A Little Proform Carb Tuning Advice Needed

[Charger_Dart]

Looking for a a little help on tuning the new Proform 950 race series carb on my Charger.

I have a Mopar Performance 500 crate motor and I have been running a Proform 750 DP street carb on a Edelbrock RPM intake for several years. It ran well, but felt flat above 4500 rpms. I finally got around to putting the car on a dyno and the chart confirmed that it was just not pulling like it should in the upper rpms. I used a wideband AFX air/fuel gauge to set up the 750 and it seemed to run best with about a 13.5 ratio at idle / cruse & 12 at WOT. I had to adjust the jets down from 74 to 72 on the primaries and 80 to 76 on the secondaries to get those readings.

So after reading about several people here (Ron comes to mind  ) recommending the Proform 950 for 500ci motors, I installed a new Proform 950 to see if I can get it run better, especially in the upper rpms. This carb has 78 jets on the primary side and 86 jets on the secondary side stock. Last night I hooked up my wideband which is installed just after the exhaust manifold and checked my readings. I get 13 at idle and 13.5 - 14 at cruise and 14 - 14.5 at WOT.

It seems to me to be running much better at all speeds (butt dyno) but the gauge is telling me its might be too lean during WOT blasts and I can hear the slight sound of a little pre-ignition.

How can those big 86 secondary jets run lean at WOT?

     

[firefighter3931]

Nice that you have a wideband to play with....makes diagnosis a whole lot easier 

Two things come to mind ; fuel delivery and float level. First thing to look at is the floats just to make sure the fuel level is showing half way up the sight glass. If the fuel pressure is dropping at WOT then it will go lean. You should have 6-8psi at WOT.

It might want more jet on the secondary side but i'd check those two things first. 


Ron

[Charger_Dart]

Thanks for you help Ron.
I have the floats set at the bottom of the site glasses so I will move them up some to get them in the middle.

On the fuel pressure, I don't have a fuel pressure gauge to check the psi. My fuel system is all stock with the vapor separator and small return line to the tank. I am sure its bleeding off some fuel pressure under all conditions so maybe that is part of the problem?  Whats the best way to check fuel pressure for testing purposes? I don't want to install anything that would change the look of the engine compartment long term. Thanks!

[firefighter3931]

With the Proform carbs you absolutely need to have the float level in the middle of the site glass. I know it's different from Holley and that's what can be confusing for those who are used to Holley float adjustments. 

What fuel pump are you running ? I like the Carter 120gph street pump which is rated at 6-8 psi. The old 440 ran great with that pump and a 3/8 line fuel system. Never a problem with fuel starvation 

As for fuel pressure testing ; you can install a temporary "T" fitting in the fuel line and run a guage taped to your windshield for some WOT fuel pressure observation. I've done it a few times and it works good to see what's going on as the car accelerates under load. Most vacuum guages also double as a fuel pressure tester....that's what i've used.

Before you do any of that set the float levels in both bowls to the middle and test. Report back with your findings 


Ron

[Budnicks]

With the Proform carbs you absolutely need to have the float level in the middle of the site glass. I know it's different from Holley and that's what can be confusing for those who are used to Holley float adjustments. 

What fuel pump are you running ? I like the Carter 120gph street pump which is rated at 6-8 psi. The old 440 ran great with that pump and a 3/8 line fuel system. Never a problem with fuel starvation 

As for fuel pressure testing ; you can install a temporary "T" fitting in the fuel line and run a guage taped to your windshield for some WOT fuel pressure observation. I've done it a few times and it works good to see what's going on as the car accelerates under load. Most vacuum guages also double as a fuel pressure tester....that's what i've used.

Before you do any of that set the float levels in both bowls to the middle and test. Report back with your findings 


Ron

Yeah, I was going to say/thinking that the size of the pick-up in the fuel tank & size of fuel line starving it possibly also, I would highly suggest/recommend to install a 3/8" pickup/sending unit in the fuel tank & 3/8" line minimum to the pump & carb too...  It couldn't hurt

[Mick70RR]

I run a Proform 950 on my 500 stroker and also have an A/F ratio gauge in the car. I've been playing around with the tune for a few years and found it doesn't like to cruise around 14.7 like everyone recommends. I drilled the idle jets out from 0.036" to 0.040" and the cruise A/F ratio is now around 13:1. Any leaner and it feels underpowered and goes lean when I give it a little gas. I have 74 jets in the primaries but I drilled the PVCR's out from 0.060" to 0.070" to richen it up to around 12:1 when the power valve opens. I jetted up to 92 on the secondaries to keep it rich enough when I floor it, around 11.5/12:1.
I also moved the idle jets to the lower position by drilling and tapping the metering block. That made a big improvement to the off idle response. I had a lean hesitation just off idle which nothing seemed to cure except drilling the idle jets to around 0.046". Once I made the mod I could use smaller idle jets without the hesitation and the idle leaned up to around 14:1.
These wide band gauges are great but they can throw you off course if you read too much into them. Tune the carb until the car runs right and then look at the gauge to see what the engine likes.

[Charger_Dart]

Great information - thanks!
I have raised the float levels to the middle of the site glass, but have not taken it out for a test drive yet. Thanks Mick for sharing what you did to get yours working, I may need to do some of the same but for now I will try larger jets in the secondaries if the float adjustment does not help.