5.7 vortec in 72 c10 issues

[lanehicks76]

Hi guys. This is my first post, but I have been reading through this site for some time now. I recently bought a roller 72 c10 long bed. I had a 98 5.7 vortec from a truck that I put comp cams magnum 280, comp cams bee hive springs with required hardware, aluminum dual plane intake, holley 750 vacuum secondaries, hooker super comp 1 7/8 headers and jegs quite flow fuel pump. I installed cam straight up as per comps tech line. IM having trouble with backfiring through carb and exhaust. It acted like the valves were to tight, but I just ran them again to zero lash plus 1/4 turn. Also I have played with timing and all the same. Has anyone had this popping, backfiring issue. Thanks in advance . Oh yeah all parts are new and the long block was running strong before it was pulled.

[geezer#99]

What method did you use to run the valves?
The spin the pushrod or the wiggle the pushrod method.
It's likely you have a couple valves hanging open!
http://www.crankshaftcoalition.com/w...raulic_lifters

[lanehicks76]

Hi there. I first set them on stand. Then I ran then with engine runnin .

[geezer#99]

What are you running for timing?
Have you proven your timing tab/balancer are accurate?

[lanehicks76]

Yes it doesn't matter where timing is. Initial set at 10. Then total 38. Then moved dist. Around. No changes with backfiring

[cadillac_al]

Running the valves with the engine running is pretty fool proof imo so they must be adjusted close enough. If you are positive that you don't have a spark plug wire crossed, then you must have a cam/lifter problem and will have to have a closer look. I crossed a couple plug wires a few years ago and it ran pretty decent until I got on the throttle and I got nice machine gun backfires. I ran it like that for a couple weeks because I was positive the wires were on correctly and an old dog like me couldn't make such a rookie mistake.

[fleetsidelarry]

x2 on the crossed wires, especially 5 and 7. could be a bit much on the total timing for a vortec

[lanehicks76]

I'm gonna change cap when I get to the shop if no good I will measure all valve travel. Thanks for all replies.
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[geezer#99]

Look for coil bind too!
Vortec's don't like more than 32 degrees too!

[BossHogg69]

I know you said it's a '98 block, but is that magnum 280 a hyd flat tappet or hyd roller?

[cableguy0]

Did you break in the cam properly and use plenty of assembly lube? Did you use a zinc additive during break in. If that cam is a flat tappet cam I really hope you didn't fire that engine up and let it idle while you attempted to adjust the valves. The first 20 minutes of a flat tappet cams life is the most important. If you didn't do proper break in I would suspect that you wiped the cam out.