2003 4.3 GL Higher WOT RPMS and ticking this season over last

[jkust]

Hi all, here is my situation. Last season my 2003 carbed 4.3 mercruiser maxed right around 4750 rpms. It pushes a heavy dry weight 19' boat of 2900 lbs with a 35gal fuel tank. Now this season after summarising with no other changes or dings to the 21 pitch, oem, alum prop, it will go up to over 5000 rpm's and higher yet with a lighter than usual load of fuel. I say to myself great time to reprop and use those rpms to get some more speed but when I am right at the point of over reving, I hear an unnerving ticking sound from the engine bay that didn't happen last year. If I back off the rpms a few hundred down to the accepted wot range the ticking is gone. Is this ticking a function of over reving just a few hundred rpm's? Any thoughts on how the engine could possible spin faster with no changes? Not sure what is going on here.

 

[jkust]

Re: 2003 4.3 GL Higher WOT RPMS and ticking this season over last

I suspect the "ticking" is the valves begining to float, NOT GOOD! As to why the higher RPM,,, perhaps the boat had a chance to dry out over the winter? (Wet foam) Better gasoline? Your praying to the boat gods paid off?

Interesting, now that you mention it the only difference was moving to 89 octane to cure my run-on which it did. Seems unlikely octane can make this much of a difference to me. I picked up over 5mph on gps more than it had ever gone before as well unlikely as it sounds. No wet foam here. Not sure what valve floating is though.

 

[gadget73]

Re: 2003 4.3 GL Higher WOT RPMS and ticking this season over last

And this is what it looks like:

http://www.youtube.com/watch?v=_REQ1PUM0rY

Very much not good for your engine.

 

[180shabah]

Re: 2003 4.3 GL Higher WOT RPMS and ticking this season over last

89 octane does not contain any more power than 87 does. It is just more resistant to ignition. While switching to 89 solved your run-on problem, it did not cure it. Hot spots in the combustion chamber, most likely carbon deposits, will ignite the fuel mixture in a cylinder. A good de-carbing will serve you better, eventually the deposits will get bad enough to ignite the 89 octane. Then what? Switch to premium?

Of course this assumes that everything else is correct. good fuel. proper ignition timing (could also effect WOT RPM's)(hint, hint), proper idle speed, letting engine cool down prior to shutdown, etc.

 

[Bondo]

Re: 2003 4.3 GL Higher WOT RPMS and ticking this season over last

Now this season after summarising with no other changes or dings to the 21 pitch, oem, alum prop, it will go up to over 5000 rpm's and higher yet with a lighter than usual load of fuel.

Ayuh,... Just how much Service, or Tune Up do you include in Summerization,..??

Just how Light of a fuel load,..??

Detonation, rather than valve float was the 1st thing that came to My mind.....
A Lean condition from Crud in the filters, + old gas maybe,...
Leaning a motor will give it a Boost,.. Just before it Blows,...

 

[jkust]

Re: 2003 4.3 GL Higher WOT RPMS and ticking this season over last

Ayuh,... Just how much Service, or Tune Up do you include in Summerization,..??

Just how Light of a fuel load,..??

Detonation, rather than valve float was the 1st thing that came to My mind.....
A Lean condition from Crud in the filters, + old gas maybe,...
Leaning a motor will give it a Boost,.. Just before it Blows,...

No tune up in summerization or winterization just the fluids/filters changed etc for cold weather storage last year which was my first year of ownership. I Simply unwinterized it.
Fuel load varies from 35 gals down to 5 gals. Faster/more rpms at 5 gals and 35 gals over last season. Have gone through two full tanks now this season. Other than the faint ticking when over reving to rpm's formerly unattainable, it runs and performs well. I am going to venture bad gas last season or the gas not properly preserved corrected by new gas and new filters. Boat had been stored in the original owners garage sitting winterized for some time hence just a few outings worth of hours on it when I got it. If my wishful thinking isn't correct, how can a person diagnose a lean condition?

 

[z284u2try]

Re: 2003 4.3 GL Higher WOT RPMS and ticking this season over last

Do you think you are trimming up more than last season and now what you are hearing is you sitting on the rev limiter. I beleive it is about 5200 rpm.

 

[jkust]

Re: 2003 4.3 GL Higher WOT RPMS and ticking this season over last

Do you think you are trimming up more than last season and now what you are hearing is you sitting on the rev limiter. I beleive it is about 5200 rpm.

No I am trimming the same. Not sure about other I/O boats since I have not driven another but this one responds well to a lot of trim.

 

[z284u2try]

Re: 2003 4.3 GL Higher WOT RPMS and ticking this season over last

Anything over 5k you are in rev limmiter area.

 

[Bondo]

Re: 2003 4.3 GL Higher WOT RPMS and ticking this season over last

No tune up in summerization or winterization

Ayuh, OK,... So just When do you get around to doing the Annual Maintanance on this barge anyways,..??

 

[jkust]

Re: 2003 4.3 GL Higher WOT RPMS and ticking this season over last

This next winterization, I will do an actual tune up and impeller. I am at 75 or so hours on it now. Annually then it has received all fluids and filters and other than draining the block and adding fuel additive for storage nothing else has been performed. It was originally purchased from the local Chaparral dealer and they shared the records with me.