Dead flat at 5k??

[Dan B.]

Put a couple miles on the Ranger today. Set up is a very healthy 387W, Windsor Sr. heads, RPM Air Gap, and Holley 750 Vac Adv carb w/ the lightest vac spring. Fuel pump is an electric Holley blue w/ the pressure set at 8.5#. Base timing is 10 degrees, the 18 degree advance bushing is installed and the lightest advance springs are in. I have a DP but it's getting rebuilt now. And to be honest I like driving the vac carb on the street.

From a stop in first gear and walking it out easy so it doesn't blow the tires off, the truck pulls hard to 6k, shift into 2nd and it pulls good until 5k and just goes dead flat.....I mean dead. The wideband reads in the mid-11's until it dies and jumps into the high teens, low 20's. If I let off and coast a couple hundred feet, I can lean back on the throttle and it will go again. This is likely a simple issue but I'm not much of a carb tuner. It's acting like it is just simply running out of fuel.

Now if I nail it from a stop, it blows the tires off, shift into second and it keeps spinning to redline again. But when I put a load on it and the motor is pulling the truck instead of just knocking off the tires is when it goes dead flat.

My first inclination is to jet up the secondaries. At a cruise and running on the primaries, the AFR is in the high 12's so I would guess they are good. Is this a good start??

What I'll likely do since I'm be pulling the carb is to try a new 850 DP that is just setting on a 429CJ. If it goes flat with this then fuel is not likely the problem.

Any ideas??

[gpfarrell]

I'm clueless, but that's never stopped me before.

I think the fuel pump isn't keeping up with extended high rpm runs.

Whn you rev it up fast it's not spending enough time at high rpms to fall behind and the fuel bowls never completely drain. But when the motor pulls all the way the pump just cant keep up.

I think if it were jets you'd never get over 5k.

Good luck!

[Dan B.]

I had that in the back of my head but was hoping jets would do it. I hate to have to buy another pump since this one only has about 500 street miles on it. Others folks have been texting me that the pump seems to be the issue. Bummer.

[Mark Aubele]

Highly doubt it is jets Dan. It wouldn't go fat then lean, and it wouldn't be that dramatic. Fuel pump, filter, float level.

Another unrelated topic, do those heads really only want 28* of timing? I don't think it is the problem, but I would run less fuel pressure, 6-7, and check it with a different gauge to be sure the one you have is accurate (just fought a bunch of carb issues due to excess fuel pressure because of faulty gauge).

[Dan B.]

This is the kind of input I am looking for. Thanks.

[Mark Aubele]

This is the kind of input I am looking for. Thanks.

Keep in mind I have zero experience with a vac secondary Holley, and a decent amount with mechanical secondary Holleys, but not an expert by any means. Others with way more knowledge (usually Torqueboxer, went9s, or another friend of mine) have helped me work through various issues and I have learned from that.

Float level is critical, and so is fuel pressure.

[Dan B.]

I'm going to double ck the float, lower the pressure and ck filter today. If those all look good, I'm going to get a new pump.

[somethingclever]

dont' get a new pump until you confirm that is the issue.

Run a line off the pressure port with a mechanical gauge up through the hood and do some pulls and watch what the fuel pressure is doing. If it's falling off then likely you need more pump or have a restriction between the pump and the spot you are checking it at.

[blksunshine88]

Possible to small of a needle and seat on the bowl, what size is the needle and seat?

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[Dan B.]

Possible to small of a needle and seat on the bowl, what size is the needle and seat?

Whatever the stock size is....not sure.

I've not tinkered with this since I posted the thread. Hopefully get to it tonight or Friday.

[torqueboxer]

Wire the secondary's shut, see if it still does it under full throttle. If not, then I'll guess that your truck doesn't like the lightest spring in the secondary's. Also set the base timing at 18-20 with the total of 28-32@2800-3000 10deg is WAY too low for idle timing, my guess is it idles at 600 rpm with 20 deg it'll probably pick up 200-300 rpm. Also check to make sure the secondary float has fuel in it at least up to the bottom of the sight plug

[Dan B.]

Drained the cell today. Flow from the cell to the pre-pump filter ran good so no clogs there. The filter is a Summit inline with a 40 micron disc. The disc was pretty well clogged between the folds so I ordered two new discs to replace the pre-pump and post pump filters. Parts should be here Monday. Hopefully that's the problem. But once that's together I'll be checking the floats and fuel pressure.

Hopefully have it together for the Tuesday night races.

[Dan B.]

Parts came today. Put it back together, dropped the fuel pressure to 6.5# and went for a ride. Pulled nice and smooth to 6K in all three gears. Going to do more testing Sunday.

[PaxtonShelby]

Alright Dan! Tuesday night the weather should be perfect for some good runs!

[Dan B.]

You going??

I've not located any track tires yet so I may just go on my street tires. ET will suffer but I'll try for a decent mph.

[PaxtonShelby]

I won't be going on Tuesday - but I can't wait to see some numbers from the beastly Ranger!

[Mark Aubele]

Parts came today. Put it back together, dropped the fuel pressure to 6.5# and went for a ride. Pulled nice and smooth to 6K in all three gears. Going to do more testing Sunday.

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