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2 Stroke 25HP Merc - Won't Run Without Throttle

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wildlandff25

New member
Serial # 0B353657

Carb Assy: https://www.marineengine.com/parts/...-cyl/0b238464-thru-0g044026-usa/carburetor-25

Morning guys,

This is my dad's old motor. He had all sorts of trouble with it the last few years - in and out of the shop multiple times. It was running alright last summer - it just didn't want to idle. I thought it could probably use a carb clean so I did just that. Put everything back together a few weeks ago - and couldn't even get it to start.

Here's what I've done between then and now:

- Replaced all fuel lines.
- New spark plugs.
- Cleaned in-line fuel filter.
- Soaked carb overnight - cleaned up and used compressed air on all orifices.
- Installed cheap amazon gasket set.
- Tested compression - 120 psi on both cylinders.
- I don't have an ignition tester, but spark on both coils look strong.

After all that I can get it to start, but I need to feather the throttle to keep it running. So I went all the way on a complete carb rebuild kit (Sierra). Cleaned everything up again. Also replaced the float and entire choke/primer assembly.

Fired it up this morning and same issues. It won't run without throttle. It'll idle up and then *cough*, sputter, idle down, then die. In fact, I need to hold the throttle open by hand a bit to get it to start at all.

This is driving me nuts. What am I missing? Timing issue? The only thing I haven't replaced on the carb is the fuel pump body - which looks like a tricky part to find.

Link to video and pics: https://photos.google.com/share/AF1...?key=TUF2cFJKTzg3MkJ2UE1BVkJwbFYwUmREbVItVnln
 
flyingscott said:
Base gasket on right? Correct gaskets in carb.
Click to expand...
Hey Scott,

I believe so. I've seen threads about guys using the wrong gasket and blocking the fuel flow. I've had this carb off and on about half a dozen times now. I'll look again tomorrow as the rebuild kit came with two very different looking gaskets.

As far as the carb itself - everything is where it should be.
 
Compression is said to be 120 PSI in post #1.-------Check reed valves.----Open low speed mixture needle 1/4 turn at a time.---Check flywheel key.
 
Morning. Added a few pictures of the reeds (they look good to me, but you guys would know better than me). Also highlighted the two different gaskets. Kind of odd - the paint surrounding it looks like it originally came with the rectangular shaped gasket - but the hole doesn't line up with the base. The circular gasket does. All the parts diagrams I've found show the rectangular gasket. Weird.

I've seen all kinds of suggestions for the spark plug on this outboard. Merc shows a BUZHW-2. My dad was running BP8H-N10s.

https://photos.google.com/share/AF1...?key=TUF2cFJKTzg3MkJ2UE1BVkJwbFYwUmREbVItVnln
 
That a chrome bore motor. I would pull exhaust cover exhaust and check the exhaust side of pistons to see if scuffed. The are known for problems if ever overheated. Compression wont tell this..
 
faztbullet said:
That a chrome bore motor. I would pull exhaust cover exhaust and check the exhaust side of pistons to see if scuffed. The are known for problems if ever overheated. Compression wont tell this..
Click to expand...
OK, that'll have to wait until tomorrow but I'll check. I ran it a bit this morning. It will start when I hold the throttle open. I was able to get it into gear without it stalling - and got the rpms up. Rpms increase until it sneezes (exhaust), then rpms drop and it sounds like it's running out of fuel. Lean condition? I've adjusted the low speed needle and it didn't seem to make a difference.

Pulled the carb again, rechecked everything. Rechecked the vent on the fuel tank (it's working just fine). The only thing I haven't replaced yet is the fuel line from the tank. It's the grey, plastic lined crap. Pulling the fuel filter assembly apart, nothing of note there. Fuel seems to be flowing fine from the tank to the motor. Bulb stays firm the entire time.
 
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