Walbro Carb Question.. Help me Obi-Wan

[litefoot]

Just cleaned and rebuilt a Walbro WS-12 on a Solo 655AV. Still have same problem. Saw will idle somewhat, but dies when you throttle up.

Took the air filter off and noticed that when it dies, I see fuel mist being blown back through the choke plate. Then I looked closer down the venturi and noticed (with saw shut off) air bubbles and fuel coming out of the main fuel nozzle. Have I got a bad check valve? And is that a replaceable item or is it time for a new carb?

 

[jeeptj19992001]

check valves mean new carbs in most cases

 

[Fish]

So,
Jeeptj is OBI-wan. I always wondered who that was......

So when the carb was rebuilt, what was replaced?

 

[litefoot]

So,
Jeeptj is OBI-wan. I always wondered who that was......

So when the carb was rebuilt, what was replaced?

It was the rebuild kit (pump and metering diaphragms, gaskets, metering needle and lever). I did adjust the lever. I cleaned all the orifices as best I could and they seemed to be fine.

 

[litefoot]

Any more ideas on this one?? The saw starts and idles nicely, and will ramp up and hold full throttle a couple of times. But after about the 3rd or 4th time at full throttle it starts missing an dies.

 

[stihl86]

The carb will only have check valves if it has a primer. Otherwise, its only a extremely fine screen in the nozzle that gives a capillary seal, Usually it wont leak.

 

[andrethegiant70]

I take it you're sure it's flooding and not starving? A bad fuel filter could do this, or a plugged tank vent. After it dies, yank the plug. If it's soaked, forget my idea. If it's dry, your fix is probably easier.

 

[litefoot]

The carb will only have check valves if it has a primer. Otherwise, its only a extremely fine screen in the nozzle that gives a capillary seal, Usually it wont leak.

I found some drawings on Mike Acres site that show a check valve on the WS-12 carb. The nozzle (with the fine screen that you mention), above the check valve. is held in place with an o-ring. It easily pops out for inspection. It looked OK. Link to drawing:
http://www.acresinternet.com/cscc.n...01612ed0b8b0294388256e19001afdf7?OpenDocument

I take it you're sure it's flooding and not starving? A bad fuel filter could do this, or a plugged tank vent. After it dies, yank the plug. If it's soaked, forget my idea. If it's dry, your fix is probably easier.

Yeah, it's flooding. Now I'm starting to think that the coil is breaking down because this happens after the saw is warmed up a bit. Would an intermittent coil make the saw appear to flood?

 

[HiOctane]

Yeah, it's flooding. Now I'm starting to think that the coil is breaking down because this happens after the saw is warmed up a bit. Would an intermittent coil make the saw appear to flood?

Can you check if your carb hold a pressure of 7-8 lbs?Then ,you would be sure that the inlet,jet as well as other parts are airtight.If you have a loss of air pressure,then it would create a rich running.I would suspect more your carb than your coil.If it was the coil,you would be feel the engine kinda sputtering,spark cutting .

 

[litefoot]

Can you check if your carb hold a pressure of 7-8 lbs?Then ,you would be sure that the inlet,jet as well as other parts are airtight.If you have a loss of air pressure,then it would create a rich running.I would suspect more your carb than your coil.If it was the coil,you would be feel the engine kinda sputtering,spark cutting .

OK, so I'm applying pressure into the fuel line up to 7-8 psi and looking for leaks/fuel out of the fuel nozzle in the venturi, right? Now, to go back, I did see fuel and air bubbles coming out of the nozzle with the saw shut off. Is that evidence enough that the nozzle or check valve are compromised...without doing a pressure test?

 

[stihl86]

I'm surprised it has one. They should open under venture vac. They close to keep fuel in the metering chamber. Old carbs only had a screen. Over time, fuel would evaporate in the metering chamber. Check valve slow that process, UNLESS the inlet needle its leaking ,which will cause fuel to leak continually out of the nozzle. Pressure builds in the fuel system and should be relieved by the vent. Is it leaking continually? If you blew compreesed air into the high speed mixture screw hole, new carb or check valve

 

[litefoot]

OK, I tore the carb apart again and checked everything out. I also put together a leak tester (don't tell my wife, but I borrowed the pressure bulb off her blood pressure cuff) and pumped the carb up to 8 psi through the fuel inlet. It's holding pretty well. Dropping maybe 1 psi every 15 minutes. Is that acceptable?

 

[HiOctane]

OK, I tore the carb apart again and checked everything out. I also put together a leak tester (don't tell my wife, but I borrowed the pressure bulb off her blood pressure cuff) and pumped the carb up to 8 psi through the fuel inlet. It's holding pretty well. Dropping maybe 1 psi every 15 minutes. Is that acceptable?

Yes,thats fine.

 

[Fish]

Take the carb apart again, remove the needle/spring/lever, and hold the carb
up to a light and look through that passage.

Then you will know what to do....

When you blow that one out, you will see light through the passage, and likely
your problem will be cured.........

 

[litefoot]

I still don't have it fixed. Here's the summary up to this point:

Solo 655AV

Symptom: Saw starts and idles fairly easily, But will not rev up and hold RPMs.

Observations: Spark plug seems to indicate flooding. Also, when I take off the filter cover and filter, I see fuel pooled up around the carb after revving. Excessive fuel is blowing back out the throat through the choke plate. At high RPMs, the fuel coming out of the venturi main nozzle appears (I'm guessing) to be excessive.

Also, the exhaust vents seems to have small amounts of fuel mix coming out.

What I've Done

1. Dismantled and cleaned carburetor (Walbro WS-12-1). All passages and screens appear to be clear, including the metering needle orifice (thanks, Fish). I didn't see a welch plug.

2. Installed new carb repair kit which included metering needle and lever. I did check that the lever is plumb with the circuit plate. The new metering diaphragm did not have a pin head to fit under the lever forks. It was just a nub. Gary advised that it wouldn't be a problem.

3. Pressure tested the carb at 8 lb. It held pressure.

4. Verified tank vent is clear.

5. Installed new fuel line.

6. Did NOT replace impulse line because the crank case end requires major disassembly to get to. But I figured it was not a problem.

7. The check valve and main fuel nozzle are an all-in-one brass piece that's fitted to the venturi with a rubber o-ring.

Again, my focus has been on the carb and I'm treating this as a flooding issue. What am I missing???:monkey: Plugged exhaust maybe?

 

[HiOctane]

DO you have your problem w/o load or loaded?Because i notice in the parts diagram that the carb seems to have a vacuum "limiter".So if you got your trouble unloaded,it could be only the "limiter" going ON, and that would be normal.