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BLP 4150 Transition Slot Questions

General engine tech -- Drag Racing to Circle Track

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63qcar
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BLP 4150 Transition Slot Questions

Post by 63qcar » Sat Sep 07, 2019 11:15 am

Just about have the carb ( mini annulars and merged collectors ) dialed in and was checking the baseplate for transition slot settings before putting it back on the engine when I saw something I haven`t noticed before . I set the primary and secondary slots at .020" and then noticed that on the primary , one of the slots was showing more than the other ..... enough that it was obvious to the eye .
So , it looks like the butterfly shaft may be bent/twisted slightly . Question is , does it really matter ( I think it does as the slots are unbalanced and that`s where the engine spends a lot of time around time around town ) and if so , can the shaft be "untwisted/bent " back ?

I may just change baseplates as I also have only 7" of vacuum at idle ( 1200 rpm ) and to get to that idle speed with the primary TS set at .020" , I have to have the secondary almost halfway into the TS . When both are at .020" , idle is in the 500 rpm range.

I have a spare plate that has 3/32" holes in the P/S butterflies and everything appears to be true on that one . I`m now trying to decide if I want to switch baseplates and what would it do for me .

Thoughts ?

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BOOT
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Re: BLP 4150 Transition Slot Questions

Post by BOOT » Sat Sep 07, 2019 9:41 pm

You might be able to get a replacement shaft form BLP
Channel about my projects https://www.youtube.com/user/BOOT350V

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Geoff2
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Re: BLP 4150 Transition Slot Questions

Post by Geoff2 » Sun Sep 08, 2019 5:46 am

I have had carbs with twisted shafts that cause uneven transfer slot opening. Have always been able to fix it twisting the shaft back to the correct position.

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MadBill
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Re: BLP 4150 Transition Slot Questions

Post by MadBill » Mon Sep 09, 2019 8:36 pm

Yes, give it a tweak; worst case, if it goes badly wrong you'll have to replace the shaft, just as you will if you don't want to untwist it. (And tweaking it eliminates the risk of mangling the screws or threads.)
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