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Question on my air fuel ratio on my supercharger wagon

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djfalcon10
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Question on my air fuel ratio on my supercharger wagon

Post #1 by djfalcon10 » Thu Apr 18, 2019 9:55 am

Ok guys I need some help. Got a 65 falcon wagon with a 300 in it with a Paxton supercharger. Just got the motor togetter. Put the blow Thur hat and hook the the piping. Have a areomotive boost reference fuel pressure gauge. I have an autometer air fuel ratio gauge.the O2 sensor hook up by the collector on the primary side of the header meaning it's running off the 1 2 3 cylinders of the front engine .And I am running dual exhaust. when I rev the motor up in idle. the fuel pressure gauge goes up so I know it's working..when I took it out the tested it. I got on it. the fuel pressure gauge want to 11 but my air fuel ratio was on the lean side it was showing 17 so I back it off. My boost gauge whole 5 lb of boost. The fuel pressure set at 6 PSI. the carburetor is a Holley 650 double pumper what's 67 Jets upfront and 74 jets in the rear. Wondering why I ran it ran lean but still had fuel pressure going up. Do I need to up on the Jets and go higher? if anybody can help me on this I work preciate it and I did check all the plugs and they're all coffee cream colored but none of the electrodes were burnt off. Thanks

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Re: Question on my air fuel ratio on my supercharger wagon

Post #2 by pmuller9 » Thu Apr 18, 2019 7:27 pm

What modifications did you do to the power valve circuits?

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MechRick
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Re: Question on my air fuel ratio on my supercharger wagon

Post #3 by MechRick » Thu Apr 18, 2019 8:25 pm

Carbs used with blow-through setups will need to be incrementally richer. I recommend getting a good book on the subject (if you haven't already). I like Street Supercharging (S A design books, Pat Ganahl). It has a whole chapter on carb tuning for use with blowers.

https://www.amazon.com/Complete-Guide-S ... 1613251319

There is an issue with blow-through carbs that will be almost impossible to tune around. At part throttle when the supercharger is making boost, but the throttle plate is allowing vacuum in the intake, the pressure difference will force power valves (or metering rods) closed (lean). One way around this would be to reference the back side of the power valve to atmosphere instead of boost. Most tuners just set the carb up extra rich.

Since you are blow-through, a smaller carb might work (and tune) better.
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djfalcon10
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Re: Question on my air fuel ratio on my supercharger wagon

Post #4 by djfalcon10 » Sat Apr 20, 2019 6:04 pm

I replace the floats and needle an seat for blow Thur. Hot rod mazgine had..how to do a blow Thur for under $50. There was a other web site that I think was called hanger 18. Showed how to make a blow Thur. I did not drill out the idle circuit behind the power valve.. I am running a 2.5 power valve cause of the cam. But it not boost reference. Any more questions. Feel free to ask

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Re: Question on my air fuel ratio on my supercharger wagon

Post #5 by pmuller9 » Sat Apr 20, 2019 11:59 pm

The lean condition is happening under manifold pressure which is where the Power Valve is also presently referenced so the reference point is not the problem. No need to drill an external PV chamber passage.

You will need to increase the primary main jets some as long as the part throttle low speed doesn't get too rich
then carefully drill out the two Power Valve Channel Restriction passages a little at a time.

Does this car see a lot of street or mainly strip use?

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Re: Question on my air fuel ratio on my supercharger wagon

Post #6 by djfalcon10 » Mon Apr 22, 2019 7:24 am

Yes . It does see lots of street time. But I do take it to the drag strip twice a year. When I am cruising the car. The a/r is reading 12.5 to 13.6.. I will be taking the car to the dragstrip next Sunday April 28th so I can do a lot of tests in tuning out there so I guess I will jet it up more and see what happens.

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Re: Question on my air fuel ratio on my supercharger wagon

Post #7 by pmuller9 » Mon Apr 22, 2019 10:26 am

Try to get the WOT A/F ratio down in the 12s BEFORE you get to the drag strip so you don't damage the new set of pistons.
I suspect you will need to drill out the two Power Valve Channel Restriction passages to get rich enough at WOT.

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Re: Question on my air fuel ratio on my supercharger wagon

Post #8 by djfalcon10 » Mon Apr 22, 2019 9:51 pm

I will do that. I will start with a 5/64 drill. Then go out and wot. And see what the a/f is.

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Re: Question on my air fuel ratio on my supercharger wagon

Post #9 by djfalcon10 » Sun May 05, 2019 3:04 pm

Hello again. Okay I drill out the power valve restrictors.when I am driving the car at normal speed let's say 45 mph. I am not in the boost but my fuel pressure gauge goes from 6 to 7 psi.the AF show 12.5 to 13. When I step on the gas a little. It drops to 10 to 11. I have step on the pedal have way. Have it shift to all three gears. And it goes up to 13.5 to 14.. the Jets in the front are 72 and the rears 74. My question is do I need to upsize to Jets more. or do I need to Floor it. at wide open throttle to see where my air fuel is.I'm just a little nervous cuz last time i did it went to17 ..I'd back door off. again thank you for your help and I think I am heading in the right direction I just want to be sure

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Re: Question on my air fuel ratio on my supercharger wagon

Post #10 by pmuller9 » Sun May 05, 2019 10:04 pm

First try to get the ratio to stay in the low 13s at half throttle while going to the gears.
Go up two on the mains. You may also need to go up on the secondary mains.

Eventually you will have to do WOT and carefully watch the A/F ratio gauge.

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Re: Question on my air fuel ratio on my supercharger wagon

Post #11 by djfalcon10 » Sun May 26, 2019 5:08 pm

Ok. Sorry it took so long. But the weather be crappy here.here what I got. The Jets are 76 primary and the secondary are 83. Took it out for a drive today. At idle in gear. It is at 12.5 to 13.1 a/f. Crusing the car at 50 mph. The a/f is at 10.1 to 10.9. now when I got on it wot it was at 11.8 to 12.3. so it not running lean. Is this good? Now at crusing it on the rich side. Should I jet it two size down.? Or just leave it alone. There was no pinging or nothing and the car pulled really hard. let me know what you think and again thank you for helping me out I do appreciate it.

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Re: Question on my air fuel ratio on my supercharger wagon

Post #12 by pmuller9 » Mon May 27, 2019 9:49 am

Both the idle and WOT are good.
It would be nice to get the cruising leaner so it doesn't carbon up the engine.
I'm wondering if the power valve is adding fuel during cruising.

Can you tell what the intake manifold vacuum is at 50mph cruising?
What rpm is 50 mph?

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Re: Question on my air fuel ratio on my supercharger wagon

Post #13 by guhfluh » Mon May 27, 2019 10:22 am

Sounds like your fuel pressure may be referenced to manifold pressure below the throttle blades? It needs to be referenced above the carb, in the hat.
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Re: Question on my air fuel ratio on my supercharger wagon

Post #14 by djfalcon10 » Mon May 27, 2019 1:30 pm

At 50 mph. It at 2800 rpms. I will have to look at the vacuum again to let you know. at idle it has 7" of vacuum. I have a ,3.5 power valve in it now.. The boost reference is attached to the carb hat
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Re: Question on my air fuel ratio on my supercharger wagon

Post #15 by pmuller9 » Tue May 28, 2019 9:55 am

If the cruising vacuum is below the 3.5 power valve rating then that is the problem.

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Re: Question on my air fuel ratio on my supercharger wagon

Post #16 by djfalcon10 » Tue May 28, 2019 11:37 am

Ok. So if my crusing vacuum say is at 12 . Then I don't have the right power valve. Correct?

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Re: Question on my air fuel ratio on my supercharger wagon

Post #17 by pmuller9 » Tue May 28, 2019 11:46 am

Is 12 what you are actually seeing at cruise?
If you are cruising at 12 the power valve is good as is.
You want the power valve below the idle and cruising vacuum so it keeps the extra fuel off until WOT or boost.

If that is the case then try dropping the primary main jets by 2 and see what the cruising A/F ratio does.

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Re: Question on my air fuel ratio on my supercharger wagon

Post #18 by djfalcon10 » Tue May 28, 2019 12:00 pm

Okay that was just a guesstimate on my on my cruising with 12 inches of vacuum.I will let you know by this weekend if it doesn't rain for sure what my vacuuming is at cruising speed

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Re: Question on my air fuel ratio on my supercharger wagon

Post #19 by guhfluh » Tue May 28, 2019 4:56 pm

Since you have a mechanical secondary, do you have a primary and secondary power valves? If so, they also sell boost only power valves that can help with tuning the fuel curve. Primary can stay regular and secondary can come in at 3+psi or whatever you want. They're for sale on ebay and take some clearancing of the carb base and blocking the vacuum reference on that valve I think.
1967 F-250 Crew Cab 2wd, 300 6cyl, T-170/RTS/TOD 4-speed overdrive
240 head, Offy C, EFI exhaust manifolds, Comp 268H, mandrel 2.5-3" exhaust, Edelbrock 500, Pertronix ignitor and coil, recurved dizzy. 200whp/300wtq

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Re: Question on my air fuel ratio on my supercharger wagon

Post #20 by djfalcon10 » Wed May 29, 2019 12:41 pm

I actually bought myself a 650 dp demon blow through carburetor. Has power valve in primary.but none in the secondarys

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Re: Question on my air fuel ratio on my supercharger wagon

Post #21 by djfalcon10 » Sat Jun 01, 2019 11:52 am

Okay I took my car out today. Cruz in the car at 50 miles an hour the vacuum reads 13. So I'm assuming my power valve on 3.5 is okay? So now I am going to go down to jet sizes on the primary and see what happens

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Re: Question on my air fuel ratio on my supercharger wagon

Post #22 by pmuller9 » Sat Jun 01, 2019 2:26 pm

Yes the 3.5 power valve is good.
Yes on two main jet sizes down on the primaries to see if it leans out the 50 mph cruise air fuel ratio.

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Re: Question on my air fuel ratio on my supercharger wagon

Post #23 by djfalcon10 » Sat Jun 08, 2019 8:24 pm

Ok. I down jeted the carb and now the reading is 11.9 to 12.5. so it's good. But now I have other problem. The blower belt keep coming off when I put a load on it. So I put on a bolt on tensioner. I think I need a spring load tensioner. But I don't know what kind to get. Hope you guys can help me with this. Here a pic of how it looks without the blower belt
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