Still having complications

i have found that this thing has more mood swings than a woman:p. ive got a 427 wtih flat tops 291 heads not sure on cam size air gap intake 850 mighty demon msd street fire distributor i believe a holley red pump,cell with half inch aluminum line front to back with regualtor, pressures carries 7-7.5. when it runs it runs great. At times i can drive it with no problems other times it seems to be flooding or running out of fuel. while cruising doesnt matter at what speed,if you try to gain speed with a little pedal push it wants to spudder like its running out of fuel but if you crack it wide open it will try to pick up and run and it doesnt do it all the time.. Can anyone help before i accidentley leave these monster on the rail road tracks???

Sounds like you need to rebuild that carb accelerator pump and maybe jets??? I would at least start there and see what happens then... Others will be along with other sugestions I'm sure

if you push the clutch in when it acts up it will take throttle no problem and it doesnt act like its running to rich? Could the carb be to big?

427 with flat tops ?boy that thing has no compression .cam could be to big for stall and low cr will make engine harder to tune in .but sounds like carb and timming thing. look at your accelerator pumps on the carb. look at were you are picking up the fuel in the tank low point sump is the best if not could be sucking air. heat could be vapor locking .could be lack of a fuel filter or floats not set right. well i see you have a stick so no stall

Pat was typing a bit ahead of me - I wouldn't think an 850 is not too much carb for the 427. Like Charlie, my first thought was accelerator pump - sounds like you're not getting enough transition fuel to carry you through the increased air flow, before the jets can react. Have you pulled the plugs to see how they look for main jet selection?

Do you have a demon with an idle-eze base plate?

You have too much fuel pressure--lower it to 3 lbs for sorting this out, check float levels--demons have site plugs

change power valve to 3.5 or possibly 4.5

what size squirters do you have and are the pump cams pink?

pat im guessing with the 921 heads ive got 9.5 9.8-1 compression yes a little low :) if i was having accelerator troubles would i be able to push the clutch in and rev with no problems? the cells outlet is on the bottom front but it does it with a full tank also, ive thought about vapor locking but not really sure how to check for it the floats are set a little higher than the middle of the glasses and new fuel filter.roger ive pulled the plugs after a highway run and they arent paper sack but they arent gas fouled seems a little rich but i didnt think it was enough to cause any issues.jerry, yes it has idle ease. 3lbs? the book shows 6-7 psi but i will try it to see what happens, it came factory with the power valve eliminator the squirters are 31s and the cams are pink

I don't believe that it came with pv eliminator--I said to lower it to 3 to eliminate too high pressure being the cause--i like 4 - 4 1/2 when i'm done--

for now---put a 4.5 pv, 78 pri 80 sec jets

have you had carb apart? some 3 or 4 years ago would have enough chips from machining in them to fill a teaspoon

turn the base plate over and set throttle plates so the transfer slots show about a .020 square hole(the transfer slots often have a big chip/burr which you can see from the top side)

set idle with the idleze screw tp around 850
if you need to lock out the timing you can use safety wire around the pins for the advance springs--i do this til i find out where the engine wants it to be---

what jets do you have in it now?

jerry you are correct sorry i was reading wrong it does have a primary power valve its shows to have 6.5 out of the box but ive never had it apart. the throttle plates have been set with the .020 square. if the power valve was blown would i have idleing issues? and locking out the timing do you mean wireing the weights to where they are fully open?

either way on the dist---just so it cant move--find out where engine is most responsive and then set max to there--change pv to 3.5 if you can find one otherwise 4.5

and what jets do you have now???

on the jets im going to assume it still has the factory 85 pri 93 sec ive never had the carb apart and the guy i bought it from said he didnt either.i have been told this carb has pv blow out protection,is this correct? what exactly does the pv do? sorry for the dumb questions im just a young pynk kid trying to learn :)

Power valve richens mixture by 5 to 8 jet sizes when vacume is lower than valve rating---

for now move 85s to seconary and get put some 78-81 or so in pri with a lower rating pv

set timing to high 20s(28,29) to max of 36-38

on the starter--do you have GM starter bolts holding it to block, and the brace from starter to block on front of it??

and do the accerator pumps give a good squirt of fuel when you work the throttle???

the starter is a mini, bolts arent factory but they are knurled no there isnt a bracket, is the bracket like the one for a small block bolts to the starter then to the side of the block? as random as this thing acts up do you think i might have some trash in the front bowl or some where maybe on occasion it floats up and blocks an orfice?

I don't think anything YET---but if you take the carb apart look into the areas behind the main jets-(looks like a bat cave!!!!) always some hanging trash from threading process---

but, you got to get to basics---fresh, clean fuel, pressure right, floats rite ht, power valve proper setting, etc

i drop the pressure tonight and see what that does and if no go there i pull the carb apart and make sure shes clean. thanx for the help ill repost when i make some progress

you have way less then 9.1 if the heads are not milled less then 108.cc and the deck is at stock deck your about 8.1 with a 4.310 bore .not much cam in this one

is 108 the ccs on a 291 rectangle port head?

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Originally Posted by Cooter1989

is 108 the ccs on a 291 rectangle port head?

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about that.. the older O ports are less cc.your never going to get to 9.5 with the stuff you have less its not what you have with them heads a 4.530 bore x 4.250 crank your about 10to1.you have no crank stroke to build CR

o port heads? im confused. the heads i have are 3964291 they are gm's hi-perf rectangle port closed chambers

yes i know them heads i had them and used them in builds . i telling you that the old O port you would have a hard time getting to9.1 not 9.5 with a flat top and a 3.765 crank

what are you meaning by o port?

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Originally Posted by Cooter1989

what are you meaning by o port?

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older O port has smaller chamber size less cc =more CR then them heads on a 427 with flat tops are not much good if it has any size cam

sooooo---what did you drop the pressure to??? do you have pressure guage where you can see it while driving?? why no answers to my questions??
Where is Sapulpa?

this may clear things up for you not trying be hard on you just can not see why you went to flat tops ? is this a tall deck bottom end ? are you sure you have a 427 and not a454? the O port heads i am talking about is the head we used with a flat top 454 engine to get around 9to1 that head was a 215 101cc.or 206 97cc. now if you have a 3.765 crank with the heads you have on there now your lucky to be at 8.5 but if it was a 454 with flat tops at would be 9.1 as it has a4.000 crank now the same build in a 496 would be 9.5 as the crank is now 4.250 .same crank 4.250 as the 496 in a 548 with bigger bore4.530 now is at 10.3 .volume in bore and storke make bigger engines and the CR will go up if the head CC in the chamber is the constant

ok got cha. im not sure on the cam size but like you say i imagine its to big for no more motor than i have. i really need to pull the heads and find out exactly what piston i have the guy that the motor came from was trying to tell me it has 12-1 domes in it but from what i can see from the plug hole doesnt look like a dome piston and it doesnt ping with 91 oct and alot of timing. ive ran a compression check on it i dunno if it means much for the comp ratio but it has 175psi cranking. here is a link to a video of it running the dominator and intake have been replaced with the demon and an air gap.
‪79 trans am‬‏ - YouTube

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Originally Posted by jerry clayton

sooooo---what did you drop the pressure to??? do you have pressure guage where you can see it while driving?? why no answers to my questions??
Where is Sapulpa?

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hey i give you the answer :).... hi jerry .... if this thing under 8.5 cr with any cam fuel is running out his tail pipes at idle

sorry jerry i missed that post. i dropped it down to 5 last night and checked the power valve it already has a 3.5 in it but didnt get a chance to drive it. sapulpa is in oklahoma. Pat i didnt build this motor so im learning about it as i go but it is a 427. im not 100% sure it has flat tops in it but with it liking alot of timing and runs with no detonation on 91 octane im assuming its a lower comp engine. so if it does have flot tops and with the heads being a 109cc it would still struggle to get 9-1 compression?

there is many things that can add or sub on CR hard to say if the heads have been cut down like .050 off then? is the block @ O deck ? what head gasket was used ? 4.370 fire ring or a 1017 fel pro with a 4.540 fire ring bigger and thicker head gasket= l less cr . the best you could hope for with the heads at 108 and O deck would be a round 8.5 like i posted on here many times :)

i know none of the above lol. surely it has more compression that that, i need to find a borea scope and see if i can tell if it has domes or not. did you watch the video?

no i did not look at the video.. but if its a flat top with stock un cut heads and stock deck height on block its less then that :) i been at this for some time on BBC .far from my first time at the Rodeo thats the carb you have on there NOW?? thats a very very old 4500 holley

i understand, not meaning to be argumentative jsut trying to learn :). it would help everyone out if i knew exactly what all has been done to it, i should yank it out and put the 462 in it i know whats in it lol

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Originally Posted by Cooter1989

i know none of the above lol. surely it has more compression that that, i need to find a borea scope and see if i can tell if it has domes or not. did you watch the video?

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you said this surely it must be more then 8.5 ? i can not tell you i do not know what you have for pistons in it ? but if flat tops and a427 with stock uncut heads it just plane can not be that with a stock deck it can be less .yes the best thing is to pull the heads off or look in the head with a bore scope and see what you have for a piston. is thats your carb on there now?? thats not a BG carb but a older 4500 dominator

i didnt mean the surely its got more bc ur wrong i ment that bc of the way its runs and sounds

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Originally Posted by Cooter1989

i didnt mean the surely its got more bc ur wrong i ment that bc of the way its runs and sounds

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well ok take that carb off and try something better and smaller .i do not know how many circuits that carb has but .jerry may . i used the 4500s holleys on the street for many years .but them older ones i have seen guys try them that did not have much luck with them .it could just be them on there tune ? as my 9377 .1150 cfm holley works ok for me

with the size of the needles/seat s in a demonator carb, it is easy for the electric pumps to override them

you can solve fuel pressure issues temporarily by just turning off the electric pump/s and seeing if it runs better before it runs out of gas

On a dominator you have 2 big accel pumps and a shitty linkage set up for driving--they are like a off/on switch--idle or wide open---no place in between

if this is a driver get a better carb

doesnt have the dominator on it that was an older video its has the demon on it now

soooo???????did you do any of the things I suggested?

and is it the same manifold???how did you adapt the 850???any vacume leaks around base plate?

its has an air gap on it now, i checked the power valve and lowered the fuel pressure but havent driven it yet

you already said that you lowered it to 5 #, I said 3#

The Dominator and the 4150/60 style carbs have different base patterns--did you change maniolds with the carb or use an adapter plate?

Did you change the jets like I suggested?

Out off several steps I suggested, you have only replied about one and you didn't go to my number(fuel pressure) The larger needle/seat sizes in performance carbs are easily over ridden with pressure so for trouble shooting you need to eliminate that possiblity

I saw that you have headers on the car---are they hooked into a system or are they just headers dumping at the collector?