View Full Version : 75hp Merc 4 stroke running ROUGH

08-08-2005, 08:27 AM
3 weeks ago on Sacto River, motor runs great- good power, no complaints other than the boat porpoising.
2 weeks ago, go to Tahoe, fuel up at a station with 91 oct. (mom and pop station :-/ )
motor runs fine- little lost power Im assuming from elevation, boat porpoises. (I know theres no relation between the two, but bear with me).
4 days ago- install hydro-troll
3 days ago, on Collins lake- motor fires up fine, but is running really rough, even at WOT and only has about 2/3 power.
With plate down, it still allowed very slow speed, and didnt die- but still ran rough - plate up AND down.
Any suggestions? Fuel Filter? Needs additive? help!!!

08-08-2005, 08:50 AM
I believe that the 75hp is carborated.Check the adjusting screws on the carbs.A friend of mine found a screw backed out on the carb. Brettski

08-08-2005, 10:49 AM
From what you said, I would suspect bad gas.

08-08-2005, 11:08 AM
bad gas is my initial suspicion (my wife will tell you that's a chronic problem, but thats a different story..) ;)
Seriously though- if that is indeed the problems...what do I do with the remaining 18 or so gallons???

08-08-2005, 11:21 AM
For some reason, that same gas runs just fine in just about any other motor you can mention: car, truck, mower. I've siphoned my boat twice over the last few years and run it in my vehicles with no problem. However, before you get that far, try running a bottle of HEET or some other fuel additive. HEET dries water that has gotten into the gas. I'm sure there are others that are multi purpose additives.

08-08-2005, 11:33 AM
HEET, huh Hinrid? Okay- I'll give it a shot.

I'm pretty sure its a fuelie, not carb- (99% sure) I assume that the HEET is not dependent upon either type?
I appreciate the input and suggestions... and if all else fails, I guess that syphoning would be the next step.

08-08-2005, 11:43 AM
Since you are in Elk Grove, drive over to Brothers Marine. Mercury makes some great fuel additives and the shop guys might have one that will not only deal with the water but clean your carb jets at the same time.

08-22-2005, 07:41 AM
Well, I'm not sure if the HEET did any good whatsoever or possibly made the situation worse.
Put the boat in the water Sat Morning @ Garcia bend-
Took 15 minutes for the beast to finally fire up- and ran even more rough than before...and continued to die after 40 or seconds in idle. Rev'ed it up and it did come to life- but still very rough...almost like not enough fuel-?
Drop it in gear, and died. Fire it up, drop it in gear, dies. Pulled the boat right back out of the water.
ran the hose to the motor yesterday, and it fired up a bit easier, but just as rough as the day before. Any other suggestions before I have drag her to the mechanic? Also- any recommendations? Was thinking either Buck's or over to Brother's boats... HELP!!!

08-22-2005, 07:53 AM
Have you looked at your plugs? It's not uncommon to foul up a set of plugs after one trip at high altitude. Running a boat off plane or trolling just makes things worse. So does running high octane fuel at high elevation. While it sounds counter intuitive, lower octane gas works best at high altitude.

Pull the plugs, wipe off any oil or grease, and clean them with a wire brush or an air powered plug cleaner. Re-gap them and carefully blow away any metal filings. If either the center or outside electrodes appear pitted or burned, replace the plugs. Next thing to do is to check the fuel line, connections, and bulb for leaks. Then replace the fuel filter. Do all this before bringing the engine in for carb service.

08-22-2005, 08:00 AM
Thanks Doc- I will follow the Dr's advice!

...he always has the answer.... ;)