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Mercruiser 470 running problems....

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Ricky Lancaster

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Just bought a 20' Sportcraft with a 470 Mercruiser inboard. It ran good for about 2 hours then it started acting like it was missing. Sounds and feels like it is firing on 3 cylinders. Can not go above 1100 rmp. Every time I try to throttle up it seems to bog down and spit and sputter. It seems to run fine in neutral and at idle. Need some advise please on what this problem could be.
 
I also just installed a new fuel filter water seperator on this vessel. If anyone can please give me some sound advise on what the possible problem is i would appreciate it.
 
Ricky:

This forum has a multitude of posts regarding "Mercruiser 470 running problems....". The condition of the spark plugs can tell you alot about the engine's ignition condition. Start w/the basics; tuneup--points, condenser and spark plugs. Inspect the distributor cap and rotor for wear and replace if needed. Perform a compression test on the cylinders. Adjust the carburetor as needed; rebuild it if necessary. Does the engine have a separate alternator or the old stator/WC regulator system?
 
It ran good for about 2 hours then it started acting like it was missing. Sounds and feels like it is firing on 3 cylinders. Can not go above 1100 rmp. Every time I try to throttle up it seems to bog down and spit and sputter.
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The fuel in the tank could be old and water infused which would contribute to the problem. The carburetor inlet filter and bowl may be full of crap. The mechanical fuel pump also has a filter item #20A inside of the cup/bowl in item #20 below.

http://www.mercruiserparts.com/Show...r=1075&bnbr=30&bdesc=CARBURETOR+AND+FUEL+PUMP

Check the plugs and ignition system; see the chart at the site below.

http://www.gnttype.org/techarea/engine/plugs.html
 
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It has the old stator/WC regulator system. Thanks for the advice.
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In MHO the old statement "If it ain't broke don't fix it." does not apply here. Upgrade the charging system to a separate single wire alternator system. It may be available from this site; not sure. EBay carries a complete kit.
 
I had this motor on a 1980 Silverline. After MANY years this problem Cropped up. Turned out to be a worn Distributor. When the Motor warmed up the shaft in the distributor caused the problem at speed but ran fine at idle. Check for excessive play in the shaft. Take her out on another trip. If all goes well for awhile then after things get hot and the problem comes back look at the Distrubitor as the cause.

Also are you running in fresh or salt water? Yes the motor has internal cooling with antifreeze but in 15 years of owning the boat I had to replace the Exhaust elbow twice. Yes I did flush the motor after every trip. Keep an eye on ALL cooling Hoses.

Did allot of water Sking with her. She would pull up three Slamon's! Had to replace the Trim pump motor brushes 4 times.

I'm not knocking the engine. It Kicked butt. Spun a 24" pitched prop and Maxed out at 57 MPH with a light load. This was in a 17 foot boat.
 
Thanks semi-retired. I will look into that. Do you have any idea of why else I may be having this problem. Like I stated earlier it seems to be missing like it is only running on 3 cylinders but again I get confused because it bogs down badly and occasionally backfires when I try to throttle up. I can run ( albeit roughly at around 1100 to 1500 rpm's ) but if I try to throttle up any more it bogs down and acts badly. Thanks for the help all. I really do appreciate all of your advice and guidance
 
Check point gap first...best case scenario...the rubbing block was not properly lubricated and the points are now gapped improperly
 
i have had the same issue all summer, the dist shaft was worn to the point that if i removed it and pushed the point cam sideways the pointt gap would go from closed to .150 thou. i got it rebushed at my local machine shop, they had a very hard time finding bushings ........but by far the next best alternative is:
http://www.iboats.com/Mallory-YL648AV-replacement-parts/dm/view_id.463610

or

http://bpi.ebasicpower.com/pc/MAL9-26111/MER37ELEC

i am not expecting the dist to last too many more years. and a new mercruiser one is way to expensive
 
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