4hp Merc bogs on full throttle in gear but not idle???

[Incahiker]

Alright, just got back from the lake. I soaked the carb for 2 days and then cleaned it out again. Cleaned out fuel line, fuel filter, etc.. and put everything back together. Seemed to be going a little faster, but not what I thought it would be.

I know it is not running lean because as when I am at full throttle and pull out the choke (half way or full), the motor dies immediately. So that is not lean, right? When I get to full throttle it takes about 10-15 seconds for the revs to get a little higher then mid point, but I still get that small burst of speed when I go from full throttle to half throttle.

Seems like I am running lean. I took the cap off the gas tank and it did nothing, so that is breathing just fine. What in the world can I do to get it to run more lean at full power? It has a fixed main jet and I played with the slow speed mixture screw and got nothing from that, that is the only adjustable thing in the carb. I also replaced the spark plug.

My boat went a max speed of 6.3 mph according to my garmin GPS. This is with a 1432 jon boat, battery, and trolling motor and me (200 lbs.) Does this sound normal for a 4hp motor? If it is maybe I am just thinking that this motor was more powerful then I hoped it to be and it is doing fine. Does this sound right? The thing is I saw a guy on a 1236 go way faster then mind with him, his wife and his kid on board. Matter of fact here is the video https://www.youtube.com/watch?v=R6evmVCm8tw

And this guy is flying way faster then me on a 2.5 hp https://www.youtube.com/watch?v=_vw6W5nTSiU. ?

 

[Whoopbass]

Sounds like the carb is not your problem. If it was starved for fuel then your RPM's should have picked up when you pulled the choke out. If you want to completely rule out the carb then you can squirt some fuel mix in the carb when your at wot and see if the rpm's pick up.
Have you checked the compression? If it has 75+ pounds of compression then it should run properly. Go buy a can of seafoam and decarb that thing.
Run the motor at night in a barrel and see if you see any arcing from a bad wire. With the motor off and in forward gear twist the throttle and visually inspect the carb and make sure its opening up all the way.
Take a wrench to every bolt and make sure their tight. Don't go over tightening but if there's some that are loose then it should be obvious.
Your outboard should be whining pretty good at full throttle. If the rpm's don't sound around 5K then something is going on.
My outboard linkage was not adjusted properly and at wot it would slow down some and when I turned the throttle back a bit it would pick up rpm's. It wasn't causing power loss but it allowed it to go past the factory setting point and the motor would open up too far and not run properly.
Good luck

 

[Bobg]

Be sure of the float setting in the carb. usually level or very close to level when installed and the body of the carb is held upside down.
Check to see if there's a filter screen at the outlet in the tank, and yes, don't overlook the ignition system.

Fuel metering and ignition system problems give similar reactions.

 

[RBuffordTJ]

Don't ever "soak" an outboard carb overnight, 1 hour maximum, in carb cleaner because they (all manufactureres) have a special coating on them to protect them and seal the metal, it will be stripped completely off by soaking overnight. If you think there may be a problem with something stuck in one of the passages (happens a lot) find a sonic cleaner and have it run in one for a little while, it uses water to clean but does better than carb cleaner.

Have you checked the fuel pump? It will be a small, low pressure pick up pump that runs off positive and negative crankcase pressure, usually getting this from a tube connected to the powerhead. They have a small rubber diaphram in them that can be damaged from sitting over time, and at idle it doesn't have much of a demand, but at high demand could be causing you this problem as it starves for fuel.

Bufford