Mercury 100 on a 1988 SeaRay Surging, Stalling, Backfiring

danwheeler

Recruit
Joined
Aug 12, 2017
Messages
1
Hello,

​I've got a 1988 SeaRay with a Mercury 100 outboard that has been running great but suddenly developed some problems. We had it out in the morning and it was running great then suddenly started surging and dropping RPMs while on plane. Eventually things went downhill and just wasn't running right.

​The night before included these changes:

​- Filled 2-cycle oil
​- Installed new accelerator pump (had been running great with it removed and the in/out plugged)
​- Filled gas tank

​First thing we did was remove the accelerator pump and go back to bypass since that had been working great. Problem was still there so we put it back in. Today we spent hours learning about this motor and checking spark on each of the plugs trying to get our heads around the rough running. For a while we weren't getting spark on cyl. 1 but that problem disappeared on its own. We spent about 5 hours trying to figure out why we suddenly lost ALL spark only to find out that the kill switch was the cause because we had the motor in a garbage can full of water (no earmuffs) and had raised it to the point where the kill switch was kicking in.

​it's been a long day... We have all 4 plugs wires firing, so we think both stators are good?

​we've got it back to the point where it will idle for a while but does run rough and will eventually die or backfire. We've been using the meter to check resistance on the stator and trigger wires. We are having some trouble finding the right specs and testing procedure for this motor but if we're getting spark to all 4, does it matter? Our red/blue and red/wh/blu/wh resistance measurements seem to be off from the specs we have but we still need to confirm that. Our purple, brown, white and black stator wires read resistance as expected.

​We've taken the flywheel off and learned that there are two stators... one to generator power and one to trigger ignition. Question - if the power stator were bad, could it cause our problem if we have a fully charged battery? Does the ignition system run off battery power or is it powered solely by the stator?

​As we have fuel air and spark, and it does run, my best guesses are fuel pressure, flooding or timing. I've removed the choke solenoid and plugged both ends thinking maybe the choke solenoid is passing fuel through causing flooding... complete wild guess though.

​just learned this motor may be a "2 + 2" system which would explain a lot of the weirdness we didn't understand like removing plug wires have no effect or spraying starting fluid into the carbs having a different effect on the top and bottom carbs.

​Any suggestions are helpful - we're in a jam here as it's our annual family vacation and the kids want to go tubing! :)

thanks,
Dan
 

Canufixit2

Petty Officer 3rd Class
Joined
May 20, 2016
Messages
99
Borrow a separate merc fuel tank and try it out. You may have bad gas / water in the boat tank. I'd verify that first .
 

444

Senior Chief Petty Officer
Joined
Jul 16, 2010
Messages
704
There's two stators, one charges your battery, the other powers the ignition system. Your engine will run just fine with a bad charging stator, just your battery will not be recharged while running and eventually restarting and using the starter will drain it. I drove mine for years like this and just topped up the battery with a battery charger before I took the boat out.

I think your problem is a fuel system issue. I would pull the carbs, clean them, reinstall with new mounting gaskets. Do a proper link and sync, fresh filters and new fuel and try it.
 

flyingscott

Fleet Admiral
Joined
Apr 8, 2014
Messages
7,985
You need to buy a factory manual if you are going to tackle that motor. The 2+2 motors are tricky to set-up and no aftermarket manual will give you any useful information. Did you look at the primer if that leaks through it will cause rough running? The accelerator pump will also cause that issue. Doubtful it would have run good with the accelerator pump disconnected. The accelerator pump is for the bottom 2 cylinders only it helps those cylinders kick in at 1800 rpm.
 
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