Mercury 25 hp 1987 engine bogs down at 3/4 to full throttle

[clintb]

my engine seems to run fine up to about 3/4 throttle and then it starts to cut out a little then if you give it all it's got it will just bog down and the rpms go way down. i can't figure it out. if i let off of it to about 3/4 throttle or so it will start funning perfectly again. it can be a little hard to crank after all this too if that helps. any ideas????

 

[war eagle]

Re: Mercury 25 hp 1987 engine bogs down at 3/4 to full throttle

Hello clintb,<br />Have you checked out the carb to see if the float or the seat is sticking,also their might not be enough gas getting to the carb or their is air getting into the line.Make sure all connections are good.Reply back if this isnt the problem and we will help you the best to our knowledge.

 

[shelbydriver]

Re: Mercury 25 hp 1987 engine bogs down at 3/4 to full throttle

I had that problem with a 200 hp. turns out the propeller was too big. went to smaller prop and ran up over 2500 rpms to 5500. It had also always ran good in nuetral or on trailer.

 

[clintb]

Re: Mercury 25 hp 1987 engine bogs down at 3/4 to full throttle

thanks for the replies. as far as the prop is concerned i have no idea if it is right or not. it is a three blade stainless prop by quicksilver. i am not sure if it is too big or not. the thing there is that it is bogging down. as far as the carb i will break it down but i was thinking that if it runs great at 3/4 throttle that everything is open. i inspected the lines and they all look good and nothing seems to be punctured. also, can't figure out how the fuel pump works. i don't see any suction lines going into it like you see on evinrudes and older mercs. i do see a couple lines coming from the side of the engine and terminating under the carb. can someone enlighten me on this? also, i see in the parts list that there is supposed to be an "idle wire" of some sort that i don't have that is supposed to connect to the primer lever. any help would be great. thanks

 

[mellowyellow]

Re: Mercury 25 hp 1987 engine bogs down at 3/4 to full throttle

agree with wareagle. stuck float causing it to flood.<br />pump works on internal crancase pressure and at<br />higher revs it sucks more. if the float ain't <br />working, it will flood and bog down.<br />good luck,<br />M.Y.

 

[clintb]

Re: Mercury 25 hp 1987 engine bogs down at 3/4 to full throttle

thanks guys. i will break the carb down and see what i find. just one thought. if the float were sticking why would it run fine at lower rpms? wouldn't it have trouble through the entire throttle range? i don't know these things so i am just asking. thanks for everything.

 

[mellowyellow]

Re: Mercury 25 hp 1987 engine bogs down at 3/4 to full throttle

as rpm's increase, so does pump pressure and it<br />starts to really suck gas hard, much harder than<br />at low rpms. it is only then that certain fuel<br />problems occur like flooding or sucking air from<br />a cracked fuel hose. sometimes you can tap on the<br />side of the fill bowl (gently) with but-end of screw<br />driver and it will unstick the float, but that is<br />temp fix. if you pump the bulb and it picks up<br />again, the problem is opposite (fuel starvation)

 

[Hank 911]

Re: Mercury 25 hp 1987 engine bogs down at 3/4 to full throttle

Make sure the fuel tank vent is unrestricted. Try loosening the cap.

 

[clintb]

Re: Mercury 25 hp 1987 engine bogs down at 3/4 to full throttle

thanks for all the input guys. i took your advice and cleaned the carb. it now opens up full throttle but i have a little hesitation at maybe half throttle and then as you give it more gas it goes ahead and opens up. should i adjust the linkages to sync the throttle with the timing advance under the flywheel. would that cause the hesitation and slow responce?