1977 Mercury 50 hp with standard 13 pitch prop

[The Force power]

I'm stumped, boggs down in gear just before half open.
Motor on boat & tied to the dock

link & sync Carbs.
Compression good & even on all 4 (130 psi)
Fires on all four
Revs up in neutral
Idles good in gear

 

[Kronos]

Can it be something that limits the fuel flow before the carbs? Bad hose from tank?... blocked valve/fitting fuel hose to engine? or maybe just old fuel?

 

[The Force power]

Hi Kronos,

I have other motors running on that hose & tank running good, I have checked the fuel delivery; would not hurt to try again.

I've have experience similar scenario with the switch-box not being warmed up doing the same thing.
(around 65 degrees at my location)

anybody else had that as well?

 

[jimmbo]

Dirt in the carbs, incorrect fuel level, restricted fuel line due to internal deterioration are some things that will cause that. So can wires that are broken beneath the insulation and break connection when moved, as may happen when timing is being advanced.
Switchboxes are heat sensitive and can fail when too hot, then work fine when cooled.

BTW there is/was no such thing as a 'Standard Prop' on Mercury engines above 20hp. Every installation is a 'selected' prop by the Rigger, whether it was the correct choice, is often questionable. Your engine needs to run between 4800 - 5500 rpm, Preferably in the upper end of the range, when at WOT

 

[QBhoy]

Just checking but when you say bogs down...you mean it stalls or won’t rev any further ? Maybe stating the obvious...but although my own boat and it’s 300+ HP runs like a champ all the way to over 5000 rpm, put in the water...I can tell you it certainly won’t get anywhere near that, if I was brave enough to try it tied to the dock or on the trailer. Just thought I’d mention..

 

[The Force power]

Thank you Jimmbo,

I will focus on the fuel-system & it's delivery
I'm doing the diagnosing for a remote friend and relaying mine and your input to him
The wire's are good because when running in neutral she does not skip a beat when moving the advance.

what I meant with the switch-box; when they were too cold it would not rev-up in gear but when warm 2 to 4 min. later it would.


To QBHOY,

Yes, I should of said; "stalls" slowly
I would tie a 50 to the dock not a 300 as I would be too worried that the "hardware" is not going to hold. lol

 

[racerone]

Open low speed mixture needles 1/8 turn at a time and test again.------If that does not work , remove lower unit and check exhaust tuner for blockage with strong flash light.

 

[The Force power]

Open low speed mixture needles 1/8 turn at a time and test again.------If that does not work , remove lower unit and check exhaust tuner for blockage with strong flash light.

the fuel mixture screw is currently at 3 turns open lol
we'll try check for blockage in fuel-system and pump check-valves first and report

thank you

 

[Sirrobin53]

Check the stator.
My problems started from PO running with a bad battery. Took out the regulator / rectifier then the stator from over charging. My symptoms were similar to what you are describing.

 

[Sirrobin53]

[No message]

 

[The Force power]

I remember your issue lol. but this has a new Stator and the voltage is good

 

[merc850]

"the fuel mixture screw is currently at 3 turns open lol" it should be 1 - 1/2 turns out; then you set it under load, warmed up & moving in F and accelerate quickly to see if it bogs out; turn the screws 1/8 of aturn out until it accelerates smoothly. A tach will help you select a prop of the right pitch that will allow 4800 - 5500 rpm operation.

 

[The Force power]

This motor apparently does not have the fuel-pump attached to side of the motor, but the fuel-line goes straight to the carbs. from the quick-connect.

how does it pump-up the fuel if not driven by pulsation? I mean; movement of a diaphragm

 

[racerone]

???----Well----It has to have fuel pumps.----So is there a cover on the side of each carburetor that hides the fuel pump diaphragms.----Easy to learn how these things work.

 

[The Force power]

Yes, it has the blue covers were the hoses connect to and I looked at the parts diagram and there's a diaphragm behind the screen(that's behind the blue cover) but what makes it move back & forth to produce a "pumping effect"?

(remember I'm not with the motor, actually working on it/seeing it)

 

[racerone]

Crankcase pulses like any other conventional 2 stroke fuel pump !!

 

[The Force power]

Yup, but from where does it get its pulse from?

I've never worked on a merc. that is that "new" the ones I worked on had the traditional one on the side

 

[racerone]

??----The pulse comes from a hole in the crankcase cover !

 

[The Force power]

??----The pulse comes from a hole in the crankcase cover !

Thank you for your efforts & attention

I know my questions are maybe; self explaining but the reason I keep asking as this is new & not clear to me.
I'm trying to help out a friend and I'm not actually see/touching the motor

Is the pulsation given to the Carbs by a hose connected to them or a port in the block that the Carbs are bolted to?

 

[racerone]

Good luck for you and your friend with this motor.--