grant-RCU

My Feedback: (10)

I have a new twin needle walbro carb thats giving me trouble. When i start the engine it will run over half throttle but below half the enigne leans out and dies. I have turned the low end needle all the way out to all the way in and it doesnt change the way the engine runs. I can stick my finger half way over the carb and keep it running below half but if i move my finger it leans out and dies. I took the carb apart and spray carb cleaner, blew 80 psi of air through the needle opening and poured water in the needle opening a tried blowing it through it. The carb is new and everything look new in it. the diaphram looks new as it is. no holes in it. The carb primes fuel easliy. After all the cleaning the carb still does the same thing. I tried the carb on a different engine with the same results. Both engines run fine with different carbs but not this one. The needles look fine with no broken tips.. I even took the low end needle all the way out while the engine was running and it does the same thing with no changes. the primer tube is capped off also.

Any ideas on how to fix the carb?

Flypaper 2

Sounds like the throttle butterfly may be closing on the wrong side of the carb. If you look down the intake side of the carb, you should see the threaded end of the screw that holds the throttle plate on.

tkg

My Feedback: (1)

Yep what he said.
If somebody changed the throttle arm and was not paying attention this is VERY common. Especially on the new Zenoah intakes

Antique

My Feedback: (4)

The venturi has 2 or 3 small holes drilled into it....The throttle plate uncovers the holes in succession when the throttle is opened..If you carb plate does not do this it's opening the wrong way... If you look closely at the edge of the plate it has a slight bevel to completely close off the venturi..If the plate is closing the wrong way the bevel will be backwards...

grant-RCU

My Feedback: (10)

Thanks for the replys guys. The carb is a walbro WT 526. I looked at the throttle butterfly and it has a notch in it that keeps it from covering the tiny holes drilled in the carb bodys venturi. the threads on the screw on the butterfly are towards the intake opeing not the engine. I blew some carb clearn into the low end needle hole and the clear comes out of the small holes in the venturi. I did this before but it still wouldnt run below half throttle. The diaphram is very flexable with no holes so itsgood . Any other ideas?

BobH

My Feedback: (2)

grant, if that carb is a typical Walbro, blowing wont clean the carb properly. Over the venturies there are welch plugs that must be removed before you can clean there. You may have a carb that doesnt have all the connections drilled in the body. I would send it back for replacement.

Antique

My Feedback: (4)

Take the cap off the primer tube...

grant-RCU

My Feedback: (10)

How do you get the welch plugs out? Why would uncapping the primer tube make it run? On another carb when the primer tube was open the engine wouldn run.

On this carb there is a small hole that has a brass colored ring around it under the diaphram. its not the pumping mechanism though it just a hole for fuel to flow through. When i take out the High end needle and bolw carb cleaner through it the cleaner comes out of this hole as well as the high end jet in the venturi. However when i blow the cleaner into the low needle hole it only comes out in the venturi and no where else. i have another wt series carb and when i do the same thing on it, carb cleaner comes out of the same tiny brass colored hole under the diaphram. so both needles feed from this same hole.

Antique

My Feedback: (4)

The small brass part with the hole in it is over the high speed needle.The needle regulates the flow of fuel after it goes through the hole on the way to the venturi..The low speed needle gets fuel from another hole drilled through the carb body just under the inlet needle lever..Some models use just one hole for both needles...
It's possible the plugged primer tube is keeping atmospheric pressure from activating the main diaphragm at lower speeds...

BobH

My Feedback: (2)

Grant, sounds like your carb doesn't have welch plugs. They are aluminum disks covering the main openings (over the needles) that feed through the carb body. Doubt if this next thing will help but.. you can check the inlet needle lever setting. This is pushed down by the diaphragm and allows fuel to flo from once side of the carb to another. If the lever is set way too low it wont allow sufficient fuel to flow past the needle. If there is no well that the inlet needle assy. sits in then set the top of the needle lever even with the top portion of the carb body. This will give the proper throw for the lever which moves the needle far enough to allow sufficient fuel to that side of the carb. If this doesnt work...send it back?..BobH.