4.3 Mercruiser not running properly

I own a 1990 4.3 V6 Mercruiser and have been having some trouble with it.
I have owned the boat for 4 years and it has 550 hours on it

A few weeks back I noticed it would not rev up past 4,000rpms and I could not hit my top speed which is normally 42 or 43mph. I replaced all the spark plugs and took it out and it ran good for one 4 hour trip and then started doing the same thing again on the next trip. Even when I just have it in idle I can hear that something isn't right. My rmp gauge even jumps a little when its in idle.
Last time I took it out, the boat took off just fine on the first takeoff and I got up above 40 mph and rmps were at about 4500. After about 5 mins of running wide open it started to run weird again and went down to 37mph at about 3900rpms.

When running the engine wide open I can hear it trying to rev up and run like it should but something is definitely not quite right. Does this sound like a spark issue? Distributor issue?

Also when running it in idle I can hear a little ticking down near my spark plugs. I took the new plugs out to inspect them and they look fine.

Any help here is appreciated. Thanks

Re: 4.3 Mercruiser not running properly

This is the first place I'd be looking.... http://forums.iboats.com/showthread.php?t=520082&p=3516412&viewfull=1#post3516412
Next I'd check the coil. Then, if the ignition system checks out fine (including checking the timing and the timing curves), I'd pull the carb and give it a thorough clean and set all the adjustments up....

Re: 4.3 Mercruiser not running properly

That ticking you sometimes hear could be an arcing coming out of the spark plug wire on the boot end . Sometimes spark plugs will get a path for electricity to make it's way out of the plug boot and follow along the porcelain and to the spark plug body . It happens periodically and you will hear the arcing noise you have described . Try to narrow down the the leaky plug wire and change the plug and plug wire boot to see if that helps .If so you can then change the rest of them . Also if a plug had arcing go along the porcelain , you will have to replace it again because an arc path has etched the porcelain

Re: 4.3 Mercruiser not running properly

Agree one or both of the above is where I would look to find a problem. Have seen Tachs go bad and do this sort of thing but it is seldom.

Re: 4.3 Mercruiser not running properly

Thanks for your input guys. Do you think this arcing out of my plug could be the cause for my engine not getting up to higher RPMS?

Re: 4.3 Mercruiser not running properly

cwoody297 said:

Thanks for your input guys. Do you think this arcing out of my plug could be the cause for my engine not getting up to higher RPMS?

Click to expand...

yes...

Re: 4.3 Mercruiser not running properly

Look at it this way. If the plug wire has spark arcing to the engine block, that spark is not reaching the plug so it is essentially acting like a hole in a garden hose. If the spark is not reaching the plug it can't light the fire in that cylinder. If the fire doesn't get lit, that cylinder is not making power. If that cylinder is not making power the engine cannot push the boat to the speed it does when the arcing does not occur. Start the engine when it is pitch dark out (and I mean a moonless night). Any arcing should be plainly visible.