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Melted velocity stacks

Anyone know what would cause my velocity stacks to do this?
Old 11-10-2015, 03:48 PM
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83 911 Production Cab #10
 
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Major backfire???
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83 911 Production Cab #10, Slightly Modified: Unslanted, 3.2, PMO EFI, TECgt, CE 911 CAM Sync / Pulley / Wires, SSI, Dansk Sport 2/2, 17" Euromeister, CKO GT3 Seats, Going SOK Super Charger
Old 11-10-2015, 03:49 PM
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Thanks, I know they need to be replaced but should I replace them before I adjust the carburetor and valves?
Old 11-10-2015, 03:52 PM
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lean pop starting fire in intake.

Get everything adjusted. Not only bad for plastic velocity stacks but bad for your engine to run lean. They won't cause any issue to run for a period of time unless the plastic if flaking off.
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Old 11-10-2015, 04:15 PM
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Thanks
Old 11-10-2015, 04:17 PM
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Are both sides doing this? Only one side points to a linkage adjustment problem. The carbs would need to be balanced L to R.
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71 911T SWT - Sun and Fun Mobile
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classicautowerks.com - EFI conversion parts
Old 11-10-2015, 04:29 PM
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Both sides are doing it but the left side is quite a bit worse than the right side. I've ordered a carb calibration gauge, should be here tomorrow or Thursday, so that's my next project. Adjusting and balancing the carbs. This is actually my first carbed car, and I've probably picked one of the most complicated cars to learn carb adjustment on.
Old 11-10-2015, 04:53 PM
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Yup, plenty of fuel vapor floating around above those stacks, and any little lean pop lights it right off. Just a quick flash, but repeated often enough and there you go. These plastic stacks melted back when the cars were new, too.

But, to the contrary, you are fortunate to have Webers to play with. Very simple and straightforward to tune. No magic or mystery. Lots of good information available out there to guide you. Get them running correctly, observe proper start-up procedure, and replace them with metal stacks cause no matter what you do its still gonna pop now and then.
Old 11-10-2015, 05:06 PM
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Yea I've found so much info on how to adjust them. I think it's that there are 6 barrels to tune that makes them seem complicated. Anyone know where you can get metal stacks for these, I didn't see them avaliable from pelican?
Old 11-10-2015, 05:15 PM
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Look up alfa 1750's eBay store. If you don't see them send a email he has come with some new parts for my Zeniths that many folks said were NLA. Good luck
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Old 11-10-2015, 10:28 PM
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************ has the metal 40mm air horns for weber or zenith. ************.com. Not cheap.
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Old 11-11-2015, 03:37 AM
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same as VW 40idf. Easy to find at reasonable prices.
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71 911T SWT - Sun and Fun Mobile
72 911T project car. "Minne" - A tangy version of tangerine
classicautowerks.com - EFI conversion parts
Old 11-11-2015, 04:17 AM
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