1983' 200hp merc, idle trouble

Hi all,

I have a 83' 200hp mercury. Starts and runs perfect (for a 2 stroke) when cold. I push the choke and she comes to life, no problem. No meddling with the throttle, no tricks.

After running it WOT for 10-15 min or so it won't idle. If I slow down and put it in neutral it dies. Then to get it started again I have to bring the throttle up 1/4 way or so. When it does start, it sputters and smokes like crazy. Then to get going I have to drop the throttle and throw it in gear before the rpms' drop below 500 or so, and give it some, or it will die again.

I am a bit of a newbie to boating, but am well versed in other
mechanical (disasters) hobbies. I have bought a Seloc Manual for this motor, and have been reading it and on this forum about trouble shooting this motor, pin holes in the fuel pump diaphram, clogged jets, air leaks in gaskets and such. I know it has fresh gas. and I know the spark plugs are new.

Since I have more than once been accused of being a "parts replacer" rather than a good mechanic. I thought I would shoot this post out there and see what comes back before I spend $$$$ replacing perfectly good parts.

On a side note: This is an 87' 21' checkmate with 83' 200hp Mercury. It has a 21" pitch S.S. Prop, and NADA says it weights 2300 lbs. When I floor it, it really dosen't do anything until it hits 2000 rpm, then you'd better be sitting down. Is this normal? Or Should it get up and go from Idle?

Thanks so much in advance for any opinion, advice, or comments.

Re: 83' 200hp merc, idle trouble

How long have you had the boat? Has the idle recently been adjusted? Sounds like you might have the idle set too low.

Re: 83' 200hp merc, idle trouble

I've only had the boat for a month.

If the idle adjustment was off, would it idle perfectly when cold?

I cleaned out the fuel filter on the fuel pump, it had a tablespoon of red gritty stuff, that problably didn't help. I also noticed that the Idle module on top of the air box was disconnected, so I looked up in my Manual the wiring diagram, and reconnected it. Don't know if this will help. I read on a forum that these Idle modules for these engines are useless, and should be disconnected. Is that sound advice?

Runs great in the back yard with the hose hooked up, have to wait until sat to take it to the lake.

Re: 83' 200hp merc, idle trouble

An cold engine requires more gas to idle than a warm one, hence the need to choke on cold startup. But that should only last for a few minutes at most while the engine warms up. If your idle is set too rich, you may be getting too much gas for it to idle when warm. Next time you start it up, do so with the engine cowl off and adjust the idle screws. Start by turning them in until the engine starts to run rough. Then, while taking note of the number or turns, turn them out until it runs rough again. The final setting should be halfway between these two points.

Re: 83' 200hp merc, idle trouble

As it turns out, there are no idle adjustment screws on this motor. It has 3 jets per carb barrel, and 6 carb barrels. (one for each cylinder) They consist of an, idle jet, a air jet, and a high speed jet. You cannot adjust these, you must have the right size jet installed.

I have not taken the carbs apart yet to find out if they are the right sizes. But I could get to the top carb's high speed jet and it is the right size.

Now I have been to the lake, all day yesterday. The Idle module seemed to fix about half the problem, and create some new ones.

When I put it in the water cold and started it, it back fired once every 2 sec or so, for 3 min then died. It never did that again all day.

A couple of times when I started it warm, it came to life and idled perfectly. and couple of times I had the same problem I had before, had to bring the throttle up 1/4 way to get it started, then lots of smoke out of the engine.

Im starting to think this is a fuel problem. Are there any more filters I can clean on this engine? Or anyone with any other suggestions?