Question about Webra .33 carb

[Papakeith]

I'm a nitro-newbie so please excuse me if this question is a stupid one.

I've got a JR Ergo 30 with a Webra .33 engine in it. I've had the heli for some time but had never gotten around to setting it up. Anyway, I took the engine out of the frame to give it a good cleaning. While I was cleaning I noticed that the carbs "natural" state is wide open.

This seems odd to me. Is it common for the carbs to be designed this way?

If I were to have a throttle linkage failure I would think having the carb go full closed would be more desirable.

[DavidH]

Yes some of the carbs have a spring that puts pressure on the barrel. It will open the carb barrel fully when there is no linkage attached. The spring is inside the carb body if it has one. This spring is there for another purpose, not to open the barrel. That is just one of the things that spring does while doing the job it was put there for.

Yes if the linkage pops off the throttle barrel is going to open fully. But that could also happen even if there was no spring inside the barrel.

David

[Papakeith]

Yup, it's got the spring inside the carb body. It pushes on the throttle valve.

what other purpose is that spring there for if not just for pushing the barrel? inquiring minds want to know.

[DavidH]

It keeps constant pressure on the carb barrel. It is was not there, the carb barrel would slide back and forth in the carb body from vibration. That would wear out the carb body and the barrel.

David

[Papakeith]

OK. Thanks.


I still don't get why someone would design it this way. Is there a reason that you want the throttle to go to 100% in the event of a failure? Or is this just an oversight by the manufacturer.

I realize this is a moot point, but I would think it wouldn't take much of a design change on the barrel to achieve a full closure upon linkage failure.

Or, I'm just overthinking this. :wink:

[DavidH]

The reason it goes full open. If you take the carb barrel out of the carb body,
You will probably find that the slot that the screw fits into that holds the barrel in place is angled. Because on some carbs the barrel slides in and out a millimeter or so as the barrel rotates to open and close the barrel opening. The way to achieve this is by the slot being angled. So with the spring pushing against the barrel, it is going to turn open till the screw hits the angled most end of the slot.

If linkage fails in flight. It is no big deal, just fly the model till fuel runs out. Been there done that. If the linkage fails from a crash it is just a roll of the dice where the motor will be wide open or not.

David