Looking for some ideas here. My GX31 worked very well on the stand. Although it was a little lean on the top end with the stock carb. However once I mounted it up on the plane and inverted it, the engine would quit when going past 3/4 throttle. So I got a WYK-16 from BCMA,,thought that would cure it but I have the same problem. Engine runs great up to about 3/4 then it falls flat on its face. I hung a WT 11mm carb on it and was able to twist the hi needle out about 1/2 a turn and bang ,,full power. But I figure I''ll loose the pump with that carb on this engine..Question is can the WYK-16 be richened up,,short of drilling the jet??? and what the heck does that black press down button do on the side of the carb??

tauri, read down a few threads to "Honda GX35 4-stroke thoughts". Yes you will have to make an external pulse line for the WT and if you use the WYL you''ll have to drill out the jets or replace them. It seems going to the WT with an external pulse line is the way to go.

Sounds like your needles need adjusting as the high seems too lean. I have used this carb in testing and have had no issues running upright or inverted. Mine is mounted inverted on the DVIII I am building. I also started with a WT carb with external pulse but the pulse line filled with oil and caused me issues. The high needle is to the right and just above the fuel inlet barb. The low is on top of the barrel and to the right of the swivel for the linkage. Look at my pictures to see what I mean. I used the stock swivel to attach my linkage to, worked well for me. I also made a manifold to rotate the carb for a straight shot linkage. So far so good. What I found when adjusting the low was to fatten it until I had a little black smoke then lean it down a bit. Tuned the high until it just stumbled at WOT then fattened it up a bit. Ran it many times in testing to fine tune and no issues to date. You will also know when it is rich on either end because you will smell like a bad running lawn mower in short order. These carbs and more important these engines tune a little different than the two strokes we use. What button are you speaking of?

Looks like something diffrent from the WYK-16 I have, Tim. Mine has no High speed needle,,Wish it did! I''d be set. The button I refered to is a start assist,,gives a shot of fuel,,kinda like a secondary primer after the primer bulb is used..

Post a picture of the carb if you can showing the top of the barrel where your throttle attaches to. I checked mine and it is a WYK-61. I may have said WYK-16 in another post so this will correct that. Are you sure there is no needle screw in the top of the barrel? Yours is a 10mm carb and mine is a 9mm. I have another one that is 10 or 10.5mm I intend on trying to see if I can squeeze a bit more power out of it. I do know guys have had issues with tuning with only one needle.

So far in testing mine is working ok. It is a Zama carb with a 10mm venturi. I added a spring to the fuel pump and used an external pulse line tapped into the intake manifold. (No problems with oil in the pulse line that way.) I was considering trying that WYK-16 carb that BCMA engines sells however just to see if it worked any better, so it would be great to see this cleared up as to whether it has both adjustments or not...

Good luck,
AV8TOR

That is the reason I had issues with oil in mine. I tapped into the case where there should be no oil. When the engine slings it and it returns the the sump is what caused me issues. Now I may have to tap my new manifold and see. Thanks a lot av8tor, more work for me.

I have been using a WYK 16-1 (10.5 mm no primer bulb) on my Gx31 Honda's for a couple of years now. From my testing they seem to be the right carb for this engine. They are available with or without the primer bulb but this changes the part number. If my memory is correct the next size up with low and high needles is a WYK 85-1(12.2 mm with primer bulb). They both have low and high speed needles. The low speed needle is under a cover in the center of the top of the carb. There is no provision on the block for the pump impulse line. If you look close you will see a small slit cut in the plastic manifold that allows impuses to be sensed right out of the manifold throat. I make my own manifolds out of phenolic and simpley drill a 1/16 th hole at an angle from the pulse location to the throat of the manifold.
What makes the WYK so hard to size is that the Walbro catologes , both hard bound and online have the sizes wrong. This may have been cured now. Mr Salis at Walbro verified this for me. These WYK carbs are the way to go IMHO. They seem to work great on the 2 strokes also. Good luck and just ask if I can be of further help. motorhd

Thanks for the info motorhd. What's a good source for those carbs? They seem to be hard to find.

Tim, I keep trying to get time to take a pic of mine with the pulse line to the carb adapter manifold, but I've been buried. Anyway, I just drilled and tapped the manifold itself and installed a pressure tap. I put the spring out of the original carb in the fuel pump of the Zama, tapped the pump cover for another pressure tap, and hooked the two taps together with tubing. I am still rather surprised that it gets enough of a suction pulse when the throttle is wide open to work the pump, but it does. No high rpm leanout, and I can easily adjust it too rich at wide open throttle, so it's getting plenty of fuel.

AV8TOR

Now I didn't tell you this, don't want to screw up a good wholesale source but, try ASE Supply at 503-288-0100. They may have to order them for you. They are retail about $50
not motorhd

Tim,,I never have any luck posting pics here,,But I do have a needle in the carb barrel. Works great for the idle,,but my problem comes at the high end. Anyway since it worked OK on the stand I'm gonna have a real close look at the tank and lines first before I go looking to drill jets.

There should be another needle to the right of the fuel line barb. At least on the two I have there is.

I'm thinking your refering to the WYK-61,,,I have the 16,,No HS needle on those...Just the idle needle on the top of the barrel.

You are correct my bad. Either way I would try to locate a two needle carb. Better tuning capabilities.