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1989 8 horse 2 stroke - what am I missing here?

G

galamb

Silver Medal Contributor
This is a little odd since I'm asking for help here. I must be missing something simple. I'm about to start losing my hair which turned white many years ago :)

Here's the history. 1989, 8 horse Merc. I've been looking after it for the past few years so know that it's been reasonably well maintained. Anyhow, owner calls me up said he had been running last years gas and it started idling like crap and stalling. Also seemed to be blowing more smoke than normal.

Tried running fresh gas - no change. He picked up a carb kit and asked me to rebuild the carb. I pull the carb - I looked good. Rebuilt it anyhow since he had the kit and as far as I know it had never been done before. New float and idle valves, everything else soaked/cleaned and blown out with air. New gaskets/seals and rebuilt fuel pump (part of the kit - gasket/diaphram).

Before bolting her back up, replaced the fuel lines from connector to filter and filter to carb (they looked old so why not). Cleaned/inspected the fuel filter - no issues - used new cover seal. Disconnected and cleaned out the bleed lines - no issues there.

Hooked her back up - same problem. Checked spark and compression (100 psi at each hole and lot's of fire) and replaced the plugs (I have case lot's for small Merc's - so again, why not).

Took another look. Noticed some "goop" in the lower cowl on the starboard side. Upon closer inspection found a piece of "gasket".

Ok, problem solved (I thought). Pulled the intake cover and found a blown gasket - missing a big chunk on the lower intake (the half of the pistons I could see with the intake cover off looked good and reaffirmed the 100psi compression). Installed new gasket and tightened everything down.

Fired it up - same thing - chuggs, stalls but starts up easy again - runs choppy if you give it a bit of gas - smoothes out with a little more rpms.

Tried a de-carb with powertune - again no change.

Checked the upper crank seal (was still fresh in my mind from replacing my own about a week ago), made sure the powerhead was torqued down to spec (it was, and no apparent breaches in the gasket).

I have got it running with a shaky idle at the moment (like a wet dog on a cold day). Achieved this by adjusting the throttle linkage to it's max (which is keeping the butterfly open just a hair). There is a perceptible "lag" between when you hit the throttle and when it decides to increase rpms. It kinda bogs for a sec an then takes right off. So I am still thinking something in the fuel system.

I'm down to suspecting 1) problem with the reeds or 2) lower crank seal or 3) blocked exhaust plate (which will be checked if/when the powerhead is pulled to get a look at the lower crank seal). But before I crack either on (which entails a fair bit more work than I have done up until now) was just wondering if I missed something simple.

To recap what was done -
new gas
new plugs
carb/fuel pump rebuilt
new intake cover gasket
compression is good
spark is good
bleed lines were cleaned
fuel filter cleaned/new o-ring
new gas line
engine de-carb'd

Did I miss anything????
 
Yes, could be - figured they would get checked if I have to pull the powerhead. Was just bangin' my head trying to think if there was anything I missed before I pull the powerhead.
 
Tank is ok - used two different tanks and hoses. Also pulled the carb again and then removed the reed cage. Gasket is good, reeds are good - nothing chipped, broken, bent - they are sitting closed within spec and move freely (no sticking).

I have given up on it for tonight - plan on pulling the powerhead tomorrow to get a look at the base gasket, exhaust plate and channels on the bottom of the powerhead. I will post what I find...
 
Finally, problem solved - have her purrin' like a kitten again.

After pulling the powerhead and replacing the base gasket - checking all the channels and exhaust plate in the process, bolted it all back up.

Fired it up, still idling like crap and blowing lot's of smoke. Figured before I started some "fine tuning" with a hammer should just suck back and give it some more thought.

Went back to my bench and started cleaning up the mess of tools, old parts, extra parts from the carb kit (kit does everything from 6 horse to 25 so always an extra gasket or jet or two). As I was "baggin/taggin" for future use I notice a tiny rubber donut, maybe 1/8" in diameter. I looked at it for a moment or two trying to figure what the heck it was - then the light came on - I had forgot to replace the seat in the primer assembly.

I pulled the carb and sure enough the old seat was almost non-existant. That was causing the carb to operate at "beyond full choke" all the time - it's amazing the little motor would even run.

Replaced the seat, bolted the carb back up, hooked up the lines and hoses and she fired right up. Readjusted the idle rpms (which I had advanced severely to keep it running earlier) and she is back to as good as new.

Lesson learned - even though I have rebuilt dozens (maybe hundreds) of these small carbs over the years, never get complacent. Check your work against the manual and make sure the "extra parts" really are extra's :)
 
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