rpm issues

[motorboatin123]

Hi again.. Ok steering cable is fixed now new problem.. Got out on the water for the first time today and one of my motors only gets up to about 3000 rpm's while the other will just keep going. I can hardly get the boat on a plane because if it. I have the gas pinned and still only 3000. could it be fuel, spark? the Carb? What is the first thing I should replace to fix this? thanks

 

[reddogg]

Re: rpm issues

Ok, since the other motor is running fine and I'm assuming they are running off the same gas tank it shouldn't be a fuel issue. Do they run off the same fuel filters or do they have sepperate one's? I'm going to make a guess but it seams that 8 out of 10 problems I see in this forum wind up being trash in a filter or dirty carbs. Thats where I'd start looking.

red

 

[PuddleJumper]

Re: rpm issues

When was it last tuned up? I had identical prob and rotor/cap/wires and plugs was done as a starting point b4 troubleshooting. That fixed it for me. Always good to make tune up as a starting point.

 

[1980Coronado]

Re: rpm issues

It might help if you tell everyone a bit more about the engines. I'm assuming they're Mercruiser I/O's because that's the forum you're in......but what size are they...what year are they? Give a little more detail and someone may be able to help you start to troubleshoot the problem.

 

[motorboatin123]

Re: rpm issues

its a 1989 thompson with twin merc 470 engines. they are set up seperate gas tanks so it could be a fuel issue. I changed the plugs and wires yesterday. I also have a spare carb which I am having rebuilt today so I can throw that on too. What about fuel pump?

 

[1980Coronado]

Re: rpm issues

What about the distributor cap, rotor, points, condenser.....? How did the old plugs look? What are the other symptoms? Was it running rough at 3000 rpm?

Could be fuel....could be ignition....have you put a timing light on it? Did you run a compression test while you had the plugs out? Start with the basics and rule out the simple things before you go changing the carb. Go through and replace all of the ignition parts, not just plugs and wires, then put a timing light on it and make sure it's set properly.