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8hp 2 stroke choke knob removal

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flamecensor

Member
The .pdf manual I bought indicates that my engine has a Walbro WM carburetor, and the first steps in removal are
"1- Using a pair of pliers, remove the Circlip
securing the choke knob in place.
2. Remove the choke knob by pulling it straight out.
Unsnap the idle wire from the primer bracket. Remove the two bolts..."
Removing the circlip was easy, but pulling the choke knob 'straight out' didn't work.
Do I need to remove something else? Thanks for your advice.
 
Sounds like your manual is missing a step or two.

Bear with me a minute here, this is one of the things that's easy to show you but difficult to explain.

"Normally" when you pull out the choke knob it operates the primer arm (that little finger on the left hand side) to give the carb a shot of gas.

Directly in front of that arm (finger) there is a retaining screw (going into your choke knob assembly).

You need to back that screw out - not quite all the way - you can leave it barely started in the threads, but back it out.

Then, use your own finger to push that primer arm down and with the circlip removed use your free hand to pull the knob straight out.

If it hangs up when you have it most of the way out, give it a twist (try both directions until it comes out a little further). There is a kinda track or channel cut into the rear barrel of that knob and it can hang up. Don't reef on it super hard, but a good tug will usually persuade it to come out if it does hang up.
 
galamb said:
Sounds like your manual is missing a step or two.

Bear with me a minute here, this is one of the things that's easy to show you but difficult to explain.

"Normally" when you pull out the choke knob it operates the primer arm (that little finger on the left hand side) to give the carb a shot of gas.

Directly in front of that arm (finger) there is a retaining screw (going into your choke knob assembly).

You need to back that screw out - not quite all the way - you can leave it barely started in the threads, but back it out.

Then, use your own finger to push that primer arm down and with the circlip removed use your free hand to pull the knob straight out.

If it hangs up when you have it most of the way out, give it a twist (try both directions until it comes out a little further). There is a kinda track or channel cut into the rear barrel of that knob and it can hang up. Don't reef on it super hard, but a good tug will usually persuade it to come out if it does hang up.
Click to expand...

Thanks very much for your excellent instructions, which worked perfectly.
Last night, I should have seen that the screw was stopping removal, but pressing down on the 'primer lever' certainly was necessary also.
http://superfly.co.nz/Mercury8hp/choke_set.jpg
With better light(a Cree bulb torch) this morning I could see what the manual meant by unsnap the idle wire, and I'll remove the carburetor next.
 
The 8 hp Mercury finally ran OK yesterday, when the carburetor was re-attached for the 3rd time.
Removing the slow idle screw and spring, and rinsing screw and threaded hole with fuel may have helped.
The engine started with the screw open 2 1/2 turns, ran very roughly until it was tightened to 1 1/2 turns, which is where I've left it for now.
The manual specifies a 25.4 mm distance the retainer's bottom edge and the float's upper surface, with the float and float chamber held upside down, and 25.4 mm looked true.
The ~3 mm brass tube inside the ~6 mm brass tube, above the high speed jet, was not truely centered, but was leaning to one edge. I pushed the small tube slightly away from the edge, if that makes any difference.
The top of the carburetor has 'WMC', so I'm sure it's a Walbro model.
 
The correct idle setting is NOT 1 1/2 turns: it's where the motor idles best, plus a 1/4 turn or so CCW.

This setting needs to be found after the motor is fully warmed up and in gear. If not in a barrel, the boat needs to be on the trailer or tied to a dock so its motion doesn't trick you.

Jeff
 
fastjeff said:
The correct idle setting is NOT 1 1/2 turns: it's where the motor idles best, plus a 1/4 turn or so CCW.

This setting needs to be found after the motor is fully warmed up and in gear. If not in a barrel, the boat needs to be on the trailer or tied to a dock so its motion doesn't trick you.

Jeff
Click to expand...

Thanks, and the motor was in a barrel yesterday.
Gears weren't engaged, but it ran for minutes, and loosening the brass screw to 2 turns open really caused the engine to shake.
Before removing the brass screw yesterday, the engine would run briefly only if I sprayed fuel against the butterfly.
 
That's kinda the procedure - piddle around with it. Every carb is going to be a little different.

Generally, you run the motor, in gear, at idle speed, with the choke knob turned fully clockwise (fast idle) back the screw out until it runs like crap (but stays running, and note how many turns out you are), then turn it in until you get the same results.

Then turn the screw to the halfway point between the two (limits) that you noted. If it's running fine, at fast idle, in gear, at that point, then as Jeff notes, turn it a further 1/4 turn counter clockwise and call it good.

When you are finding the limits adjust slowly, 1/4 turn at a time, and give the motor a few seconds to adjust to the change (could take upwards of 15 seconds for it to fully adjust to the change you made)...
 
flamecensor said:
The 8 hp Mercury finally ran OK yesterday, when the carburetor was re-attached for the 3rd time.
Removing the slow idle screw and spring, and rinsing screw and threaded hole with fuel may have helped.
The engine started with the screw open 2 1/2 turns, ran very roughly until it was tightened to 1 1/2 turns, which is where I've left it for now.
The manual specifies a 25.4 mm distance the retainer's bottom edge and the float's upper surface, with the float and float chamber held upside down, and 25.4 mm looked true.
The ~3 mm brass tube inside the ~6 mm brass tube, above the high speed jet, was not truely centered, but was leaning to one edge. I pushed the small tube slightly away from the edge, if that makes any difference.
The top of the carburetor has 'WMC', so I'm sure it's a Walbro model.
Click to expand...

I have the same problem with the brass tubing off center. I dont think any gas can even get to the fuel bowl. Is it a good idea to be bending the small brass tube back to center? Is it even supposed to be in center, seems it should be.

Also with only pumping the fuel line, is that enough pressure to run gas through the carb? to make sure its freely flowing fuel
 
Northport Skiffer said:
I have the same problem with the brass tubing off center. I dont think any gas can even get to the fuel bowl. Is it a good idea to be bending the small brass tube back to center? Is it even supposed to be in center, seems it should be.

Also with only pumping the fuel line, is that enough pressure to run gas through the carb? to make sure its freely flowing fuel
Click to expand...

1. not sure, but my 8hp Mercury now runs
2. not sure again, but if the 3 mm brass tube in your Walbro WMC also was leaning against the edge of the 6 mm tube, maybe that's Walbro's design, which I've now altered(could you get Walbro's phone number and ask them?)
3. I think that pumping the fuel line only fills the carb bowl to the plastic float level, and that manifold pressure from the piston upstrokes draws fuel from the carb bowl, through the high speed jet, which is below the 3 mm brass tube in my Walbro WMC, to the crankcase,.

I can't remember how forcefully I bent the tube, or how well I centered it, but it wasn't perfect, and I remember the brass tube looking slightly 'bowed'.

The 8 hp Mercury started and ran twice last week in the 55 gallon drum but, each time, it didn't start on the 1st, 2nd, 3rd, 4th...maybe 5th or 6th...pulls...but finally started and ran.
I ran 2 carb bowls of fuel dry each time, and it started 1st pull every time(6 total, I think) when warm.
Pulling the choke knob 'full out', as the cowl text instructs, certainly forces a plastic lever down on the blue plunger of the Walbro's primer, and the throttle linkage moves forward when the 'full out' knob is rotated clockwise to start.
With the choke knob pushed all the way in, rotating the knob seems to have no effect on the throttle linkage, so I hope I got the 'worm drive' in the barrel end of the plastic shaft correctly engaged with the 'throttle moving plastic' inside that I can't see.
I have to keep experimenting with cold starts, because it starts tough only when cold. Next test, I plan to pump the blue primer, on the Walbro, by hand.
So far, I'm not sure that the 'fast idle' position has helped at all.
 
Last edited:
Did you ever get to the bottom of this as I have exactly the same on a 6hp 2 stroke.... a pig to start from cold but once running will start and stop all day.
Regards Kevin
 
flamecensor said:
The .pdf manual I bought indicates that my engine has a Walbro WM carburetor, and the first steps in removal are
"1- Using a pair of pliers, remove the Circlip
securing the choke knob in place.
2. Remove the choke knob by pulling it straight out.
Unsnap the idle wire from the primer bracket. Remove the two bolts..."
Removing the circlip was easy, but pulling the choke knob 'straight out' didn't work.
Do I need to remove something else? Thanks for your advice.
Click to expand...


*** I need a part for my 2001 mercury 15 hp 2 stroke. The part that the knob goes to that attached to the motor, a ear broke off for one of the screws. Anyone can help? I have a email. [email protected]
 
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