Walbro carbs made easy (or get that weed wacker started!)

pishta

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Walbro carb on a 2 stroke, These little pumping carbs are amazing on their simplicity and ability to be fixed with 2 dollar membrane gaskets. I recently rescued a Ryobi BP42 backpack blower out of the dumpster at work, seems someone dragged it to work and tossed it in the "controlled" waste, ie EVERYTHING. Well, I can't let a challenge go to waste so I hauled it out and did a quick analysis: No start, primer bulb cracked, fuel lines rotted, straps falling apart. Well, off to youtube on this and I found the ultimate reference on Walbro pulse type carbs.



This guy explains it all and even 3D printed a 10:1 scale model to show the details of this amazing fuel pumping carburetor. What I got out of it was my high speed jet was either clogged or not getting fuel. It would idle all day once I replaced the fuel lines but would not accelerate past idle. Kinda hard to start too....so I bit the bullet and bought a new carb on Ebay for a whopping $20 shipped (under advice from another youtube video, "Don't rebuild a Walbro, just buy a new one") that included a bunch of stuff I had already bought (fuel lines, spark plug, primer bulb) so I should have just bought this first and saved $15. Anyway I got the new carb, bolted it up, pushed the primer bulb 3x and it was already hard, full of fuel. That didn't happen on the old carb. I choked it and pulled twice and it barked to life for an instant. I took the choke off per the starting instructions and the next pull it started and climbed up to a steady idle, blowing a little white smoke then clearing. The test: I waited 20 seconds per the instructions and then goosed it, it climbed right up to max RMP and held there like it was brand new. Another gas engine saved from the landfill. Now to attack that weed wacker that has been down for 4 years.....

What I learned in a nutshell. Fuel lines rot in ethanol, first observation. If your pulse walbro carb or clones primer bulb doesn't get resistive (full) in about 4 stroke your bulb is cracked...OR your "disk diaphragm" is bad (perforated). Its the one under the 4 screws. This is the diaphragm that pushes on and opens the high speed jet fuel supply under load. These diaphragm gaskets are about $2 on ebay, and the fuel pump diaphragm on the other side of the carb under the 1 or 2 screw plate are as cheap. If these are porous (hold it up to the light) they wont hold the vacuum the primer bulb supplies. Or if brittle, they wont flex/pump as designed. Once you know the basic operation of these little guys, it should be a walk in the park getting that motor started again.

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They even have a 2bbl....
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Professor Fate

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The Zama carbs are similar and just as simple to work on- but like you found out, sometimes you can get a whole carb for near the price of a rebuild kit.
One worthwhile investment: a lot of the newer carbs don't use phillips or slotted mixture screws anymore, they use various splined, D, or double D headed screws; either to discourage tampering or to encourage you to take it to a service center.
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Carb tools are cheap, it's worth it to get a set just to have when you need them; because there's three absolutes in life: death, taxes, and that a 2 stroke carb will eventually need adjusting.
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mopowers

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Was the ebay carb a genuine Walbro? I've been tempted to buy one of those cheapie replacement carbs, but they all seem to be offshore copies, so I've been a little reluctant to pull the trigger.
 

RustyRatRod

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I wonder if I can get a two barrel adapter for my weedeater? hmmm
 

Syleng1

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Triple twos on my leaf blower. Now…. Where to find the air cleaners?
 

pishta

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The carb was a knok-off, HUTZL brand. Worked like a champ and everything short of the pump side cover was the same, it was a 2 screw instead of the cast 1 screw Walbro design. I attacked my 4 year old weedwacker and i had no pumping action. Took the pump side off and cleaned it, then took the diaphragm side off and checked that too. After putting int back together 2 more times and still no pump I found a wire gauge passage on the pump side plugged or something as I put a wire in there and finally got suction. Put it ball back together, got a hard bulb and it started but didnt run great. found the cone shaped idle screw is not even touching the throttle bracket, may be bent? Arm got tired so I am looking into replacing it as they are so cheap to buy new. FYI I bought this at Spring Fling 2018! $10 on Amazon next day shipping. Cant beat that.


Interesting....amazon link wont post.
 
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SpeedThrills

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Two stroke tips:
-If you prime a two stroke engine, use gas that is mixed with two stroke oil. Otherwise, you could seize it up.
-If it doesn't kick on a prime, (and it's not lack of spark) it's got more serious problems. A two stroke needs compression to pop.
 
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