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Pressure on a TD .051 Empty Pressure on a TD .051

Post  Matt1967 on Sun Sep 30, 2012 12:05 pm

I have a TD that has a pressure tapped backplate and the pressure tap on the plastic carb body is closed off.

What is the difference between using one or the other?
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Post  SuperDave on Sun Sep 30, 2012 4:47 pm

Matt:

The previous owner may not have realized that the pressure tap on the plastic venturi body must be drilled out to work so ke installed a tap on the backplate????????

Either way should work fine.
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Post  ahrma_581 on Sun Sep 30, 2012 5:18 pm

Convenience: may be easier to get to bleed on back of engine or on side, depending.

Getting fuel line to stay on carb mount nipple can be difficult, so I've read. No barb. Maybe intended by Cox as an anchor for starter spring and then turned into pressure port by ambitious types later?
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Post  Matt1967 on Sun Sep 30, 2012 5:30 pm

ahrma_581 wrote:Convenience: may be easier to get to bleed on back of engine or on side, depending.

Getting fuel line to stay on carb mount nipple can be difficult, so I've read. No barb. Maybe intended by Cox as an anchor for starter spring and then turned into pressure port by ambitious types later?

Ok Sounds like it they are the exact same function.

Question #2 While on the subject, I thought I once read that you should not use crank pressure on a throttles engine, only muffler pressure with a throttle. Is that valid?
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Post  jsesere on Sun Sep 30, 2012 5:38 pm

You have to add a barb like the ones I have for sale.
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Post  RknRusty on Sun Sep 30, 2012 7:36 pm

The nipple on the carb body was always intended for a pressure tap. The springs didn't appear until later. You can get timed pressure in pulses every time the intake valve opens, or you can tap the backplate to get steady pressure. Use whichever best suits your fuel system, they have different applications. There are a few members here that know enough to give you more specific answers, so check back after the weekend. It gets pretty quiet here on Saturday and Sunday because everyone is out playing.

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Post  raglafart on Sun Sep 30, 2012 8:57 pm

We used to use the TD 049 and 051's for 1/2 A pylon racing here in Australia many years ago. The main use for the pressure tap is to enable the use of a larger venturi which will give more power.
We were using some pretty trick fuels back in the day, 50%- 60% nitro with some propylene oxide and all Klotz oil. Propped for 19000 - 20000 on the ground, any more and the rods became vulnerable.
Getting back to the pressure nipple, we all universally used the back plate pressure nipple. The timed pressure from the crankcase nipple was just too much and made needle tuning that much more of a hassle.
If you have a pressure back plate, I'd use that and leave the one on the carb body alone. We used the Kirn Kraft back plates along with the fine thread KK needle valve assemblies and the check valves too. Also used the Glow bee button heads with the clamp rings.
happy days, biggest shame was when the rule makers said you couldn't get 049/051's and went to 10's then 11's and then 1/2A as a class died. Crying or Very sad
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Post  ekitten2 on Mon Oct 01, 2012 3:46 am

<< rembers the good ole days out at SSME
http://www.ssme.org.au/
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Post  ekitten2 on Mon Oct 01, 2012 9:45 am

im concidering useing both rear pressure and a tuned pipe set up for a future rebuld of my mini hydroplane

can any one advise on a sutable tuned pipe??

and would pressure be helpfull as it wont be doing aerobatics or such (just low level speed runs) ?

your help is always well appreicated fanks ...Gazza
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Post  SuperDave on Mon Oct 01, 2012 11:49 am

Question on pressure fueling":

If an engine is turning, at say, 18K RPM, what's wrong with using the "pulse" from the venturi body?

Seems that would produce an plenty adequate flow of fuel. Huh... Huh...

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