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5.0 and 5.7 Discussion, 1987-1990 Carburator...replace? in Cadillac Engine Technical Discussion; A well setup Q-Jet will take NO pumps to start, simply a slight depress of the pedal to allow the ...
  1. #16
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
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    Re: 1987-1990 Carburator...replace?

    A well setup Q-Jet will take NO pumps to start, simply a slight depress of the pedal to allow the choke to set. The choke is trying to set once it cools, but the tension of the choke on the throttle linkage won't allow it to. So once you relieve that, it sets. You should hear it snap closed if you listen (Cadillac might need window down... My Cutlass you didn't). Then crank it, it should startup and stay running. If it dies, front vacuum break is bad or the opening needs tweaking. This is one area I had to tweak as I had a 350 with a 307 carb, so I needed to open up slightly more (I used my 1976 FSM to get adjustments from), so it ended up being perfect. Mine started better when -10F than my 91 Bonneville 3800 did.... It was fantastic running. But I am picky on how mine run.

    IIRC the owners manual says only when it is very cold to actually press pedal to the floor prior to starting. Else just tap pedal.

  2. #17
    N0DIH's Avatar
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    Re: 1987-1990 Carburator...replace?

    Oh, and as a "performance mod" do NOT remove the deflector between the front and rear. It keeps the air pressures better equalized in the float bowl, as that is the bowl vent. Too much airflow into the secondaries disrupts that pressure, and causes mixture variations that aren't good for power. Some people think it causes airflow restriction, look at it, think that can hurt airflow???

    Ready for mods now???

  3. #18
    joe_padavano is offline Cadillac Owners Member
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    Re: 1987-1990 Carburator...replace?

    Quote Originally Posted by N0DIH View Post
    A well setup Q-Jet will take NO pumps to start, simply a slight depress of the pedal to allow the choke to set.
    I think we're saying the same thing here. To me, (and I suspect to most people) if you need to touch that gas pedal, you're "pumping" the accelerator. EFI engines don't require you to touch the pedal at all, which I suspect will be what most people think of when told "don't pump".

  4. #19
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    Re: 1987-1990 Carburator...replace?

    His creeping from stoplights really makes me think he has a faulty tcc switch, I have lived through that and many other 307 problems. 12 to 15 mpg how much better do you think your going to get with a 307. Mine runs perfect and the best I ever got was maybe 17,18. btw like I said mine runs very well but I still have to pump the gas 2 to 3 times to get it fired when its cold

  5. #20
    N0DIH's Avatar
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    Re: 1987-1990 Carburator...replace?

    My dad got 27.3 best on his 307 powered Cutlass. 2.14 gears and no OD. A friends parents did the same with 2.56's and OD, running 80 mpg across New Mexico and Texas.

    EPA rating for the 307 in a D Body was like 24 mpg, so very likely it should be not too hard to do. My 76 Olds Delta 88 (larger than a 77-96 D body) got 18 easy highway at 75 mph. 4860 lbs, 2.73's, 350 Olds, 225 75 15's and it even got as high as 23 a few times, but 18 was most common. I got 13 driving for Dominos Pizza. If you get worse than me you have REAL problems with it!!

    EPA rating was 13/17 for the 350, and 12/18 for the 455. So if you don't better 18, you could drop in a 455 Olds and get a mpg improvment.... All without OD and even more weight.

  6. #21
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    Re: 1987-1990 Carburator...replace?

    It sounds like there could be a number of problems in my case. Is there more definitely way to figure what the problem is? I'm on a limited budget and cannot afford to fix more than one major issue at a time.

  7. #22
    N0DIH's Avatar
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    Re: 1987-1990 Carburator...replace?

    Try this, push on the accelerator pump not the arm with the linkage, just the pump. If you depress it fully and quickly, it should stall the engine. Does it?

    And when the engine stalls you should hear a clicking noise from the carb for a few moments before it stops.

    If not, on 1, replace accelerator pump seals. If not on 2, you need to look into the M/C (mixture control) solenoid. Blue Connector on top front disconnected or loose will do it. Or a broken spring, or something jammed up.

    Start there. While you are at it, look for leaks on the baseplate gasket. GM specs that the carb to intake bolts be retorqued every 6 months to 10 lb/ft. You have done that right? Tighter than that can crush carb. I know, I have one laying around for parts that was crushed by a gorilla mechanic. I had to replace the whole carb it was so badly damaged in the TPS section.

    Once you have that nailed down, look for other leaks, idle off, timing off, bad plugs/wires should also be inspected. They all contribute to a poor running 307. The 307 isn't a powerhouse, but it isn't a weakling either.

    I should write up something on tips that I have ID'd on the 307 that help over time.

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