This carb is a Walbro WT-739 and was used on DL-50s and Echo cs330T chainsaws. However the DL50's 739 carbdont have the port in the metering bowl, and I cant find photos of the said chainsaw with carb exposed..



So that port in the metering bowl should communicate with the crank case?



I believe that the black port there is the fuel pick up? Is this indeed the case?



ok it's DEFINATELY a 739! LOL! sorry gotta show off macro shots...lol</p>

yes, that black port is fuel inlet, and the port on the metering plate is supposed to go to atmosphere, I would run a tube into the fuselage to get a nice stable reference

Thank you!! 

So how is the diaphram above the metering plate manipulated so as to open the metering port?  Is it via the 2 holes circled in blue?  If not what are those for?

The center circled hole goes the LS needle valve

The one off to the side goes to the HS needle valve

The brass thingy is the back end of the high speed nozzle check valve

http://wem.walbro.com/distributors/s...s/WTseries.pdf

thank you!!! Yall rock!!!

When there is a vacuum in the venturi, the vacuum pulls on the 3 or 4 little holes in the venturi uncovered by the butterfly that ultimately goes back up through the needle valves and to the chamber under the metering diaphragm drawing the diaphragm down and pushes on the lever and opens the needle and seat, therefore letting fuel pressurized by the pump into the metering area.

The engine doesn't draw the diaphragm down, atmospheric pressure pushes it down.

Sorry W8YE, just couldn't help myself.... Just giving you a hard time, though strictly speaking that is true.

AV8TOR

Thanks for the heads up.

Does anyone ever thank you for the time and effort you put into these forums W8YE? I hope so, and I thank you as well. You obviously have a lot of experience, and it is really great that you share it and take the time to moderate and contribute to the forums.

Take care,
AV8TOR

A lot of it is information retrieval.

You look up the key words with Google like parts sources and prices

In the above example, I feared a mistake after I posted, so I Googled Walbro and looked at the manual.

I think I'm right from looking through the explanations in the PDF manual

So I posted a link to the manual also.

Also I did a casual on the carb number but didn't immediately pull up any applications for that number so went on to other things relative to the subject of the post.

i did a thread about this on hbf. the same should apply to any walbro membrane carb. javascript:mox();<div>
</div><div>let me know if the link works. i have been having trouble with the links here.</div>

thank you for all the help with this carb! But now I have another question for you guys - can one add a primer bulb to this carb? As the carb is now there is only a fuel inlet on the pump side and I REALLY dont want to have to deal with only the pump clearing the air from the carb.

Here's the parts list

http://wem.walbro.com/walbro/product...&amp;Series=WT

The body air purge part number isnt listed, but does that mean that it's incompatable?

most of the carb bodies with a purge setup have a smaller brass tube sticking out the side of the carb that goes to the purge bulb or back to the tank

I was looking around and found all kinds of numbers but no pictures

Here's a bolt on type with the outlet tube made into it. WT-813 carb

Just look up the part number for the purge pump on the Walbro WT-813 in your other site that you were using

I did that as well from several different carbs, but Im left wondering if the carbs with the onboard air purge have a port that allows the fuel to bypass the metering diaphram.  From what I can tell both my 529 and this 739 don't have a port to send fuel to the air purge body.

I guess the only way to tell for sure is to buy a carb with the on board air purge?

Suction on the lower side of the metering diaphragm opens the needle and seat.

Continued suction will suck fuel all the way from the tank even through the pump

Hi guys...

I too have a Walbro WT-739 on a DL50 and I had a great season last year with this engine.

This year I transplanted the engine into a new airframe and I cannot get a reliable idle out of it. It starts ok cold (will not restart hot) runs a while at idle then dies without loading up as if it runs out of fuel.

I have tried a totally different fuel supply chain so it's not that. I have done all the obvious stuff, check for air leaks, good batteries, new plug, fresh fuel etc etc.

I have it narrowed down to the carb or the ignition module.

I pulled the carb apart (and bear in mind I don't really know what I'm looking for except something out of the ordinary) and came here to compare pictures.

The only difference I see is that my high speed nozzle check valve (if I am looking at the correct part) is blocked by some hard black stuff and I'm wondering if that should be cleared as per Bump's picture...

Your thoughts gentlemen.....?

Cheers

Goose

I would say that black crud is your problem...of the 6 odd carbs I have, none of them have that on the check valve. You can rule out the ignition by first warming up the engine until she quits like normal, then pull the plug, plug it into the boot, ground the threads, then hit the nose cone with the starter. If the ignition is bad (from heat) then there won't be a spark. If it's good then there will be lots of spark...

Hi Bumpinyota...

Thanks for your reply.

I was wanting confirmation regarding the black crud but I don't understand how a blocked high speed check valve would affect fuel draw at idle, but there is lots I don't understand

I will get that out of there and try again.

Thanks for your help.

Goose

Some high speed check valves have a little black rubber diaphragm in the end of them. Could that be the "black crud" that you are seeing? If you take that out, the carb won't work unless you replace the check valve.

AV8TOR

Ok, thanks... I will check it out.

G

I just got this carb. Its a WT-117.

Which is the fuel inlet tube, the brass curved one or the black plastic one on the primer plate?

Also, If I wanted to lose the primer could I just replace the primer plate with a standard plate and gaskets on this particular carb?

My intention is to eventually use this carb on a four stroke conversion after modifying the diaphram cover to add a pump return spring.

Thanks,
Mike

Yes the curved tube is the inlet.

take off the plastic purge pump and replace with the steel cover for the regulator (they call it the metering diaphragm)

Thanks w8ye!