Question about 1985 Chevrolet Chevy

4 Answers

Gm carb 305 timing problem

I installed a used gm 305 into my truck, replacing a old 305. The truck will only run withthe timing very advanced (maybe 20 degrees) and doesn't have much power and bogs down when you get hard on the gas. distributor is fine and was installed correct. Any suggestions?

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  • 2 more comments 
  • kyle_hansen Jul 25, 2009

    The Distributor was out of the motor when i picked up the motor. The motor is used but it looks like the distributor is new. I set the motor to TDC and distributor was installed at 6:30 possition (at #1 plug).

  • kyle_hansen Jul 25, 2009

    Just tried old distributor off of my old motor, witch worked fine, and it still didn't change anything. Both distributors are HEI. Could a gumed up carb be the problem?

  • kyle_hansen Jul 29, 2009

    I tried a different carb, that wasn't the problem. Seems to be clearing up on its own. Its not bogging down as often when i floor it but its not idling as well as it was. I can turn the distributor back closer to 8 degrees advanced and it will run now but still not as well as when its cranked. I even ran some card and combustion chamber cleaner through it but i'm not sure if that helped or made it worse, it really didn't want to start up again after that. I think im just goin to run the thing hard tomorrow and see how it works.

  • Ned C Cook
    Ned C Cook May 11, 2010

    Sorry, I sense you have left a critical piece of information out. Why did we have the distributor out? and what other work was done?

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4 Answers

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  • Chevrolet Master
  • 3,433 Answers

On the distributor, Check for advance weighrs. As your rpm increases the weights advance the timing. If they are rusted or a spring is streched or broken you will have to correct that. Hold the drive end and rotate thw rotor end back and forth to make dure the advance plate works freely and not sticking. It should spring back when you release it after turning it.What yr. is this rngine?Carburated, never mind. Ok, making sure the distributor is all free and cleaned up. Turn the dist. upside down and shake to make sure nothing falls out. You seem to have the timing thing down, but let me go through it just so I keep my train of thought.Actually I'm thinking out loud. #1 cyl on comp stroke-timing marks set to 8 degreesBTC. GO TO DISTRIBUTORdeternine #1 plug wire tower. Regardless of distributor body position as long as little tin window is around 6 o clock, Insert the distributor so the rotor is pointing at #1 tower.the mark you made so you know where that is..Should be @ 4 or5 o clock. When you drop the distributorin you will notice it turn so compensate soby dropping it a tooyh or two back.The rotor should be in the sweep of the #1 tower when you rotate the distributor. Hook up the coil wire and put the clamp on the distrutor but don't tighten it.With ignition on, #1 plug in #2 wire, lay the plug down on a good ground. Now slowly rotate the dristributor until #1 pops out a spark for you. You may have to go back and forth until you feel comfortable with when the coil fires. I don't know if you have a vacuum advance or not, but the vacuum advance points in the direction of distributor rotation. You want the spark to hit as you are rotating the distributor against the rotor rotation. Now the spark will hit at 8 degrees BTC before any weight or vacuum plays into it. Snug down your distributor and if you do have a little tin window, Stick the ole' in there and adjust the points to 28-32 degrees dwell. If no window, no sweat. It's an HEI, right? Let me know if you run into trouble. You can check your max advance if you like butgoing by that is assuming it's ok when it's not doing 3000 rpms. Better we assume the max is ok and know the bottom (start and low speed) is right on. Good Luck.

Posted on Jul 25, 2009

  • Ned C Cook
    Ned C Cook Jul 29, 2009

    Suggestion: Get it to idle at 8 degrees. Adjust everything , balancing the carb and making sure you have no vacuum leaks. It needs to idle right or the other circuits within the carb won't come into sction properly.Fuel at an idle is critical because that pretty tells you if you have sufficient ule to accelerate.with as moth curve, Your accelerator pump is only ther for your sudden acceleration like stomping on it. Running it hard like you said is a good way to vent your frustration but it won't make the problem go away. So, let's figure this out before changinging any parts for now. There are still a few things to ck, are you willing?

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  • Chevrolet Master
  • 3,433 Answers

On the distributor, Check for advance weighrs. As your rpm increases the weights advance the timing. If they are rusted or a spring is streched or broken you will have to correct that. Hold the drive end and rotate thw rotor end back and forth to make dure the advance plate works freely and not sticking. It should spring back when you release it after turning it.What yr. is this rngine?Carburated, never mind. Ok, making sure the distributor is all free and cleaned up. Turn the dist. upside down and shake to make sure nothing falls out. You seem to have the timing thing down, but let me go through it just so I keep my train of thought.Actually I'm thinking out loud. #1 cyl on comp stroke-timing marks set to 8 degreesBTC. GO TO DISTRIBUTORdeternine #1 plug wire tower. Regardless of distributor body position as long as little tin window is around 6 o clock, Insert the distributor so the rotor is pointing at #1 tower.the mark you made so you know where that is..Should be @ 4 or5 o clock. When you drop the distributorin you will notice it turn so compensate soby dropping it a tooyh or two back.The rotor should be in the sweep of the #1 tower when you rotate the distributor. Hook up the coil wire and put the clamp on the distrutor but don't tighten it.With ignition on, #1 plug in #2 wire, lay the plug down on a good ground. Now slowly rotate the dristributor until #1 pops out a spark for you. You may have to go back and forth until you feel comfortable with when the coil fires. I don't know if you have a vacuum advance or not, but the vacuum advance points in the direction of distributor rotation. You want the spark to hit as you are rotating the distributor against the rotor rotation. Now the spark will hit at 8 degrees BTC before any weight or vacuum plays into it. Snug down your distributor and if you do have a little tin window, Stick the ole' in there and adjust the points to 28-32 degrees dwell. If no window, no sweat. It's an HEI, right? Let me know if you run into trouble. You can check your max advance if you like butgoing by that is assuming it's ok when it's not doing 3000 rpms. Better we assume the max is ok and know the bottom (start and low speed) is right on. Good Luck.

Posted on Jul 25, 2009

  • 1 more comment 
  • Ned C Cook
    Ned C Cook Jul 25, 2009

    No, A fouled carb shouldn't affect the timingwITH THE ENGINEOFF, look in the carb and see if your accelerator pump is working. You know, some of those small blocks had fiber cam gears. The best way to ck that is to hand turn the crank shaft back and forth and see how much play there is before the cam moves in each direction. If the crank turns, well you know. The cam should move in direct relationship to the crank movement. Vk it out and let me know. Ned

  • Ned C Cook
    Ned C Cook Aug 22, 2009

    Just following up. Did you ever get your timing abd related problwms resolved? - Ned

  • Ned C Cook
    Ned C Cook Aug 23, 2009

    Eh there, Just checking to see if all worked out ok and your problem was resolved. Were you able to benefit from the advice? Hopefully so. Ned

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  • Master
  • 372 Answers

The distributor can not be installed properly. It has to be off a tooth or two

Posted on Jul 25, 2009

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  • Expert
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Unplug vacuum advace if u have one, plug it, set the timing at 36 degrees total timing,try that all small blocks run best at 36 and big blocks at 38 degreees total timing,hope to help

Posted on Jul 25, 2009

  • 1 more comment 
  • robert bishop Jul 25, 2009

    get a timing light to see where you are in timing,and set it 36 degrees



  • robert bishop Jul 26, 2009

    yes for sure the carb. being gummed up it will cause it to pop and backfire and smoke . rebuild it or get new one and try it. if other distributor did it the same way., has to be carb, hope to help,

  • robert bishop Jul 29, 2009

    u might have almost fouled the plugs, run hard and clean ,it may come alive if you gap the plugs at .060, most small blocks run great at that ,total timing is 36 degrees, try that, hope to help

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