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.

Backfiring with AIR Pump hooked up??

Discussion in 'The Garage' started by sled_dog, May 7, 2003.

  1. sled_dog

    sled_dog 1 ton status

    Joined:
    Sep 3, 2002
    Posts:
    16,870
    Likes Received:
    0
    Location:
    Austin, TX
    I put the belt on my AIR Pump this morning since I took it in for emissions testing. Well when its hooked up taht thing backfires like mad. I mean like flame shooting gun shot rivaling backfires. Without the AIR pump it just crackles a little but with it is full on drive by sounding backfires. I actually saw little children run when I just went for a drive and it surely sounds like crap. Sometimes it sounds like it might be misfiring too. I just checked and reset my timing to 4 degrees(factory for my 305) it was at 6 degrees. Still does it. I was thinking that maybe my vavles are badly adjusted and slightly open making it so the air ramming in forces into the exhaust valve and makes it misfire then load up on fuel. Sounds good in my head not sure if its the problem. Anyone have opinions on this matter?
     
  2. sled_dog

    sled_dog 1 ton status

    Joined:
    Sep 3, 2002
    Posts:
    16,870
    Likes Received:
    0
    Location:
    Austin, TX
    by the way I am running a QJet and my cats are gutted. I have a friend with an 84 K20 and when he put th ebelt back on his air pump it crackled more than it did without.
     
  3. morphed86k10

    morphed86k10 1/2 ton status

    Joined:
    Jun 25, 2001
    Posts:
    463
    Likes Received:
    0
    Location:
    Reno Nevada
    Mine did this once, but not when driving, only when decellerating. Turned out it was the diverter valve on the AIR system that was causing it. Something about forcing oxygen into the exhaust at the wrong times (i.e. under motor conditions that might allow unspent fuel into the exhaust, like coasting). Once that was replaced, it was fine.
     
  4. sled_dog

    sled_dog 1 ton status

    Joined:
    Sep 3, 2002
    Posts:
    16,870
    Likes Received:
    0
    Location:
    Austin, TX
    My mechanic friend says it makes sense to him, cool air introduced into the very hot exhaust. And then no cats to break it up. Whatever I Just blocked the tubes off so they look like they work but they don't, solved it all. In fact ti doesn't crackle like it used to.
     
  5. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

    Joined:
    Feb 17, 2000
    Posts:
    7,385
    Likes Received:
    0
    Location:
    Atlanta
    You think your buddies "adjustments and modifications" to your carb from your post yesterday has anything to do with how rich your truck now runs? /forums/images/graemlins/shocked.gif
     
  6. sled_dog

    sled_dog 1 ton status

    Joined:
    Sep 3, 2002
    Posts:
    16,870
    Likes Received:
    0
    Location:
    Austin, TX
    you like copy and paste huh? And I said it seems like its fouling out and then running rich. I also noted that blocking off the air pump fixed it right up. Something about air pump without cats I figure.
     
  7. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

    Joined:
    Feb 17, 2000
    Posts:
    7,385
    Likes Received:
    0
    Location:
    Atlanta
    [ QUOTE ]
    you like copy and paste huh? And I said it seems like its fouling out and then running rich. I also noted that blocking off the air pump fixed it right up. Something about air pump without cats I figure.

    [/ QUOTE ]

    THink here for a second.
    Back fire is unburnt fuel. Unburnt fuel needs air to burn. The prupose of a air pump is to help completly burn the 'NORMAL" amount of unburnt fuel that will be expelled.
    a good rebuilt engine that is not burning oil and has proper compression and a reasonable cam is going to run right. When you screw upo the fuel mixture is when your going to have problems.

    A auto manufacture is not going to pu anything on a vehicle that is not absolutly needed. Even if it's only .05 cents when you build a million of them that's a lot of cash.

    You have three posts. One from two days ago saying you modified the choke and messed with the blend doors on the secondaires including removing the vac operated door lock out that shuts down the secondaries on deceleration.


    http://coloradok5.com/forums/showflat.php?Cat=&Board=garage&Number=739179&page=3&view=expanded&sb=5&o=&fpart=


    You have a post about how you just failed emmisions today and this post. It's all related.

    You need to put that carb back to stock or your not going to pass emmissions. You have to have the air pump to pass visual an if it's backfiring they are going to know something aint right and look for problems.

    If it's running right it will pass even with gutted cats. I know because I have done it twice and I didn't have gutted cats I had straight pipe and the dork didn't look for the cat the first time. The dork looked the second time after he already ran the sniffer and had it logged in the computer and no easy way to back it out. I did it on r92 octane pump gas with no additives.
    What did I do....I tuned the engine for optimum performance. The truck barked second gear under full throttle. My wife had a habbit of running hondas off the road with it when they tried to jump traffic on her. 10 degrees of timing and set the carb up properly so I was geting the proper stoic mix. I didn't just mak the grade I showed lower emmisions then my other car that was a 4cyl with fuel injection. Cats are a patch for a mildly out of tune engine from owners that don't take care of their junk. It was pushed by big buisness to shift the blame for smog namely the local power companies.


    Hit the parts store and pick up a book called Rochester tuning and perfomance. It will have the information you need to fix your carb. If it's trully screwed up then get a rebuilt carb.
     
  8. sled_dog

    sled_dog 1 ton status

    Joined:
    Sep 3, 2002
    Posts:
    16,870
    Likes Received:
    0
    Location:
    Austin, TX
    thanks for this info. It was totally screwed up before I will look into it. Though I doubt much in depth. I would like to learn a bit about the rochesters just to add my knowledge and ability. Besides sounds like it will be sitting in my driveway till august to be nice to my friend. It always seemed to run real rich before just with the air pump it seems to misfire too. My dad seems to feel I need to adjust my valves. I really don't feel like doing it but again in the next 2 months i will probably break down adn do it. I bet that thing will be running better than it ever has the day it leaves my possession.
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

    Joined:
    Dec 13, 2000
    Posts:
    26,977
    Likes Received:
    189
    Location:
    Roy WA
    Are you running a solid lifter cam? If not, and there is no obvious valvetrain noise, it's not going to be valve adjustment thats your problem.

    They don't magically go out of whack unless something fails (or a nut backs off, at which point you'll have more problems, since the valve won't ever open), then you've got to tear into the engine.
     
  10. Blazer1970

    Blazer1970 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    1,600
    Likes Received:
    0
    Location:
    Old Mission, MI
    It's running way rich. Unburnt fuel going out the exhaust as Grim says. What kind of mileage are you getting?
     
  11. sled_dog

    sled_dog 1 ton status

    Joined:
    Sep 3, 2002
    Posts:
    16,870
    Likes Received:
    0
    Location:
    Austin, TX
    I have a slight valve chatter. Also I get 5 mpg most of the time. I don't drive efficiently but trying I have gotten like 6. Its been that way since i got it my recent changes haven't affected my mileage. If anything I think it may have gone up since i haven't put gas in in a couple days.
     
  12. Blazer1970

    Blazer1970 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    1,600
    Likes Received:
    0
    Location:
    Old Mission, MI
    Get a carb on there that works right, and you will pay for it pretty fast with the extra 10 mpg you will get. You will also get better performance, and maybe be able to pass emissions too.
     
  13. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

    Joined:
    Feb 17, 2000
    Posts:
    7,385
    Likes Received:
    0
    Location:
    Atlanta
    I got 9mpg towing 7500lb 110 miles then towing the 3k trailer back 110 miles on a BIG Block and it had FOUR bad plug wires I found out a week later. My 75 Jimmy that's 7ft tall slinging 35's with 4.10 gears gets over 10mpg (Speedo is 7mph slow at 65mph and it shows 9mpg when I figure it with the off millage) and it doesn't have overdrive.

    Ya got some carb problems.
     

Share This Page