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Perry Pump Carb on Webra 145

Old 01-08-2005, 05:50 PM
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MTK
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Default Perry Pump Carb on Webra 145

As many have realized who run this engine, the standard TN carb tends to get a bit touchy when the weather changes. After almost 700 flights now, mine is tending to need a click more or less between cold (45- 50 deg) and warm (70-75 deg) on the main needle, and I find I am fiddling more than I want to, often between morning and afternoon.

I purchased the Perry no 5003 pump carb from Conley Competition Prod a few monhs ago for breaking in my 160, but soon as winter came around in NEFla, (when the temperaure tends to vary greatly), the 145 in my primary model started to act up so I decided to try the Perry carb on it.

A quick note about the Perry: it's housing OD is a slip fit into the Webra crankcase. In other words, perfect match dimensionally. BUT the 5003 also has a rather cavernous venturi at 0.437", compared to the stock TN (or MC) venturi of 0.353". I felt that if the .353 was finicky the .437 would have been impossible so I bushed the ID. Interestingly, I found that a standard Gator aluminum stab tube was just the right size, reducing the venturi to 0.375". This is a little larger than stock, which means the engine actually develops a little more power than had been typical. Most noticeable on the Snapping Bump in P05.

The Perry required a slight leaning of the idle ring (approximately 1/32" leaner), due to the smaller venturi ID, but it has been well within the carb's available adjustability. Main needle is 1 3/4 turns open, and it is very slightly rich at this setting at full throttle. The carb tends to run very slightly lean in mid range but throttle response is quite snappy through it, and the engine does not hesitate. Particularly evidenced on the bottom of the P05 Triangle, going back up, the engine takes the throttle much better, inscribing a better diagonal to the top. Idle rpm is significantly lower which helps the spin entries

I have about a dozen runs so far on this set-up and so far I like it better than the TN. I will post again as I get more runs and the settings finalized.

MattK

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