350 sbc timing question?

[cberry121]

Ok so here's the deal. I bought a new GM goodwrench 350 crate engine, also have a brand new rochester quadrajet, and new msd ready to run distributor and coil. To set timing I put my finger over the #1 cylinder spark plug hole as i cranked the engine until i felt compression. I then put it at TDC. Which means i was on compression stroke. Truck fired up decent, even idled at about 700 no problems. Give it any throttle at all and it backfires through the carb with mostly gas and the occasional 2 foot flame, and stalls out. I then tried resetting timing at 8 degrees BTDC. Same issue. Firing order is perfect, rotor on the dist points right at #1 cylinder like it should. I have no clue what else to do. Is there a carb issue? mismatched timing tab and balancer? or is my timing just that far off?

[pwradder]

timing definately sounds off, try just advancing it untill it runs good then check it with a timing light. was it a new balencer? i've seen the outer ring spin on some of those. also make sure that the balencer and timing tab are a matched set, they had at least two different locations.

[terryj]

Check your vacuum advance line, make sure your on the "vacuum timed port" on the carb.

[LONGHAIR]

Originally Posted by terryj

Check your vacuum advance line, make sure your on the "vacuum timed port" on the carb.

Now why would you say that?
First of all, with an aftermarket distributor, it is probably set-up to run with full vacuum. I would hope so anyway.
Second, if it is popping back through the carburetor, the timing is late or there is a plug wire out of order, and taking away the vacuum to the timing will just make it worse.

Cberry121,
One would like to assume that the timing mark and tab are correct, but it's not necessarily the case. I would verify that first. A simple piston stop will make that easy.
After that, I would check the firing order again. It is very easy to get them crossed.
It could also be a lean condition causing the pop/stalling. Check the fuel supply and make sure that you are getting the accelerator pump shot.

Also, since this is a "new motor", you need to get it started and get it revved up, don't let it sit and idle for the first 20 minutes or so. It's nice to have a helper for this. They can keep the idle up(varying the rpm ) while you check everything for leaks. Fuel, oil, coolant, exhaust, etc.

[INSIDIOUS '86]

Originally Posted by terryj

Check your vacuum advance line, make sure your on the "vacuum timed port" on the carb.

This is a ford thing. Must be why they are always behind
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[cberry121]

ok so i rechecked the plug wires and firing order, all is good. i noticed when i put my timing light on it, the timing mark jumps around a lot, about 2 inches back and forth. so it is really hard to try and set timing with it doing that. what would be the cause of that with everything on the motor brand new?

[cberry121]

UPDATE: i did absolutely nothing to it, fired it up today, started fine still had the backfiring through the carb. This time i decided to just punch the throttle to the floor, and the engine ran great at 4000 + RPM. let off the gas and it went to idle, gave it gas slowly it backfired just a little. Now i can rev it up fast or slow with no backfiring at all.. im sort of confused. not sure about the timing mark though. I melted the number 3 cylinder wire so i cant really use a light just yet.

[INSIDIOUS '86]

You need to break in that cam first. Otherwise your going to rebuilding a new motor
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[88Jimmy4x4]

Originally Posted by INSIDIOUS '86

You need to break in that cam first. Otherwise your going to rebuilding a new motor
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I agree