What do I try now?

[Ginder75]

I have a 1977 Mercury 200 (20hp) serial number 4580916. Here is what I have done. Rebuilt Carb, Decarbed the Motor, New impellar and water pump, cleaned the plugs, and have fresh gas at a 50:1 oil mix.<br /><br />Here is my problem. It will idle all day long, but I think it would shake itself apart. There is a lot of vibration and shaking going on. However when out on the water and in gear it smothes out about half throttle and runs great all the way to WOT. But when you bring it back to idle it goes to shaking. <br /><br />I don't know how to define the problem other than the vibration. I am not sure if it is missing, electrical problems, or if it is timing. I am waiting on a manual to help with this, but thought I would offer it to the board for help.<br /><br />Ginder75

 

[quantumleap]

Re: What do I try now?

First make sure you are getting spark at all cylinders. Then check idle speed.

 

[KCLOST]

Re: What do I try now?

Check the compression also on all the cylinders, and post results along with the spark test...

 

[BF]

Re: What do I try now?

Does it have CDI or points? Sounds like timing to me, maybe base timing is off, and when you advance the timing as you give throttle it smooths out.<br /><br />Brent

 

[Ginder75]

Re: What do I try now?

This may dumb, but how do I check spark on a surface discharge spark plug? These are the NGK's. They look relatively clean, but I wanted to check. I have read on here that it is better to check the spark through the plug to the block and not between the boot and plug. Second question for a newbie, how would I tell a difference between CDI or Points? It is a 1977 model if that makes a difference.<br /><br />I know it has good compresion, it was checked before I bought the motor. Not sure of the exact numbers. I will try and check it this weekend. I am loading up the boat and heading to Texas for some fishing this holiday weekend. I will post any observations or additional information when I get back on Tuesday. Thanks for all the help.<br /><br />Ginder75

 

[Ginder75]

Re: What do I try now?

The compression checked out at 125 on both cylinders. I tried to adjust the carb again and both better results since the recent decarb. It still has a sputter at low idle but it is far better then it was before.<br /><br />This motor wants to test me everytime out. Today, it decided that it did not want to run on both cylinders for some time. Once I cleared the no wake zone and was able to open it up to WOT this too cleared and away we went.<br /><br />I think I am going to run it most of the weekend and see if that will help resolve some of my issues. Thanks for all the help.<br /><br />Ginder75

 

[achris]

Re: What do I try now?

1977 will be CDI. Check for air leaks in the engine too. have you got a hose that has fallen off (or forgotten to put back on). When it's idling, try pulling the plug leads off, using something that's not conductive, and see if it's only running on one pot. Have you tried a couple of new spark plugs?<br /><br />Chris............