motor running like a pile of......

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duster340

street racer
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just cant figure this out myself
engine runs rough up to about2300 rpm during low load as soon as giving more throtle it runs nice and smooth from 2300 and up runs very smoth, except about 3500rpm and up when it starts missing almost like ignition is turned of or running out of fuel just a fraction of a second then power comes on again (but week) and then missing again very frustrating have tried pulling it up to about 6000rpm this way , i know its not right but things happen pretty quick when floring the loud pedal..
responds nice and quick reved in neutral
motor is a 11.9:1 compresion stock stroke 340 with ported eddy heads small compcams solidroller ( 242/[email protected] and .570/.576" lift )
now it has a rpm airgap intake..
msd probilet distributor and 6AL box
750 proform dp carb (have tried two of them since i have another one)
carter mechanical high volume fuelpump (about 3years old have checked fuelpreasure at idle)

have changed wires ( they are all in betwen 74 and 114 ohm)
new cap and rotor
changed old 6a box for new 6AL box
have done leaktesting with motorstarter gas and no leeks anywhere
changed all sparkplugs, did find one with cracked centerporceline but would gues thats just a "monday misstakeproduct" since all the other ones where fine motor runs alitle fat but not crazy fat)

cant even do a burnout with this:( even with 3200rpm stall and 3.21 gears(gears will change)

help:S need to get this thing running as hard as it should so i can start playing with the nitrous.......
 
That distributor the one with all the adjustments in it? Could be something whacky with it
 
68 Sedan said:
That distributor the one with all the adjustments in it? Could be something whacky with it
Click to expand...


probillet is the simplest distributor i can imagine it just has mechanical advance and a pickup in it thats about it no vacum or strange electronics

running 18degre of timing at idle and 36total all in at about 3000rpm
 
Sounds like you've checked everything but the distributor. And if you know what it isn't, then that kinda tells you what it is
 
What size fuel lines? I would try a different distbuter too.
 
its 3/8" all the way from the fuelcell dont realy know where to find another probillet distributor just to try, can it be measured some way?
 
will do, i am very sure i got it right but since i dont have a pic to prove it to myself i have to check it
thanks!
 
update: remeasured the cam and its installed just right:(
anymore sugestions?
could it be running out of fuel at higher rpm? hard to tell by looking at the plugs since i have to get out of the throtle pretty quick when it starts acting up? will try to measure fuelpresure while driving tomorow and see.
the bad running at lower rpm may just be from the tune being way of...
is the carter high volume mechanical fuel pump realy enough for this kind of motor?
 
That pump should be enough. You've checked the cam timing. Did you check to make sure your distributor drive is in right and the rotor is pointing @ #1? Do you have a dial back timing light and have checked your timing across the RPM range?
 
Did you build the carb or buy it done?

If you built it and started with a 650DP, I've read about issues with the stock holley metering blocks and proform main body not playing nice.

Do you know anyone that has a carb that is a known good piece to try?
 
Have you tried to put your hand over the carb while running to limit the air intake and richen the mixture? If not try that and see if the idle smooths out. Could be a vaccum leak in the carb or elsewhere.
 
68 Sedan said:
That pump should be enough. You've checked the cam timing. Did you check to make sure your distributor drive is in right and the rotor is pointing @ #1? Do you have a dial back timing light and have checked your timing across the RPM range?
Click to expand...


timing is set at 18 at idle and 36 degre all in at about 3000 rpm with a timing tape dont have a dialback timinlight just a standard one so that seems about right, should i try geting a faster advance curve or slower?

crackedback said:
Did you build the carb or buy it done?

If you built it and started with a 650DP, I've read about issues with the stock holley metering blocks and proform main body not playing nice.

Do you know anyone that has a carb that is a known good piece to try?

carb is a known good proform 750 that has worked good before on a 383 chevy but is now jetted back to stock have annother one that did run fine on this same engine last year just changed to my second carb to verify the carb to be right they are both bought complete from proform and both have been taken apart for a good look over
Click to expand...

SGBARRACUDA said:
Have you tried to put your hand over the carb while running to limit the air intake and richen the mixture? If not try that and see if the idle smooths out. Could be a vaccum leak in the carb or elsewhere.
Click to expand...
have tried that but will have to try it with a rag cause my hand cant cover the countured top of the carb any good but it almost dies if i just tuch the accpump without opening the throtles so i gues its not to lean from a vacumleak

redfastback said:
what are your jets? what springs in the distributor?
Click to expand...

they are 74 front and 84 rear with a 4.5 powervalve in the front
cant for my life remember what springs but timing is all in at 36 degres at about 3000rpm

fuelpreasure is also verified to be very consistent thru the rpm range dont realy trust my holley fuelgauge since it reads 10 psi but it never dips even at higher rpm or when shifting. fuelpresure does move around alitle at a shaking 850-950rpm idle but goes very steady as soon as there is some rpm
 
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