1967 GT500 baseline carburetor settings - Ford Mustang Forum
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post #1 of 2 (permalink) Old 12-20-2019 Thread Starter
Brawlin' Boss's Avatar
Joined: Jan 2012
Location: Laredo
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1967 GT500 baseline carburetor settings

Hello, I'm working with a customer's '67 GT500 dual carb setup with a stock healthy 427. The engine is rather slow to rev, just not as reponsive as I would expect it to be honestly. I just sent the carbs out to get re-done and well they came back looking beautiful but they ran like crap once installed. I had to reposition the throttle plates since they were sticking and wouldn't let it idle below 1600 rpm. Once I got that settled I noticed they stumbled quite a bit more than they used to. I noticed that one downleg booster on the front carburetor just pukes fuel on acceleration and on test drives like I said it cruises fine just doesnt have that hellacious throttle reponse I would expect it to have. Timing is on the money with 34 total timing and it starts and runs just fine. I just really want to get the customer excited about his car when he revs and maybe punches it. I decided to just take the carburetors back off and go through them myself to try to figure out what size jets, discharge nozzles etc.. they have to attempt to help make them better. I have experience with carburetors but far from an expert. Dual carbs I imagine are a little more complex in tuning. So I was hoping for some baseline info to help me get the carburetor to at least factory glory. Anyone know stock jets sizes, discharge nozzles, etc... and any idea what I should look for for that one booster that pukes fuel on accel.

Thank you!

Current cars: 2012 Boss 302 C/O 11.84 @ 117
1999 Pontiac T/A LS3 427 Drag car - Low 10's
1985 Chev. Z28 355 Drag car

Project cars: 1970 Hemi 'Cuda
1971 Dodge Demon 340
1978 Ford Mustang II 2011 3.7/6M swap
1993 Mazda RX-7 LS1 swap
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post #2 of 2 (permalink) Old 12-20-2019
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Joined: Apr 2011
Location: Yadkin Valley
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I've never done a dual setup but I can't imagine it is proper for one jet to squirt more than the others.

The "expert" who rebuilt them probably removed the throttle plates which is why they were binding. Unless you have to replace or re-bush a shaft those screws should never be touched, because they are staked to prevent backing out, getting swallowed and then you know what. If he messed with the screws then buy new ones so you can align the plates properly and stake the screws down. Don't rely on Lock-tite.

The same joker probably used a wire to clean out the pump orifice that is puking. I have seen, recently, an after market adapter set that turns the single stream into a fan shape so that may be an option to make a repair.

2005 4.0 MT dual exhaust GT mufflers GT suspension and wheels
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