Need carb help!

[Quick281]

Have a holley 650 ultra on a 306, was running great but now it idles rich as hell and the front idle mixture screws have to be all the way in to make it run half way decent. Has a new power valve and new gasket. No signs of a vacuum leak anywhere. Im thinking the metering block may be junk but im new to this carb stuff :idk:

 

[Michael B]

What are the cam specs? what jet numbers are in now? what is power valve opening hg? what is your target idle speed? what is base timing set at?

 

[Quick281]

Advertise Duration .006 - Intake:278 / Exhaust: 286
Duration at .050 - In:222 / Ex:230
Timing events at .050 - In: 1/41 Ex: 45/5
Lobe Lift @ Cam - In:.320 / Ex:.320
Gross valve lift w/ 1.6 - In:.512 / Ex:.512
Lobe Seperation 110
Degree intake lobe to 106

71/75 jets
4.5 pv
13* base timing
idle is set around 750

 

[Quick281]

Advertise Duration .006 - Intake:278 / Exhaust: 286
Duration at .050 - In:222 / Ex:230
Timing events at .050 - In: 1/41 Ex: 45/5
Lobe Lift @ Cam - In:.320 / Ex:.320
Gross valve lift w/ 1.6 - In:.512 / Ex:.512
Lobe Seperation 110
Degree intake lobe to 106

71/75 jets
4.5 pv
13* base timing
idle is set around 750

 

[Quick281]

When i first put the carb on everything was adjustable. I downsized the primary jets because it was a little rich and then it went to hell.

 

[Michael B]

Start with all idle mixture screws 1 and a half turns out from lightly seated. use a vacuum gauge to get highest reading. what were the original jets on the primary side? I'd have to pull my race setup apart to see the jets but I think they were 72/78. how much fuel pressure are you running?

 

[Quick281]

71/77 when i got it. Highest vacuum is when front idle screws are all the way in. 5 1/2 psi

 

[Michael B]

are the secondary throttle plates closed or slightly open? it sound like the primary plates are open too far and you are transferring to much fuel.

 

[Quick281]

They are closed. Got it all apart now. Cleaned, shot with air, new gaskets and trying again

 

[Quick281]

Running compression test also

 

[Michael B]

you may have to open the secondary's slightly to allow the primaries to close a little and cover the fuel transfer ports

 

[Quick281]

Must have had a stubborn piece of crud in there. 150 psi on all 8 cylinders. Still seems to be idling a little rich, but the idle screws are adjustable again. Breaks up a little a high rpm. Looking for new plug wires to try.