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25hp ml xd 1986

G

GDBrown

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First trip out was fine. Second trip I noticed rough idle. Third trip started OK with primer pulled out as before and got up to WOT with no problems. As soon as I throttled back to idle it got real rough and stalled. Managed to get back near the dock but could not get it started long enough to get onto the trailer, I had to pull the boat on my hand. All these trips were on consecutive days with my grandkids.

I have spent three days now working on cleaning and rebuilding the carb, checked and replaced the plug wires, plugs, fuel, etc. Everything looks normal, BUT!

Now it will only start if I give it a lot of open throttle while pulling the starter rope and will run above idle but stalls as soon as the rpm drops low enough that the idle mixture would be controlling rather than the high speed jet. Yes, the plugs are wet and I'm wondering if there is something that is causing it to flood like a stuck float? I'm also thinking that the spark advance may be off but none of that has changed from when it ran fine.
I have rebuilt carbs on several other Mercs in the past and this one was very similar to them.

Any ideas at this point will be appreciated.

GD
Hillsboro, OR
 
..."I have spent three days now working on cleaning and rebuilding the carb..."

Did that include removing, soaking and blowing out all the little emulsion tubes and etc? ("Cleaning" the carb without doing the above is a waste of time.) If you did it right, then one of two things is happening: The carb is flooding (float too high or not seating--it happens), or the idle mixture is way off.

Pull the carb again and clamp it in a vise, then jury rig the gas hose to it and pump it up hard. If it floods (obvious) lower the float 1/8 " and try again.

If it didn't flood, try adjusting the idle with the motor warmed up and in gear. You might need an assistant to give the carb a bit of throttle to keep it running since there's no idle up on these (which I hate). Keep dialing the idle mixture in until it idles the best, then open the adjustment 1/8 turn CCW.

Jeff
 
Fastjeff,
Thanks for the quick reply, it's always nice to find help when you get stuck and need a fresh perspective from someone with more experience. I only do these things every few years. Maybe if I kept a boat longer I might do it more often.

Yup! I dunked, soaked, blew with a high pressure air hose, fed micro wire through openings dunked again, blew out again. Then rebuilt with new kit. That's why I'm thinking the float might be stuck! I'll tear it down again for a second look. I'm quite sure the mixture screw is not far off because I checked it before tear-down and put it back to the same location (1 7/8 turns out from a light seat). I'll let you know what I find and we can re-access the problem.

GD
 
You have the WMC carb? If it is flooding than you can't always see it because the primer injects from an orifice on the base flange. The check ball gets jammed inside the spring coils.
 
timebandit said:
You have the WMC carb? If it is flooding than you can't always see it because the primer injects from an orifice on the base flange. The check ball gets jammed inside the spring coils.
Click to expand...

Would the check ball jamming act the same as the float being stuck? I just checked the float, it is a white plastic ring and was adjusted to 7/8 inch. I moved it to 1" which is what my book indicated was the correct level then I finally got close to idling with 1/2 turn on the slow speed mixture. I was just going to ask if there was anything else that might allow fuel in at idle that I'm not aware of?

GD
 
If the "choke" (actually the enrichener) linkage is adjusted wrong, the motor will suck in excessive gas at idle (which is how cold starting is supposed to work).

See that little plunger that gets pushed down when you choke the motor? It should be ALL the way up with the choke off.

Jeff
 
GDBrown said:
Would the check ball jamming act the same as the float being stuck? I just checked the float, it is a white plastic ring and was adjusted to 7/8 inch. I moved it to 1" which is what my book indicated was the correct level then I finally got close to idling with 1/2 turn on the slow speed mixture. I was just going to ask if there was anything else that might allow fuel in at idle that I'm not aware of?

GD
Click to expand...

Yes it would. Other than that either the reeds are bad or the lower main crankshaft seal has a vacuum leak.
 
Thanks, I'll check to make sure the primer plunger is not being held down when the level is pushed all the way in. Will let you know what I find.
 
Does anyone know exactly how long the wire is that goes from the fast idle lever back to the trigger assembly that advances the timing? I need to make a new one because they don't sell them anymore.
 
I had to make one myself. The trick is to get some fine stainless wire and start bending. No rocket science project: the spark must advance "a bit" with the "choke" all the way on, then go away as the choke is opened. Idf it doesn't idle high enough when cold, you add a bit more advance.

Jeff
 
I tried that and I think I have it right but not sure. If I find the source of the additional fuel maybe that will settle things down so the rest of the problem will be easier to solve. I'm also having problems with the wire harness getting in the way of the lever that keeps the crank from being pulled while the engine is in gear. I'll try and post of photo of where mine is routed and maybe you guys can tell me if that is the correct position. I'm out of town for the weekend but will be back on monday to start anew!

GD
 
So the problem turned out to be the check ball in the primer! I found it half way up the inside of the spring! I took the carb apart 4 times but never took the primer apart after replacing the diaphragm. Took it to the lake and it works perfectly. Now I have too much power! I'll need to trade it for a 15HP. 28MPH is too fast for me alone in the boat.
 
Re: 25hp xd 1986 new post 2016

Anyone have the method to pull the drive shaft seal so I can replace this one that is destroyed?
i appreciate the help big time!
 
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