Help troubleshooting 1989 Maxum engine. Barely running...

Summary:
Boat trouble after head gasket replacement. It runs, but quickly revs too high and then dies when trying to pull back the throttle.
1989 Maxum I/O with 3.0L Mercruiser GMC engine.

Full Story:
Owned for 13 years. Ran well until I let it set for the last 2 years (with Seafoam in the gas) because life got busy.
New Battery. New Starter. New ignitor coil. Got it running briefly on the lake, but wanting to die. Tweaked idle adjustment. Would run well on earmuffs. Got to the lake. Runs, but instantly dies as soon as I engage the motor (put under load). Replaced plugs and wires. Had hell of a time starting. Burnt through new starter and battery. Replaced both AGAIN! Drained old gas (yes I feel stupid for waiting this long) and replaced with fresh gas and seafoam. Can't get it running. Replaced carburetor. Can't get it running. Checked compression and found cylinders 2 & 3 were very low. Pulled the head off and found gasket was clearly blown between cylinders 2 & 3. Replaced head gasket and valve cover gasket. No other gaskets needed because exhaust and thermostat were removed WITH the head. Upon first attempt, it fired up nicely, but quickly rev'd too loud. I backed it off and it died. At this point, it's tough to get it fired up, but when it does it revs too high and dies when I back it off.

It really feels like something easy an amateur mechanic, like myself would have missed, like cable adjustments, plugs wired incorrectly, etc... Please give me ideas of what to check.



Note: When pulling the head, I didn't move the crankshaft. I also didn't unbolt or adjust the valve rockers because I was able to loosen the head and then pull out the rods. I kept them in order and replaced them the same way the were removed.

This has taken me about 2 months to work through all this. I was ready bite the bullet and take it to a mechanic, but all local guys are booked out for at least 4 weeks. PLEASE help me diagnoses so I can get back on the water!

Firing order 1,3,4,2 clockwise
What value did you torque the bolts to and in how many steps?
loosen a remove all pushrods, Install 2 in the first posiion. rotate motor until a intake rocker opens and closes, adjust those 2 pushrods, for no vert movement then tighten an additional 1/2 to 3/4 turn
then do the next position the same way.and so on.

Sounds like you might have a vacuum leak. I suggest you pull the exhaust manifold off and take a look. Easy to mess that gasket up.

Jeff

Bt Doctur said:

Firing order 1,3,4,2 clockwise
What value did you torque the bolts to and in how many steps?
loosen a remove all pushrods, Install 2 in the first posiion. rotate motor until a intake rocker opens and closes, adjust those 2 pushrods, for no vert movement then tighten an additional 1/2 to 3/4 turn
then do the next position the same way.and so on.

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Thank you for your feedback!
-I double-checked and I have the firing order correct.
-I torqued to 90ft-lbs in the correct pattern and performed many steps jumping up approx. 20ft-lbs per step.
-I'm not quite sure about adjusting the push-rods. This part is new to me. I think I'll need to Google this a bit more before I'm comfortable with this. If they were off, it wouldn't run at all, right?

fastjeff said:

Sounds like you might have a vacuum leak. I suggest you pull the exhaust manifold off and take a look. Easy to mess that gasket up.
Jeff

Click to expand...

Vacuum Leak on exhaust side...? I think you're stretching my mechanical knowledge here a bit. Please note that I did not remove the exhaust when I did the head gasket. I left it attached to the head.

Played with it more today. Tried to tweak the idle adjustments on the carb. No improvement.
I did notice that after it shuts off, the carb will drip fuel through the two circles for about a minute. Is this normal?

My best (uneducated) guess is that the boat is acting like it's flooded. Revs too hard at first, won't idle, and then very hard to start after this. I left it sit WOT for 5-10 minutes and I can get it fired up again (briefly).

ignisuti said:

I did notice that after it shuts off, the carb will drip fuel through the two circles for about a minute. Is this normal?

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Been reading a TON online and think I may be on to something. All replacement fuel pumps are all sold with multiple gaskets. I read in many forums that you need a thicker gasket (or even a spacer) in order to provide distance to the striking lobe to reduce fuel pressure. I know I had my fuel pump off awhile back and am wondering now if maybe I installed it without the spacer.

Can you guys educate me here? Is this spacer a known/common thing that IS for sure needed? If so, I'd bet money this is the last item keeping me from running right.

IDK about the spacer thing but I do know that tweaking the idle adjustment does nothing for your acceleration issue. If anything it would seem that you have fuel starvation problem. Could be anything in the fuel delivery system so very difficult to troubleshoot from this keyboard.

a spacer adjusts pressure...and I can offer you a helluva deal on some swamp - I mean prime real estate in Georgia...

Seriously, check the fuel pressure to see what it delivers...and no, the carb shouldn't 'drip' fuel when shut off...

I'd also suggest pulling the dipstick and get a whiff - if it smells of any gasoline, it needs to be changed immediately...

Did you ever determine the cause of the original head gasket failure?

what did you 'replace' the carb with?

makomark said:

a spacer adjusts pressure...and I can offer you a helluva deal on some swamp - I mean prime real estate in Georgia...

Seriously, check the fuel pressure to see what it delivers...and no, the carb shouldn't 'drip' fuel when shut off...

I'd also suggest pulling the dipstick and get a whiff - if it smells of any gasoline, it needs to be changed immediately...

Did you ever determine the cause of the original head gasket failure?

what did you 'replace' the carb with?

Click to expand...

Carb was replaced with identical unit from a rebuilt shop. I sent my original in as a core once I was done.
Not sure of the gasket failure. I figured once I have it running I'll keep a close eye on the temp gauge to see if it's overheating. I had the tail dug into mud right before this. So, wondering if I gummed up the water intake with mud and just didn't notice it overheat...

Update...
Replaced carburetor again and also fuel pump just to be certain.

Note: New fuel pump was the exact part recommended according to my engine serial number. However, I noticed the level was slightly different.

Still having trouble. I checked my spark and noticed no spark on cylinder #3. I traced this down to the distributor and replaced Cap and all electrical components under the cap.

NOW IT RUNS!!! SORT of....

It fires with ease and idles better than it ever has in the 10 years I've owned it. Appears to run great on the ear-muffs. I got it to the lake and I can get to full throttle. The engine bogs down. Everything I've read suggests fuel starvation, but I can smell fuel... which makes me think it's too rich... Is that even possible with this carb setup?
Plugs are brand new (again).

I would suspect timing issue, but I don't believe I've changed anything relating to that...

Any further thoughts to help me troubleshoot?