[hungry69bird]

my motor has ran great the last two years...even after the winter, fire it up an runs great.
then i was messing around and went to go from 1st to 2nd and had a brain fart and went into neutral. after that i was popping and by the next day it was popping loudly at idle.
changed plugs...(autolites) and it seems that it ran great for a day and then started popping again, though not as bad. also noticed that my insulator on #1 plug was offset a bit so i ordered another box of ngks and put them in...was less noticable but still there...since i have not been able to get rid of the popping.

at idle and up to maybe 1800 rpm all is well then it starts missing...popping out exhaust and around 2500 it allmost feels like something is dragging on the car due to the surge then after 3200 or so it seems to lessen up some. (all at very light or no throttle)
now if i give it a lil gas it smooths out and with the foot in it it will pull to redline with out missing a beat.

ive bypassed my ignition box, hooked up diff coil, swapped out my 850 with my 750...(better throttle response) also hooked up a hp150 pump with 100 micron filter in front and 1/2 line and better regulator...
i figured for sure this had to be fuel related since as soon as u give it some fuel it seems to go away but the 750 seems to act the same way. ive jetted up and its not lean.

so....any ideas before a light a match?

[sleepy]

Timing chain might have jumped a tooth.

[bnorris_74]

Over-revved it?
Could be broken valve spring, collapsed or pumped up lifter, bent valve, rocker arm out of adjustment.

[Kitch428m21]

Put a timing light on it.

[PunchT37]

Check for bent pushrods also.

[Half-Inch Stud]

Compression test all 8 CYLS to find that bent pushrod. OR pop the valvecovers and feel each rocker combo OR just start-it-up and see which rocker does not rock like the others. HIS

[hungry69bird]

no bent pushrods...running smith brothers 5/16x .116 push rods along with
a stud girdle.
compression was all 148-152. my compressor is dead so no way to do a leak down test.

also no broken springs. also did i mention car has no lack of power and throttle response is good, as long as you are stepping into the throttle.

[hungry69bird]

i'll double check the timing but last i checked it was sitting at about 14 initial which has been checked since it started doing this.

doubt timing chain...no popping through carb and motor is probably under 5000 miles (billet chain)

[guccieng]

i don't think we understand exactly what 'popping' is. out of the exhust? carb? is it constant or rhythmic? how loud? sound muffled? increase with rpm? sorry, but we don't have alot to go on here.

[hungry69bird]

Originally Posted by guccieng

i don't think we understand exactly what 'popping' is. out of the exhust? carb? is it constant or rhythmic? how loud? sound muffled? increase with rpm? sorry, but we don't have alot to go on here.

i think i stated its out the exhaust. starts about 1800-2000 rpm..its not a bang but a gargled poppping missing sound..along with a definate surge feeling. around 2500-2800 is where it seems the most present. the surge then feels almost like something is dragging and releasing. in neutral its harder to tell but sounds like a gargled miss.

my pipes are 3 in with dynomax race bullets and no tail pipes so its far from quiet but the sound does seem to be coming from the rear part of it.

as the rpms get higher i think maybe the cycle of the missing becomes faster...making it less noticeable.

i can drive up a road with a slight incline and its pretty un noticable.

[hungry69bird]

sounds wise especially just revving in neutral it almost sounds like the exhaust is under water

[hal101]

wow i had that kind of a prob when a power valve stuck open ran great with my foot in it
but when i let up on the throttel it would start surging and poping it almost sounds like the exhaust is under water

but with two dif carbs wow??

could it be the first carb the power valve stuck and the second carb is just way rich?

[BVR421]

how old is the gas in the tank? anything over a week old is suspect
now that I think about it gas fresh from the pump is not necessarily any good either. I bought a full tank of crap a few years ago and spent weeks trying to find the problem. new gas solved the problem
I had to dispose of about 8 gallons as the lawnmower wouldnt even run on that crap.

Your symptoms also sound like my ford holley with a blown power valve

if its a qjet check the power piston is stuck open or closed, you can do that with a soda straw dropped in the bowl vent, see if it goes up and down with change in vacuum

[guccieng]

do we all agree that the sound is 'afterburn' in the exhaut pipe?

[hungry69bird]

as far as the power valve.... i would suspect...because its the same power valve. had to take the one out and put it in the other carb due to only 3.5 i have. however........it idles fine...does not seem to be loading up. i'll find out soon enough though because i have a 2.5 pv that should be here in the am. (had already ordered it)..

gas....ive pretty much ran out twice and put more in since. id suspect the station but i run the same stuff in my jeep with no problem.

[hungry69bird]

Originally Posted by hal101

wow i had that kind of a prob when a power valve stuck open ran great with my foot in it
but when i let up on the throttel it would start surging and poping it almost sounds like the exhaust is under water

but with two dif carbs wow??

could it be the first carb the power valve stuck and the second carb is just way rich?

i was running a 76 jet in the primary of the 850...have a 72 in the 750 vac 2ndary thats on there now...shouldnt be too rich... the 850 i ran for two years with no jetting issues just like that. same pv also

[Tom Vaught]

Check all of your wires and the carbon button inside the distributor cap.

Tom Vaught

[hungry69bird]

checked the button and wiped the inside down earlier (msd)....the wires msd also are not that old but one did get a lil burnt from a header once..course that was quite a while ago, over a year..at the time i just have it isolated where it cant jump to anything and never caused an issue before. all the plugs are burnt very clean (white) so i figure they must be firing..all look the same also

[hal101]

ok if jeting is good then i think it's the power valve

yea mine idles fine to with the bad power valve

[hungry69bird]

i'll find out tomorrow i think...hopefully your right...