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 T slot question 
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Joined: Sat Jul 25, 2015 2:31 pm
Posts: 75
I have a pair of 660 carbs. You guys helped me to get them set up on a tunnel ram. I never paid any attention to the t-slot on both primary holes on one carb. Not sure how I missed it, just assumed they would both be the same. When I set them initially to get the engine to idle, I set the slot to a square on both carbs and then used the secondary to adjust the idle. I pulled them off the other day after they had been sitting for awhile, and I noticed that one slot on the primary is correct, still a square, but the other primary is not showing at all. It is even with the throttle blade. Does it matter that it isnt showing that little square or should I take a file and lengthen it like the other one is? The base plates are billet from Allstate Carbs, if that matters. I havent measured their length to see if they were the same length or just cut in the wrong place.


Thanks guys


Wed Jul 13, 2016 7:14 pm
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Joined: Fri Feb 08, 2013 2:37 pm
Posts: 1701
Determine if the slots are different length, or if the shaft is out of plumb, or if the base is lop-sided (thicker on one side than the other). Perhaps the throttle shaft is twisted or there are burrs on the flats where the butterflies mount. Is a butterfly in upside down? (don't laugh) In other words, figure out for sure what is wrong. Hold the base up to a light and look at the light leakage around the closed butterflies. Determine if the light leakage is the same in both (or all) bores and how well the butterflies seal off the bores. Loosen the screws and shuffle the shafts and butterflies to the best fit.

The original 660 secondary slots are not exposed at idle. It is usually best for most carbs to have no secondary slot exposed so when idle vacuum varies with RPM or increases with cruise RPM the vacuum change does not have so much influence on secondary idle circuit flow when the secondary throttle is not opened.


Wed Jul 20, 2016 12:49 am
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Joined: Sat Jul 25, 2015 2:31 pm
Posts: 75
Thank you Tuner.

I'll check out the primary side as you suggested.

I looked at the secondary side, the slots are showing just a tad, you can barely see them. I will close the secondary plates until the slot is not visible. It will need air, so I need to drill holes in the primary plates I presume? If it needs more than drill the secondary? It has a pretty healthy cam in it, so it will need the air.


Wed Jul 20, 2016 5:40 pm
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Joined: Fri Feb 08, 2013 5:50 pm
Posts: 2302
No, leave drilled holes as a last resort, see where it ends up first. You have 8 barrels to get air in, may not need it.


Wed Jul 20, 2016 7:23 pm
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Joined: Sat Jul 25, 2015 2:31 pm
Posts: 75
ok, thank you. Will try it this weekend to see where it ends up. I hope it wouldn't need any holes drilled, it was just a question to see which plates you would drill if needed.


Wed Jul 20, 2016 8:22 pm
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