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Replaced GM 43L Wonbt Start

D

Dan Schmidt

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"I just dropped in a new long

"I just dropped in a new long block from Jasper motors. It's a 1991 model 4.3L V6 Merc. It has thunderbolt electronic ignition.
Engine won't start. It seems to get close (fires a bit and backfires / spits fuel up carb). I tried rotating distributor to and fro. Verified fuel entering carb, and I tried starting fluid. Verified spark. Rotor aligned w/ #1 wire with timing mark at 0 deg TDC.

I tried 180 deg distributor rotation but didn't even seem to fire.

Help please. Ideas on where to continue?"
 
"Dan,
Make sure distributor o

"Dan,
Make sure distributor on #1 compression stroke, valves adjusted,run oil pressure up for 5 minutes or until oil is running from all valve rockers before starting engine.
If there is not oil in the system the valves may not work as they should. Not enough lift. Plus it is not a good idea to start a new engine without oil pressure."
 
"Check plug gap
Check carb ga

"Check plug gap
Check carb gasket to manifold ( for good seat )
Check all vacuum ports on carb
Check that all intake manifold openings are plugged, there is sometimes one for divorced choke that needs a blockoff plate or it will kill engine vacuum.
As you can probably tell, I am leaning toward a vacuum problem."
 
"doubt collapsed lifters or pl

"doubt collapsed lifters or plug gap (if there is any gap) or air leaks are the problem. You do need fresh plug though.

backfiring up the carb sounds like ignition timing issues or firing order. Make sure the plug wires are on the right plugs from the distributor.

Approach timing methodically. Roll the engine over to TDC #1 firing position. Replace distributor with rotor pointing to number one plug wire under the distributor cap. Engine should run at Top Dead Center. With engine running and a timing light, turn distributor to advance timing to set base timing specs and tighten down.

Use a can of carb cleaner to spray down the carb throat to prime just before cranking. A couple sprays and you'll know you have enough fuel to get it to fire."
 
"Actually the 4.3 will fire on

"Actually the 4.3 will fire one tooth off advanced or retarded... allbeit rather cranky. Sounds like firing order to me, also ensure the rotor is fully seated in the distributor housing. Wires hooked up right on the side of the distributor?"
 
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