1993 mercury 9.9 power loss after warm up

[dukchunter]

Hey guys,

I have a 1993-94 mercury 9.9 2 stroke that has been having issues for a long time. Took it to 2 different Mech. to get it looked at and see why it had a lack of power. For starts, the motor starts first second pull, idles fine without choke.

The mech did tuneups, replaced fuel lines, etc. The one said the exhaust was blocked and a ran a drill bit through it and opened it up.

well none of these things helped much so I tore into it. I tore everything down and cleaned it thoroughly(carb and everything fuel related). I took the exhaust tube out and found that it was blocked at least 80% so I cleaned that all up and reassembled every thing, put it in a barrel and started on second pull, idled fine rev'd up better than ever.

I through it on the boat and headed to the water to test it out. once on the water it ran like brand new, planed the boat out with 2 guys in it which it never did before. after running around with it for about 10 minutes the motor began to surge... eventually got to the point that it wouldnt plane the boat at all. if i would stop and let the motor idle for a few seconds and try to go to WOT again it would go to full throttle then die to almost an idle then surge. i tried running it with the choke on and pumping the primer bulb and neither helped..

It is running on both cylinders and has spark to both, carb has been cleaned thoroughly.

Needless to say i am now stumped... the only thing i can say i saw that may affect anything is a little bit of rust on the lower reeds in the intake.

Any input would be appreciated

 

[Star]

Re: 1993 mercury 9.9 power loss after warm up

Sure sounds like fuel pump or feed issue to me try pumping the primer bulb when it starts to die.

 

[oldman570]

Re: 1993 mercury 9.9 power loss after warm up

Have you rebuilt the fuel pump? the ethenol in the gas today is bad on the older rubber hoses and anything rubber. the diafram in the pump could be the trouble because of the ethenol. It will pump enought to idle the motor but not enough to run faster and cause the surging. The buildup in the exhaust tube is a sign that the motor is not running correctly and is not getting hot enought, or your doing alot of idleing and could be fouling out the plugs.

 

[dukchunter]

Re: 1993 mercury 9.9 power loss after warm up

Have you rebuilt the fuel pump? the ethenol in the gas today is bad on the older rubber hoses and anything rubber. the diafram in the pump could be the trouble because of the ethenol. It will pump enought to idle the motor but not enough to run faster and cause the surging. The buildup in the exhaust tube is a sign that the motor is not running correctly and is not getting hot enought, or your doing alot of idleing and could be fouling out the plugs.

No I have not tried that and will asap. Of course I'm not totally sure where its located on this motor. Pumping the primer bulb has no affect but pulling the choke out at wot helped for a few seconds... The exhaust has been clogged for some time I bought The motor used and it has ran like crap ever since. It had a hole the size of a small drill bit from the mechanic that did it but still was blocked. I'm sure using it with all these issues has not helped it at all but I really didn't have any other choice. And I never idle for long periods. It is usually started and then ran at wot or whatever is the fasest speed for it which used to be like 1/4 power ate wot.

 

[dukchunter]

Re: 1993 mercury 9.9 power loss after warm up

No I have not tried that and will asap. Of course I'm not totally sure where its located on this motor. Pumping the primer bulb has no affect but pulling the choke out at wot helped for a few seconds... The exhaust has been clogged for some time I bought The motor used and it has ran like crap ever since. It had a hole the size of a small drill bit from the mechanic that did it but still was blocked. I'm sure using it with all these issues has not helped it at all but I really didn't have any other choice. And I never idle for long periods. It is usually started and then ran at wot or whatever is the fasest speed for it which used to be like 1/4 power ate wot.

Well i tore into it again today and found the float was sticking. I managed to resolve that and moved on to the fuel pump. after tearing it apart I found that it had been rebuilt to some degree so i called the mech. that i took it to last and he said he did it when the carb was done. So i guess that rules that out. I took it out on the water again and it did the exact same thing as last time but this time i pumped the primer bulb as hard as i could and it made it better for a few seconds then began to die and surge. i took the cover off and on the side of the carb is a blue button thing ( what it is i do not know) i decided to push that button repeatedly for about a minute while at wot. the motor ran better than ever the whole time during and after i pushed that button. I even shut the motor off and started again, ran to wot back to an idle multiple times and it never surged or died again. ran around at wot for about and hour and ran perfect... could the carb have been air locked somehow?

 

[Mi duckdown]

Re: 1993 mercury 9.9 power loss after warm up

That blue button you were pushing is the enricher/ choke. ask the mech if rebuilt that. Never seen a carb air locked, or even if it possible.?? .02

 

[dukchunter]

Re: 1993 mercury 9.9 power loss after warm up

That blue button you were pushing is the enricher/ choke. ask the mech if rebuilt that. Never seen a carb air locked, or even if it possible.?? .02

Yep it was rebuilt too he said he did everything that was attached to the carb assembly.. I don't understand it but the motor is still running better then ever....