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I need help
I gotta 71 Mach 1 with a 351C 2V inside. I replaced the intake manifold with an Edelbrock Performer intake and slapped an Edelbrock Thunder AVS 650 on top of it. My problems are that the engine will idle fine, but when I adjust the fuel/air screws I get no RPM increase or decrease when adjusting the left one(passenger side). Only changes when adjusting the right screw(driver's side). When I put the car in gear, she stalls and starts to backfire. I've searched for vacuum leaks, but so far I haven't found any. I move all the old vacuum plumbing over from the Cleveland intake. When I had it on the road after the swap, the engine would sputter, surge, and stall. When I open the throttle, I get a high pitched squeal, and I've checked for belts slipping. Is this all related? The reason I switched everything over, I was tired of rebuilding the autolite 2100 every time the car sat for an extended period. Any points in the right direction will be greatly appreciated.

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You may need to try slowing the idle speed down a bit then try to adjust the idle mixture screws until best vacuum is achieved. If the idle speed is set to high the carb idle circuit becomes not functional. A severe vacuum leak is very possible and worth checking out. Good luck.

351w - Ford racing GT40X 178 cc aluminum heads - Ford racing(crane) 1.7 roller rockers - Comp Cams 280H magnum cam .544" / .544" lift - ARP fasteners - hedman longtubes - magnaflow exhaust with X pipe -  MSD digital 6al box - MSD coil - optima red top battery - tuff stuff 140 amp alternator - ported weiand stealth intake  - edelbrock 1406 600 carb  - march pullies and brackets - Be cool fan controller - derale electric fan - FMX trans - motive 4.11 gears - traction lok - competition engineering subframe connectors - lakewood traction bars.                                            

Can you get your hands on a vacuum gauge? that will tell you what's going on
I'd also get a timing light to check timing and/or points. The backfiring could be timing related?

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The left air/fuel circuit in the carb is plugged, or major vac leak.
Disassemble, remove adjustment screws and clean every orifice and transfer port with carb cleaner and compressed air. Gotta be spotless, and not just pretty to the eye.

Squeal could be from a bad/slipped/improper sealing base gasket.

My bet is on the carb.

Pete - MotoArts Decals and Signs
'71 Sportsroof 351C-4V/4-speed - FINALLY under construction - no, wait, on hold again...
'90 Mustang 7-Up 5.0 ragtop, rolling beater
'66 Sunbeam Tiger Mk.IA, survivor
Sounds like a vac leak. I had the same problem which ended up being the stock 4V carb spacer. I swapped out with a cheap Mr Gasket spacer and she ran fine.

I'd also double-check timing, but I'm assume that's the very first place you checked.

-Former 70 & 72 Mustang Owner.
-69 Torino GT, Formal Roof, 351W, Edelbrock 600 cfm, Edelbrock 351W Performer RPM intake, headers, AOD trans, dual flowmasters w/H pipe, Pertronix II Billet, 3.5 TRACLOC g/r, 15" Magnum 500s, 100A alt, aluminum radiator, electric fan, Pro-car seats, mini-starter...owned since Dec 13.
-70 Mach 1, 351W, Edelbrock E-Street EFI, VHX instrument cluster, Hooker headers, dual flowmasters, Pertronix II, 15" Magnum 500s, 150A alt, aluminum radiator, dual electric fans, Pro-car seats, mini-starter
Did you just do the swap to the Performer intake? Our Cleveland engines are prone to vacuum leaks due yo improperly sealed intake manifolds. You really have to use a lot if gasket sealer in the front and rear valleys.
Yep, vacuum leak for sure. Rear of intake manifold. Gotta wait for engine to cool before ripping it apart :-(
When my buddie and I did my intake, we used a tube of gasket sealer that you can put in a caulking gun. Made it easier to make a mound of it along the front and rear edge.
On a Cleveland, I'd suggest NOT sealing around the intake ports themselves with RTV, only the water ports, end rails and corners.
Gas will eventually swell the RTV and turn it to snot, then get sucked in causing another leak.

Been there.

I'd first glue the gasket to the head (with a little 3M spray adhesive or dabs of contact cement) to keep them from slipping, then apply sealer where desired and install.

Pete - MotoArts Decals and Signs
'71 Sportsroof 351C-4V/4-speed - FINALLY under construction - no, wait, on hold again...
'90 Mustang 7-Up 5.0 ragtop, rolling beater
'66 Sunbeam Tiger Mk.IA, survivor
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