1991 Mercury 200 Too Rich

[gsutton]

I have a 1991 Mercury 200 that is running way too rich. It starts fine and idles great. As soon as it is put into gear it runs poorly and shakes vilontly until you go above 2,000 RPM. After 2,000 RPM it runs flawlessly. The carbs have been cleaned and they are not adjustable. It does not seem to be an electrical problem, but I could be wrong. It seems to be running on all cylinders. Please help!

 

[dilligafda]

Re: 1991 Mercury 200 Too Rich

Have you checked the enrichener system? If memory serves me correctly, this engine is equipped with a thermal air valve that restricts air to the carbs (making a rich mixture) when the engine is cold. If failed, it will cause the engine to run rich at idle. I will have to look at the manual when I get to the shop tomorrow to be sure, but it's a start!

 

[gsutton]

Re: 1991 Mercury 200 Too Rich

Would that still be a problem after the engine has warmed up? We can run the engine all day and with out fail between putting it in gear and 2,000 RPM it shakes terriblly.

 

[dilligafda]

Re: 1991 Mercury 200 Too Rich

Yes it would be. I checked the manual here at the shop and if that thermal air valve is plugged it will be rich until the throttle plates open enough to run the engine leaner. To test it, you can disconnect the hose (temporarily) and see if the engine smooths out when warm. Let us know what you find out!

 

[mellowyellow]

Re: 1991 Mercury 200 Too Rich

agree with above advice. enricher acts almost<br />like the old chokes used to.

 

[Kenny Bush]

Re: 1991 Mercury 200 Too Rich

Could it also be the mechanical adjustment for the enrichener. The one connecting the throttle linkage.

 

[gsutton]

Re: 1991 Mercury 200 Too Rich

I will disconnect it and give it a try. Will let you know what happens.

 

[gsutton]

Re: 1991 Mercury 200 Too Rich

Please bear with me, I am learning as I go. I tested the valve per the method in my Clymer manual. This proved the valve to be operational. The test mentioned above seemed a little different as if it tests the thermal air valve. I did find that the hoses were attached backwards on the enrichment valve. I don't know if that makes any difference other than no choke. I really appreciate the help and look forward to more information.

 

[gsutton]

Re: 1991 Mercury 200 Too Rich

dilligaf,<br /><br />Which hose should be disconnected to test the thermal air valve?

 

[dilligafda]

Re: 1991 Mercury 200 Too Rich

The hose between the valve and the carb. This will allow air into the carb and a leaner mixture. <br /><br />Stay in touch!

 

[gsutton]

Re: 1991 Mercury 200 Too Rich

We were unable to locate a thermal air valve and hose. Unless it is just under the flywheel and not connected to the carb. Removing that did not help. The engine has been rebuilt twice and maybe they used different carbs. We removed the plastic air cover and you can see fuel dripping from the middle carb. Also, what spark plugs should we be using? On other posts I saw the thermostat associated with similar problems, any thoughts?

 

[gsutton]

Re: 1991 Mercury 200 Too Rich

Is it possible for a fuel pump to cause the problems?

 

[mellowyellow]

Re: 1991 Mercury 200 Too Rich

re-built twice with NO attention to pump kit?<br />a better guess is air infiltration somewhere in<br />the fuel system.<br />good luck,<br />M.Y.

 

[gsutton]

Re: 1991 Mercury 200 Too Rich

mellowyellow,<br /><br />I am just throwing out ideas, have you read all of the above? Thank you for your help!

 

[Hooty]

Re: 1991 Mercury 200 Too Rich

If you can see fuel dripping from center carburetor, you may need to replace that needle and seat.<br /><br />c/6<br />Hooty

 

[mellowyellow]

Re: 1991 Mercury 200 Too Rich

gsutton, my apologies... I did miss the post re:<br />gas leaking from carb. Hooty has the answer.<br />the float is stuck causing it to flood. sometimes<br />a gentle tap on the side of the bowl will free<br />it up. if it's got crud keeping it from seating<br />properly, may need to R&R the carb.<br />good luck,<br />M.Y.

 

[shelbydriver]

Re: 1991 Mercury 200 Too Rich

the thermal air valve should be on the starboard side of engine hooked into the head I believe. It has two nipples on it and one has a hose plugged into the carbs and one open nipple. there should be a pic in one of the cheap manuals. <br />Tim <br />94 200 merc<br />wheaticat@aol.com