Gm crate?

[78C10BigTen]

So workin on the bosses 77 gmc value van 35 replacing the water pump and wondering if this motor is a gm crate replacement. The cast number appears to be 90s like a gmt 400 and the stamp on the front block pad is a sticker that i cant figure out. Did they make a long block crate motor like this or was it a short block with the original top half put on it. Also its runs like complete , replaced cap, rotor, coil, plugs n wires and still misses n studders. Twisted the distributor forward and in park it runs alot smoother, put it in gear and it studders and shutters and misses. Any idea why?

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[Blue Ox]

I don't think GM gave engines metric names until 1980 so I doubt that it is original.

 

[1987 GMC Jimmy]

You’re no freshman to this so I’ll just list my concerns and let you run with the ball...

• Gas Quality/Age or water in it
• Fuel filter or even fuel pump - check filter and perform volume test (20 oz Coke bottle in 8 seconds is correct)
• Incorrect timing, set it with a light
• Check for timing chain/distributor wear with timing light by watching the mark and blipping the throttle to see if it wobbles
• Improper curb idle speed and/or mixture setting, might be too lean and/or low - adjust after sorting out timing
• Vacuum leaks

This assumes the carb is in okay shape also. That could need some attention and be causing problems. Sounds like the ignition system is good to go besides the dizzy. If it has high miles, between 200K to 300K, the bushing could be worn out.

 

[78C10BigTen]

You’re no freshman to this so I’ll just list my concerns and let you run with the ball...

• Gas Quality/Age or water in it
• Fuel filter or even fuel pump - check filter and perform volume test (20 oz Coke bottle in 8 seconds is correct)
• Incorrect timing, set it with a light
• Check for timing chain/distributor wear with timing light by watching the mark and blipping the throttle to see if it wobbles
• Improper curb idle speed and/or mixture setting, might be too lean and/or low - adjust after sorting out timing
• Vacuum leaks

This assumes the carb is in okay shape also. That could need some attention and be causing problems. Sounds like the ignition system is good to go besides the dizzy. If it has high miles, between 200K to 300K, the bushing could be worn out.

It has a quadrajunk and the filter has been changed. Im pretty sure gas quality is good as its driven daily. Havent a light on it yet.

 

[bucket]

Looks like a crate engine.