Bad landing?[&o]

Bill

Poor hovering.

Actually to be fair to him I think the throttle servo stripped the gear. That was the only thing we could find wrong with any of the systems. For a while I thought he got hit and the PCM kicked in and cut the throttle. Then he told me he punched it to pull out and nothing happened. Well sort of anyway!!

tim
darn thats harsh. condolences

Tims220225.....Thanks for the specs! There was no model or serial to be found on this engine. Im hoping it is the 38cc. When you start talking venturi sizes, thats a whole new book of questions for me. Going to a 13mm, is that getting a new carb? How do you tell what size is on it now?

I just looked the carb over and found a wt3 stamped on it. Still need to be bigger?

I would say the information I found and the fact the carb is WT-3 confirms that you have the 38cc engine. I would run the engine with the carb you have assuming it is in good shape to get a baseline. You can get a rebuild kit for around 5 dollars or so. Then switch to a larger one and you should see a good gain in performance. Also, this carb has no choke per the Walbro Parts & Service Manual. When you do go to the bigger carb try for one with a choke. If you need a carb let me know, I have dozens and would ship you one for $15.00. I bought 200 of them from a guy that went out of business. Kept the ones that work for plane engines and scrapped the rest. As for sizes etc, the 13 mm or in your case the 9 mm is the size of the venturi on the side of the carb that fits to the intake manifold. The other side has a raised number cast into it. In your case it may be a 20 or 24. This is the size of the intake in 64ths of an inch. Thats about as simple as I can make it. The more you do the more you will understand. What does the engine weigh as it sits?

Tim

Tim... yep your right! it has a 24 stamped on the intake. And I dont have a scale, but I would guess between 3 and 4lbs the way it sits in the pics. So try runnning as is be fore going to a bigger carb? Another question, What prop size do you recommend tostart out with?

You talked about a choke, this carb has a choke plate{mechanical} on it. Is that what you were talking about?

tim220222,

Thanks for the information about carb markings, which was extremely interesting. Learned something new today.

Can you shed light on the following carb markings?

Body
WT732
535

Throttle plate
34-121

Venturi marking – This one is obvious and it measures .408”which is about 10.4.
10.5

Bill

BillS & Go-verticle,

Try the links below. It is the Walbro page link for the WT-3 and WT-731. Here you will see an exploded view of the carb. You are talking about item #14 the throttle "butterfly" if you will. Retail in my 2005 book was $0.79. When you look at this diagram remember that not all carbs are created equal as the picture shows every part and number that could be on a particular carb. In the case of the WT-3 there is no choke built into the carb as the parts listing for the WT-3 will show. The second line item in the description on the diagram shows the venturi in mm. The choke go-verticle refers to sounds like it is mounted to the air cleaner or something and it just rotates and is not actually part of the carb. If that is the case remember you won't use the airbox when in the plane.

Unfortunatley there is no information available anywhere from Walbro showing the numbers cast into the intake side of the carbs. The carbs I have have numbers from 18 to 42 and run like this: 18, 20, 24, 28, 32, 34.... A rule of thumb I have developed in my experience says to multiply the intake number by 2.5 and then round the decimal to the next highest even number. It is right on the money to the number in 64ths that is in the casting. An example may help. My WT-439 has a venturi of 12.7 mm, so 12.7 X 2.5 = 31.75 and rounds to 32. The exact number that is cast into the carb. Works with every one I have.

http://wem.walbro.com/walbro/product...num=WT%2D3%2D1

The link below is for the WT-731 which is not in the book but on the web. This is a 10.5 mm carb. This one also has no choke.

http://wem.walbro.com/walbro/product...32-1&Series=WT

Enjoy the links and look around the pages from Walbro.

As for props I would think nothing less than a 16/6 or 8 to start. Like I said some time ago, the Poulan 42 I did worked best with a MA 18/8. It turned 8000RPM.

Good luck and have fun.

Tim

Thank you all for your great input, comments,specs, and expertese! All the valuable information is being put to work! Just wanted to say how grateful I am and how nice it is to have a place to come to maybe help or be helped by other rc enthusiasts. Thanks! Al

No problem at all. Not everyone can pop big bucks for a DA, BME etc. There really are no secrets to these engines and nobody minds sharing the knowledge or experience. Funny thing is I had to buy a DA 100 as there are no twins to convert, yet they thought it necessary to grind off all the numbers on the carb. Now how are we to know what carb rebuild kit to buy if needed? Not like we can't figure out what it is. What are they hiding? They didn't invent the carb. Good luck.