-85 200 2.4 rough idle, stumble, extreme fuel consumption, cold idle

[Roos]

Hi,

I have a Mercury 2.4 200 hp from 1985 which have been giving me a few problems since I got it.
At first it overheated at idle and at WOT.
I have a transom mounted water pickup and when I finally got a larger sice nipple in the lower unit the cooling is much better.
Haven't been doind a lot of WOT runs with it since but it seems much better than it was before even if the temp gauge still creeps upward to 185-190 (though I have reason to believe it shows a little high).

I have then swapped to solid mounts and I have noticed a very small dribble / water leak from one of the mounts, just in case it might be related.
I have also cleaned out the carbs and installed new head-gaskets (mostly since I was looking for debris in cooling system).

As it is right now the motor is quite hard to get started and then idles really rough. It needs probably around 1200 rpm to stay running.
When idling like this the motor can go several minutes without reaching more than about 130 degrees temp. So it idles really cold and the thermostats won't open.
Could the low temp issue be caused by the small leak by the top motor mounts? Or should I suspect my poppet to be stuck open?
Could it be the cause for rough idle or be caused by rough idle?

When putting it in gear it is hard to get the motor not to stumble and die. Same thing goes for throttling up. Once on plane and above about 2500 rpm the engine seem to works just fine.

When pulling the heads I noticed that the engine seemed to have digested something sometime during its life span. In the top port cylinder there was a couple of small marks on the piston. Though compression is even throughout all cylinders. 125 psi +/- 5 psi.
Could there be a chipped reed and would that explain my issues?

Also when running the boat this year we have noticed an extreme fuel consumption.
The boat is a 17ft sports boat easily managing 70 mph and even though we are not really sure how many miles we traveled we used up around 20 gallons on what we think is 20 miles. Meaning 1 mpg. Could be 30 miles and 1.5 mpg but not anymore than that.
I did however find a small crack in one of the oil-mixing lines where it connected to one of the carbs (oil mixing has been removed) and it seemed to have been spraying or seeping a bit of fuel out that way. Thought I might mention it anyways since I guess it could be relevant to the rough idle if the engine is beeing flooded or something?

Thanks,
Mike

[XstreamVking]

Carbs, clean em. Replace needles and seats. Seems to be flooding out. Reeds are also a possible suspect.

[Markus]

Carbs, clean em. Replace needles and seats. Seems to be flooding out. Reeds are also a possible suspect.

Agree.

Also, have you checked idle timing?

[Roos]

Hi Markus! Long time!
Haven't had much time for the hydrolift this year.
Though I have at least tried it but didn't drive much as it was 1) nearly impossible to use since it stumbled on us all the time and 2) it ate the entire 20-ish gallon tank and my brother had to be towed back. =)

I haven't checked idle timing. How would I do that?

Thanks,
Mike

[Go Time]

Check to make sure your pulse pump doesn't have a diapharm leaking into the intake. Also check all your bleed lines.

[Roos]

After a quick google on bleed lines I realized it was one of these lines that were previously leaking. That may explain (at least) some of the bad fuel economy.
Though we drove the boat after this fix and still had the rough idle and stumble.

Thanks!

[Go Time]

Could also be the low side of the stator.

[Dutch]

Are you sure you didnt put the top mounts in backwards? It can be done easily and will cause it to leak very little

[Roos]

One of the floats in the bottom carb was full of fuel.
Carb no WH-40-3.

Does anyone know the Partno of the float?

Mike

[XstreamVking]

Boats.net has a good parts breakdown.

[Roos]

Thanks,

I think I need a 1395-9267 float. Sure looks like mine, or rather I have 1395-7623 which have been replaced.
Any ideas of who could have them in stock that wouldn't charge a fortune to ship them to me in Gothenburg, Sweden.I found them online at a parts store (Mallory part) but they charged 55 bucks for shipping.

Thanks,
Mike

[Roos]

I finally found one at iboats where the shipping werent to extreme, still more than the part itself but they had it in stock, only 1 in stock though! =)

Thanks,
Mike