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Thread: Boggs down under hard acceleration.

  1. #1
    Deer Slayer 2FNFAST's Avatar
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    Boggs down under hard acceleration.

    I built a pretty healthy 350 about 2 months ago. Here are all the specs. 1972 350 bored .040", 4 bolt mains, stock cast crank cround .010/.010, stock "X" rods, 9.6:1 compression ratio, "041" heads with 2.02/1.60 valves and 64 cc chambers. The cam is a L82 corvette cam with .450" of lift on intake/.461" on exhaust and the duration is 224*. On top of it all I have an Edelbrock RPM Air-Gap which powerband is 1500-6500. And I have a electric choke vac. secondaries 750 edelbrock. Ok finally got that out of the way! Now when I am at a complete stop and push it to the firewall it boggs down real bad sometimes it backfires or almost dies or completely dies. I have tried everything and am getting discouraged. The oil smells a little gassy. Do you guys think some smaller jets might help? Or should I just buy a 650 Holley?? Thanks for all the help I really appreciate it! Sorry about the novel! Anyone have any ideas? The timing is good been cheacked and rechecked and checked again.
    88 S10 Blazer - Work In Progress 360 hp 350/TH400 coming soon....

  2. #2
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    A backfire when you stomp on it sounds more like a lean condition. You might want to tune on the accerator pump linkage. What do your plugs look like? maybe you are running rich in steady state/cruising loads, but under acceration it leans out.

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    Deer Slayer 2FNFAST's Avatar
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    I haven't pulled my plugs but I will first thing in the morning and post it here ASAP. I put the linkage in the very bottom hole of the linkage to the accelerator pump and it didn't seem to help. Do you think i should put smaller jets in the secondaries maybe??
    88 S10 Blazer - Work In Progress 360 hp 350/TH400 coming soon....

  4. #4
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    Get the calibration book from Edlebrock. You might just need to change springs on the metering rods. They are sensative to vacuum changes and a bigger cam can make them difficult to tune.

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    Deer Slayer 2FNFAST's Avatar
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    I am a stupid ass when it comes to carbs but I will see if I can figure it out.
    88 S10 Blazer - Work In Progress 360 hp 350/TH400 coming soon....

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    LQ4 m8w6r77's Avatar
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    i think that carb is too big. either djet the carb or get a 650. i never had good luck with those carbs.

  7. #7
    Deer Slayer 2FNFAST's Avatar
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    I pulled a plug and the white stuff is black and the arm is also black and they smell gassy. Does this mean it is rich? I will probably be buying a Holley 650 very soon like I should have in the first place. Check out the pic it makes it look tanner than it is.
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    88 S10 Blazer - Work In Progress 360 hp 350/TH400 coming soon....

  8. #8
    Registered User label_sk8r's Avatar
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    it looks to me like that is a rich condition
    is there like a black ash or soot on the plugs?, cause if there is thats gas deposits that haven't burned off, try puling a couple plugs if they are all the same then yes look to the carb but if only a couple look like that one then the problem could lie in the ignition, maybe only a couple cylinders are getting the spark power needed to burn all that fuel

    but more than likely its a rich condition which would explain the bog on hard acceleration, i also remeber when my 2.8 was running really rich i was getting backfires up threw the throttle body too, try and find someone with good knowledge of carbs, and let them lean out your condition a little
    good luck
    86 s10 blazer 2wd
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  9. #9
    Senior Member bigjsp's Avatar
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    Originally posted by knudsonm
    A backfire when you stomp on it sounds more like a lean condition. You might want to tune on the accerator pump linkage. What do your plugs look like? maybe you are running rich in steady state/cruising loads, but under acceration it leans out.
    What he said. :bigthumb:

    Learning to adjust your edelbrock carb will be more valuable than just throwing a holley on it......... then learning to adjust the holley.

    A 750 will work fine on that motor.

    If its really rich it will run better when its cold than when its hot, although if you are fighting an accelerator pump problem it would still act lean and backfire.

    Check your fuel pressure or regulator setting.

    Watch for the carb boiling over after you stop.

  10. #10
    Deer Slayer 2FNFAST's Avatar
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    What do you mean boiling over? Take off the cleaner and check if it is boiling gas out of the top? If it is what does it mean?
    88 S10 Blazer - Work In Progress 360 hp 350/TH400 coming soon....

  11. #11
    LQ4 m8w6r77's Avatar
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    also another thing. go to hotter spark plug will also help.

  12. #12
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    Do you guys think smaller jets would work in the primaries and secondaries or what? What size should I get?
    88 S10 Blazer - Work In Progress 360 hp 350/TH400 coming soon....

  13. #13
    Senior Member bigjsp's Avatar
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    The "bogg" is more related to the accelerator pump and / or vacuum secondary opening rate than jet sizing. Don't get me wrong, Jets are still important but a real bogg probably isn't going to be cured with just rejetting.

    Check the accelrator pump and make sure you are getting a good shot of gas.

    the "boiling over" is when the carb dumps fuel after the engine is off and the heat soaks into the carb and expands fuel enough to dump into the motor, usually 5 to 10 minutes after you stop. It is also recognized by having to floor it while cranking it to get it started after its been run but yet an hour later it will start easily. This can "gas " down the oil and give the wet appearance on the plugs even when the motor is running correctly. This is an instant where the float level can be too high. I have also seen where it wouldn't boil in the garage with the hood up but the extra temperature caused when the hood was down caused it to happen.
    Last edited by bigjsp; 03-31-2003 at 09:34 AM.

  14. #14
    Puttin the "Sport" in SUV hivoltagedriver's Avatar
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    this could also be a timing issue, or a vaccuum advance not tuned or working properly, or as stated plugs that are too cold or not gapped right. I wouldn't jump to the conclusion that the carb is the issue. I have had good luck with the edlebrocks, even putting a 750 on a stock motor. The backfire makes me lean more towards a timing or ignition issue of some sort.

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    Deer Slayer 2FNFAST's Avatar
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    Do you guys think I should get a better distributor? I read my owners manual and it didn't say anything about changing the secondaires opening rate. Is there a spring or something I can change? Thanks guys I really appreciate all the help!
    88 S10 Blazer - Work In Progress 360 hp 350/TH400 coming soon....

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