merc 800 hard start, won't idle

[Yachtzee]

I picked up a 1971 merc 800. It had been sitting for a few years. It has excellent compression and a hot blue spark on all four cyl. I have it running but it will not idle.

When I bought it it would not fire at all. new plugs, took off carbs and they were a mess, full of gunk. I pulled them apart and cleaned everything, compressed air, gumout etc. new gaskets and float needles. New fuel pump kit too. I can get it to fire now, though it does not start easily, a lot of choke and cranking. It will stay running if you keep it at very high RPM, (bad to do on muffs I know) but it will not sustain an idle no matter what I try. The idle screws are at 1 and a half turns out. turning them has no effect. If I keep pulsing the choke it will try to keep running. Bulb stays hard. I can not detect any blow back from the carbs. Could this be caused by a leak in crank case? or bad reeds? What would be the most likely cause, maybe bottom crank seal? Or the joint between the two halves?
Is there a good way to diagnose crack case leaks, reeds? The couple of reeds that you can see with the carbs off look like new

I'd appreciate some suggestions! Thanks

On another note, with a fresh waterpump kit the telltale still peeing is at a trickle. There is a plug you can pull out in the water jacket between sparkplug 2 and 3, it has a full stream of water. I assume I need to pull the exhiaust cover and clean?. the darn bolts that hold it on always break off on these old mers for me!

 

[Moody Blue]

Re: merc 800 hard start, won't idle

You're headed in the right direction. Have you performed a full sync and link on the motor? There is an excellent post in the FAQ section describing how to do it. That should help with the idle problem. Ignition timing is critical.

As for the hard starting, that is typical of the old Mercs. They are a bear to start cold but once warmed up they kick over with just a touch of the key. LOTS of fuel and crank away. I have the exact same motor as you.

If you are running on muffs then don't expect more than trickle/dribble at idle from the telltale. You will see a huge difference once the LU is dropped in the water.

 

[Fuzzytbay]

Re: merc 800 hard start, won't idle

If you pulled the carbs, it needs a link and sync. I'd also check the distibutor cap, make sure its clean, and no cracks. Check out the bottom end oil too. No sence not checking it all over, before you get too far into a reconstruction. On the idle issue, they need to warm up for a couple mins at high idle, 1500 rpm or so, before you can get them to idle down.

 

[Yachtzee]

Re: merc 800 hard start, won't idle

Thanks for the fast replies!
Fuzzy, and Moody, I used the "real Close" Link and Sync" method published by clams casino some time ago. I use it on my merc 650s and they run super. they usually fire over inside a couple of seconds.

Hard to do in a test tank (ok its not a tank, it my garbage colletor" big cart on wheels don't tell him!) and really hard to do when you can only run wide open or not at all.) The thing is all over the place.

There is another post open here right now, a guy with maybe a bad trigger that sounds an awful lot like what I am seeing. But not exactly, It will run a bit after I release the key, his does not. After I mess with the thing for a while, it starts to spill fuel from the top carb but not the bottom. If I keep hitting the choke I can kind of keep it running. Some where in its past life it had a bit of a fire I suspect, the boot on the coil connection is charred and the little plastic "drip pan" under carbs is a bit melted. (*Backfire maybe?)
If this was a motorcyle or some other 2 stroke, I'd swear it was carbs, but I was pretty thorough, I even pulled out the little metal disks that cover over the idle circuit and cleaned in there and then replaced them with new.

I am not sure I can bear the thought of pulling the power head off of the thing right now, to look at the bottom crank seal. and maybe cracking the case to look at reeds. Those bottom crank seals are a double seal right?
You wonder how they ever leak? But I know they can and I had one motor suck water in through there.

I have not pulled the distributer cap off yet. I will look in there next just to be sure there are no cracks or carbon tracks etc. Though I do not see spark jumping anywhere. and I have even run it in the dark to look, The wires may be a bit leaky as I have gotten zapped a couple of times when getting my fat hands too close to the plug wires. MY 650s never do that to me and they have older wires thatn this motor. I took one across the chest this AM, Scared the P*** out of me!