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Discussion Starter · #1 · (Edited)
need help (update)

my freind has a 74 model c10 383 dart heads msd ingnition. i just cant fingure out wats wrong with it. it idles fine when u give it gas it starts poping out the carb no fire just gas i have put new plugs in tryed another carb checked the timming checked the rocker arms checked the spark plug wires everything is fine any ideas.......................................................well did a compression test some good but 3 & 5 had 0 so ethier the rings let go or he has some bent valves he bought this truck with the 383 all i did was put the heads on it wat i fingued maybe someone reringed
the engine when they should had bored it out
 

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Since there is no fire when it pops through the carb as the motor revs up i dont think its ign related esp since you just installed new ign parts & i assume you got the firing order correct. (1,8,4,3,6,5,7,2)

When you hear a poping sound through the carb with no fire that speeds up right along with the rpms i would look for incorrectly adj valve/s,a loose rocker/s that fell off a valve/s,a cam lobe/lifter went bad/worn down,a rocker stud backed out/loosed up,motor was over reved and bent a valve(do comp test),broken valve spring/s(do comp test),an intake valve adj too tight hanging a valve open not letting it seat which will makre a poping noise up through the intake manifold & carb just like you described (do Comp test),etc.

Scott
 

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Discussion Starter · #3 ·
ok thanks for the reply i checked and see if a rocker came off they all still looked good now he could have over reved it ill do a comp check tommorrow and see wat comes up
 

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I agree whole heartedly. its prolly just a valve adjustment prob. back em off a touch and should go away. Bill
 

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double check the order of #5 and #7 plug wires. 4 and 8 are easy to get reversed too.

Have you checked the timing with a light?

If nothing else shows up do a check to see that all the valves have the same amount of lift. just disconnect power to the ignition and pull the valve covers. have somebody crank the starter while you look at each valve in turn, see if any have less movement than others.

Post back here and let us know what you find.
 

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Discussion Starter · #6 ·
well did a compression test some good but 3 & 5 had 0 so ethier the rings let go or he has some bent valves he bought this truck with the 383 all i did was put the heads on it wat i fingued maybe someone reringed
the engine when they should had bored it out
 

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Zero comprression is not usually worn/broken rings,thats usually bent or broken valve/s,spring/s,possibly both intake & ex lobes are worn off on those 2 cylenders,broken/bent pushrods,etc.

Scott
 

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Discussion Starter · #9 ·
well i did a leak down test with the piston at tdc its blowing air out the carb i am taking the head off if its a bent valve can i see that its bent when i take the head off and flip it up side down?thanks
 
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