1996 Merc 90HP Losing Power

[chrisczub]

I am new to the boating scene so hope this doesn't sound stupid. Took my boat out for the first time. Starts great and goes into gear with no problems. When I go to open her up to full throttle she runs for about 15 seconds then loses poser. I've replaced all 3 plugs and new fuel filter. If I back off the throttle 10 seconds or so then throttle her back up she'll do the same thing. I just replaced the primer bulb but haven't had a chance to see if that was the problem. What else should I be looking for? Possibly the fuel pump? I'll probally be taking it in to the marina if I can't get her working right and she could probally use her carbs beieng adjusted to the correct mixture too.

 

[WillyBWright]

Re: 1996 Merc 90HP Losing Power

Welocme to iboats <br /><br />Your fuel pump sounds suspect. Rebuild kits are cheap. If you have portable tanks, make sure the vent screw is open. Also, make sure it's pumping water and that the gearlube is full.

 

[chrisczub]

Re: 1996 Merc 90HP Losing Power

Thanks for the reply... Replaced all fluids before launching her this past weekend (lower unit, oil tank and all new gas). Vent was open. To be it seems like she's "starving" for fuel. Should I also try rebuilding the carbs?

 

[andy6374]

Re: 1996 Merc 90HP Losing Power

Well cleaning the carbs is always good if the engine has sat up for awhile. But, I would go ahead and make sure it isn't the fuel pump. While @ WOT, have someone else pump the primer bulb. If these keeps the engine at WOT then it is your fuel pump to blame and it needs to be rebuilt. A rebuild kit very cheap and the task easy to do yourself.<br /><br />-andy

 

[chrisczub]

Re: 1996 Merc 90HP Losing Power

Bump... Ok.. went ahead and did a rebuild on the fuel pump checked compression(125 on all 3 cylinders) and has good spark on all 3 as well. Got my idle down to where it should. Doesn't sound like she is running right. Should I just bite the bullet now and check the carbs?? That's the only thing I could think of beofre I have to start really tearing her apart and check for an internal problem. Starts on one turn of the key and will hold idle but sounds a little rough.

 

[andy6374]

Re: 1996 Merc 90HP Losing Power

Do a carb cleaning. Take the carbs off the engine, disassemble the carbs, soak them in the carb cleaner you can buy by the gallon (Napa carries some), dry and blow out every litte orfice with compressed air, then reassemble with brand new gaskets and you should be good to go. <br /><br />And...when you take the carbs apart, more than likely they will look clean but don't decieve yourself. Pop them in the carb cleaner and what the black gum pour out.<br /><br />It's a quick job and if it is your first time, from the time you take them off till the time you have them back on the engine should be no more than 4 hours (Most of the time (first time) spent being careful and weary when taking off the engine and disassembling, take pictures if necessary)<br /><br />-andy

 

[chrisczub]

Re: 1996 Merc 90HP Losing Power

Thanks Andy... With the carbs off should i be looking for anything else on the powerhead before I put them back on?? Been reading alot online and saw some stuff about the reed valves. Looking in the Seloc book it says I should be able to see them with the carbs off. What should I be looking for if anything.

 

[chrisczub]

Re: 1996 Merc 90HP Losing Power

Pulled the carbs yeterday. Top carb had a bunch of junk in it, bottom carb had a little junk in it, but the middle carb was shot. The needle is siezed and won't come out!! Lots of corrosion too! Have a new carb on order. Took a look inside the powerhead past the carbs and everything liiks good. No corrosion. Hopefully this will fix my problem.

 

[andy6374]

Re: 1996 Merc 90HP Losing Power

Check the condtion of the cylinder(s) that the middle carb was feeding. If it wasn't getting any fuel/oil it could have seized as well. Do a compression check. Take out the spark plug and with a flashlight do a visual inspection to see if there is any scoring to the piston or cylinder walls.<br /><br />-andy

 

[chrisczub]

Re: 1996 Merc 90HP Losing Power

All 3 cylinders are 125psi.. Already did that. No scoring in any of the cylinders. It was getting fuel/oil but not enough.