I have a blazer with a small block 350. Rebuilt the engine was starting fine i adjusted the valves and now it spins shots fuel out of the carb or runs for a few seconds then stalls shoots fuel out of carb. I assumed this is a timing issue I brought the engine to TDC pulled the distributor aligned with number one same result though it could be 180 off rotated it same results. Don't understand how started fine fine Untill tuned the valves with it running now have this problem. I rest the valves with the engine off same result…

 

could be a stuck carb float BUT.... ok after rattle just quit how far did you tighten rocker nut - sounds more like valves are still out of adjustment and you have a few too tight or too loose - too tight on the intake valve and it will blow back as piston trys to compress and will do the same on exhaust stroke - exhaust too loose will blow back in the intake as intake valve opens

 

Adjusting Valves​
Small Block Chevy​
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Get #1 to Top Dead Center

Exh.- 1 – 3 – 4 -8​
Int.- 1- 2 – 5 - 7 ​
​
Get #6 to Top Dead Center

Exh.- 2 – 5 – 6 – 7​
Int.- 3 – 4- 6 - 8​
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Adjust until pushrod will not spin between fingers and then add ¼ turn and tighten poly lock.

You will only turn the engine 2 times. TDC #1 and TDC #6
This is how I adjusted the values spun them till would just stop spinning and gave the a 1/4 turn it also seem to blow pressure out of the exhaust pipe once or twice. When it starts it will run no knocking or shaking of the engine but you can here a back fire…could I have fuel fouled plugs? There new? Am I timing it wrong. Im
Going to pull all the plug wires off and start from scratch but it seem unlikely

 

double check your fireing order with plug wires and timing - as far as valve setting goes I always had better luck getting them right the old school way and setting them while engine was running, back nut off till rattle, tighten till rattle just stops then slowly a 1/2 to 3/4 turn more - I had a old chevy van with a 350 that would not take anything over a 1/4 turn, anything more than that they were too tight and she would backfire and cough out the carb. - back in the day the only way service manuals showed how to set hyd lifters was while running and solid lifters were set with the engine not running and set by feeler gague - I don't know maybe I had a lifter not fully inflated or something everytime I tried dry setting them or i'm just too darn old to learn new tricks