looking for ideas. I have a dead spot at 2000-2300 rpm. Engine seems to work hard and exhaust raps off(not a backfire). Don't know if its too lean or too rich.

Engine:
400 .030 over
flat top hyperutes
stock heads
xe256
headers 1 1/4 duals w/ h-pipe
holley4160 600 cfm

Holley:
64 jets
6.5 power valve
black secondary spring

Ignition:
78 duraspark
med/med springs
10 deg initial
10l weights

 

what do the plugs look like ?

 

last I had them out, a nice brown, but i have made timing changes since. Normal driving stays out of this range, so plug color might be decieving. Thinking of a lighter secondary spring, but the constant rpm says timing. I do have the vacuum advance pretty tight(slow).

 

you timing sounds well enough to run strong, but it hit me to ask if you have a spacer plate under the carb. even a 1" could help eliminate your 'dead' spot. My first 400 had similar issue. 4V carb Edey perf 400, 214/0.524 single pattern Crane, and this spot would not go away until headers were installed. There's nothing like banging third gear in a 77 highboy and getting it sideways!

 

Sorry it took so long to get back. It was deer hunting in Wisconsin.

Right now I don't have a spacer installed, but I do have one laying around. Maybe I'll have to try that. You thinkin maybe a touch too much fuel and not getting good atomization at middle rpms?

 

not so much that there is too much fuel, but more that there are so many cylinders being supplied by the plenum volumetrically, and then there's that plenum floor so close under the carb. even shorter on that short side, assuming dual plane. I've run edy streetmaster, and holley street dominator intakes and both are open plane, and both seemed more happy with at least a 1" spacer. on my race engine, my brother/crew chief bought a 2" phenolic spacer and I swear it added 25hp just for the cooling properties of the material.

another consideration should the spacer show no result would be to put in a stiffer secondary spring. xe256 are known for great vacuum, and if your 4160's secondary opens too soon it will have a stumble also.

"The first thing many people do when they first disassemble the diaphragm assembly is throw out the small metal ball that is contained in the vacuum passage in the lower housing, without really knowing why it is there. At first glance, it looks as if it would block the flow of air, but a close inspection will reveal a small groove in the seat under the ball. This groove acts as a restriction, so that the secondaries open in a slow controlled manner.
Removal of the ball will allow the secondaries to more or less flop open and may cause a bog, so unless your driving is restricted to the track, leave the ball in place."
From: Holley 20-13 Instructions.
Sounds like you need that little check ball put back in?

Holley TV : Vacuum Secondary Throttles

how was hunting btw?

Side reading?
http://www.musclemustangfastfords.co.../photo_31.html

 

Those are impressive numbers from fast fords. My 400 rarely sees 3500rpm, so I don't know how much heads would do for me.

As for the secondarys, I already have the heaviest(black) spring installed. The check ball is also installed, did it myself.

might have to try the paperclip trick up to 2300rpm. Yes, the intake is dual plane. Next chance I get I'll put in my phenolic 1".







Hunting sucked, thanks for asking. Have a doe only season in another week. Hopefully I'll have better luck.

 

UPDATE:

Changed thevacuum secondary black spring to the plain spring and seems to have helped quite a bit. I'll have to tow something to find out for sure.