OK here is what I got and how it is setup. I am positive there are no fuel pressure problems. I have a OVERKILL fuel system.

-Holley 750 DP
-Primary side: 68 Jetts with a 7.5 power valve
-Secondary side: 80 Jetts with a 5.0 power vavle
-Secondaries are 1/8 turn open
-Transition slots are about 0.05 uncovered from beneath

Motor is a 386 with a HUGE cam. 246, 254 duration on a 108*

Motor makes 8.5" of vaccum at idle. and idles at 900 PRM, with the wideband reading 14.7.

Thats about it.

Anyways, she runs strong in 3rd gear ot WOT, but for some reason when I shift, go to 4th at WOT, she runs SUPER SUPER lean. like in the 20s on the wideband.

Any idea what is going on? Should I just jump the jets up on the secondaries first?

Thanks for any help.

-Dennis

 

Now that is really, really weird. Should be jetted square when using 2 power valves. The 7.5 seems high as well given your idle vacuum.

Why are you positive about fuel delivery? Because of the parts, or because you are monitoring fuel pressure when it goes lean?

 

both reasons you said.

I monitor with a gauge in the interior and cuz the parts used. Big Holley electric pump, all 8-AN lines and so on. Way overkill.

Can't be lean do to delivery.

I have told this problem to 3 people already, old guys that have been around x5 longer than me and they all have no idea what the car is doing.

I hate it when multiple experts can't figure it out. I was on the dyno for 4.5 hours with the head tunner not able to figure this out. I since tunned it a LOT and got it to transition well, but now the uppper end is leaning for some reason.

Oh and I didn't know that it should be jetted square. I am affraid that if I went down i would just become even more lean.

 

If this is on the dyno, that eliminates jet extensions as a cure.

You may have a needle/seat flow restriction. Fuel pressure would stay up, but the bowl may still get sucked dry. This could be from too small needle/seat, or float not dropping properly (if you are using jet extensions, you need a dimpled float).

 

I am not using jet extentions.

My needle and seat got clogged once, but I cleaned the pri. side out really well and they seem to be fine. I guess I can pull them out again and double check.

I was going to swap in bigger secondaries anyways this after noon. I was going to go with 83 and see what happens.

When I do that, I guess I can double check the needle and seat. Sorta don't think that is it though, as the dyno guy was watching the motor and bowls when it was making a pull, said he never saw it go dry. But I will check anyways.

 

If it was secondary jetting, you'd be lean from the hit.

Do you have bowl windows or clear sight plugs?

Can't imagine it happening, but your manifold vacuum isn't going above 5" Hg, is it? That would close the secondary PV. But, your jetting is big enough that even if it did close, you shouldn't go that lean.

You might try a PV plug on the secondary, but again, hard to imagine it's causing your problem.

Another question about the specifics: Is it going lean as soon as you shift to 4th, or as you pull in 4th?

 

Only when I mash 4th down to the floor.

Thats it. I can drive normally in all 6 gears just fine. Its at WOT, even then 1 2 and 3 seem to be ok, and even 4 sometimes.

Its when I go WOT in 3, then go WOT in 4. LEANNNN....

I had the PV blocked b4, adding the 5" PV on the sec side seemed to help with the transitions.

Oh and I have sight plugs so you can see the float level.

Thanks for your help so far. Hope I can at least sorta know what to look for in the next couple weeks as I decide where to take the car in terms of a dyno tune.

 

Get a remote fuel pressure gague on the thing so you can see it while driving. I know you've got enough fuel system on there IF IT'S WORKING RIGHT. Until you KNOW your fuel pressure under these conditions you could chase your tail forever. You need to be sure. Trying to tune around fluctuating fuel pressure is nothing but frustration.

I have a cheap setup that I can duck tape to the windshield (temporarily!) and make a couple quick runs. If you're having fuel delivery issues it'll be obvious. Pressure will nose-dive just prior to seeing you O2 lean out.