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Sanity check on hesitation and popping.

Discussion in 'The Garage' started by norville, Aug 30, 2006.

  1. norville

    norville 1/2 ton status

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    Hey folks, just keep me honest here. The burb has been sitting for a while. I've put in about 10 gal of fresh gas. I believe there was about 10 in there. I've changed plugs,wire,cap,rotor, and coil fuel filter.


    When it idles it's nearly perfect but if I run the idle @ like 1500rmps then goose it I get a hesitation and on the down side I get some popping in the exhaust. Now I drove it the other day and it felt real weak. I just dumped a bottle of seafoam in the tank. I don't have a full exhaust yet.

    Secondly which way does the little brass filter go into the carb??

    It's the gas right or vacumme leak are my valves bad. I hate digging when it most likely is something simple.

    thanks

    bob
     
  2. diesel4me

    diesel4me 1 ton status Premium Member

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    hesitation is caused by...

    Retarted timing can cause hesitation--make sure its set to spec,the vacuum advance works,is hooked up properly,and the advance weights are free and snap back when you twist the rotor---other causes are a bad accelerator pump in the carb,maladjusted secondary throttle air butterfly (on a Q-jet carb only),and other things like fouled spark plugs..I'd guess its timing,if its low on power too..

    The "open" end of a brass filter faces the fuel line..I'd ditch that style filter and install a normal "in line" universal one..the threads strip too easy in the carb,and those filters do nothing--when they clog,the spring behind them lets them move back,and unfiltered gas goes in the carb!..:doah:
     
  3. norville

    norville 1/2 ton status

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    Well I already picked up a clear plastic universal filter. Do I leave the old one in there?? Also what the best way to fit in the new one I don't like it low where the rubber starts. Should I just cut the steel line or look for a nipple at the carb?

    I check the butterfly and the weights in the carb. I'll do the timing next. What should a stock 400 be running at??? I'll also check the vacumme.

    thanks for the reminders

    bob
     
  4. diesel4me

    diesel4me 1 ton status Premium Member

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    filters..

    I'd toss the brass filter and the spring--rely on the in-line filter instead..stacking too many filters can cause fuel starvation sometimes..I cut the steel line to install a in line filter,far enough away from the air cleaner so it wont rub on it,not far from the alternator..keep plastic ones far away from the exhaust or intake manifolds!..or from anything it could rub up against..

    The timing on a stock 400 SB can vary quite a bit--I'd guess anywhere from 4-8 degrees BTDC is close,I dont have a timing spec chart handy...I usually time my engine by "ear"...keep advancing it until I hear pinging at light throttle about 20-25 mph,then retard it a little at a time until you barely hear any pinging or none..I've found I can increase gas mileage as much as 5 mpg this way..often the timing marks have "slipped" on the harmonic balancer,and cant be trusted to give accurate readings...

    I also hook my vacuum advance to manifold vacuum,it seems to idle smoother and get better "around town" mileage that way..might not hold true for ALL motors,or those in higher altitudes than I'm at..I live in a place only 35 ft above sea level,so I can get away with a bit more advance than the stock settings..:crazy:
     
  5. norville

    norville 1/2 ton status

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    Well some updates, or just more info. the popping only seems to happen when its warmed up. And mostly when I let off the gas, there seems to be a miss also. This is not because I only have and xhaust that ends at the muffler? Next I found a fuse in the cvacumme line going to the dist. I pulled the line to set the timing and Found that fuse pluggin the hole. I removed it and still have the issue.

    I did not set the timing I hooked up the light but couldn't find the line ot the reference guage??? I feel like such a noob..

    Why only warm???

    bob
     
  6. broncoman6524

    broncoman6524 1/2 ton status

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    thats weird i have this exact same problem except mine is only when its cold...weird. lol
     
  7. norville

    norville 1/2 ton status

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    I'll trade you.

    bob
     
  8. broncoman6524

    broncoman6524 1/2 ton status

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    im alright lol
     
  9. norville

    norville 1/2 ton status

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    I messed with it for a few minutes this morning. I can't take it on thee road it's registered anr insured. But I advanced the timming some and still something is not right.

    As I roll the throttle up I think I getting a miss as the rpms are about 2K I'm getting that popping panging noise in the exhuast. I smell fuel but I can't tell if it's normal or not. An the other sign is if I goose it just s throttle bump I get the pop in the exhaust or is it a pang???

    bob
     
  10. norville

    norville 1/2 ton status

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    PO had 1 and 3 wires mixed up? :( All is good.

    Where is the timing mark and reference on a 400??? can't find it.

    bob
     

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