Merc 75 HP will only run at High Idle

[Slickcraft]

I put in an entry last night about a mercury 75 that won't start. <br />Serial #6503194<br />Model #1075524<br />year 84ish<br />well it started and will run but at high idle only. anytime I pull the throttle back it stalls. I have tried adjusting the idle mixture screww with only a little success. The manual says bring it back to 1&1/2 turns to start at idol but it won't start at Idol only with full throttle. I let it run for a while (20 min) hoping it would help it out in some way but when I pulled idle back it stalled again. Any Ideas. I have continued to adjust idol screws going CCW and that hasd helped but I still can't start engine in Idol or bring back to idol do I keep going richer.<br /> <br />ANy help is appreciated<br /><br />Slickcraft

 

[Elmer Fudge]

Re: Merc 75 HP will only run at High Idle

Could be it's time for the carbs to be rebuilt.

 

[kev_79]

Re: Merc 75 HP will only run at High Idle

Have you checked the timing?

 

[Slickcraft]

Re: Merc 75 HP will only run at High Idle

How do I check the timing and what is invovled in rebuilding carbs. I have taken them apart cleaned them and replaced needle and seat as well as the gaskets anything else.

 

[Elmer Fudge]

Re: Merc 75 HP will only run at High Idle

what's the condition of the plugs? do a compression test and post the results.

 

[Slickcraft]

Re: Merc 75 HP will only run at High Idle

Originally posted by Elmer Fudge:<br /> what's the condition of the plugs? do a compression test and post the results.

How do I do a compression test? and the plug seem to be in good shape fairly clean and good spark.

 

[Elmer Fudge]

Re: Merc 75 HP will only run at High Idle

remove the sparkplugs and ground the sparkplug wires to the motor, then screw on a compression guage in the top plug hole.<br />crank the motor for about 4 to 5 turn overs and write down the highest number reading.<br />Do this to all the other cylinders.<br />If a cylinder reads less than 15 psi of the highest number retained, try using some seafoam or quicksilver power tune to clean out any carbon buildup .

 

[Slickcraft]

Re: Merc 75 HP will only run at High Idle

IS quiksilver power tune or seafoam just a good idea anyway?... what is it and where does it go?also what is involved in cleaning carbs?... I have everything apart including fuel pump I was going to order a new diaphram should I consider ordering anything else...

 

[Slickcraft]

Re: Merc 75 HP will only run at High Idle

Ya know I would really love to get his boat in the water before the summer is up. Does anybody else expeirence the money pit of owning a boat or is it just me...

 

[Elmer Fudge]

Re: Merc 75 HP will only run at High Idle

Go to the FAQ section of this forum and click on decarb. If you have'nt a service manual for your motor, you can obtain one at the bottom left of the page. you'll need it to proceed