loss of power

[scrapeeape]

I have a 1986 bass tracker with a 40hp EL model Mariner 2 stroke twin carburetor motor. The motor starts, idles, runs at low speed with no issues, but when I open it up it boggs down and won't plane out. It also seems to be fouling the top cylinder. I have changed the fuel, plugs, cleaned the fuel lines, filter and pump, checked and cleaned the carburetors also adjusted the fuel mixing jets. Not sure what to do from there. I have been told by a few marine shops it sounds like a carburetor issue and quotes I've been given average 350.00.
Need some advice on what the issue may be, and how to proceed. Also can anyone tell me what the proper plug gap is?

 

[Scott Danforth]

You most likely have to clean the carbs.

 

[CharlieB]

You can't go wrong running a spark plug gap between .032 and .035

Verify cyl compression and spark to make double sure there is no mechanical problem with the motor.

Carb float height is critical to running the correct fuel mixture. A high float will run rich and can cause problems, a low float will run lean and can burn a piston causing very expensive problems.

A leaking needle/seat will also run rich so while checking float height with the carb held upside down, blow into the fuel inlet, it should not pass any air until you move the float with a finger.

Once these are done you still need to verify the fuel pump is pumping adequat fuel for the motor to perform at WOT. A weak fuel pump will not be able to keep the upper carb full and it will misfire, losing power.

Disconnect the fuel h ose to the carb, point it into a suitable container and crank the motor. You should see a strong pulsed fuel stream. a weak stream then order a fuel pump rebuild kit.

 

[scrapeeape]

I checked spark and have weak spark on top plug and good spark on bottom plug .

 

[scrapeeape]

I have already cleaned the carbs. Twice ! Second time was just to be sure. They are in very good condition as far as clean goes.

 

[Mercurylips]

Obviously not fuel and carburation issues causing the weak spark on the top cylinder. Switch the plug wires if you can and see if the wires are both OK.

 

[scrapeeape]

Wires are not long enough to swap them. The problem seems to be more intermittent now after checking and cleaning the connections. Think it maybe the ignition coil #84874M or the switch box.# 84872M . The ignition coil is 189.00 and the switch box is 375.00 ; so my question to is , Anyone know if there is an alternative replacement part that will work for less $$$$ ?