MerCruiser 3.0 Runs Poorly As It Warms Up

[twerth]

The power valve itself unscrews from the floor of the bowl you may need to cut a slit in a bigger flat blade. If you took it out and cleaned behind it just make sure the pin that sticks up moves freely.

the actuator in the bowl top is peened in there. No need to remove just make sure it moves freely.

Not sure what ignition set up you have. My 91 had the distributor less igniton which has separate coil packs on starboard back side of engine, and what looks like a sawed off distributor base as the trigger. The more common and more durable Delco Est is likely what you have. YEs on this you need to put in in base mode to set timing which is not hard. If you have a light check to see where timing is without putting it in base mode should be around 12-15 degrees at idle and go up to about 24-26 total at 2800 rpm or so.

Also get a spark gap tester to see how much gap it can jump . this is a quick test for spark strength. should jump 3/8 or more and be a nice blue spark. If weak or orange maybe issue with ignition system. Take a look at spark gap test when it is running good and then when it is missing see if there is a diff

I'm pretty sure I removed the PV and cleaned the passages, but one more time can't hurt. Just for grins, I've ordered a new float (they're relatively cheap). When that gets here I'll check the power valve while I'm installing it.

My ignition is the typical electronic type with single coil and distributor. I've checked spark with a gap tester both in my driveway on the hose and on the lake when it was acting up. I only had ~1/8" gap, but I got similar results both ways. That doesn't appear to be the culprit.

Any thoughts on the potential manifold leak? That's still my prime suspect.

Thanks again!

 

[Scott06]

I'm pretty sure I removed the PV and cleaned the passages, but one more time can't hurt. Just for grins, I've ordered a new float (they're relatively cheap). When that gets here I'll check the power valve while I'm installing it.

My ignition is the typical electronic type with single coil and distributor. I've checked spark with a gap tester both in my driveway on the hose and on the lake when it was acting up. I only had ~1/8" gap, but I got similar results both ways. That doesn't appear to be the culprit.

Any thoughts on the potential manifold leak? That's still my prime suspect.

Thanks again!

1/8 gap is too small to verify good spark should be able to jump like 3/8"

I thought you replaced the manifold gasket but I see you mention it still gets affected by spraying cleaner on surface. If that is the case yes you need to fix it. did you check the manifold and head for warpage, pitting etc anything would would create a vacuum leak ? Is it possible the carb cleaner is getting sucked in under carb base ? where carb is located could be sucking it up there? Just seems odd that manifold would leak after gasket replacement as you seem relatively competent mechanically.

Last time I did a mercarb it came with two base gaskets one two hole and one oval. manifold have oval opening with two hole gasket. So I thought Id be smart and use oval gasket cant explain it but idle mix screw behaved wonky, changed out gasket and responded normally to changes in mix

 

[twerth]

I finally solved this one, so I thought I'd put a bow on it in case someone else has the same problem. I replaced the electronic module and pick-up coil in the distributor and now it runs like a champ. I think it was temperature affecting the module, but hard to tell since I swapped two parts at the same time.

Thanks to everyone for your help.