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Author Topic: apt screw  (Read 4513 times)

Offline sticknstring

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apt screw
« on: February 22, 2011, 07:25:57 PM »
I've been searching the forum but I can find the answer to my question. Which direction leans out the mixture when adjusting the apt screw? Thanks, Bill
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Offline omaha

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Re: apt screw
« Reply #1 on: February 22, 2011, 11:07:34 PM »
what is the carb number? I believe that turning the apt screw "clockwise" will allow the needles to sit lower in the jets, therefore leaning the mixture. (the vacuum pulls the needles down against the spring).
This is of course is applicable to the later type of apt, accesible through the top of the  carb. (easily accesible when the carb top casting is off).  I do not know about the early, baseplate type of adjustment. It might be the same deal but I do not remember.
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Offline sticknstring

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Re: apt screw
« Reply #2 on: February 23, 2011, 05:05:55 AM »
Omaha, thanks so much for taking time to help me. The carb seems to be for a 1979 Buick. I've used cliff's recepie #1 for a 1971 455 olds w30 motor with headers and edelbrock intake. The carb # is 17058241. My problem is the adjustments to the apt either way don't seem to make much difference. The idle and and part throttle seems rich to me. Last night I moved the accel pump back to the outside hole and rechecked the float level and adjusted/lowered the primary needles, Do the primary needle need to just seat in the jet at the lowest position? I've never seen this explained. Anyway it seems better, maybe I'll try another apt adjustment tonight.
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Offline Cliff Ruggles

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Re: apt screw
« Reply #3 on: February 24, 2011, 03:49:03 AM »
Use the "tip in" test from our book.

If you don't observe a notcable speed increase during that test, the jet/rod relationship is not allowing full control of the A/F ratio via the APT.

What jets and metering rods are you using?

What is the float level and fuel pressure?

What size fuel inlet seat?.......Cliff
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Offline sticknstring

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Re: apt screw
« Reply #4 on: February 24, 2011, 05:24:22 AM »
Hi Cliff, I am using the tip in proceedure. I'm using 73 jets per your recomendation with the 44 primary rods you sent me. The fuel pressure is set by my Mr Gasket regulator at 5 psi and the float level is 1/4 inch.  Last night I adjusted my primary hanger/ power piston to try and get the rods to hang even. I adjusted the height to get the rods seated but loose in the jets when the piston is down, Is this the correct way to adjust the height of the rods? Thanks again, Bill
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Offline Cliff Ruggles

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Re: apt screw
« Reply #5 on: February 26, 2011, 04:37:58 PM »
The metering rods should be on the upper portion when the piston is down, and up on the tips when in the up position.  The APT screw will provide a range of adjustment as it locates the upper section of the rods in the jets, and they taper toward the tips....Cliff
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