Mercruiser tune-in!

Loa

Cadet
Joined
Jul 2, 2004
Messages
8
Hi all!<br /><br />As season here in Sweden is ongoing so is my engine problem....<br /><br />My problem is that ive lost like 4knots since last year.<br /><br />What has been done!<br /><br />1/ Carburator rebuilt by marin workshop. At first it only ignite at full throttle but it never start, so i had it returned and he adjusted the float level.<br /><br />2/ Whole electrical system replaced, Cap, rotor, coil, spark-wires and sparks. Timing set at 8degres.<br /><br />3/Fuel filter has been replaced. <br /><br />So, with all this done it should go better or atleast same as last year.<br /><br />My engine is a Mercuiser 5.7 -91 rebuilt -01. Carburator is a Rochchester 4barrel. <br />rpm is 600-700 at idle and at 4400-4600 full throttle. It runs very smooth at idle and sparkplugs are looking shiny and new after aprox 10h running. <br /><br />Im thinkin that ive lost few knots its not running as it should, also the tachometer goes +/-200 rpm randomly, not all time tho.<br />Earlier this year i also got a mysterious knocking sound from lower region of enginge. It sounded like loose part being smashed around by the crank. But now its all silent again.<br /><br />Is this a tune in problem or what?<br /><br />Thanxs in advance<br />Magnus
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: Mercruiser tune-in!

Hi Magnus,<br /><br />Try a de-carbonizer, like Quicksilver Power Tune. I have had excellent results form this product in the past.<br /><br />Have you done a compression test? This would be the first place to start.<br /><br />Chris...........
 

sculbert

Petty Officer 2nd Class
Joined
May 22, 2004
Messages
160
Re: Mercruiser tune-in!

If the knock dissapeared after you tunes the engine, most likely you had the timming advanced a little more back then and you got the extra top end. You can tweak timming to get more bottom end or more top end. If you advance it too much you will get better top end but have a possibility of getting spark knock. This would bee a knocking sound from deep in the engine. nomally under a heavy load. I suspect you fixed the knock and caused yourself to loose a couple knots. <br /><br />If you can live with it there it might be best to leave it. Or try moving your timming up 2 degrees at a time.
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,458
Re: Mercruiser tune-in!

If the engine is turning the same RPMs as last year,<br />I'd be looking at the Prop,+ the Boat Bottom...........<br />Is the boat Moored ????<br />Is the boat bottom Clean ?????<br />How Beat-up is the Prop ????
 

Loa

Cadet
Joined
Jul 2, 2004
Messages
8
Re: Mercruiser tune-in!

Boat bottom is clear, or has been while i did early tests. Propp is inspected....for this spring but i can tilt it up for new inspection.<br /><br />I think il go for comp test as well as the timing adjustment. Do you guys adjust timing when u cruise aswell as doing it idle with forward gear?<br /><br />Thanxs for quick replys<br />Magnus
 

sculbert

Petty Officer 2nd Class
Joined
May 22, 2004
Messages
160
Re: Mercruiser tune-in!

Your timming needs to be done at idle and in neutral. 700 rpms.
 
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