3.0L rough idle issues

[havoc_squad]

Re: 3.0L rough idle issues

Well, go figure the carb is still a boat load of fail. After two lake tests after the carb rebuild professionally done. First test run getting the idle mixture dead on personally (me) on the water adjusting it under load at 600 rpm's per service manual procedure.

If the air mixture is correct, the boat idles just FINE. None of these symptoms I've investigated point to any other factor than flooding of the intake manifold.

Bone cold start is "slightly" easier than warm, but not a whole lot.

The carb instead now is flooding the intake after shutoff. Why I mention this, almost every time to get it started, I have to open the throttle full for about 7 seconds before it catches. Every once in a while, I get fortunate and it doesn't take much.

Then when I pull it back after it catches and gets the engine going, it wants to sufficate like someone with an Asthma attack when I pull it back to idle.

Exact symptoms:

Takes WAY too much throttle to get it started, hot or cold
Has a tendancy to kill itself in idle after near or at operating temperature after a long run or extended idling.
After shutdown, and a quick restart, it takes full throttle to coax it to start. (Flooding behavior)


Is there any good companies for a high quality remanufacturered Mercarb for the 1991-1993 Mercruiser 3.0L 2bbl carb? Preferrably with a real waranty worth more than the paper its printed on.

 

[fishrdan]

Re: 3.0L rough idle issues

Replaced fuel pump, ......... runs however idles badly on muffs.

Are you sure the fuel pump is good, not putting out too much fuel pressure and leaking past the carb's needle and seat? This has come up several times with others and some of the new fuel pumps put out too much pressure. It should be something like 4-7PSI, anything more and it will flood the carb.

I'd jerry rig a fuel pressure gauge between the pump and carb for testing. (Don't cut the hard line.)

 

[ENSIGN]

Re: 3.0L rough idle issues

While the engine is running spray some carb cleaner along the manifold where it meets the engine block.This gasket sometimes leaks and will lean out the fuel mixture causing a rough idle.

 

[havoc_squad]

Re: 3.0L rough idle issues

Verified with the engine cold using generic WD-40 spray "safely" that there is no leaks near the carb base or manifold gasket area. I had it idling at 800 rpm on muffs, then begin spraying. I was liberal enough with the spray that it should have sped up or stumbled if it was leaking.

My tach did not act up when testing today. However I have seen it act up at intermittent times. This makes me concerned about the coil acting up when warm.

Plugs were proper model and size set (NGK's), installed properly during last March with standard gap of 0.035 per service manual.

Any way to verify either a lean or rich condition when I have to open the throttle all the way to get it to start?

Any way to specifically test the those mercruiser EST coil modules? I tested with an Ohmmeter to see if I could get any readings from it, I got a lot of nothing. (I made sure all leads were unplugged when testing the coil).