New Cam, Heads & Carb: Backfires Does Not Run

[xcookpac]

It has a been awhile since I posted last. I have been very busy with work and working on my 85 el camino as time permits.

I am at what should be the end of a relatively long project for me working as time permitted. My 85 EC had a 305 with almost 100k miles. It still had the stock heads and manifolds with the CCC carb. I did a compression test on the old motor and I had about 180 pounds of pressure for each cylinder, I decided to improve the camino by removing the smog stuff and replacing stock with the following items:

1.) new Comp Cams 388-12-4 camshaft with conventional hydraulic lifters about 440 lift;

2.) rebuilt corvette 113 aluminum heads with d port exhaust (similar to the fast burn heads) and factory guideplates;

3.) LT1 exhaust manifolds as they handle the angle plug heads without problems;

4.) HEI distributor with mech and vacuum advance; and

5.) Summit roller rockers with 1.5:1 ratio;

6.) edelbrock aluminum performer intake; and

7.) Mountainman Qjet rebuilt.

I also added the serpentine belt system.
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I cannot get this motor to run. Just came back inside after pulling number one plug and rolling motor to TDC. Distributor was a little bit more advanced previously. Reset timing static to a couple degrees before TDC. Still the motor does not run. The motor has backfired a couple of times (most recently through carb but with previous timing also through exhaust). I have checked the firing order repeatedly. I have checked the voltage at the battery (13.2V). I have checked the sbc distributor rotation as clockwise.

My current plans to fix include:

1.) Cap off fuel line from tank and use ether/starting fluid to try and start vehicle in an effort to isolate carb from the fix (if EC runs on ether sprayed into carb but not on 93 octane from carb then we have a carb problem).

2.) Pull all the plugs and do a compression test (if they all have good compression and they are all within 5% of each other then we can eliminate valve lash and camshaft installation.

By the way the motor has oil pressure when cranking and was lubed by cranking oil pump with adapter prior to installing distributor (and lifters were soaked in oil for days prior to assembly and all cam lobes were were lubed).
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Anybody have nay suggestions on where to go next with figuring this out?

I look forwarding to hearing from the board's collective wisdom.

 

[81Regal]

My first thought would be the distributor is in 180 degrees off. How did you check it to verify TDC?

 

[xcookpac]

My first thought would be the distributor is in 180 degrees off. How did you check it to verify TDC?

That was my guess also. So I pulled number one plug and rolled motor to TDC with starter (I could feel the compression with my finger). Distributor was a little bit more advanced previously (about 25 degrees of advance and now about 4 or 5 degrees). I then reset the timing using the static postion of dist rotor (to a couple degrees before TDC). Still the motor does not run. The motor has backfired a couple of times (most recently through carb but with previous timing also through exhaust). I have checked the firing order repeatedly. I have checked the voltage at the battery (13.2V). I have checked the sbc distributor rotation as clockwise.

Your thoughts please.

 

[81Regal]

Since you are positive its not a timing issue although it still sounds like it to me, pull the valve covers and make sure you don't have the rocker arms adjusted too tight and verify both of the valves are completely closed when the piston is at TDC. You don't say if you used a replacement timing chain or not since you swapped out the cam.
I really don't think it is fuel related issue.

 

[chevy2480]

If dist is in right. It sounds like rocker arms are adjusted to tight and not allowing the valves to close fully. Been there done that.

 

[SonOfRDgear]

try to loosen the rocker arms so they have a little bit of wiggle to them (not too much obviously) and then try to start it. If it runs you just had your rockers too tight. Its rather easy to overtighten the rockers.... ive found the easiest way to lash the rockers is to keep the valve covers off and tighten them so you can just barely wiggle the rocker side to side, run the engine a little bit, tighten again, and keep repeating until they seem to stay tight. if you follow the whole spin the pushrod then go another 1/2 turn rule of thumb youre more than likely going to overtighten.

just as a rule of thumb the engine will run better with the rocker arms a bit too loose than it will with them a bit too tight.

 

[xcookpac]

I will try loosening up rockers. If I do a compression test won't that show which cylinder(s) have overtightened rockers?

Thanks

PS Do you agree one possibility: Backfire >>> Caused by Valve(s) Hanging When Supposed to Be Closed >>> Valve(s) Hanging Open Caused By Overtightened Rocker Arms

 

[seawolf18]

When you put the cam in, did you make sure to put the cam and crank sprocket dot to dot? I've forget to do that in the past.

 

[xcookpac]

I tried timing the motor with my timing light using the starter to rotate the motor. What I found was that we are about 45 to 60 degrees retarded (I don't understand how the static timing could be that far off). In the meantime, my timing light stopped working (let's see if I can fix it). Then I will pull distributor and reinstall it so that I can the spark advance timing sufficiently. I will let you know how I make out. Hopefully this is the end of this nonesense,

 

[xcookpac]

When you put the cam in, did you make sure to put the cam and crank sprocket dot to dot? I've forget to do that in the past.

Yes, dots were lined up on cam and crank gears. In addition, I used a harmonic balancer cover with timing marks which I fine tuned to TDC with an adjustable pointer at about 2PM before installing heads.