Carb acting up.

Discussion in 'The Venerable Q-Jet' started by eagleguy, Nov 23, 2013.

  1. eagleguy

    eagleguy 1971 Skylark Custom

    Any ideas why all of a sudden my car would run at a higher idle in park/neutral and lower idle while in gear to the point of almost stalling when at a stop? :af:It used to be my idle was around 800 rpm at idle and around 650-700 in gear. Now she's at 1000 at idle and an erratic 400-500 in gear. Keep in mind these rpm's are based on my tach and may not be exact but things have changed drastically overnight and I have not adjusted or touched anything. I had a similar problem awhile back when unless the car was set at a high idle it would stall in gear at a stop. As this just made my drivetrain bang when going from park to drive I had the Qjet rebuilt and the problem seemed to be addressed as the carb ran the engine at a lower idle. I did recently add some carb cleaner to the gas tank but don't know if my current issue which just started tonight is related or just a coincidence. If I am hard on the car there is no miss and she runs strong leaving idle as my only problem. Tomorrow I plan on taking the air cleaner off and spraying her down with carb cleaner just in case I sucked up some crap. Opinions or suggestions welcome.
     
  2. carmantx

    carmantx Never Surrender

    Check for vacuum leaks. Sounds a lot like you have one. Maybe a hose came loose or something.
     
  3. eagleguy

    eagleguy 1971 Skylark Custom

    Vacuum is low enough with the 284 cam so you may be on to something. I will take a look tomorrow.
     
  4. Briz

    Briz Founders Club Member

    That was my first thought also.
     
  5. DaWildcat

    DaWildcat Platinum Level Contributor

    Check to see that no fuel is dripping from the primary boosters onto the primary throttle blades at idle. If there is, some debris may be keeping the needle from sealing on its seat causing the float bowl to overfill.

    Devon
     
  6. eagleguy

    eagleguy 1971 Skylark Custom

    OK I checked every vacuum line, cleaned the pcv valve which was sticking a bit and even tightened down the carb. At idle if you cover up the carbs throat with your hands she will stall. I then sprayed the outside and inside linkage of the carb including choke and butter fly. Sprayed one full large can of Gumout Carb/Choke Spray in the primaries and some in the secondary's sucking it through at high idle. Result is that I have gotten the "in park idle" close to smooth 800+ but in drive she is still rocky around an erratic 500 and almost stalls but by a "hair" hangs in there. Looked into the primaries while running in park @ idle and I see nothing dripping. I was going to get another can of Gumout but I'm not sure if it will make things any better. I was then thinking of getting a bottle of the new CRC total fuel system cleaner which is said to be the strongest on the market and throw it in the tank on top of the Gumout cleaner already in there but I'm not sure if mixing things up at this point is a good idea!
     
  7. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Steve,
    Just pull a plug and make sure they aren't fouled. Also, recheck your timing at idle.
     
  8. eagleguy

    eagleguy 1971 Skylark Custom

    I was just thinking the same thing and getting ready to add that to my post. I recently changed the plugs and went from AC to NGK? They are a pain to do with the A/C and headers but you have a good point! At the time (about 2months and 250 miles ago when I made the change the timing was fine) but you never know! Could bad plugs cause an erratic idle in drive but not in park?
     
  9. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Yes, it is possible. Which NGK plugs did you use?
     
  10. eagleguy

    eagleguy 1971 Skylark Custom

    Larry, I had AC Delco R45TS gapped @ 45 and went to NGK UR-4 gapped the same. I believe total timing was @32* with the 284 cam, but might be wrong. I'll pull some plugs when the motor cools off and see if they are fouled. FYI, the carb although not that old of a rebuild was lacquered up a bit as was the pcv valve when checked and cleaned today. In addition, I had some carbon on the previous plugs which was the reason for the plug swap. Thanks, Steve
     
  11. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    That plug should be fine. I was more interested in what your timing was at idle, in gear. Most cams will like idle timing up there around 14-16*, but you may need to reduce the mechanical advance down so the total isn't too much. You can also use vacuum advance attached to manifold vacuum to give you more advance at idle.
     
  12. eagleguy

    eagleguy 1971 Skylark Custom

    10/4, I'll post what I see on the plugs but for some reason (and I'm hoping) I think its a fuel issue as everything was fine until I added the damn Gumout, that's why I asked about the new CDC product.
     
  13. TexasJohn55

    TexasJohn55 Well-Known Member

    I will assume that you have bottomed the idle mixture screws, removed them, blown compressed air into the holes and re-adjusted your idle mixture.

    Do the idle characteristics change between cold and hot engine idle? I ask this because a mechanical fuel pump can dump gasoline into the oil causing a highly volatile mix which is then pulled thru the PCV into the intake.

    I had this happen on a '71 Pontiac Grand Prix 400. I had noticed my idle erratic when hot so I adjusted the mixture screws and smoothed it out. The next time I cranked it up cold I had a cold idle issue even after choke opened so I adjusted it again. Vicious cycle. When I pulled the dipstick and filler cap I found the problem, more gasoline than oil. It is a wonder that I hadn't blown the oil pan off. John
     
  14. ceas350

    ceas350 "THE BURNER"

    Burn through that tank if gumout stuff then fill up with your highest octane and report back. :)
     
  15. eagleguy

    eagleguy 1971 Skylark Custom

    Pulled a few of the NGK plugs. Other than looking a little lacquered over and having a fuel smell they had no odd or bad (black, white) coloring. Keep in mind they are not that old. As it may take a bit to run through a full tank of gas might I benefit from adding octane booster now, or it just a waste of $ and time? In addition if a mechanical fuel pump allows gas to mix with oil as mentioned would that make it defective?
     
  16. ceas350

    ceas350 "THE BURNER"

    Yes very defective. IM sure 5 or 6 wot blast will drain that tank :)
     
  17. eagleguy

    eagleguy 1971 Skylark Custom

    Please explain how the pump may defective. I replaced it awhile back as it leaked but didn't know one could go bad other ways. I have been running her hard to eat the gas up bit as she is not a daily driver so its gonna take some time which is why I questioned if the use of octane booster.
     
    Last edited: Nov 26, 2013
  18. carmantx

    carmantx Never Surrender

    the over the counter octane booster do not do much at all for a tank of fuel. So not worth the money.

    A bad fuel pump will leak past the diaphram, either on to the ground like yours probably was, or it is possible to leak inside the engine, and mix with the oil which is bad. a smell of your oil will be the indicator for that for you.

    How long ago was this carb built? You may be leaking raw fuel from the bowl, or the needle/seat may not be sealing correctly any more.
     
  19. ceas350

    ceas350 "THE BURNER"

    I've never known a fuel pump to allow gas and oil to mix besides my weed eater. That just don't sound right. Some one correct me if IM wrong and I'll say sorry...
     
  20. carmantx

    carmantx Never Surrender

    Ceas, back in the old days, I have pulled them out of a chevy where they had pumped a bunch of fuel in to the engine. There are bypass holes on the outside of the pump, designed to dump fuel out when the diaphram is bad, but it is supposed to dump it out on the ground. When they are covered in dirt and grime and crap, then those holes are sealed off and the gas goes in to the engine.

    I don't think that is what is going on here though. Just describing what was mentioned.
     

Share This Page