GM small block mechanic help

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  • boogieman

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    Nov 14, 2009
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    I have a 1987 gmc Jimmy that I just did an engine swap in and can’t get it to fire. I went from a tbi to carb engine and just a crate 350. It wii crank but not fire. Are there any mechanics out there or someone that you recommend that would be willing to finish working on this engine for me? If available I could drop it off Thursday or Friday. I’m bringing it up from New Mexico and won’t be back until Wednesday or Thursday and have to return the uhaul trailer br Friday. After that I will probably have to get it towed. I’m located just north of Indy in Noblesville.
     

    churchmouse

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    So did you go with a distributor/coil set up.....Does the distributor have a solid 12 volts on it with the key on.

    Timing is close enough to start...???
     

    HoughMade

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    If you were nearby, we'd get this figured out promptly...my shadetree skills are more than adequate for a carbureted small block, I wish I was closer. I love this kind of thing.
     

    HubertGummer

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    I would check for 12V at the coil while cranking. I've heard of ignition switches going bad and preventing that. If it does then I would see if it will fire when putting starting fluid or gas directly into the carb.
     

    jkaetz

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    Engines need three things to run, fuel, spark, and air. Start with spark, it's the easiest to check. Then check fuel, air shouldn't be an issue with a carb. From there you get into other things like timing. Granted I'm sure others are more will versed than i in the intricacies of carb engines than i. I prefer the computer powered route. Concept is still the same though, just different tools and controls.
     

    Bennettjh

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    Check and double check the distributor has 12v and the rotor is on cylinder 1 on the cap, while the piston is at TDC on the compression stroke. It's easy to mess up. If all that lines up, maybe the ignition module is bad.

    I know a little about Edelbrock carbs but not Holley, Quickfuel, etc. A 1406 cannot exceed 6.5 psi. Even if your carb isn't dialed in exactly you should still get some kind of response out of the engine. Have you tried putting a little fuel straight through the carb into the intake?

    BTW, I love that body style.
     

    churchmouse

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    Is it barking and coughing out the carb and the exhaust. If so it could be the plugs are not wired to firing order or yes, it is out of time.
     

    boogieman

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    It’s the new model edelbrock 1906 that is replacing the 1406, and I did pour some gas straight into the carb. It’s not doing anything besides cranking. No coughing or choking no spit sputter or anything just crank. When I get back to Indy I’ll mess with it more. I set tdc and set the rotor to no 1 from there
     

    churchmouse

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    It’s the new model edelbrock 1906 that is replacing the 1406, and I did pour some gas straight into the carb. It’s not doing anything besides cranking. No coughing or choking no spit sputter or anything just crank. When I get back to Indy I’ll mess with it more. I set tdc and set the rotor to no 1 from there

    Just making a diagnostic guess over the internet but 12V check 1st. While cranking.
     

    Mongo59

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    It might be as simple as the battery terminal. These had two wire pos, one to the starter and the second to the fuse box. The oem had a lead disc between the two wires where the one closest to the battery had connection (crank) but none to the electronics (fire).

    Aftermarket sometimes had them molded into one terminal end for the side post batteries.

    I am with all those who said check for constant 12v.
     

    rem788

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    Apr 19, 2009
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    The original HEI distributors were pretty basic. As others have said, check for continuous 12 volts while cranking the engine. GM usually used a pink wire to the distributor for ignition voltage. Also make sure the distributor is rotating while cranking the engine. If not, check to be sure the cam and distributor gears are meshing correctly. Check the spark plug wire routing, if memory serves the firing order should be 1-8-4-3-6-5-7-2. Here is the procedure for setting initial ignition timing: ( this should get the timing close enough to start the engine)
    1. Bring cylinder #1 up on compression stroke
    2. Align the base timing marks on the harmonic balancer and the timing indicator attached to the block.
    3. Turn the ignition switch to the run position
    4. Attach a spark indicator to the number one spark plug wire
    5. Make sure the rotor is pointing to the #1 spark plug wire tower in the cap
    6. With the distributor hold down bolt loose, rotate the distributor until you get spark at the #1 spark plug wire. This will take some practice, sometimes you have to rotate the distributor fast enough to generate a signal from the pick up coil in the distributor to trigger the module to fire the coil.
    7. Tighten the distributor hold down bolt slightly to prevent the distributor from moving while you start the engine.
    8. Start the engine and follow the procedure for setting the ignition timing with a timing light.
    If the engine still does not start, there may be other issues.
    Good luck.
     

    churchmouse

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    He did say it was set up originally as TBI. I know some swaps if you dont get another ecm thats set up for your swap would have to be reprogrammed.

    You made me go back and re-read his OP.....:)

    He went from a TBI to a carb which eliminates the ECM unless you stay with the electronics to run the trans. That should be a stand along TCM module.
     

    1775usmarine

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    You made me go back and re-read his OP.....:)

    He went from a TBI to a carb which eliminates the ECM unless you stay with the electronics to run the trans. That should be a stand along TCM module.

    You should still need an ecm for several sensors on the motor and cooling system. I dont know how in depth the ecm was for an 87 and what it all controlled as vehicle computers were only starting to become more prevalent, but todays ecms are much more powerful and control pretty much everything.
     
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