1999 225 hp Mercury won't rev up

[Loch Baird]

I have a 1999 225 hp Mercury, carbureted outboard that frequently won't rev up under load. Starting from idle when I hit the throttle to max, it will get up to ~ 1500 RPM and just bogs out. This also happens sometimes when I ease the throttle up. I can't tell if the carbs are loaded up or if there is some kind of spark advance that is not functioning. This happens more frequently if the engine was at idle for a longer period of time. If I kick it out of gear and rev it up, it works fine, but I get some blue smoke (not sure if this is normal). I need to do this to "clear it out", then put it back in gear and it will come up to speed under load. Sometimes I need to do this 2 or 3 times until it will work. I have had it to the shop 2 times now with no success. The last time they adjusted the throttle position sensor and now it idles a little higher than before (~1100 rpm - was ~ 900 rpm). Any suggestions?

 

[Bugsy's Baits]

Re: 1999 225 hp Mercury won't rev up

are you sure there is tps on a carb motor?????

 

[CharlieB]

Re: 1999 225 hp Mercury won't rev up

Possibly the spark plugs are loading up from either age, incorrect plug for the motor, excessive oiling adjustment at idle.

You didn't mention when you last changed your spark plugs, age, fuel/oil deposits on the plugs ground out the spark while under load, yet rev quite freely in Neutral, reving tends to 'clear out' the plugs and may be successful for a time but can be dangerous as 2-strokes WILL rev extremely quickly and it is very easy to OVER-REV a motor and cause extensive damage, like a connecting rod thrown out through the side of the block!

Take a close look at your spark plugs, see if the porcelain area between the electrodes has a carbon accumulation built up on it, if so, install a new set of plugs and retest.

Also check the oil pump linkage to be sure that the alignment marks are adjusted as spelled out in the service manual. Excessive oil at idle may contribute to premature spark plug failure.

Lastly, always carry a spare set of plugs on your boat.

 

[Loch Baird]

Re: 1999 225 hp Mercury won't rev up

Thanks for the reply but the plugs are brand new. We looked up the correct ones to be sure. Yes I understand and am quite cautious about reving in neutral. Not sure how to check the oil injection settings. Any suggestions?

 

[Loch Baird]

Re: 1999 225 hp Mercury won't rev up

Yes there is a TPS on the top carb starboard side. I can actually see the screw marks indicating where it was prior to the adjustment.

Thanks for the reply but the plugs are brand new. When I bought them we looked up the correct ones to be sure. Yes, I understand and am quite cautious about reving in neutral. Not sure how to check the oil injection settings. Any suggestions?