Danh4

My Feedback: (5)

As my first foray into gas, I've got a Ryobi 31cc with a Walbro WT324 (28/32 venturi) on a Giant Super Sportster. The engine ran great on the bench last week, 6300 rpm with a Top Flite 18x6 and it transitioned nicely. Put it on the plane without touching anything and the first time to the field it would not draw gas to the carb, we could only get it to run by squirting a little gas into the carb and then it would only run a few seconds until that was gone. I then discovered that it would prime if I held my finger over the hole in the choke butterfly while I flipped the prop. Back to the field today and I was actually able to get it to start by hand flipping it if I left the choke half closed. But it would only run on the prime until we opened up the low speed needle, finally it would run! The problem is that it will not throttle up, it dies every time. We opened the high speed needle all the way but could never get it to transition, then we tried it with the choke half closed and that worked much better. With the choke wide open the engine seems to be getting way more air than it has fuel for, or not enough fuel for the amount of air. I don't think the carb is too big for the engine because it ran great on the bench. My friend thinks there may be some crud blocking the high speed passages somewhere and that's why it's not getting enough gas. Sounds reasonable to me and I'm going to pull the engine tonight and look at the carb but I'm not sure how to clean/check it. The only other difference between the bench and plane is that I now have a felt clunk in the tank and a longer run to the carb, about 10". I'm using 3/32" neoprene tubing. Sorry for the long winded explanation but with all that info, does anyone have any ideas why it's not running like it did on the bench?

Dan

warbird72

My Feedback: (79)

How old is the carb? It sounds like the pump diaphragm is geting stiff. Stiff diaphragm can cause all kinds of adjustment problems. And also check to make sure the carb retaing screws are good n snug. Also make sure the fuel lines are right. Ernie

tim220225

My Feedback: (4)

You have in my opinion the correct carb on the engine. It has an 11.11mm venturi. Any of the WT-324 carbs I have also have a return line on them. They also all are 28mm on the intake. Look in the intake and see what number is cast there. Should be a 28. If it is bigger you are getting too much air for the little compressor. The return line needs to be plugged. A piece of fuel tubing with a screw works fine. I use extra aluminum filler plugs from a 3 line glow tank system. Also your RPM's sound pretty low. I usually prop my engines to run around 7000 on the ground. If your carb is adjusted properly and 6300 is all you get I would drop the diameter. Others may say they have theirs in that RPM range but that engine wants to run.

Danh4

My Feedback: (5)

No idea how old the carb is, I got it on ebay. I don't think it was ever used but it could have been sitting around for years. A stiff diaphram would explain why it wouldn't pump gas up to the carb at all the other day, right? But it did work when it was on the bench. The carb screws are good and tight and I'm pretty sure the fuel line is attached to the right nipple on the carb. There are two brass tubes coming out the same side of the carb, one I have plugged off because I think it was the return line to the tank (although this carb doesn't have a primer bulb?) and the other is closest to the diaphram side of the carb and I have the line from the tank attached to that one. It wouldn't work at all if I had them reversed would it?

Danh4

My Feedback: (5)

It was capable of running at close to 7000 rpm, but after we richened it up we were around 6300-6500 rpm and felt that was good to start with. Since you're also using the WT-324, can you confirm that the nipple closest to the smooth steel cover plate is the right one for the gas line, I have the other one blocked off like you describe.

tim220225

My Feedback: (4)

You have had it running so you have the lines correct. FWIW the tube to plug is the one on the same side of the carb as the stamped cover with the small pressure hole in it. The other side is the fuel inlet and pump side. Also has the large screw in it for idle adjustment. Needless to say you can remove the screw. I would lean it out a bit more on the high end to a few hundred off of max. My personal method. Same with the low.

Danh4

My Feedback: (5)

The way you describe it is exactly the opposite of the way I had them hooked up. The line I had plugged is the one closest to the cover that is held on with one large screw in the center. The line from my tank connected to the inlet nearest the smooth cover with the small hole that's got 4 screws holding it on. Mine was definitely running, but it wasn't running right, would it run at all if the lines were hooked up wrong?

goafterit

Just wondering if you have a vent line out of the tank. If not, make a loop near the end closest to the motor and let it hang down below the plane. This allows you to do rolls, etc without losing fuel.

captinjohn

goafterit: I see with only 7 posts you are new to RCU. Welcome aboard. There is a lot of good data in the engine forums. best Regards Capt,n

Danh4

My Feedback: (5)

Yep, vent line exits bottom of plane and is not plugged up or obstructed in any way.

tim220225

My Feedback: (4)

When you change them around you will be fine. The cover with the single big screw is the pump cover. The other cover with the hole senses pressure the pressure of the air through the hole. Way over simplified explanation but that is what it does. Anyway make sure you have a loop or two in the vent line so when you fly inverted etc. you don't have a siphon issue. PM me your email and I will send you some Walbro information.

Hey Capt,n I finally finished moving and am setting up shop again. My son and I have the lathe all leveled and ready to take a test cut to make sure I don't turn unwanted tapers. Maybe I can get back to conversions in the near future and the BME twins I picked up. Still need to maiden my 35% Carden Edge too.

Danh4

My Feedback: (5)

It sure looks like I had them hooked up backwards, how could it even run like that though, is it possible? I'll switch them around and try it again tomorrow. Thanks so much to all you guys for helping me out!

Dan

av8tor1977

My Feedback: (6)

The incorrect line is also a path to fuel for the carb, it just doesn't go to the pump. It's possible that the engine could get enough fuel to run a bit, or intermittently while hooked up incorrectly. The proper line goes to the fuel pump chamber, and the pump draws it's fuel at that point. The "incorrect" line, or tube, needs to be plugged. It is where the primer bulb was connected originally, to pump fuel to the carb for an initial start until the fuel pump took over and filled the carb normally.

AV8TOR

rangerfredbob

My Feedback: (13)

I had them backwards on my mac 32 when I was testing it in the garage and it ran sorta... flipped them and it ran a whole lot better.

Danh4

My Feedback: (5)

I should have thought to switch the lines around while we were fiddling with it today but I didn't think it would run at all if they were backwards, now I know it is possible and I can't wait to try it again tomorrow hooked up the right way! Thanks for the explanation.

Dan

seagull extra

My Feedback: (12)

Dan I am very interested to here how you are making out with your carb problem. I am having a very simular problem with mine. It runs fine with the stock 8mm Zama carb but when I tried a walbro that a friend gave me to try I had simular results to yours. It would only get the fuel it needed intermitantly. I thought I may have damaged the carb when I reamed it out from the stock 8mm to 10mm with my prop reamer so I also ordered a carb on e-bay with a 12.5mm bore. Even before I attempted to start it with the new carb I knew I had trouble because the fuel would not move up the line when I flipped the prop. With the stock carb on choke the fuel moves at least 1" with each flip. I hope there is not a problem with pulse signal on this engine when running a larger carb, I can'nt see why a larger carb will not draw fuel because of the fuel pump built into the carb,I thought I was going to get rid of my fuel draw problems when running gas.[&o]

Danh4

My Feedback: (5)

Hey Seagull,

Well, my carb problems are solved thanks to the help I got here last night. I simply had my supply line connected to the wrong tube on the carb, once I got that sorted out it ran fine and was easy to tune. In fact, I maidened my Giant Super Sportster today and the engine ran perfectly. I'm really new to this so hopefully a few more experienced guys here will help you like they did me. That being said, my engine was difficult to prime when the line was connected wrong, I had to hold my finger over the hole in the choke butterfly and flip the prop 6-8 times to get gas to the carb. Besides hooking the lines up right last night, I also soldered up that hole and it was easy to get the gas up to the carb today but that might be due to the fuel line being correct more than anything.

Dan

captinjohn

For people that do not care to solder....a short piece of neopreme fuel line with a rivet stuck in the end makes a very good stopper. It can aways be changed later also. Its also a good way to plug up, your fueling tee. Capt,n

av8tor1977

My Feedback: (6)

Danh4 - How do you like the Giant Super Sportster? It keeps begging me to buy it... []

AV8TOR

Danh4

My Feedback: (5)

I'm very happy with it! Like I said, this is my first giant scale and gasser and I think it was the perfect plane to start with. It's super easy to put together, I had no issues with any of the parts or hardware. Go ahead and buy one, I don't think you'll be disappointed.

Dan

av8tor1977

My Feedback: (6)

After asking you how you liked it, I did a search and read a thread about the plane in "ARF and RTF" here in RCU. Everyone said they liked the plane, but apparently there is an issue with the horizontal stab having a weak attachment and also with elevator flutter. Once fixed, everyone says the plane is great. You might check into that thread. They recommend that the elevator hinge gap be sealed, that the linkage be nice and tight with no slop whatsoever, and that you add bracing to the horizontal stab. The "fixes" are easy to do, and worthwhile to prevent losing the plane!

AV8TOR

Danh4

My Feedback: (5)

I was aware that there were a few issues with the tail but mine appeared to be nice and solid so I didn't do any additional bracing. I suppose I should though, just to be on the safe side. So, are you getting one?

av8tor1977

My Feedback: (6)

Still considering it. I would really like one but I have so many planes it's hard to justify, or find space for another one. I may see if a friend of mine would be interested in buying my Giant Stik first.

AV8TOR

av8tor1977

My Feedback: (6)

Thought I better add something about this plane and flutter.

Apparently the shape, size, weight, and location of the elevator in the Sportster series of planes is conducive to flutter. Your horizontal stab and elevator assembly may seem secure, but if flutter occurs, something is going to give. It would be a really good idea to look into the "fixes" that I believe Great Planes published for the other Sportsters. Fixes for problems like this generally include sealing the hinge gap, setting up the ideal control linkage hookup, and in some cases mass counterbalancing the control surface. You might also add simple cable bracing to the horizontal stab and vertical fin, or some streamlined aluminum tubing below the horizontal stab to the fuselage as bracing.

AV8TOR

seagull extra

My Feedback: (12)

I'm still having fuel delivery problems with my walbro. I took the carb apart and their was some crud under the diafram and I cleaned it out and reinstalled the carb. Now when I flip the prop with the choke on I can see the fuel move in the line with each flip but it still does not run properly. It responds to low end needle adjustments but the high end does not respond to the needle at all, it just dies when you give it over half throtle. I think my next step is to borrow a carb from another club member that I know works and see if it is completely a carb problem or if there is something with this engine that will not allow a larger carb to draw the fuel it needs.