86BlackMax Idling Problem

[MarshMan73]

Just got this boat a few weeks ago and have run it 100 miles over the last weekend. Today I put it in the water and it didn't want to start. Finally got it to start and ran out to my fishing ground 10 miles away. Motor ran strong and true until I got there and was trolling around at idle speed then it died. Cranked it back up and was fine again. Choking does not seem to help, but seems to flood out the engine so I think the enrichener is working. Will stay idling in the water in gear as long as you feather the throttle very lightly to get RPM to 1000-1100. Hole shot is great, top end is great only idling. Got it home and would die on the hose sometimes. As soon as it goes below 900 RPM it starts sounding like it's missing and then stalls. Turn the timing adjuster bolt a few degrees retarded and it stayed running, but still can hear the occasional light miss every few seconds. Checked plugs, fuel system and am running SeaFoam in the gas. Going to go get a compression tester and start there tonight. Any ideas?
OK I just checked the compression and I got 105 on all cylinders on slightly warm engine. Cranked it up again and it does seem to smoke more than before at idle. Could too much oil be causing this? I don't remember my old Johnson plugs coming out wet like this even when using SeaFoam in the gas.

 

[j_martin]

Re: 86BlackMax Idling Problem

Check your bleed lines and the check valves associated with them.

Next, look for vacuum leaks at carb and reed plate gaskets.

Next would be carbs. Put in gasket kits, giving you an opportunity to make sure all the little ports are clean and they're adjusted right. If they look too good, then take a look at the reeds before you put the carbs back on.

I'm assuming you have good compression on all cylinders. If so, then carbs, bleed lines, or reeds is about all it could be.

hope it helps
John

 

[MarshMan73]

Re: 86BlackMax Idling Problem

Ok checked my fuel and bleed lines and all look good. I hate to tear my carbs off on this beast. It doesn't look like any fun getting the rear section of the airbox off and whatever electrical devices on the sides of the top 2 carbs. Motor is still wetting the sparkplugs heavily at idle. Bought the Clymer manual for this motor today. They did not have the Seloc one. This manual doesn't explain clearly how to get them off, but it did have an article that describes my symptom. It says a pinhole in my fuel pump diapraghm could cause it to load up on fuel at idle and then run great at higher speeds. Going to check it first, since it is much easier to get too. Other thing I found was the variable oiler system is clearly not set. The alignment mark is on the "leaner" side of the alignment mark. It is smoking heavily. Can you go past the minimum setting and start feeding too much oil at idle?

 

[j_martin]

Re: 86BlackMax Idling Problem

VRO idle setting is critical. Set it dead on to start. If it idles too oily sometimes you have to fudge it up to 1/2 turn on the turnbuckle leaner.

I think you found it. Fuel pump is usually considered an annual maintainance item. Not expensive or difficult.

Front of the motor peels off in layers. Airbox usually has a bunch of electrical junk attached to it. Not related, it's just an easy piece of metal to mount stuff on. Carbs are each held on by 4 studs. Reed plate comes off easily with about a dozen bolts. Torque wrench is critical on reassembling that piece. New gaskets are always needed when you tear into this stuff.

Do yourself a favor and get a Mercury manual. Look it up and mercruiserparts.com in the parts list for your engine.

hope it helps
John

 

[MarshMan73]

Re: 86BlackMax Idling Problem

Ok I pulled the pump and inspected. Could not find any tears or pinholes anywhere. It was the black diapraghm. I put it back together, lined up the oil system marks per the book, synced and linked the carbs, drained the bowls and disconnected the idle stabilizer. Cranked it up and wound up retarding the base timing a little. Engine now cranks and idles fine, however it is running about 1000-1100 on the hose in the yard. I assume this will go down to normal 700-800 in gear in the water. I will bring my entire toolbag when I go out on the water and set the base timing again if necessary. Since this motor doesn't have idle mixture or speed adjustments on the carbs, am I correct that adjusting base timing is how you set idle speed?
Today I came home, did not pump the primer or mash the choke and just bumped the starter. It roared to life at about 1600 RPM and then started to idle down a little. I didn't let it run but about 15 seconds out of respect for the neighbors. Was this high idle because it was probably running lean due to not priming and choking? Really hoping I don't have another motor like my old Johnson 60 that has loose trigger magnets in the flywheel.

 

[MarshMan73]

Re: 86BlackMax Idling Problem

Put the boat in the water today and it started right up. Only died once while putting in gear. Still is smoking pretty heavily and sounds like it's loading up at idle. Runs great over 1100 RPM all day long. Acceleration is smooth and reaches WOT quickly. Plugs are still coming out wet with fuel/oil. Primer bulb gets hard as a rock. Tilting the motor up or down does not effect the idle, tells me my carbs are not flooding. What else can it be?

 

[CharlieB]

Re: 86BlackMax Idling Problem

Most carbs with fixed idle mixtures use idle air bleeds.

Dirty and restricted air bleeds cause a default rich idle.

If the air bleeds are dirty, you have to wonder what else may be getting dirty.

Sorry, but those carbs really need to come off for cleaning. It may be tedious, but, that should cure your fat idling, and who knows, it could save you from a burnt piston if one of the mains is starting to get too dirty.

 

[MarshMan73]

Re: 86BlackMax Idling Problem

Bummer! Didn't want to hear that, but makes sense now with the air bleeds. I guess no amount of SeaFoam is going to clean the air bleeds since only air goes through them. Also will explain how even though I bumped the idle RPM up a bit by turning the base timing back some, it still idles way down in gear. It will go from 1100 at idle to 800 in gear and sound like it wants to die, but usually keeps running on somehow.
When I get the carbs off, where are the idle air bleeds? Where do they pick up air that could have clogged them?