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Ford 9N, 2N & 8N Discussion Forum

on jet size...

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ron,ar

07-21-2006 07:15:01

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Last night some of us hashed out a problem with my carb problems. It was suggested that I might have the idle (low speed) jet and the main (high speed) jet in the opposite places. I disassembled the carb this morning, measured the two jets and they are NOT the same size outside diameter. The main jet is smaller outside(157 thousands) but has a larger orfice. The idle jet is larger outside (184 thousands) but has the smaller orfice. I did have them in the right place, they are not interchangable. I removed all jets, nozzles and other parts. I stuck the hose on our parts washer (low pressure) into the hole that the main nozzle tube goes in and got good full return back through all passages. I am fairly well convinced that the carb is right. Despite what has been said in articles I have read, the adjusting needles DO NOT seat in either jet. I think the jet that is under the main nozzle tube is a fuel limiting jet. The Main adjusting needle actually seats against a fixed brass jet/tube in the bottom of the carb. Air crosses the surface of the main nozzle and sucks fuel through the opening between the fixed tube and main needle, up through the limiting jet (economizer jet) and out the main nozzle into the venturi.Vacuum loss anywhere will cause my problem I think. Is this about what you guys see here?

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flathead

07-21-2006 09:52:46

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Re: on jet size... in reply to ron,ar, 07-21-2006 07:15:01

Ron,

The idle and main(aka maximum fuel limiting) jet will not interchange. The idle jet has a larger diameter. The economizer jet has the same diameter and thread pitch as the main jet. The economizer will fit in the main jet hole but the main jet will not fit in the economizer hole (located in the throttle body) due to a shoulder on the main jet. The economizer jet has no shoulder. By the way, the main jet is located directly under the main nozzle in the lower body.

I"ve seen posts of folks quoting jet orifice sizes, but they are inconsistent with what I"ve measured (using fine drill shafts and a micrometer).

Also, be aware that the idle and economizer jets changed between the tsx33 and the tsx241(series). The main remained the same on all 9n, 2n, 8n carbs.

Hope this helps.

flathead

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ron,ar

07-21-2006 10:51:01

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thanks flathead in reply to flathead, 07-21-2006 09:52:46

That confirms my own findings. I will look for a vacuum leak around the manifold later today. I will post the results. Thanks again.

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flathead

07-21-2006 11:02:28

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Re: thanks flathead in reply to ron,ar, 07-21-2006 10:51:01

Another place to check for a vacuum leak is the throttle shaft. A drop or two of heavy oil (like gear oil) can momentarily seal up a vacuum leak between the throttle shaft and bushing and help confirm or eliminate this location.

best of luck.

flathead

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K.LaRue-VA

07-21-2006 12:32:50

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Re: thanks flathead in reply to flathead, 07-21-2006 11:02:28

How rotten is your manifold? It is possible, since this is all one casting, that you may have an internal crack or corrosion that has joined the intake and the exhaust. This could cause very strange things to happen.

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