Carburetor tuning

[Aron Gleason]

Well I found out I had to turn the idle screw down from 4 turns out down to 1 turn out on the wagner pcv valve. Everything else is the same, in fixed orfice mode with the high vacuum spring in, cruise screw flush. Afrs are better at cruise but I still have a really bad stumble from cruise to wot. My afrs will jump to the high 16's.

 

[Geoff 2]

Plug looks good. Stumble like this =more fuel needed.

 

[Aron Gleason]

Plug looks good. Stumble like this =more fuel needed.

I was told to go bigger squirters. And to put the 6.5 pv back in. Right now if have a 4.5 pv.

 

[Orig69]

The first thing I would do is install the vacuum gauge at operating temperature to see if there was any change, I believe you had 12 inches in park and 10 inches in drive.

 

[Aron Gleason]

The first thing I would do is install the vacuum gauge at operating temperature to see if there was any change, I believe you had 12 inches in park and 10 inches in drive.

Yes that's correct. Cruising i have 15-17 inches of vacuum according to my autometer vacuum gauge

 

[hunt2elk]

Best way to determine a power valve size is to get a vacuum gauge in the cockpit and watch it as you are driving. Pretty sure you can go even higher than a 6.5. A power valve can even be a higher value than idle vacuum because it is not in the idle circuit.
As far as the transition stumble, have you experimented with different pump cams? I would mess with them before changing squirters.

 

[Aron Gleason]

Best way to determine a power valve size is to get a vacuum gauge in the cockpit and watch it as you are driving. Pretty sure you can go even higher than a 6.5. A power valve can even be a higher value than idle vacuum because it is not in the idle circuit.
As far as the transition stumble, have you experimented with different pump cams? I would mess with them before changing squirters.

I have a vacuum gauge on the cowl. As long as a higher value pv wont cause the plugs to look rich I can go bigger. And ive experimented with pump cams and squirters when I was running breathers with hoses running out the atmosphere. And now im running a tunable pcv valve that makes a world of difference.

 

[Geoff 2]

The PV is merely a switch. It controls when more fuel is added. It does not control the volume of fuel added for enrichment; that is done by the PVCRs, two holes in the PV cavity. These may need to be enlarged to get more fuel into the engine. Some H carbs have fixed PVCRs that need to be drilled out, others have replaceable jets.

 

[hunt2elk]

I put those Wagner PCV valves on my cars as well. They seem to work well. I didn't have to retune the whole carbs, just the idle however. What carb do you have? Like Geoff stated above, the pvfr's may need to go bigger (mine always do). That is where it is nice to have a vacuum gauge and an air/fuel meter in the car. You can watch when the power valve is opening and make those 2 jets bigger to add more fuel during that transition if needed.

 

[Aron Gleason]

I put those Wagner PCV valves on my cars as well. They seem to work well. I didn't have to retune the whole carbs, just the idle however. What carb do you have? Like Geoff stated above, the pvfr's may need to go bigger (mine always do). That is where it is nice to have a vacuum gauge and an air/fuel meter in the car. You can watch when the power valve is opening and make those 2 jets bigger to add more fuel during that transition if needed.

I have a vacuum gauge that's permanently mounted on the cowl. Carburetor is a 950 double pump quick fuel carburetor, the metering block has fixed pvcr's. And i also have a afr gauge hence why I know the number its at while at cruise and wot.

 

[hunt2elk]

Kind of surprised that carb doesn't have replaceable pvfr's. I run Quick Fuel 850 double pumpers and also have 750's, they all have replaceable pvfr's.