Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

DANGNABBITTT!!!! WTH is up this THIS!?! (q-Jet problems)

Discussion in 'The Garage' started by zakk, Sep 19, 2002.

  1. zakk

    zakk 1/2 ton status

    Joined:
    Sep 21, 2001
    Posts:
    4,762
    Likes Received:
    0
    Location:
    San Jose CA
    Ok, here are the specs:

    Brand-new GM motor with 475 miles on it.
    engine goodies include:
    Summit Headers
    Uber-Spark wires
    Curved HEI
    Well tuned q-jet
    edlebrock Performer manifold
    fliped air cleaner

    Brand new tranny with 475 miles on it.
    w/ mild shift kit

    POS K5 of mine, a gazillion miles on it. One ton, X-over steering with 20 miles on it. 39.5's that are "balanced" only in theory.

    I keep spitting vaccum port caps. particularly (remember, i cannot speel!) the rear 3/8 one facing the trans tunnel.

    I have a Kragen Q-jet that i have had ZERO problems with after we tuned it. I have no choke, no nada. and it is getting to be a pain in my phat arse to crawl under there every day to replace these caps.

    it does backfire a bit when cold, could that be it? can i crazy glue the damn cap on??? or is this a tell-tale sign that my engine is gonna go :boom: on me?

    /forums/images/icons/smirk.gif

    *signed*

    the fat kid that hates vaccum stuff.
     
  2. florida4x4

    florida4x4 1/2 ton status

    Joined:
    Sep 9, 2002
    Posts:
    255
    Likes Received:
    0
    Location:
    Florida
    so waz the problem? you forgots to tie wrap them vac plugs on? that must be some backfire you gots there. mebbe time you look see if the caps are really soft. if so then need replace em good ones that hold on better.

    Also so did that backfire flip you air cleaner lid or was that an intentional modification? /forums/images/icons/wink.gif /forums/images/icons/grin.gif /forums/images/icons/tongue.gif
     
  3. Blazer_Boy

    Blazer_Boy 1/2 ton status

    Joined:
    Dec 16, 2000
    Posts:
    1,669
    Likes Received:
    0
    Location:
    Sioux City, IA, USA
    Whats your timing setup? Rate, amount, initial, vac advance amount, etc. I remember when I put a questionable MSD box on my shortbox and it blew off every line on the carb! I guess that answered the questions.
     
  4. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

    Joined:
    Feb 17, 2000
    Posts:
    7,385
    Likes Received:
    0
    Location:
    Atlanta
    Once it's running, even with loose caps, the only way it could blow the caps off is if your getting positive intake pressure. You have some sort of problem in the motor. Hopefully just a timming issue. Check your distributor and make sure it's not hangin advaced. Also check base line timming.
    Where are you pulling vac for your vac advance on the distributor? Facing the carb on the truck the correct port is on the front right (driverside) just above the base plate.
     
  5. zakk

    zakk 1/2 ton status

    Joined:
    Sep 21, 2001
    Posts:
    4,762
    Likes Received:
    0
    Location:
    San Jose CA
    the distributor is HEI, so there is no vaccum advance. I am running the soft caps, but i am squeezing on a size smaller, still blowing them out.

    So i have either positive vaccum, or could the backfiring be doing it?
     
  6. zakk

    zakk 1/2 ton status

    Joined:
    Sep 21, 2001
    Posts:
    4,762
    Likes Received:
    0
    Location:
    San Jose CA
    </font><blockquote><font class="small">In reply to:</font><hr />
    ...and make sure it's not hangin advaced. Also check base line timming.


    [/ QUOTE ]

    please advise as to what "hanging advance" is. Also, the engine is at 12* BTC, IIRC. It ran like a champ until this cap problem started...
     
  7. dubl_t

    dubl_t 1/2 ton status

    Joined:
    Jun 8, 2002
    Posts:
    141
    Likes Received:
    0
    Location:
    Oregon
    don't hei's have a vac adv?
     
  8. k5ntexas

    k5ntexas 1/2 ton status

    Joined:
    Oct 29, 2001
    Posts:
    2,517
    Likes Received:
    0
    Location:
    corpus christi, texas.
    the earlier models of hei are vaccum advanced while later models are electronically controled. i don't know what years that started tho. i'm sure someone will chime in tho. later.

    jacob
     
  9. zakk

    zakk 1/2 ton status

    Joined:
    Sep 21, 2001
    Posts:
    4,762
    Likes Received:
    0
    Location:
    San Jose CA
    mine is electric
     
  10. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

    Joined:
    Mar 5, 2001
    Posts:
    15,683
    Likes Received:
    1,392
    Location:
    642 Days to BB2018
    I don't know the answer, but bring it by the house tonight for the BBQ and ask Scott to check the timing for total advance and see if it's somehow "sticking"? (I don't have a GOOD timing light...the one with the adjuster knob, so if you have one, bring it.)

    Anything short of a "demonic possession" in your engine, and Scott can figure it out! /forums/images/icons/cool.gif
     
  11. zakk

    zakk 1/2 ton status

    Joined:
    Sep 21, 2001
    Posts:
    4,762
    Likes Received:
    0
    Location:
    San Jose CA
    it won't even make it. i would love to bring it over and have the guys gimme their opinions on what is wrong, but it died going to the mailbox yesterday! /forums/images/icons/shocked.gif
     
  12. TopOff

    TopOff 1/2 ton status

    Joined:
    Jan 16, 2002
    Posts:
    1,760
    Likes Received:
    0
    Location:
    Folsom, ca
    So you have a curved hei that is electronically controlled by the computer? Never heard of it.

    I presume this has been running well before???

    *IF* the HEI checks out, as a non-computer controlled HEI, you must be getting some CRAPPY gas mileage on the freeway.

    IF it is computer controlled, you NEED to make sure the HEI is on the right timing tooth. Even if it is set correctly. You CAN get backfires.

    Are you sure your spark plugs are setup in the correct order? I have messed up my #5 and #7 too many times to count!

    Tight valves?

    Lean Carb?

    Good luck.
     
  13. zakk

    zakk 1/2 ton status

    Joined:
    Sep 21, 2001
    Posts:
    4,762
    Likes Received:
    0
    Location:
    San Jose CA
    the HEI was "worked" by a buddy. that is all i know. i traded $10 and a six pack for it. it ran great in the old motor, no reason to think it is bad now.

    my truck doesn't have TBI or anything...so computer controled it isn't. all the wires are right. I do not think it is a tooth off, but that is atleast a suggestion.
     
  14. TopOff

    TopOff 1/2 ton status

    Joined:
    Jan 16, 2002
    Posts:
    1,760
    Likes Received:
    0
    Location:
    Folsom, ca
    hmmm Tooth off would really only apply to computer controlled.

    Get a timing light and verify it advances the timing as the rpms go up.

    Good luck.
     
  15. Twiz

    Twiz 1/2 ton status

    Joined:
    Mar 8, 2001
    Posts:
    3,729
    Likes Received:
    0
    Location:
    Clearfield Ut.
    </font><blockquote><font class="small">In reply to:</font><hr />
    - It does backfire a bit when cold, could that be it?
    - I have a Kragen Q-jet that i have had ZERO problems with after we tuned it. I have no choke, no nada

    [/ QUOTE ]

    On a cold start, the carb can deliver a A/F ratio as rich as 1 to 1. What actualy makes it to the cyls is far leaner than what is flowing from the carb tho'. Partly due to the in-activity of the air in a cold engine and low engine speeds (low air speed vilosity). These conditions cause the fuel to puddle and collect on the intake manifold walls and floors. The problem is even more pronounced if the stock air cleaner heat-riser is not used.

    The stock choke system on a Carb will increase the booster signal by as much as three fold or more, richening the mixture as needed to compensate for the cold climate conditions.

    A lean engine may back-fire through the carb. (increaseing intake manifold pressure above ambiant air pressure)
    A rich engine may back-fire through the exhaust.
     
  16. zakk

    zakk 1/2 ton status

    Joined:
    Sep 21, 2001
    Posts:
    4,762
    Likes Received:
    0
    Location:
    San Jose CA
    I also axed the stove pipe, so my problem may be as simple as hooking the choke back up? i drove it one day, gave it 5 minutes to warm up, and didn't blow a cap. Maybe i just need the choke back on it....
     
  17. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

    Joined:
    Feb 17, 2000
    Posts:
    7,385
    Likes Received:
    0
    Location:
    Atlanta
    The mechanical advance under the rotor. Make sure it's not hanging.
     
  18. zakk

    zakk 1/2 ton status

    Joined:
    Sep 21, 2001
    Posts:
    4,762
    Likes Received:
    0
    Location:
    San Jose CA
    ah...another thing to check /forums/images/icons/grin.gif

    thnaks grim!
     
  19. Twiz

    Twiz 1/2 ton status

    Joined:
    Mar 8, 2001
    Posts:
    3,729
    Likes Received:
    0
    Location:
    Clearfield Ut.
    </font><blockquote><font class="small">In reply to:</font><hr />
    so my problem may be as simple as hooking the choke back up?

    [/ QUOTE ]

    Possibly, are there anyother drivability problems that could be related to this?

    If it is a A/F ratio problem when cold.
    You could just keep your big-fat foot off the gas pedal till it reaches opperating temps.
    Or richen up-the idle mix a bit.

    Thats all well and good now, but when it gets colder outside, you may have problems getting it to start.
     

Share This Page