Carb Help

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Joined
Jul 6, 2015
Messages
4,348
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209
Location
Iowa
My Car
1973 Mustang Grande 351C 2v
Ok. need some suggestions here.

Engine is 408 Cleveland Stroker kit from Tim Meyer
Cam is 229/239 @ .050", 114 LSA, 108 ICL, .614"/.623" lift. Full Roller (spec'd by Brent at Lykins)
Air Gap Intake
Trick Flow 225 CC Alum Heads
Static Compression at 10.9
Dynamic is about 8.4
Carb is QF 750 DP Diamond Series. (Elec Choke, hooked up to dedicated 12V switched circuit)
3.7 gears
5 speed Manual
Distributor is a custom from Performance Distributors

Here is where I am at with tuning.
Using Vac Gauge and car warmed up
Initial Timing at 16 BTDC (Vac Advance disconnected)
All in at 36 BTDC around 3,300 RPM
Using the 4 corner idle, I adjusted via 1/4 turns to get the highest vacuum reading of 12.5. This also happened to be at the point if I adjusted them either in or out I would loose RPM so it should be the sweet spot. Idle speed is set around 850 - 900. High Idle circuit is around 1,650. Went cruising last night and car ran fantastic, no bog, very snappy, smooth idle, no dieseling when shut off. I do have a slight heat soak issue as when hot it turns over slow but always fires off. Decided I was just going to take it to work today so I didn't take it back to the shop last night. Went out this am, gave it a few pump and it fired right off into high idle. Let it run for a good 2-3 minutes (ambient temp was 65) Kicked it out of high idle and immediately died. No cough nothing. Started it back up ran good when on the gas. Let off gas coming to next stop light as I put the clutch in and again died. Decided to just get it back to the shop and take my daily to work. Got to the shop and it was warmed up and idled just fine at 850-900. Any thoughts? I tired to include as much info as possible in the initial post.
 
My thought is you leaned the idle circuit out too much. The actual engine idle demand and the "high gauge vacuume reading" often are not compatible. Quick and simple fix may just be 1/8th turn out of all four idle screws. This just may be a case of giving a particular engine what it wants vs the general rule of thumb high vacume reading.
 
Backed out he screws all 1/4 turn. Fired it up let warm up in high idle for a couple min and kicked it down and it kept running and idling smooth. Granted it is now 76 outside. I will test out again when it is cooler out. But thanks for the help. I'm sure I sill have more tuning to do on this carb so I may be back for more advice in the near future.
 

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