Carb tuning and suggestions plz

[stang387]

89 mustang
DSS 306 9.5 compression
4:10 gears
t-5 transmission
Victor jr. intake
Non-smog legal AFR 185's. Not ported but 100% polished.
Z-303 camshaft
1 5/8 long tubes, full mac exhaust.
Holley blue/regulator
10 Lbs vacuum at idle.
I have a 6 / 5 power valves in.




I had a similar setup 5 years ago and it flew with my holley 4150 750 DP.
Im using the same carb and its being a bEaCh!
It being a pain to get setup due to the big aftermarket parts on such a small engine with little vacuum.

Im needing advice on what to do.

I having a hell of a time getting my fuel ratio above 11.8 at idle and it even drops when i ease into it. I did drill a 1/16th hole in the primary butterflies and it seemed to help alittle.

It had a bad stumble at idle. The Innovate fuel/air meter said it was super lean during the stumble so i drilled out the shooter .004 and that fixed the stumble.
When i increase speed from a dead stop the stumble is gone, so i ease into the throttle then punch it. It gets even fatter. 11-10 and even to a high 9 on fuel ratio. I can probably fix the fat condition by changing jet sizes.

What is driving me nuts is the 11.6 at idle. I screw in the four adjusters slowly and equally in and it wont fix the 11.6. Then of course if i keep screwing in the four adjusters it creates a bad idle tries to die.

Took the carb off to turn the secondary idle up just alittle so i could close the primary as much as possible so less air would pass the idle transfer slot.

Today i drilled the idle air bleeds in the primary .002 and that still didn't change the A/F at idle.

Im about to give up and by some speed demon prbably in the 670cfm range.
Im dont want to put a small carb on the car and kill the 5,000+ powerband.

At the track i don't see that car ever getting below 5,500 so i would hate to choke the engine with a small carb.

Any idea welcome

 

[93 LX]

whats your vacuum at idle? If its low you may need to change the PV to help with your acceleration.

 

[Killer50stang]

Your not running a 750 with that setup are you? I wouldn't go over 650, you don't want to run too rich.

 

[12sec67]

did you check the float level?

Also for the stumble you can change you pump cams.

 

[12sec67]

Your not running a 750 with that setup are you? I wouldn't go over 650, you don't want to run too rich.

no, A 650 would be better off the line slightly but with the cam and the heads he is running the carb size is fine. I ran a 650 dp on my 306 with canfield heads and X-cam and a cam and then went to a 750dp and picked up a consistant 1.5mph in the 1/8.

 

[93 LX]

My Capri ran better with a 700 dp instead of the 650,,, better acceleration and higher speeds on the top end....

 

[Killer50stang]

no, A 650 would be better off the line slightly but with the cam and the heads he is running the carb size is fine. I ran a 650 dp on my 306 with canfield heads and X-cam and a cam and then went to a 750dp and picked up a consistant 1.5mph in the 1/8.

As long as it's tuned properly. I would think a 750 would be too much. I added a 750 when I went with my blower and it was plenty big.

 

[stang387]

Any more ideas would be appreciated.

The 750 is big for a 302. But when your setup for racing its fine.....it just needs extra tuning on the idle circuit.
I took a similar setup to the track 5 years ago and made one pass. Because of a mistake putting an evac system on a car with mufflers it only went 11.88 blowing oil everywhere. Evac doesnt work on cars with mufflers.....wish someone would have told me
Its getting 10 lbs of vacuum at idle.

Im thinking about putting a 650 demon on but im afraid of losing HP from 5,500 to 6,800rpm's.