Mercury 40HP 4 Cylinder only starts with throttle, otherwise runs fine.

[Marble_Charlie]

I got this 94 motor along with a pontoon for a couple grand 4 years back. In recent years I have rebuilt the carbs (but not replaced the floats). Replaced all internal fuel lined (not external yet), put in a new water pump and also replaced the entire ignition (trigger, stator, regulator and power pack). I have not done new coils or wired but the plugs are brand new.

It runs great but it always needs a bit of throttle to start. I rented a pontoon with the same motor recently and it ran like a top! I travel a lot for work and sometimes my wife likes to take the kids out on the pontoon (she doesn't like taking our Malibu wakeboat in and out of the lift).

I just cleaned and checked the carbs again last weekend. Should i start with the fuel line and bulb? Rebuild fuel pump? Replace floats? Replace wires?

What would you start with?

 

[RCO]

Do some diagnosis before throwing parts at it. Could be as simple as a minor adjustment. When you say you cleaned the carbs, did you actually disassemble them, or just spray cleaner through them?

 

[racerone]

Checked operation of choke / enricher -----Pushing key in while cranking it over ?

 

[ondarvr]

Most of the things you mentioned won't effect starting much. Check the other things suggested first.

​Also, not all older motors require the same starting method, some tend to start easier using one method compared to another.

 

[Marble_Charlie]

Do some diagnosis before throwing parts at it. Could be as simple as a minor adjustment. When you say you cleaned the carbs, did you actually disassemble them, or just spray cleaner through them?

I completely removed and disassembled them. Soaked in carb cleaner and cleaned with pressurized air. I should probably toss some floats in, but they looked really clean. I did adjust the floats as they were the tiniest bit off. I have new needles in them.

To Racer One: I just double checked, the enricher is working properly, but that's a great piece of advice!

It is actually starting better this weekend. Maybe chalk it up to old gas from storage. I'm trying to run it to fumes and then refill with non ethanol gas.

New issue though and I might start a new thread: I rebuilt the water pump after it exploded last weekend. I now have a weak stream (it was strong for the first few days after rebuild). I am about to do some googling, but if anyone has any quick diagnostics I am waiting for some drizzle to pass before we go out wakesurfing in the other boat. Have a few minutes to troubleshoot.

 

[roscoe]

If the old impeller exploded, you likely have chunks of it in the motor, thermostat, or telltale hose.
Disassemble thermostat and clean, flush with garden hose, run a wire through the telltale.