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2x4 on 383 Carb question Jump to page : 1 Now viewing page 1 [50 messages per page] | View previous thread :: View next thread |
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chefothefuture |
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Member Posts: 49 Location: Chuckanut Mountain, Washington | Hi all- I recently had a pair of AFBs pro rebuilt. 2652 and 2653. 1) On the primary carb (2653) the idle speed screw has to be opened 3 1/2 turns before it has any effect on the idle speed. The secondary(2652) effects the idle speed at one turn. Is this normal? I'm also having trouble getting an idle speed (at full engine temp) of greater than 630RPM. 2) When the idle mixture (not speed) screws are just adjusted where the engine runs smoothly, there's excess smoke at the tail pipes indicating poorly burnt fuel; when the screws are adjusted leaner to where the exhaust is fairly clean, the engine idles poorly. Any thoughts appreciated :-) Cheers, chef | ||
ABloch |
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Expert Posts: 1476 Location: Pacific Northwest | Timing? Have you tried bumping the timing up a few degrees? Might help on curb idle then back off a smidge if there is too much pre-detonation under load. | ||
chefothefuture |
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Member Posts: 49 Location: Chuckanut Mountain, Washington | Two things with the dizzy. It’s an MSD Ready to Run so I’ve been adjusting the timing as well as using different springs for different advance curves. W/o the vacuum advance connected, I have it at 12.5BTC. The vacuum port on the carb is below the throttle plates so with the vacuum line connected it’s at @ 14.5BTC. Yet even at this amount of initial advance, I’m still having issues with rough idle when the idle screws are lean enough for the exhaust to be fairly clean. | ||
57chizler |
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Expert Posts: 3776 Location: NorCal | With the primary carb idle screw in 3 1/2 turns, you might be exposing too much of the transition slot which will cause a rich idle. You might try opening the secondary carb more and closing the primary carb some (same amount of turns on both) to allow the correct amount of air without exposing the transition slot in either. | ||
Shep |
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Expert Posts: 3393 Location: Chestertown, NY ( near Lake George) | Assume the carbs are balanced, referring to throttle blade positions at idle? If not you will find it difficult to set mixtures. | ||
chefothefuture |
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Member Posts: 49 Location: Chuckanut Mountain, Washington | 57chizler - 2021-10-13 2:33 PM With the primary carb idle screw in 3 1/2 turns, you might be exposing too much of the transition slot which will cause a rich idle. You might try opening the secondary carb more and closing the primary carb some (same amount of turns on both) to allow the correct amount of air without exposing the transition slot in either. The screw that's open 3 1/2 turns is the center idle speed screw; a brass screw with a 9/16" hex head. Did you mean the mixture screws on either side of that? It might be beyond my knowledge but thought the speed screw allowed air to bypass the butterflies to increase or decrease the idle speed. | ||
60 dart |
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Expert 5K+ Posts: 8947 Location: WHEELING,WV.>>>HOME OF WWVA | With the primary carb idle screw in 3 1/2 turns, you might be exposing too much of the transition slot which will cause a rich idle. i did this yrs ago and it didn't take long to learn not to do it again -----------------------------------later | ||
57chizler |
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Expert Posts: 3776 Location: NorCal | chefothefuture - 2021-10-15 9:15 PM 57chizler - 2021-10-13 2:33 PM With the primary carb idle screw in 3 1/2 turns, you might be exposing too much of the transition slot which will cause a rich idle. You might try opening the secondary carb more and closing the primary carb some (same amount of turns on both) to allow the correct amount of air without exposing the transition slot in either. The screw that's open 3 1/2 turns is the center idle speed screw; a brass screw with a 9/16" hex head. Did you mean the mixture screws on either side of that? It might be beyond my knowledge but thought the speed screw allowed air to bypass the butterflies to increase or decrease the idle speed. I wasn't aware that both carbs have the center idle screw, I thought you meant the butterfly idle screws. Do the carbs have both the center idle screw and the idle screw that opens the butterflies or just the center screw? | ||
chefothefuture |
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Member Posts: 49 Location: Chuckanut Mountain, Washington | 57chizler - 2021-10-16 4:22 PM chefothefuture - 2021-10-15 9:15 PM 57chizler - 2021-10-13 2:33 PM With the primary carb idle screw in 3 1/2 turns, you might be exposing too much of the transition slot which will cause a rich idle. You might try opening the secondary carb more and closing the primary carb some (same amount of turns on both) to allow the correct amount of air without exposing the transition slot in either. The screw that's open 3 1/2 turns is the center idle speed screw; a brass screw with a 9/16" hex head. Did you mean the mixture screws on either side of that? It might be beyond my knowledge but thought the speed screw allowed air to bypass the butterflies to increase or decrease the idle speed. I wasn't aware that both carbs have the center idle screw, I thought you meant the butterfly idle screws. Do the carbs have both the center idle screw and the idle screw that opens the butterflies or just the center screw? I probably should have been more specific. Both primary (2653) and secondary (2652) carbs have the center screw for idle speed. (In the 300E supplement they're referred to as "Idle By-pass air screws") | ||
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