i have a 86 sbc 350 4bolt main. took the shortblock and threw a set of camaro heads on it from my last motor that ran good. and put on my edelbrock intake and edelbrock carb and put the motor in my car. started it up and played with the timing and it will run fine but it has a loud pop coming up the carburator.

i tried playing with the valves with the car running but am having no luck with the poping going away. need some help and sugestions.

had two sbc motor heads come out and they think i have a valve thats not seating or is burnt up.

these heads came off another 350 motor that ran good and i just put them on this motor so i know the heads were in good working order before they were put on.

any help or sugestions would be greatly appreciated.
thanks.  

The valve adjustment being WAY off could cause this. Broken pushrods or pushrods that are WAY too long could also be a culprit. Or, it could come down to a camshaft lobe & lifter failing or that has failed.  

um newer cam with less than 1000 miles on it. edelbrock cam and lifters and new pro comp push rods. i inspected everyone before instal. all lobes are same after i used the caliper to check them.

maybe i have to pull the distributor out n move it a tooth back?  

You "played with the timing" does this include using a timing light? If you used a light and the mark is in the ballpark, moving the distributor a tooth will be of no help. A new cam with "less than 1000 miles" would be a prime suspect of lobe failure like Gib mentioned if it did not survive the break-in procedure. When do you get the pop? Idle, accel?  

i had a 350 inmy camaro and decided to go with a diffrent 350. i took the cam out of the other motor as well as the lifters and push rods cause they were all brand new. the cam is broke in and so is everything else. nothing is worn. all the measurements of the lobes are as they should be. lifters are still flat and cam lobes are all equal.

i had put this motor in just this last week and fired it up for the first time and i had this pop coming through the carb.

this is a 86 350 from a truck. i am using a i am using a distributor that has the vacume advance on it from the other 350 that was run with my cam, carb and intake also the heads from the other motor as well. only thing that i sdifferent from my setup now from the last motor is the shortblock.

compression is pretty much all equal to on all eight cylendars. i was told that i could need a curve kit for my distributor.

anyone know what a curve kit would do for me?

since on a sbc the distributor sparkes twice for one rotation its almost as if its pre sparking on one of my cylendars and causing the fuel to pre ignite and backfire up through the carb.

im not sure whats going on here but im really running out of ideas.  

A curve kit is not going to fix your problem. If the timing is within 15° of where it should be the rate at which it comes in isn't going to cause a backfire. As long as your timing isn't A LONG WAYS OFF, that isn't your problem at all.

Did you put the lifters on the same lobe that they were on in the previous motor? The lifter MUST stay on it's lobe that it was broken in on.  

hmm thats a good question. i know that i put them in the box in order from front to back but idk if i turned the box around or what.

if i dont know what should i do? should i buy new lifters? or would i have to buy new cam and lifters?  

Cam and lifters are mates for life... You should NEVER install new lifters on an old cam or vice versa. When breaking in a new cam and lifters, they develop a distinct wear pattern therefore the lifters must stay on the exact same cam lobe or premature failure will occur. If it were me I would go with the new cam and lifters.


But... I dont think this is your problem just yet. You said you fired the motor up and it was popping right away if I read the post correctly. It takes a little time for cam and lifter failure.  

There's a very good chance that the cam will go out in the future if it already hasn't started. Especially if you didn't run another break-in period the first time the engine started after swapping cams it will especially not stay together.

The popping you're describing really sounds like a cam is starting to fail so I'm afraid that's too coincidental that your measurements are okay. I would be getting that engine apart and getting a new cam and lifters.  

It sounds like you might have the plug wires on cylinders 5 and 7 swapped.  I'd check your wires again just to be safe.  I've done that myself a time or two.  

thats such a bummer if thats what it is. i just bought that cam not to long ago and it has about 1500 miles on it. itran perfect in the other motor. you really think that would be the issue? there goes $200 for that cam.

and plug 5 and 7 are not swaped. i quadrupled my second guesses on the plug alignment.

lets say if my cam isnt bad and my plug wires are fine. any ideas after that?  

Sticking or bent intake valve? Wires #5&7 parallel next to each other?  

4&7 do the same thing. I would go with the sticking valve. How long has it been since the heads were used? Cam could be a possibility. Just pull a valve cover when  its running, and watch rocker movement. A bad cam will have next to nothing. Just for ha-ha,s pull a plug wire at a time till your popping goes away. That will at least put you on your problem cylinder(s).  

JW454:
4&7 do the same thing. I would go with the sticking valve. How long has it been since the heads were used? Cam could be a possibility. Just pull a valve cover when  its running, and watch rocker movement. A bad cam will have next to nothing. Just for ha-ha,s pull a plug wire at a time till your popping goes away. That will at least put you on your problem cylinder(s).

thats a good idea i never thought of that. i will do that tomorrow and see what happens. i already have another set of heads that i have cleaned up that i am going to throw on there and try.

and i havnt ran these heads on this motor for about exactly 1 year. i ordered another cam so im going to throw my new cam in as well as change these heads.

ill post a new thread after i do the instalationand tell you all about it.
thanks guys  

My typing is lousy, I meant to say 4-8 do the same as 5-7. Make shure after you get things fixed that 4-8 5-7, are not able to touch each other, that is where you will have cross-fire problems. Good Luck!