Buford T Justice -- the full tour

[TheSilverBuick]

Was your gas can test a gravity feed or did it feed the inlet of the mechanical pump? If you used the mechanical pump with the gas can it could be pump limited. That is the problem I ran into last Drag Week at Thunder Hill, had enough air to max out my fueling.

Factory 3/8ths or 5/16th line?

[milner351]

I'd be tempted to swap fuel pumps.

[tedly]

Restriction at the carb inlet maybe?

[Brian Lohnes]

Randal, we plumbed the can into the pump. You think the pump could be running out of snot at 240/250hp? I am not ruling anything out, but I was thinking that the carb wasn't pumping itself dry because that condition would have shown up on the dyno charts as big waves in the AFRs. They just stay dead ass flat, for the most part. The runs where they aren't flat are when we were messing with stuff. Here's one of the sheets from today to give you an idea:

[STINEY]

Pump not keeping up is my bet also.

Any butt-dyno guess on how many seconds pass when it hits the 3500 rpm point?

My guess this is exactly the point the bowls are running low. Not dry, but not full and happy.

[andy30thz]

Where is the O2 sensor placement? If its stuffed in the end of the tail pipe....there are a lot of places for unmetered air to sneak in and foul up your reading.

If you have a welded bung in the collector and no header gasket leaks...I'm clueless!!

[Brian Lohnes]

Andy, this time it was in the tail pipe, but the last time we were there (and getting the same readings) it was in the header collector.

The pump very well could be it, guys. I was taking for granted that it had enough guts, but maybe not.

Stiney, so when I am in the car, I bring it to 2500 in third gear, hit the green button and then roll into full throttle. 3500 is about the point that it is really starting to work and then it climbs steadily to 5500 when it clips the rev limiter. So from 2500-3500...maybe a couple of seconds, and then significantly longer than that from 3500-5500

[andy30thz]

I'm assuming this is just a el'cheapo stock fuel pump. Is it possible to for a mechanical pump to be weak?
I always assumed a mechanical pump worked, or it didn't.
But man it would seem like at the beginning of the pull the AFR's would be OK and drop over the pull....

At what point would you expect the engine to break-up/pop/fart from going lean? Past 14:1?

No detonation? What do the plugs look like? They should be white as a ghost!

[andy30thz]

Is there a display where you can read the O2 at idle?
Can you change the idle mixture and see it change on the screen?

I just have a hard time believing the sensor with all the changes you've done with no impact on AFR?!!?!?
What the *&%(^* is going on here?!?!?!

[Brian Lohnes]

I am reasonably sure the pump on the car is an AirTex 40987, which is a standard issue mechanical pump that would have been found on Camaros and stuff in the early 1970s. The car had a return style mechanical pump on it with a deep well or bowl. I wanted to go to a shorter "standard" pump because it was all really tight with the steering components and stuff. I have the former return line capped (spoiler alert, I will need it in the future). We uncapped it to see if the tank was air locking or something without that line open. It wasn't.

Anyway, the AirTex pump is rated at 40 gph free flow. Of course this is not free flow as there are restrictions and stuff with the pump pushing the fuel into the carb. I am honestly not sure of the math on what the actual output of this thing is when being used as opposed to openly flowed.

In comparison, Edelbrock's 1721 mechanical pump moves 110 GPH. There's a lot of variation in the mechanical pumps, obviously!

[Brian Lohnes]

Andy, yes we were tuning the idle mixture and watching the AFRs move real time as Travis and I adjusted the mixture screws.

It really is frustrating as hell, but on the flip side I am happy that it'll make 10 pulls and drive 30 miles each way!

[Barry Donovan]

nice write up on the driveshaft..

the frustration of being the biggest chassis and oe parts already, there is no way to go, but some hefty dollars. that is a nice piece they made.

To go along with how serious that is, I dismantled an awd Subaru to find 3 cracks in the tunnel and two rub spots that went through all layers into the car...past marks of a grotesque driveshaft failure. The luck for this cheap buggy was that the next model car up had a bigger diameter. Now faultless.

your current posts with the fuel, I agree..time to scrap those old fuel pumps.

you do have new pipes, and large.. that will be a leaner for quite some time. and also, if it is a 16 afr with a good pump, just retard timing.
I am playing with the same realm right now, gauge up and running at all times.

this chase in circles does end.

[andy30thz]

What did the plugs look like? Did they confirm your lean readings?

[Brian Lohnes]

They showed all the signs of lean-ness.

[andy30thz]

Is the fuel pump ordered yet?