Walbro WT - 682 - Flooding from fuel return line?

[philbbb]

Gas is continually leaking through the carb.

It appears to be coming from the fuel return line. This got me to thinking, there doesn't appear to be a one way valve on the fuel line. What is supposed to keep the fuel coming back in to the carb?

Ill attach photos if that would be helpful.

But.... since the metering side essentially has a hole that connects directly to the return pipe/line. I cant for the life of me understand how the fuel is supposed to stop flowing back into the carb? It seems to me given the lack of a one way value that (by all rights) it should just be flowing back into the metering chamber and out the check valve. What am i missing?

 

[Chevboy0167]

https://www.walbro.com/wp-content/uploads/2016/01/WTseries.pdf

 

[philbbb]

https://www.walbro.com/wp-content/uploads/2016/01/WTseries.pdf

I have a copy of this, but haven't been able surmise the answer from it. I'm wondering if it has something to do with how the fuel lines are arranged.

For now i've simple got the end return line at the top of the fuel tank, well above the fuel. So it doesn't flow back.

 

[SteveSr]

Gas is continually leaking through the carb.

It appears to be coming from the fuel return line. This got me to thinking, there doesn't appear to be a one way valve on the fuel line. What is supposed to keep the fuel coming back in to the carb?

Ill attach photos if that would be helpful.

But.... since the metering side essentially has a hole that connects directly to the return pipe/line. I cant for the life of me understand how the fuel is supposed to stop flowing back into the carb? It seems to me given the lack of a one way value that (by all rights) it should just be flowing back into the metering chamber and out the check valve. What am i missing?

The purge bulb sucks fuel through the carb and discharges it back into the tank. There are a couple of check valves in the carb that have to be working properly and most importantly, the carb has to be plumbed correctly!

What saw is this on and can you please post photos of the plumbing?

 

[philbbb]

The purge bulb sucks fuel through the carb and discharges it back into the tank. There are a couple of check valves in the carb that have to be working properly and most importantly, the carb has to be plumbed correctly!

What saw is this on and can you please post photos of the plumbing?

Thanks Steve,

Its actually a trimmer, but the carb is common across a number of tools, as I'm sure you know.

Its definitely plumbed correctly. Fuel line with filter from the tank to the bulb, fuel line from bulb to fuel pump side input-flowing in the right direction, fuel return from the metering side exit to the tank.

Is the vacuum of the fuel tank and lid valve supposed to prevent the fuel from flowing back into the carb perhaps?

I just don't get it. the metering side pulls the fuel in from the pump side, but the return hole is also there in the same chamber recess that feeds the nozzle check valve, and the nozzle check valve allows fuel to flow into the venturi. I just don't see why the carb should stop the backflow of fuel from the return line.

That's wrong of course, but i just don't see the mechanism to prevent it...

ps. let me know if you'd still like a photo. I'm fairly confident about the fuel line plumbing but if that doesn't sound right i just have to pull the cover off to snap a photo.... Thanks again for chiming in.

 

[philbbb]

pps....

Ive also realized that having the fuel line going to the tank above the fuel must be wrong as the carb must be gulping air in. The motor is running poorly and will die eventually. I imagine this is the reason. But with the return line exit hole in the fuel, the carb leaks, as mentioned above.

 

[philbbb]

The purge bulb sucks fuel through the carb and discharges it back into the tank. There are a couple of check valves in the carb that have to be working properly and most importantly, the carb has to be plumbed correctly!

What saw is this on and can you please post photos of the plumbing?

I Just reread your post.... Im sorry, then it sounds like I have plumed it wrong.

So the bulb doesn't push fuel into the pump side, it pulls it through the metering side? If that's the case then i have it wrong indeed.

 

[sean donato]

Fuel line should go as following. Fuel line with filter to inlet side of carb. Carb return line to purge bulb, purge bulb to tank. The purge bulb has check valves in it.

 

[philbbb]

Fuel line should go as following. Fuel line with filter to inlet side of carb. Carb return line to purge bulb, purge bulb to tank. The purge bulb has check valves in it.

Yes, this appears to have fixed everything.....No leaking and its running well now.

Wow, where did i get so much misplaced confidence about the plumbing. It all seemed to make so much sense hahah.

Thanks guys!!!

 

[SteveSr]

Yes, this appears to have fixed everything.....No leaking and its running well now.

Wow, where did i get so much misplaced confidence about the plumbing. It all seemed to make so much sense hahah.

Thanks guys!!!

This is why God gave you a cell phone to take "before" photos! Disclaimer... This only works if the plumbing is correct BEFORE you take it apart. I once got 2 Wild Things for free and someone else had already screwed up the plumbing before I got them!

 

[Bigjimmythunder]

One of the best overviews of how a Walbro carby works
https://www.helifreak.com/showthread.php?t=326599

Written in context for a model helicopter but its still a Walbro WT series same as in many saws
If you want to really understand how it all works as well as how to maintain them have a read through

 

[sean donato]

Walbro has several free pdf manuals that cover exactly how every available feature of a carb works.
https://www.google.com/search?q=wal...xGSBwQyLjE0oAfibw&sclient=mobile-gws-wiz-serp
Sorry for the Google search link, the service manual is too large to upload.
It can be had at the second result, first is a lost of all the manuals for the individual carb series.

 

[Pioneer]

Found out that the carbs with the fuel return will not work properly without a working purge bulb. It needs the one way valve in the bulb to prevent air being drawn back in to the carb. It will mess up the mixture and it will never run right without it.

 

[sean donato]

Just plug the return off.