Cap and Rotor Change?Tune Up-Mercruiser 3.0L

enginesilo

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Is there a recommended internal to change the cap and rotor on the Mercruiser 3.0L? My engine is almost 10 years old and I've never changed it before. Boat runs fine but it does have a slight hesitation when coming out of the no wake zone and I accelerate hard. I know this can be carb/fuel related, but I also read a few archived posts where people were having issues under heavy load and a cap and rotor was suggested.

Should I change out the cap and rotor if the boat seems to run fine otherwise? What is a common interval to change these out on the 3.0L?
 

fishrdan

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Cap, rotor, wires and plugs are normal maintenance items, and at 10 years they are over due, so yeah I would change them. Through, this sounds like it's more likely the accelerator pump in the carb, time for a carb rebuild. Also, change the fuel filter in the fuel pump.
 

enginesilo

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Cap, rotor, wires and plugs are normal maintenance items, and at 10 years they are over due, so yeah I would change them. Through, this sounds like it's more likely the accelerator pump in the carb, time for a carb rebuild. Also, change the fuel filter in the fuel pump.

Thanks, figured you would say its time to change them. So Cap/Rotor/Wires/Plugs. I've done my plugs before, just never the other components. Is this a simple job? Can I throw the boat's timing off by mistake when I remove the cap, or is that adjusted from the screw on the bottom of the distributor? Wanted to ask to be sure I don't go cause any issues. And for parts, OEM stuff? I've seen people say go to Napa for these components.

On to the accelerator pump issue, a year or so back someone told me to check if my carb squirt gas while pumping it in neutral before starting it as a test. The carb did spray a nice fat stream of gas as it should. Would this be a way to diagnose a worn accelerator pump? Any other way to test it? I was thinking a carb rebuild would be in order but the boat runs/starts fine otherwise and only shows its face on a hard launch so I have been dealing with more pressing issues. Any tips on this appreciated.
 

alldodge

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My 95 Rinker has never had the wires changed, Changed the cap, rotor and plugs a couple years ago just because. Owned the boat since new and have had no issues. The original installed "Champion" plugs still look just fine, but replaced them with MR43T, picked up 36 of them on sale.

Sounds like you do have a current carb issue with the hesitation, probably the accelerator pump. Pumping the throttle and looking for a stream is a good way but it may or may not be putting enough fuel in when you pump. I would recommend just rebuilding the carb
 

Silvertip

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When installing the new cap, hold the new one in the same orientation as the old one and then transfer one plug wire at a time to the new cap. The reason for this is YES, you can throw timing off if you screw up the placement of the wires from one cap to the other. Look for something to orient the caps with such as the mounting screws. And make sure you gap the plugs before installing them. Many folks think they are properly gapped when new and in some cases they are. But keep in mind that one plug type may be used in many different engines, all of which have different ignition systems that require different gap settings.
 
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Blind Date

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Plugs wires on marine engines don't see the extreme heat like they do in an automotive engine and therefore last almost indefinitely. At 10 years they are probably still like brand new. If they are soft & pliable I'd save my money.
 

fishrdan

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On to the accelerator pump issue, a year or so back someone told me to check if my carb squirt gas while pumping it in neutral before starting it as a test. The carb did spray a nice fat stream of gas as it should. Would this be a way to diagnose a worn accelerator pump?

the boat runs/starts fine otherwise and only shows its face on a hard launch

Yes... Did you open the carb slow, medium and quick, to see if all these conditions produced a nice steady stream of fuel.

The boat "falling on it's face" when you hammer the throttle is classic accelerator pump problems.
 

Alumarine

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If you're going to change cap/rotor/wires I'd certainly change the points and condenser as well.
You'll have to set the dwell on the points and check the timing.
 

Blind Date

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His motor is only 10 years old. That makes it around 2004/5. I would think that engine doesn't have points/condensor. My '90 4.3 was electronic. If it does, spend the money and put an electronic ignition in it.
 

alldodge

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The serial number listed by the OP indicates it has EST ignition setup
 

enginesilo

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Yes... Did you open the carb slow, medium and quick, to see if all these conditions produced a nice steady stream of fuel.

The boat "falling on it's face" when you hammer the throttle is classic accelerator pump problems.


Thanks again everyone for the replies and suggestions. The motor is a 2005 and I'm almost certain it is electric ignition. Boat is still shrink wrapped so I can't go looking right now, but its definitely a 2004-2005 build.

I'll have to test the carb spray again once I get it uncovered. I think you are right since everything I search comes back to "accelerator pump problem" symptoms. I read that the carb has 3 settings on the accelerator to spray more or less gas into the carb, could adjusting this possibly help? This was a post someone put up from the manual on the topic. Is this possibly a fix worth trying? Guessing 10 years of ethanol and all probably means a carb rebuild/refresh, but figured I'd ask so I could try this first if it was worthy.
 

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fishrdan

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I'll have to test the carb spray again once I get it uncovered. I think you are right since everything I search comes back to "accelerator pump problem" symptoms. I read that the carb has 3 settings on the accelerator to spray more or less gas into the carb, could adjusting this possibly help?

It certainly wouldn't hurt to try, but if it was running properly before it shouldn't need more-less acc pump shot.
 
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