Popping through carburetor during acceleration

Posted By: moparjim87

Popping through carburetor during acceleration - 03/02/15 03:54 AM

My dad and I just put a 360 in my truck within the last month. It's a completely new engine. It had the stock tbi fuel injection at first, and now is carbureted. The truck is a 90 w150, previously a 318 truck. We have pretty much ruled out ignition/fuel delivery as a problem, and have installed/tried factory adjustable rockers. There's a brand new cam and lifters in it, and when we swapped the intake, the cam looked in good shape. Is it possible the lifters (stock replacement Johnsons) could be pumping up when oil pressure when the engine is revved up? We are going on 4-5 weekends worth of trying to get this truck to run correctly, and are about at the end of our rope as to what could be wrong. Any and all help is appreciated.

Posted By: dvw

Re: Popping through carburetor during acceleration - 03/02/15 04:03 AM

If it's a single pop at the hit it's lean. If it sounds like a continuing popping noise, like a machine gun, you have a exhaust lobe worn off the cam. Pull the valve cover you'll see it as the rocker will barely move.
Doug

Posted By: roadhazard

Re: Popping through carburetor during acceleration - 03/02/15 04:11 AM

Three things come to mind....
Verify ignition timing and phasing is correct
An Intake lobe could be going flat
Or the camshaft is not in proper time

Posted By: rowin4

Re: Popping through carburetor during acceleration - 03/02/15 07:01 AM

As stated above , cam lobe, also check to see if you have a plug wire mixed up, possible cracked distributor cap? Bent intake valve, broken intake valve spring.

Posted By: Cab_Burge

Re: Popping through carburetor during acceleration - 03/02/15 09:00 AM

Quote:

as a problem, and have installed/tried factory adjustable rockers. There's a brand new cam and lifters in it, and when we swapped the intake, the cam looked in good shape. Any and all help is appreciated.

It sounds like you have the lifters preloaded to much, try going back and readjusting the preload so you have no more than 1/2 turn of preload after making sure you have the adjusters looses enough to have a tiny bit of up and down rocker movement at TDC of each cylinder on the firing stroke before setting the rocker adjuster preload

Do this on a cold or slightly cool motor, not on a hot motor the first time

Loosen the rocker adjusters up enough so they becomes loose enough to have some lash between the rocker arm tip and valve stem, tighten it up slowly until the lash is gone, try turning the pushrod with your fingertips while doing this also, when the lash is removed the pushrod should spin harder

Take your time to make sure you get zero preload and zero lash, once you got that, tighten the adjuster up between 1/3 and 1/2 turn more and lock down the locknut tightly while making sure the adjuster doesn't tighten up anymore

Do one cylinder at a time and go to the next one

I try to do them in the firing order on most stock motors that don't have a fully degreed harmonic balancer, dampener, to work off of

It might be best to start on number one(verify that it is on the firing stroke, not the overlap stroke

) and then turn the crankshaft 90 degrees clockwise and do the next one, #8, turn another 90 degrees and then do #4 and so on. The Mopar V8 firing order is the same as BB and SB Chevys, 1-8-4-3-6-5-7-2. Let us know if that helps or not

Posted By: Crizila

Re: Popping through carburetor during acceleration - 03/02/15 04:09 PM

My first guess is it's going lean - especially if it occurs after the peddle has been on the floor for a bit ( upper RPM range). Check fuel delivery first.

Posted By: dynamite

Re: Popping through carburetor during acceleration - 03/02/15 05:47 PM

If it's a constant pop,, and if you still have an EGR valve on it..look there for sure !!

Posted By: moparjim87

Re: Popping through carburetor during acceleration - 03/02/15 06:45 PM

Egr deleted, stock stamped rockers back on it, timing on cam is correct, exhaust sounds glass smooth at idle and under load, cap/wires/rotor/plugs all new, heads are completely new (redone with new valves/springs/locks/retainers), and 1406 edelbrock carb, just rebuilt by my dad yesterday. This engine did this with the fuel injection on it also, which is why we put a carburetor and old school electronic ignition on it, thinking it might have been a problem. The throttle response is now where it should be, and it is definitely running alot better, just no power and pops through the carb. (not backfire popping, just like its pushing compression back through the intake. My dad has been building engines for the better part of 30 years, and he adjusted the valves when we tried the adjustable rockers, so I know they were good. We were trying to figure out whats possibly wrong, and we thought one or more lifters on the intake were pumping up when the oil pressure is higher, thus holding the intake valves open.....
(sorry for being long winded, just trying to give any and all info so youns get the whole picture)

Posted By: MR_P_BODY

Re: Popping through carburetor during acceleration - 03/02/15 06:51 PM

Do a compression test and a leak down.. see if your
bleeding off pressure to the intake side... but the
spark chases the fuel so its telling you its on the
intake side

Posted By: moparjim87

Re: Popping through carburetor during acceleration - 03/02/15 07:11 PM

We leak checked all 8 cylinders and they were all under 3-4% leakage. It only pops when you rev it up and idle is glass smooth. Like I was saying, we've checked pretty much every parameter of the engine that could be a problem. The only thing that is still the same is the fuel delivery system which is the stock in-tank pump with a mallory adjustable bypass fuel regulator, and it is set to 6 psi at the carb.

Posted By: MR_P_BODY

Re: Popping through carburetor during acceleration - 03/02/15 07:16 PM

Quote:

We leak checked all 8 cylinders and they were all under 3-4% leakage. It only pops when you rev it up and idle is glass smooth. Like I was saying, we've checked pretty much every parameter of the engine that could be a problem. The only thing that is still the same is the fuel delivery system which is the stock in-tank pump with a mallory adjustable bypass fuel regulator, and it is set to 6 psi at the carb.

Next question... does it only do it at temp or cold
or both... is the vent on the tank clear... also
is your gauge mounted under hood.. if so.. is that
gauge liquid filled..if it is.. drain it.. that type
of gauge will give you bogus reading when hot

Posted By: moparjim87

Re: Popping through carburetor during acceleration - 03/02/15 07:37 PM

It pops hot or cold, temp doesnt matter, and the gauge is liquid filled, but is accurate, we've had this regulator setup on another truck and haven't had a problem with it.

Posted By: MR_P_BODY

Re: Popping through carburetor during acceleration - 03/02/15 07:51 PM

Quote:

It pops hot or cold, temp doesnt matter, and the gauge is liquid filled, but is accurate, we've had this regulator setup on another truck and haven't had a problem with it.

Drain the gauge... I know for FACT it WILL give you
a bogus reading.. if you keep turning down the pressure
its just gonna lean out... and its not the regulator
that has the problem.. its the gauge.. reason is
that the liquid inside it heats up and presses on
the internals to give a high reading

Posted By: JAKE68

Re: Popping through carburetor during acceleration - 03/02/15 08:10 PM

Well based on what everyone has suggested and your response, im betting you have a cam lobe out and you missed it when you inspected it or valves are too tight. I may have missed this in your post but are you running a vacuum advance if so plug it off. May be over timing for your combo.

Posted By: qwkmopardan

Re: Popping through carburetor during acceleration - 03/02/15 08:31 PM

Exhaust lobe wiped out. Pull the covers and rotate engine while watching rocker arms. You will see if one or more are not moving, or are barely moving. Exhaust can't escape because exh. valve doesn't open, so when the intake valve opens the exhaust escapes into the intake manifold. This is your pop.

There are plenty of known good engine builders that have had camshaft/lifter failures. Lack of good stuff in modern engine oil and/or improperly manufactured cam and/or poor quality cam cores. All though the cam manufacturers won't admit it.