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2003 4.3L Power Struggle

Searay03

Searay03

New member
Have an '03 Searay w/4.3L mercruiser 18'6" bow rider, by the way I am a mechanical novice, still learning the ins and outs. WOT range is 4400-4800. In the past I have been running in the lower end of this range right around 48-50 mph (thinking of dropping to a smaller prop). Starting this season it is struggling to hit 4000-41000 RPM's at I think the fastest it has topped out at is about 45-46 MPH. Same prop (turbo 21 pitch) absolutely nothing has changed. Temp wise it runs just a bit above 170 deg. on the gage when warmed up. I took the dist. cap off and cleaned it as there was quite a bit of build up and also ran some sea foam through the engine trying to see if there was some build up I could release. Changed plugs, dist cap and rotor the summer before last. Cleaned flame arrestor 2 weeks ago, no luck... I do run 87 octane in it, unsure if a higher octane will help. My next effort is changing the fuel filter/water separator. At full throttle engine just simply sounds weak.

Any thoughts and opinions are appreciated.
 
Re: 4.3L Power Struggle

I'm having the same problem with a 2007, 220hp 4.3L MPI Mercruiser. At WOT, 4400-4800rpms has been normal, but this year I can't get it over 4100rpm. The boat is a 21' Hurricane. She used to top out at 50-54 mph at 4800rpm. With a new prop (same pitch & diameter as before), I just cannot get her at the proper speed & rpm at WOT. I know I'm driving her correctly (trimmed properly). The gauges seem to be working normal (I do not suspect anything wrong with them since both would have to be off and they are not reliant on one another). She runs smooth and perfect expcept at WOT. I am running her with a new fuel filter and also have tried fuel cleaners/injector additives, etc. I now suspect the possibility of the throttle cable being stretched and not allowing me to actually achieve full throttle, particularly because she doesn't sound as beefy as she should at WOT. Just an idea that you might want to check out. If anyone knows how to test the throttle cable for this problem & an easy fix, I'd also appreciate the feedback.
 
Re: 4.3L Power Struggle

Compression test both of you then get back to us. Different threads so we guy's work on one boat at a time.
 
Re: 4.3L Power Struggle

Thanks for the input but if you knew you would realize that cleaning my boat was one of my hobbies. I have pretty much ruled out the dirty hull theory. I have also heard that many race boat teams will actually take fine sand paper to the bottom's of their hulls to scuff them up a little bit. This creates bubbles and more hull lift. Thanks.
 
Re: 4.3L Power Struggle

Did i read nothing changed ? Something did change didn't it? Or you would be running the same as last year !

Compression and vacuum test.
 
Re: 4.3L Power Struggle

Make sure all of the plug wires are snapped on tight. One loose wire can make a big difference.
 
Re: 4.3L Power Struggle

Yeah, last week I took the dist. cap off and noticed quite a bit of build up on all of the contacts so I cleaned it off (checked all connections as well). Still didn't notice any improvements after this but I think for $20 it is worth it just to go ahead and put on a new cap and rotor. I did notice some moisture inside of the cap itself.
 
Re: 4.3L Power Struggle

I changed the fuel filter a couple of days ago and noticed rust around the top of it and sand/gunk in the filter. Took the boat out this afternoon for a quick run and it seems as if it is back to normal. Engine sounds healthier at higher RPM's and RPM's have gone up to where they were, top end and hole shot has improved as well. Cheap fix!

Thanks for your comments/help.
 
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