost spark a while back and have since replaced the entire ignition system. I bought the boat with MSD aftermarkert marine ignition already on it, so I rebuilt to duplicate that since I was going piece by piece. Also replaced the fuel pump and rebuilt the carb. (or had a professional replace the fuel pump and rebuild the carb)<br /><br />Spark has returned, but now RPMs wont go above 3200. I have checked timing and did everything I could to fine tune it under load, but dont know where to go from here. It ran great prior to loss in spark, replaced with exact same parts.<br /><br />Appreciate any help, and keep in mind, I am a layman with limited access to the boat (its in high and dry with what is close to banking hours).

 

[Haut Medoc]

Re: Max RPMs at 3000

Welcome to iboats. ...If you are sure you have all of the ignition components correct, I wuold look at the carb. next....Why did you re-build it? This is a good reason when you have a problem, not to throw parts at it..Now you don't know whether it is a fuel or ignition problem...or both...So for starters, did you get all of the wires right? What kind of carb. are we talking about?....BTW, stick around and you will get plenty of feed back....JK

 

[Bondo]

Re: Max RPMs at 3000

Well,...........<br /><br />Welcome to the forums here at iboats.com,.......<br /><br />If you'd look at the top of This Page,... There's a Big Red Search Button,.........<br />There've been Several other guys with the Same Issue as yourself here Quite Recently,.......<br /><br />Obviously,... In Your Case,....Not being a backyard Wrench is a handicap,..<br /><br />If you want to do a Diagnosis Yourself,.......<br />Type in "FreeBeTony",...........<br />The Masterminds have All Spoken in Tony's thread about Not being able to pull more than 3200rpms.........<br />Every,+ All of the Diagnostic Theory's have been written in these forums since about last May or June,.............<br /><br />Enjoy the Read,+ Come On back with More Spefic Questions,.. After you've read Tony's Threads................. <br /><br />Good Luck......

 

[FreeBeeTony]

Re: Max RPMs at 3000

I don't think that's a compliment....... <br /><br />Hope my dilema helps........

 

[Bondo]

Re: Max RPMs at 3000

Originally posted by FreeBeeTony:<br /> I don't think that's a compliment....... <br /><br />Hope my dilema helps........

Actually,.. It Is,............<br /><br />Tony,.......You've carried this project real well in the threads,......<br />It's a nice Easy to find dilema.............

 

[FreeBeeTony]

Re: Max RPMs at 3000

Wasn't so easy for me!!!<br /><br />Hope the new heads and manifold fixes it.....<br /><br />As soon as the rain stops I plan on putting it back together.<br /><br />And thanks for the compliment bondo.......will keep you posted on my progress.

 

[FreeBeeTony]

Re: Max RPMs at 3000

 

[Scottshipm]

Re: Max RPMs at 3000

OK, I have searched for FreeBeTony, FreeBeeTony and BabylonBoater to try to find those threads, but the search only returns current results and I cant figure out how to find older ones (from may or June).<br /><br />A link would be greatly appreciated.

 

[Haut Medoc]

Re: Max RPMs at 3000

The archives are not archiving....I fear that alot of information is lost....If you had looked 3 months ago, there would have been a ton of info...Have you checked the advance curve of the timing?....Or tried a different carb?.....JK

 

[paulie0735]

Re: Max RPMs at 3000

Make all the fuel lines are clear and change the filters while you’re at it. Also check that your are actually getting full throttle by setting the control at full and have a look down the carb throat and make sure the butterfly valves are fully open. What was your max engine rpm before the work was done?

 

[FreeBeeTony]

Re: Max RPMs at 3000

I would make sure you are firing on all 8 cyl's first.<br /><br />Does the engine miss or sputter at all?

 

[Don S]

Re: Max RPMs at 3000

Your problem has many causes. Below is a chart of possibilities. About all you can do is start eliminating till you find the problem.<br /><br />