Carb too lean?

Discussion in 'The Venerable Q-Jet' started by FireRedGS455, Dec 18, 2021.

  1. FireRedGS455

    FireRedGS455 Founders Club Member

    I need some help determine what my problem really is.
    If the post is in the wrong section, please move it.

    The problem is my engine gets warmer and warmer the longer the distance and at increased speed.
    At normal drive around town the temp is around 180 to 200F.
    If I cruise at low speed, tight traffic, many start and stops the temp goes up.
    If I drive on the highway at 60 to 80mph for more than 10 to 20 miles, the temp goes to 220 - 230F.
    If I drop the speed to below 60mph the temp start to fall back down to 210F.

    Everything works perfect, starts, accelerates, no hesitation, no detonation.

    Engine was dynoed at Westech, CA. 393Hp at 4800 and 487Torq at 3600.
    Here is my build:
    455(1973) is 0.030 over. 9.3:1 comp with Felpro gaskets. At some point, I changed the head gasket to 0.027 from TA. So it should be around 9.6:1 if calc. correctly.
    1970 iron head with Stage1 valves, 68cc, very little clean up and 1970 iron intake.
    The cam is KB118. KB 2" pulse headers. Full 3" TA exhaust, H-pipe and Ultra Flo mufflers.
    Roch Qjet 7041540 with following setup, see pict. Dist. Was also done. See same pic. For spec.
    Power timing according to Larry description.
    Complete TA timingcover. TA high perf. waterpump. Stock wing, thermal clutch and shroud.
    THM400 with shiftkit. KB 2600 stall. Rear is 8.5 with 3.42. Fairly huge transcooler in front of radiator.
    Tires are BF TA 225/70/14.

    Readings posts on similar issues I added a AFR and it is around high 14’s to low 15’s.
    Only at WOT it goes to 12 to 13. Then imidiatly back to high 14's to low 15's.

    Any idea why it gets warmer and warmer or suggestions were to look?
    My own theory is that the carb is too lean?
     

    Attached Files:

  2. LARRY70GS

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

    You told us everything except the most important things.

    What radiator are you using?

    What thermostat?

    Are you using vacuum advance? If so, have you verified that it is working? What is the actual ignition timing at your cruise RPM.

    AFR sounds perfect.

    If you are getting sufficient air flow, and I'm sure you are on the highway, you have insufficient cooling capacity in whatever radiator you are using.

    It looks like an aluminum radiator in the picture.
     
    Last edited: Dec 18, 2021
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  3. FireRedGS455

    FireRedGS455 Founders Club Member

    Yes of course. Good questions.
    Correct, the radiator is a Griffin alu. I don't recall number of rows of tube size.
    Thermostat is either a 160 or 180. Believe it was a 180 when I got the car and changed to 160 at some point.
    Yes, vacuum advance. It has been working, but I need to check to be sure.

    Timing at cruise RPM I don't know - how do I do that?
    at 70mph it is approx. 2900rpm if I remember correctly.
    The timing is set at 34 at 2600rpm.
     
  4. 72STAGE1

    72STAGE1 STAGE 1 & 2

    I would change the stat for starters, half are junk and put a 180 back in, look at the plugs for lean condition also.
    Also use a laser temp gun to see if your gauge is wrong, I had similar problem and found my guage was 10 degrees off, along with faulty thermostat.
     
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  5. LARRY70GS

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

    Radiator should be good then. To see what your timing is at cruise, just rev the engine to 2900 in Park, and either use the dial back feature, or a 30* mark to see what the ignition timing is. With the VA, it should be in the mid 40's. As far as thermostats go, they will be fully open 20* after the temperature they are rated at. That means a 160* will be fully open at 180, and a 180, at 200* If you see the temperature go above that, the thermostat has lost control of the system temperature. Thermostats should open just enough to keep the temperature they are rated at. Are you running more than 70% anti freeze? I ask that just to make sure as some think if a little is good, more is better. The more anti freeze you run, the worse your heat transfer.

    Your AFR's are exactly what my Q-jet runs at. I do not think it is lean.
     
  6. CJay

    CJay Supercar owner Staff Member

    Low 15s is pretty lean. I run my AFR at 13-1
     
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  7. LARRY70GS

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

    Not for a Q-jet. Mine runs that all the time. It idles at low 13's, but 14.7 is what modern FI strives for, and that is where mine runs on the highway, 14.7-15.2. Never any surge or missing. WOT, it's 12.5-13.0.
     
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  8. Mart

    Mart Gold level member

    You could try no thermostat to see if temp stays low while driving.
     
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  9. CJay

    CJay Supercar owner Staff Member

    Every carbureted car I've ever owned complained over 14-1
     
  10. dentboy

    dentboy stacy kelevra

    Afr sounds real lean,, when your crusing your more than likely on the idle circuit, I'd start by fattening that up,, cant compare modern fuel injection with individual injectors per cylinder with a carburetor. Also where is your o2 sensor? In one header tube or slightly after collector. Any exhaust leaks?, at end of day always check the plugs,, they will tell you exaclty what the motor is doing and wants. My cruise is mid 12s, with my carburetor, thats what my motor wants, I could keep chasing and tune the idle circuit buy my motor build is different than yours. Are you running a stock type fan and shroud?
     
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  11. TORQUED455

    TORQUED455 Well-Known Member

    Is the A/C functional? Are the condenser fins clean and straight? Are you checking total timing with or without vacuum advance hooked up?
     
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  12. CJay

    CJay Supercar owner Staff Member

    Im sure you can adjust the q-jet to run at 18-1. Doesn't mean the engine is going to like it
     
  13. LARRY70GS

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

    The car ran 11.60's with that Q-jet on one of the best Cecil days, and then got 16 MPG on the way home. I'd say it likes it just fine.:)
     
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  14. LARRY70GS

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

    Not mine. When I say mine runs at 14.7-15.2, I mean at light load cruise. Anytime I am accelerating or putting a moderate load on the engine, it is 14.0 or lower.
     
    Last edited: Dec 19, 2021
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  15. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    Mine is more responsive at 13ish:1 vs 14ish:1. I have it tuned to cruise in the 14s and the secondaries bring it to 13.0 at wot..

    Either way high 14s low 15s isn't lean enough to run hot.
     
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  16. Canadian GS 350

    Canadian GS 350 Well-Known Member

    Your quadrajet is set up very well. Both my Olds and my GS cruise at those AFR’s under light load and with vacuum advance are running 44 to 46 degrees of timing at light cruise, no issues. I had a similar issue as you, noticed the upper rad hose….not the lower was collapsing when engine fully warmed up and rpms increased to say 2,000 ….observed this by flake one day. Purchased a new - proper style rad cap, issue resolved.
     
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  17. FireRedGS455

    FireRedGS455 Founders Club Member

    Huge thanks to all. Super good info and suggestions.

    I will start with following:
    Yes, the O2 sensor is not in the headers, but in the pipe. I will check for leaks in the weld and change collector gaskets.
    Check plugs.
    Check vacuum advance is working.
    Check timing at 2900rpm with vacuum advance.
    Get a laser gun - new toy :) like that
    Get a 180F stat and check/change upper rad hose. Is it the opper or lower that has the spring inside? New rad cap.
    Make sure anti freeze and water mix is 50%. I think it is higher.

    Car is winter storage, so I will see what I can do now.

    Thanks.
     
    72STAGE1 likes this.
  18. Cliff R

    Cliff R Well-Known Member

    Your carburetor isn't "lean" and forget targeting any particular A/F ratio as it can vary considerably depending on engine load, RPM's, throttle position, etc. If you are using some sort of aftermarket carburetor an no vacuum advance (common in this hobby) then you are going to see 12-13 to 1 A/F readings as more the norm followed by heavy fuel consumption, black sooty tailpipes and carbon building up on the plugs, pistons and combustion space.

    If the engine was unhappy with the A/F ratio it will let you know as it would NOT be smooth right off idle, lack power, sluggish, backfiring up thru the carb, hesitation, stumble, surging at light load or just plain "lazy" in the "normal" driving range. A well tuned engine using a Q-jet and correctly set up distributor you may see A/F clear into the mid to high 17's at very light load, but typically it will range between 13-16 to 1 or so in most other "normal" driving scenarios.

    No carburetor number given that I can see but 75 jets are PLENTY if you are using a 1971-74 Buick 455 carb and 45B rods are about right depending on if you are using the APT feature in the baseplate or not........
     
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  19. BrianM

    BrianM Active Member

    had similar issue and mine turned out to be too much vacuum advance at cruise (54* of advance). I had to remove the springs and put it to full manifold vacuum to get a good reading of "way too much"
     
  20. TORQUED455

    TORQUED455 Well-Known Member

    You’ve stated earlier that your timing is set to 34°@2600 RPM. Is this total, aka doesn't go higher with more RPM? You don’t want to check your total timing with the vacuum advance hooked up. Total timing is usually considered to be the timing your engine has at wide open throttle. At WOT, there won’t be any vacuum advance. So if you've already set your total timing to 34°, did you do it correctly? Even if you have 34 w/ vacuum advance, that shouldn't cause your engine to run hot. A lot of folks run 34 locked or 34 total w/ initial and mechanical, and that in itself doesn’t cause an engine to run hot.

    So once again, is your A/C functional, and are your condenser fins straight and not plugged-up? I’m still guessing you have a cooling system issue, not a timing issue that would cause overheating, or an A/F issue that would cause overheating. How big is your trans cooler?
     
    Last edited: Dec 21, 2021
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