1998 3.0l mercuisrer carb adjust help

[brucetech09]

boat was idling a little low this season and would sometimes stall kicking into gear. Sooo I adjusted the idle screw in gear to just under 800rpm and I adjusted fuel mixture screw and it runs very good and starts very easy now. One problem, when in neutral it idles around 1100rpm but once in gear it drops to about 800rpm. Is there a way to adjust it so it stays around 750rpm in gear and neutral? I read it shouldn’t change. Am I risking damage as is?

 

[brucetech09]

Anyone?

 

[TurtleTamer]

It'll change, though a 300+ rpm difference seems high. Make sure the throttle cable is adjusted to have a little pressure against the carb linkage to make up for slack. If there's any slack it can cause it not to return all the way back to closed when you drop the throttle to idle.

 

[brucetech09]

It'll change, though a 300+ rpm difference seems high. Make sure the throttle cable is adjusted to have a little pressure against the carb linkage to make up for slack. If there's any slack it can cause it not to return all the way back to closed when you drop the throttle to idle.

Would I adjust the throttle cable in gear as well? I am not really sure how to do it.

 

[wellcraft-classic210]

If your able to set the carb idle via the idle screw on the carb to the proper range -- usually about 500 WHEN WARM with NO CHOKE. If it returns to 500 RPM when you back off on the throttle then the cable's wold seem to be working as it should.

How smooth does it idle ? Idle fuel mixture ?

I ask as it seems possible this is a tuning issue -- via poor fuel delivery at idle or spark related.

Are you stalling only when going INTO gear ?

If its only when your coming OUT of gear then the shift interrupt ckt would be a possible cause.

 

[brucetech09]

before I adjusted the mixture and idle, in neutral it was 600-650 and would run rough when cold. I would put it in gear and and the RPMs would drop a little more and stall. So I put the boat in gear and adjusted the idle to about 800rpm in gear, i then adjusted the mixture until it ran very smooth (I screwed it in and backed it out until it sounded smooth). When I go back into neutral the rpms go higher. I am using the tach on the dash, so it may not be perfect. I read about preloading a little. I just need someone to explain the the process to me.

 

[brucetech09]

To answer you questions.

How smooth does it idle ? Idle fuel mixture ? very smooth now.

Are you stalling only when going INTO gear ? neutral and in gear when cold. when warm only kicking into gear.

 

[TurtleTamer]

When the engine is warm and you have the idle adjusted smooth and it'll run warm, in gear, at 600-700 rpm (I've never once had my engine run anything resembling right at 500rpm) then go to the back of the carb where the cable links to it and push the plates closed. If they go further and the engine stalls, you're looking at not enough pressure on the cable (slack). This is why I brought it up in my earlier post. If you've got ANY slack in that cable, you can adjust idle all day long and as soon as you go in and out of gear a few times you'll be out of adjustment again. Not uncommon to get idle adjusted to 700-800 warm and in gear only to pop it back to neutral and have it go up to 1000-1100 because the cable didn't push the plates closed. Only sometimes, because it's slack and unpredictable, they DO close, so if you adjust it at all back down from the higher idle, now you go to put it in gear and it stalls.

 

[fishrdan]

Sounds like you're close, and need to make the final adjustment on the water.

- Launch boat and take it for a 2-5 minute run to warm up the engine
- Slow boat and bring engine back to idle, leave it idling "in gear"
- adjust idle speed, then idle mixture, (speed, mixture, speed, mixture, etc) until the engine is idling smoothly, in gear, at it's correct idle RPM (650-700???)

When I adjust the carb on land, I shoot for 750-800 RPM out of gear. With the boat in the water, the load of being in gear and exhaust back pressure will drop the idle RPM 100+-RPM

You don't want the idle at 1000rpm as this is very hard on the drive, when shifting into gear. If you can't get the idle down and into spec, the carb may need to be rebuilt, ethanol likes to clog tiny carb idle passages. I have to rebuild my carb every 3-4 years to keep it idling well.

 

[brucetech09]

Great thanks! I should get a chance to do it this afternoon I will follow up.