455 eldelbrock heads,Harland sharp rollers rockers,Lunati cam,Quick fuel 850,Tremec 5 speed,355 gears.Pertronix billet Distributor 24 mech 34 with vacuum.60 000 volt coil.Holley electric fuel pump all new 3/8 lines.
Had a 650 Holley last year car ran great but fell on its face at wot,jetted and still same deal.was suggested i needed a bigger carb bought a new 850 quick fuel Runs a little stronger but at wot falls on its face again.Installed a 37 squirter from a 35 no change.
I changed timing various ways by either retarding or advancing a couple of degrees either way with no change anyone have an idea what i am missing?If i let off on it it is fine but at wot almost like you shut it off no backfire let up about 3/4 and away it goes could drive it all day as long as no wot.Pulled a plug and it looks good.

 

You don't have enough timing if you set it to 24 without vacuum, it needs to be around 34-36 without vacuum all in at around 2800-3000 rpm. With vacuum in the upper 40's and no more than 50.

 

Eric, I think he means he has 24 mech. add that to initial and he might have enough.
Op what is your total timing? And squitters don't have anything to do with wot once the throttle has been depressed.
Fuel pressure?
My bet is it'll end up being that distributor. Haven't had very good luck with their stuff. Just sayin.

 

Total timing should be good ill check again today when i get a chance.I tried my original hei with accel coil and pickup,and another hei new stock and then pertronix billet with igniter lll all with the same responce.It is like it dies at wot no bog no backfire just like it was shut off no surging.

 

Are you sure that you fuel pump is working well, with no restrictions in the lines?

As Mark said, What's your fuel pressure?

- Eric

 

New holley pump all new 3/8 fuel lines front to back and 7psi

 

Put everything back the way it was with the carb. most likely your issue is not there since it did the same thing with two different carbs. so now you have fuel lines and pump , check and replace the filter first. just because you have 7psi sitting there doesn't mean you have any flow so you will need to verify your fuel pressure at WOT . can you do that ? a lot of folks just put a gauge at the carb and that only tells you what you have at idle since you can't see it while driving. use an isolator kit and put a gauge in the dash so you can see you pressure at any time . that way when it falls flat take a look at the pressure that will eliminate your fuel supply very quick.

 

tape your cell phone in place on the engine watching the fuel pressure while you do a run. Record it all. Then.... youtube that video! for us....

 

outstanding idea !!! lol

 

Had the same issues with my 455. Changed carb but still fell at wot. Changed distributor to a Msd ready to run, but no difference. Turned out to be a sharp bend on the fuel line between pump & carb that caused it. Just my experience.

 

ok down the road with fuel pressure gauge strapped to the hood 6 psi wot so not a fuel delivery problem.

 

I am not convinced your problem is not the fuel supply. where is your filter located ? at the carb or in the line at some point.. is this a returnless fuel system ? regardless you should not see any drop in PSI at any rpm or that is an indication of a restriction also what pressure is the pressure relief set at and can it be adjusted? that could cause similar issues. have to ask a lot of questions because we cannot see what you have and how it is put together. pics might be helpful to locate a possible problem.

 

you drove your car while strapped to the hood?!

:-0

 

Well, you've had the same problem with two different carbs, a few different jet combinations, different ignition timing settings, and you've got good fuel pressure at full throttle, so I'd recommend checking your ignition - Could be that that fancy billet distributor and 60,000 volt coil are to blame.

Get an old points distributor and coil off the shelf and plug 'em in, set the dwell and timing, then go for a spin around the block.
If it runs fine at WOT with the old distributor, I'd start by replacing the 60,000 volt coil, and if that doesn't fix it, I'd try the module next.

- Eric

 

Here's what I wrote before rereading the whole thread...its late...
Im with MD your lean at WOT. There's a restriction somewhere. Fuel filter??? Put a PSI gauge just before the carb and stick it to the windshield take it for a kill run and see if the systems keepin up. If the fuel psi doesnt drop off much then its the carb...
So you did that. So its the carb if in fact it is fuel related? But whats the chance of 2 carbs doing it...slim but plausible,
How sure are you its not the ignition VDC falling off when demand is full on...Do same thing with a volt meter on the coil. See if your gettin steady 12vdc min at WOT, Alternator or ignition could be the culprit? Belt slippin?

EDIT...And MD beats my slow azz again at typing.

 

I still think we need some clarification here. How is your timing set?

 

Another thing to check would be linkage and throttle operation. Sorry for the simple suggestion but it's worth a look.

 

Do you have a full 12v going to the Pertronix dist or are you using the resistor wire? That can cause it to fall on it's face.

 

Baseline approximate timing for a carbureted, iron headed, 9.5:1 to 11:1 comp ratio, street/strip, run of the mill, mildly tweaked 400/455 on 91-98 octane is:

Base 12-14*BTDC
With an adjustable stop (not adj. rate) Vacuum adv... add another 10-12* for 22-26*
Mechanical(centrifugal) "all-in" around 2800RPM +2 to 300, -0*
So your total event at say 3000rpms should be between 34-40* total depending on the many variables...gas, driving style, altitude, cam profile, plugs etc etc...


So if I read the original post it looks like your about there with 24* and 34* total. You just have it flip flopped as 24 mechanical and 34 vacuum.

This is a ballpark setting Ive had success with for years. Use it to start with then go from there.

 

" at wot falls on its face...
If i let off on it it is fine
at wot almost like you shut it off
let up about 3/4 and away it goes could drive it all day as long as no wot"
=============================
Holley carb huh? I am not that familiar with them. The QJet has a linkage which prevents the air valve from opening too suddenly and causing the symptoms you describe here. In my youth I "adjusted" this system to death and then had stumble at WOT and it took a while to learn why that happened. Turns out that carefully engineered system doesn't work so well when you modify it w/o understanding how it should work. But, maybe you were not so foolish.

What is the system that holley uses to prevent the secondaries from opening too far too fast?

I agree that a simple distributor change would at least rule out ignition or not and get you on the right path. Is there a rev limiter in the ign system?

 

holley carbs are either vacuum secondary or mechanical the mechanical ones use a secondary fuel pump to cover the big hole when you stomp it which you can change cams on to adjust amount and rate at sustained wot it uses vacuum to pull the fuel through the venturi. so you can try to pump the throttle and that will make the secondary pump shoot some more fuel in so I would think if it is starving should make it jump a little then die back down once it burns up the extra fuel.

 

Yeah, the Holley vacuum secondary carbs have a vacuum diaphragm that opens the secondaries, and many "hot rodders" put a screw through the link to force it to act as a mechanical secondary without the benefit of an accelerator pump to prevent WOT bogging.

Can't tell you how many times I saw that back in high school.

 

How is your electrical system? Do you have a good solid ground to the engine block and another between the engine and the chassis? The positive voltage should have a good connection as well. Are you getting massive torque at WOT? I have seen cars with seriously hacked electrical systems that worked while sitting still but when under load the electrical (ground) connection opens up because the engine and trans mounts were getting torqued out of shape. There are a lot of contact points that should give you a decent ground circuit but under extreme load, things change.

 

This has me so stumped,not my first time doing this and not from lack of spending money.
New 650 Holley Double pumper
New 850 Quick Fuel Double Pumper
New Lunati Cam
New Roller Rockers
New Eldelbrock Heads
New Holley Electric Pump
Old gm Hei
New gm Hei
New pertronix Billet igniter lll
60000 volt coil
Eldelbrock Fuel filter at tank all new 3/8 fuel line front to back
No vacuum leaks
Timing set to 34 all in without vacuum
Ground from block to body
New ground from battery to Block

Now i am going to check altenator output 3000 rpm and also check for 12v at coil at 3000 rpm

I used to have an old Holley spreadbore Double pumper i used for years worked awesome but finally wore out thats why i bought new.Never used a quadrajet not saying i havnt had them just never had one work like it should.I have had vacuum secondaries just prefer mechanical.Also with the tremec 5 speed i figured mechanical was a good choice,but just my preference.
I have my own shop i paint and restore cars,i have worked on stock cars for years.That being said this is not my first time doing this or anything like it,this is why i am stumped.If it was a bog or a stumble would be easy
but it is just like i shut it off till i let off,no backfire pop or surge,no black smoke plugs read well.
I dont think i missed anything but if i did let me know I dont race my car much just dont need a rice rocket making me look bad.

 

only thing I see that rings a bell is you said 'new filter at tank' the filter should be between the pump and the carb so the fuel is pushed through the filter not drawn through that can cause some issues. barring your throttle actually hitting the coil wires and shorting it out or something like that it still sounds like a fuel issue to me, especially with it being at a certain rpm. you have checked the float levels I am sure but it sounds like you are running out of fuel you let up and it's ok when you lower the fuel demand.

 

From my experience with ignition system is misfires at top end. Fuel issues act like it is shutting off. I hope it is a high flow course filter between the tank and pump?

 

What Holley fuel pump is it? They make a few different ones. Where is your fuels filter located? You NEED to have one before the pump mounted above it. The fuel pump also needs to be below the lowest point of the fuel tank or it will starve it self. Electric pumps are pushers, not pullers and need the gravity assist to function properly.

 

13 volts at coil,fuel filter above fuel pump,Pump below tank,14 volts charging no change at higher revs.

 

What about the fuel sock in tank. Has it collapsed?
Since you have a filter back there just remove the sock. Having plenty of fuel pressure means nothing if you don't have the volume

 

And which pump is it? Blue? Red? Or Gerotor type? It all makes a difference as to how much fuel you are getting.

It sounds like the installation is sound though.

 

Funny i was wondering about the fuel sock the other day i guess thats next.It is a red holley pump.

 

What are you running for a fuel pressure regulator?

 

Okay so i put 650 back on at wot little surge but managable tuning should work,850 took off better 650 seems a little leaner on the front half but its not falling flat on its face.Some progress at least.No regulator on it have one just never installed it.going to start over recheck timing and maybe try different jet combo's

 

You should always run a regulator with an electric pump.

 

some food for thought, the .110 needle/seats flow advertised 295 lbs./hr @6psi converted to gph comes out to just over 49 gph double that and you have 98gph potential flow at WOT that red pump deadheads at 7psi and is rated at 67gph at 5psi I run 7psi minimum and if you try that you will drop your gph number even lower. do you see where I am going here? that pump is barely adequate at best in the most perfect world even the blue pump is not quite what I would like. you either don't have enough flow altogether or you have some kind of restriction that is slowing it down.

 

Huh? A comma or period here and there would help. Thank you.
295lbs/hr would equate to enough fuel for about 590hp at a bsfc of .5. That's plenty of fuel for his application so based on your info that shouldn't be the issue.

But please explain if you would how the filter knows the pressure drop across it is from a vacuum on one side or pressure from the other. Putting the filter before the pump is fine. In fact lots of people put filters on both the low and high sides of the pump. PUMPS work better pushing, on filters it doesn't matter.

Op, I think you're on the right track, pull the sock out of the tank and check that first. You may want to also just let the fuel run into a can for a little bit to see how well it flows continuously.

Hope this helps.

 

Bumping for any new updates or progress on your problem, as I have a similar one at WOT.
Pertaining to the quote above, IF it's a fuel delivery problem, wouldn't the 650 actually improve on the condition, since a 650 has less CFM than the 850?
My thinking is less air flow is available, so less fuel is needed, resulting in the engine running a little better, but still not enough air/fuel, similar to running a NASCAR restrictor plate.

 

You're thinking about the carburetor's flow rating wrong. It's not as if the 650 or 850 is some hard limit. Rather, it's how much air the carb flows at a stated pressure drop (which I believe is 1.5 inches of mercury standard for 4 bbl carbs). The fact is that at a given RPM the engine will draw a certain amount of air through the carb no matter how big or how small the carb is. It's not the CFM that changes, it's the pressure drop. So a 455 spinning 5000 RPM will draw pretty much the exact same amount of air through a 650 carb as through an 850, but the pressure drop will be larger through the 650.

Of course, that is a bit of an oversimplification, and if you take it too far (too high of RPM, too small of carb), the airflow will really be restricted -- which is what NASCAR is doing with the restrictor plates.

 

Got the 850 back on the carb came with 80 jets in front and 86 in back was way rich so I went to 73 in front and 76 in rear almost all cured little lean so I went to 76 in the front good driver right now from all the reading I may have to up the rear as I suspect a lean condition at wot.i have no power valve in the rear so lots of trial and error.

 

Ok, I'm with you so far.
I guess I'm kinda stuck on the '650 will flow the same as an 850'.
How does pressure drop affect engine performance in relation to fuel delivery?
I was thinking in order to maintain the proper air/fuel ratio, more fuel would be needed on an 850. If the fuel system isn't providing enough fuel, an 850 would be 'lean'.