I have a buddy that has a problem with his boat and would like some feedback where he should start looking.

It is a 1999 Mercury Carb motor 200HP and it idles fine. When he goes to get on a plane has a little hesitation through out the planing process but does get on plane. Getting on plane does not do as well as it used to.

At WOT when he used to do 5600 RPM the motor will only do about 4800 RPM with a little miss.

He has not added any extra weight to the boat and used STABIL for the season. He says he has ran about 100 gallons of fresh gas through the boat and still has the same problem. He is using the same prop as well.

This is the only thing he has done. He says it really does not bother him but thinks it could be fixed.

Any help or is this too vague????

Hard ta say. Could be as bad as a clyinder goin' down ta as easy as a bad ground wire. One thing ya need ta think about is tha fact that something is wrong and a possibility of it leading ta something a lot more damaging ta tha motor...........T

check your reeds in all your cylinders.

Do a compression check first thing. Leak down test if ya got tha stuff ta do it with..........

make sure all the plug wires are on GOOD!

pull to plugs to see if one is wet! if it's wet it's not firing. could be a bad plug or a coil.

Thanks for all the info and I will pass it on....

John

The first two places that I would look is #1 fuel pump diaphram, #2 stator, After that ohm the coils for one that is ever so slightly different. Look at the plugs carefully. One will be slightly different, by that I mean, the engine is running fine at lower rpm and everything is happy. At high rpm one cylinder is missing out, not all the time, just occasionally. It will show up as a different color on the spark plug or different carbon deposits on the spark plug. Sometimes a new set of plugs will help but more than likely it's one coil going south. One way to test this is put an inductive timing light one each cylinder, If that cylinder fails to spark "in-the-hole" the timing light will not light up and will intermittingly go dead.

I know my older Merc does this if there is a problem with the hose or bulb between the motor and the gas tank. Even a loose hose clamp will cause it to do exactly the same thing. I can usually tell when that's the problem because the bulb won't stay hard for very long.

My friend did say that he has to pump his bulb every time he goes out. Even if he is using the boat the next day.

I personally have never had to do this with any of my boats. Only after running out of fuel.

He also said that the bulb does get soft and it takes a miracle to get the bulb hard. I will pass this on to him and Mike thanks for the technical help....

John

Somethings your friend may try before reaching to far into his back pocket.
1. Anti-siphon valve. They will harbor debris and/or stick closed. The result of one sticking...fuel restriction. This will make pumping up the bulb difficult, as well as, harder to get on plane and lower rpms at wot with a little miss(could be a cylinder starved for fuel).
2. Primer bulb. Just like the anti-siphon valve the check valve inside the bulb can stick closed and not work correctly. Try holding the bulb vertical with the flow arrow pointing up.
3. Fuel hose from bulb to motor. Mercury fuel hoses have been known to come apart on the inside. I had a mercury fuel hose on a 02 suzuki that started running much like your friends. Turned out to the merc hose...it looked like it was full of plastic....$2.99 for a fuel hose from o'rielly's and it ran like new again.

Don't overlook the small stuff. There may be nothing wrong with the motor at all.