aceairspeed

Can anybody please tell me what that pluged up hole is on the back of my Webra .91? Its about a 1/4 inch with an alum. screw in it?
Ace

Azcat59

If it is like the Webra 120, it is an access hole for engine disassembly.....you use one of the backplate or head bolts, which screws into the wrist pin, allowing you to pull the wrist pin out of the piston so you can then get the piston out of the cylinder. Unless you are taking your engine apart, it should be left alone.

Clair Sieverling

aceairspeed

Thanks Clair that helps clear the air!

cougar27mtr

My Feedback: (2)

I have a .91 webra with a fitting drilled into the backing plate.. What is this for? I would think that this would cause a lean mixture all the time letting air being sucked in through that fitting.. Is this needed? Can I plug it?

Thank you guys

William Robison

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Cougar:

The hole in the backplate should be plugged unless 1) you are using a Perry pump, the pressure pulses operate the pump, or 2) you are using a Cline fuel system, in which case the pulses afre fed to the tank through a check valve.

You must have gotten the engine used.

Bill.

cougar27mtr

My Feedback: (2)

William

Yes I did.. I could never get this engine to run correctly.. I since stripped out the glow plug hole and ordered a new head for it.. But when I removed the engine from the plane I noticed the hole. I figured this maybe why I am running lean? I am sure plugging it will help tuning.. Because the motor would not idle ai crashed (but repaired) the plane.. I hope this will help solve my performance issue.. I am running a perry carb on it.

Thanks for the advise..

Hobbsy

My Feedback: (102)

If you bought the engine with the Perry carb on it, it could very well be a pump carb and was equipped with a pump before you got it. If so it will run lean if you run it without a pump, it has narrower fuel passages than the non pump carbs.

cougar27mtr

My Feedback: (2)

hobbsy

How can I check to see if I need to add a pump? Is there markings on the carb that will tell me? I do not want to put this into the ground again because if ignorance. It seems to me to be much easier to ask the experts on this forum then to be stupid and spend more money.. I have read good things about these engines and do not want to upgrade unless I have too..

Thanks again

William Robison

My Feedback: (3)

Cougar:

Contrary to what Dave said, the fuel passages aren't really different, but the carb bore is so large on the "Pump" version carbs that they don't draw fuel well, needing the pressure feed. The standard carbs work fine with muffler pressure.

I've attached a picture of two K&B 40 engines, the one on the left is the 8360, with the Perry pump built in and the "Pump" carb. You can see it's much larger than the carb on the 8350 to the right, which is also a Perry carb.

The "Pump" carb has an extra screw visible on the upper face, between the intake venturi and the mixture disc/high speed needle. This is an auxilliary flow regulator for inverted mounting, normally left screwed in fully, at its maximum flow position.

If you have the pump carb you will most likely be unhappy with the engine unless you get a pump to go with it, or replace the carb.

If you have a standard carb plug the crankcase tap and go fly.

If you have the pump carb and would like to replace it with the standard Perry, I probably have one to fit, if I do I'll trade you straight up if yours in not damaged.

Bill.

cougar27mtr

My Feedback: (2)

bill..


Thank you I will run home and check this out.. What would be the main difference between the two? I mean is it better to put a pump instead of the standard carb? Mine should be fine as I have ran the motor over and over again trying to tune it :-) In the crash the prop did not break so the motor has no damage at all.. But if the pump gives me better performance then I think I would rather go this route. Where might I find a pump for this engine (if I need it?) Again It is nice to have such a nice and informative group to deal with

William Robison

My Feedback: (3)

Cougar:

The VP-30 pump is available from most hobby suppliers, here's the home page for Perry, part of Conley Precision:

http://www.perrypumps.com/

You can also find the carbs listed there.

Using the big carb is good or bad, depending on the application.

If you need max rpm, the pump carb will raise the available speed a good percentage over the stock carb, it's like putting twin carbs on you hot rod, lets it breathe more freely. And it needs the pump.

But if it's a large plane that needs a big prop at lower rpm, you'll be burning more fuel without going any faster. The smaller bore carb just works better at the lower rpm. And does not need the pump.

In either case, though, if you want to put the tank on the cg, or any distance from the engine, the pump does very well.

My C-3/10 twin uses a single tank in the main fuselage, each engine has its own pump. See picture.

Bill.

Hobbsy

My Feedback: (102)

Robert Varsane told me about the finer metering slots and Clarence Lee mentioned it in a response to someone, also the Perry pump carb for my Fox .74 does not have the extra screw shown in your picture but has a huge bore that is straight through, the only thing resembling a venturi is the spray bar sticking about halfway across the carb. The non pump Perry carb for the other .74 has a slightly smaller bore and some semblance of a venturi.

William Robison

My Feedback: (3)

Dave:

You're probably right about the slit sizes, I've just never noticed it. And "Venturi" is a term of convenience, even the smaller Perrys are pretty much straight through.

Maybe a slight venturi on some, but the Perrys on all my little HB engines, and the K&B 21 are straight through with no real venturi at all.

Your Fox "Pump" carb without the flow regulator is a new one on me - never seen a pumper version without the aux regulator. What's the bore on yours? Another thing I've never seen is a pump carb with less than 0.375" bore. Are you sure it's not a standard that you were told would work with the pump?

While I don't put myself up as the Perry expert, I have around fifteen engines with them, so I think I can speak with some authority. Whenever I buy a replacement carb it's a Perry. The people who have trouble with them usually are the ones who don't take the time to learn how to operate them.

Bill.

aceairspeed

Can anyone tell me what the power output is on a Webra Speed .91 ? Webra doesn't publish any such information but I'm hoping somebody knows. Also, what is the power difference between the Webra .91 and an OS .91 FX ??
Thanks
Ace

Hobbsy

My Feedback: (102)

Webra is smart in not publishing the HP numbers and neither does Fox, at least they didn't used to, but it will turn a 14x6 at a little over 10,000 on 5% nitro.

cougar27mtr

My Feedback: (2)

Why is it that on other engines they recooment a higher nitro then webra? Are they that efficient? What happens if you run too much nitro? I usually run ys20/20 in all my planes. I am so new to this I have no idea about the small details :-) I have 10 planes in my hanger anywhere from a 40 size trainer to a skybolt bi-plane and a 232 cap.

Thanks again

David_Moen

A used Webra that I was recently looking at to purchased turned an APC 14x6 at about 9850 rpm. It was an excellent starter and ran very smooth. Unforunatley it woudn't tun for long . I suspect it had something to do with the ST carb tha somebody had put on it.

Engines designed for the European market are set up for little or no nitro because it is very expensive over there I am told.

cougar27mtr

My Feedback: (2)

Does it hurt them to run more nitro then required? Is nitro like octane in a car? The more you run the cooler the engine runs?

David_Moen

I think that I've heard that the more nitro you run, the hotter the engine runs. Usually, if you are going to run more nitro than the manufacturer suggests, you need to install a metal shim between the cylinder and head. The Webra I was playing with had one.

The information that I have seen also says that more nitro also makes the engine more tolerant to needle settings.

cougar27mtr

My Feedback: (2)

Thank you all..

I added a pump today to my plane... It idles like a champ.. I am so excited I too off of work tomorrow to go play ;-) I could not resist.. Thank you again to all whom helped me.. Nice to have a site like this to get good help from good people


Keep the your wings level and safe flying

Hobbsy

My Feedback: (102)

I suspect that the ST carb on the .91 needed the spraybar rotated a few degrees to clean up the midrange.

David_Moen

Yeah, I heard you could do that.....after 3 nasty dead sticks....