3.0 Mercruiser Runs great than not so great...

[LiL Fella]

I have a 1983 Century 5 meter with a 3.0 mercruiser. I bought it last year and after a couple of times out my alternator took a crap on me. Well I replaced it and had no mechanical issues with the boat all summer, it ran awesome.

Well fast forward to this summer first time out won't start, no spark, replace condenser and coil next trip out fires up instantly runs great.Well after running for about 20-30 mins. it starts spitting and sputtering. I head back to the launch and the whole way back it will barely stay running but every once in a while it starts to run fine again. Then back to running like crap.

So I go home and fill up the tank with fresh gas and a couple cans of dry gas and a thing of carb/injector cleaner. Next trip out same story runs great for 30-40 mins and starts running horrible stuttering bogging etc. then every once in while taking off like a bat out of hell.

Tonight I went out armed with my out board gas tank fresh gas clean tank etc. Same thing all over again.

Any idea's????

 

[Rhadley]

Re: 3.0 Mercruiser Runs great than not so great...

I'd replace the spark plug wires. I get the same issues when they are bad.

 

[marinetech77]

Re: 3.0 Mercruiser Runs great than not so great...

Start with fresh spin on fuel filter. Also change carb fuel filter located at fuel inlet of carb under the 1" hex nut. If you changed the points and condenser and didn't set the dwell with an analog dwell meter you maybe experiencing an issue.
Generally the start of a boating season with your motor should result in fresh fluids and filters throught. Tune up kit,plugs, cap and rotor, wires only if bad, fresh lower unit fluid, grease gimbal etc.,set timing. Doing this preventative maintainence along with keeping fresh fuel in your tank will keep you running.
Without hearing your boat run sounds like fuel. It might be time to freshen up the carb. Is the accelerator pump in carb spraying a nice stream of fuel down the throat of the carb when you apply throttle?

 

[LiL Fella]

Re: 3.0 Mercruiser Runs great than not so great...

Yeah I replaced both fuel filters and I have a good stream of gas when I pump the throttle. I will check the dwell.

 

[smarks]

Re: 3.0 Mercruiser Runs great than not so great...

If you ran an external gas tank and bypassed the spin on filter and experienced the same problem, it's probably not the spin on filter but likely the fuel filter up on the carb. is pluged.

Give that a try and let us know.

Steve

 

[smartwork]

Re: 3.0 Mercruiser Runs great than not so great...

When I read this post, it sounded EXACTLY like one that was posted here just recently. I'm not positive, but I thought that person's issue ended up being electrical and the run-time was heating something up, causing expansion, and therefore causing a "disconnect". When he brought it home, it cooled, next time, it fired right up and ran well... until the same run-time had passed again. What are you gauges doing when the engine's sputtering? Are they operating correctly or whacking out too?

 

[LiL Fella]

Re: 3.0 Mercruiser Runs great than not so great...

Well I picked up a new dist cap and wire set so we'll give that a try... We'll see.

 

[LiL Fella]

Re: 3.0 Mercruiser Runs great than not so great...

Well I replaced the dist. cap, plug wires, spark plugs, and I also disassembled and cleaned out the carburator. After running for about an hour or so it started to hesitate and back fire, But the hesitation and power loss were not nearly as bad as before. After returning to the dock I pulled the spark plugs and they were black and sooty... I am going to follow the mercruiser manual steps for adjusting the carb. Does anyone has any other ideas???

 

[LiL Fella]

Re: 3.0 Mercruiser Runs great than not so great...

When I read this post, it sounded EXACTLY like one that was posted here just recently. I'm not positive, but I thought that person's issue ended up being electrical and the run-time was heating something up, causing expansion, and therefore causing a "disconnect". When he brought it home, it cooled, next time, it fired right up and ran well... until the same run-time had passed again. What are you gauges doing when the engine's sputtering? Are they operating correctly or whacking out too?

Gauges really don't do anything abnormal while its hesitating.

 

[Rhadley]

Re: 3.0 Mercruiser Runs great than not so great...

Have you solved this one yet? I thought I had, since I checked for spark on each wire with the timing light and found 1 that was not hitting all the time. Replaced the wire (had extra on board) and it ran great the rest of the time. But next time out, it was back to the same problem; about 15-25 minutes at 100%, then misses, and sometimes it runs perfectly for a second and back to missing. Seems to me it has to be due to heating up, and the only electrical components that should be sensitive to that are the ignition coil and condenser.

Not sure how a filter can cause a problem only after heating up....

 

[Blk-n-Blu]

Re: 3.0 Mercruiser Runs great than not so great...

Condenser inside the dizzy could cause these symptoms. I've seen bad ones right out of the box. Cheap to try. Do the points too.