Fuel system needs help.

Discussion in 'Troubleshooting & Diagnosis' started by Speed Happy '77, Mar 7, 2009.

  1. Speed Happy '77

    Speed Happy '77 Veteran Member

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    I mentioned part of this in another thread, but something else occurred to me when I brought it up. To start, I should mention that I'm not familiar with carbs... never had formal training for mechanics, just learned by necessity you know. I have a starting problem, got a high-torque starter and brand new battery last summer for it, but after two, three hours it will start for half a second, then die and refuse to start till you pump the pedal a perfect number of times.
    I mentioned it to a friend and he said there must be something wrong with the carb bowls. I already need to fix the choke (cold idle is 2500, warm idle is 600 and it stays on high idle way too long), so I have a Holley 650 cfm.
    Now comes the next problem. I'm driving and it starts to sputter at 3,600 RPM about a week ago. I thought I floated the valves, ignored it. Yesterday, it happened at 3,250 on my way out of town, then again several times on my way back as low at 2,800. Today it did it at 2,300 going uphill, but revived going downhill at went fine at 2,600 when I let off the gas a little. I'm guessing fuel pump does fine with flow but can't push out a lot of pressure? This all happened in fourth gear, I might add. Also in third gear when I tested it on a road outside my house. It only happens when I push hard on the gas. I can keep the pedal low and steady and get high RPMs without it happening.
     
  2. Speed Happy '77

    Speed Happy '77 Veteran Member

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    So the question is really three parts:
    I) Am I right in assuming it's the fuel pump (current one is mechanical, if that helps)?
    II) Can I use the fuel pump off my dead '82 Z-28 (it's electrical, I believe)?
    III) I figure now would be a good time to install the new Holley. Is there anything I should pay attention to while doing it, anything I should tweak like fuel/air mixture to see if that helps the sputtering out issue?
     
  3. Erics69

    Erics69 Veteran Member

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    The first thing is to make sure the floats are adjusted properly or it will cause a number of problems. If they are then the stock jetting (70 primary 75 sec.) is most likely too rich for you'r engine. I would rejet the primarys to 66's and see how it does. I have found stock 750 Holley's jetting and idle circuit way too rich for any moderatly built 350; which has the same jets and idle circuit sizes as the 650. You shouldn't have a problem but if you do replace the stock fuel pump for another stock mechinical pump. The electric pump in the 82' isn't worth the hassel of trying to get it to work with your fuel tank along with adding wiring and a fuel regulator to bring the pressure down to a carb healthy 5-7 psi.
     
  4. 68400BIRD

    68400BIRD Veteran Member

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    It sounds like the problem is getting worse as time goes on. If the floats are set wrong they will not get set worse as time goes on. Now the fuel pump might get weaker, fuel filter might get more plugged, ignition could get worse. Burnt wires, crusty cap, etc. Check all of your tune up options then start dialing in the carb with first adjusting the floats. How is your timing?
     
  5. Speed Happy '77

    Speed Happy '77 Veteran Member

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    My timing mark is really off, don't know why, but I did a TLAR advance (That Looks About Right) on 87, then turned an extra couple degrees for premium (pumps keep running out of premium, thus the slightly retarded timing, but I advanced it to the max on 87).
     
  6. Speed Happy '77

    Speed Happy '77 Veteran Member

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    Oh, ignition. New spark plugs and wires. The cap and rotor were in good shape, so I just cleaned them, but I have new ones to replace them. I know it might sound stupid, but I only run Shell because of the gunk buildup, but I can run some cleaners through the system... what ones would you suggest?

    I was leaning toward the fuel pump getting weaker.
     
  7. 79supergasdriver

    79supergasdriver A Scholar and a Gentleman

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    Since you like acronyms...here's a familiar one: KISS! Change the fuel filter first. Cheap and easy. While you're changing the filter, check the pump output by sticking the supply hose into a metal container and having buddy crank the engine for a few seconds. Observe a steay, solid stream projecting into the container. If it surges or barely trickles out, go ahead a swap on another stock replacement. Those are pretty cheap too. If those two suggestions don't fix your problem, we'll dive into the good old "guess-and-check" remote tuning discussions.
     
  8. Speed Happy '77

    Speed Happy '77 Veteran Member

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    It only does it (sputters out... off for a second, lurches for a second, over and over) in high gear. I'll try that anyway, sounds sensible. Haha glad you liked my initialism there.
     

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