Heat soak -- which thick gasket?

Discussion in 'The Mixing shop.' started by bostoncat68, Aug 8, 2020.

  1. bostoncat68

    bostoncat68 Platinum Level Contributor

    68 430 - stock. I have been having a miserable summer with what appears to be heat soak. I got a new carb from Ken last spring and since then honestly, the car runs worse hot than it did with the wrong carb on it (had a 70 350 carb the PO had someone install). I've adjusted timing, the choke is perfect, used vac gauge to set idle screws (and had someone else 2x check my work). Runs fine when it's cool or when it's moving but if you sit in traffic for a minute or two it starts to get cranky fast. Parking lots after coming off the highway, same deal - will stall and just not run worth a crap. No vacuum leaks at base or intake (had that 2x checked too). So, I'm going to try a thick gasket. Not sure which is appropriate for my intake. see pics the open one is a 1703B "plain one is 1703 -- these are from the quadrajet parts page. Pic of my intake also attached -- thanks!
     

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  2. mrolds69

    mrolds69 "The Cure"

    This is what the stock gasket should look like:
    https://www.ebay.com/p/75052758
    There's a lot of stuff that could cause those symptoms. You did check the fuel filter, right? The accelerator pumps can just go for no reason. I know Ken would have used good stuff. Then there's all the rubber lines and the fuel pump, too.
     
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  3. bostoncat68

    bostoncat68 Platinum Level Contributor

    Yes fuel pump swapped couple years ago with timing cover, fresh fuel filter and this winter i replaced all the fuel lines and red koted the tank as i wanted to freshen up all my lines and decided to coat the tank too. Filter was cmean when i swapped it. I think if accel pump was bad it would bog down...
     
  4. gszinny

    gszinny Platinum Level Contributor

    Did you contact Ken yet?
     
  5. DEADMANSCURVE

    DEADMANSCURVE my first word : truck

    agreed - check with ken first .
    4 hole . and no matter which thick gasket you pick use one with the 4 inserts to prevent over tightening .
    if using non ethanol gas are you using additive like seafoam or stabil etc ?
    and , i hate to mention something so redneck , if you have metal line from pump to carb try attaching a bunch of wooden clothes pins to line . acts as a heat soak .
     
  6. LARRY70GS

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

    Iron intake? Crossover passages open? I wonder if you can block off the smiley groove. That might be super heating the front of the carburetor.

    How hot does the engine run? Do you have a vapor return line?
     
    Last edited: Aug 9, 2020
  7. bostoncat68

    bostoncat68 Platinum Level Contributor

    Larry, bone stock. Yes it has a vapor return and I replaced that line, the primary line and hoses (for general safety not a defect but it was doing this prior too) this winter and I checked it all the way to the tank when I had the sending unit out to coat the tank. Yesterday afternoon I installed an insulated sleeve over the steel line to the carb but have not driven it since. Yesterday morning I was in some traffic and it died in a very busy intersection....that's a bridge too far for me. I keep everything I own (from the weedwacker up) so that starts and runs every time. Not staying this way.
     
  8. TORQUED455

    TORQUED455 Well-Known Member

    Fuel pump, filter, accel pump, etc won’t cause your symptoms. HOW did you check for vacuum leaks? Smoke-test is a great way, and propane enrichment will tell you if you are fighting a lean condition or not.

    Some of those base gaskets with the torque-limiting bushings are not what they used to be quality-wise. There isn’t enough thickness in the gasket to provide proper “squish” when you come up against the limiters. Small vacuum leaks in the mounting gasket will cause havoc with hot idling.

    Another thing to keep in mind is the very different properties of today’s pump gas that do no lend themselves well to old carbureted engines. Rough idle, stalling and hot-soak hard restarts are the usual symptoms. If you have a station near you that sells race gas at the pump, you may want to try a tank load of that for diagnostic purposes.

    You won’t be stopping or slowing down heat soak for very long with any particular gasket type. Don’t believe me - use an IR gun and experiment.

    Are you using ported vacuum or manifold vacuum for vacuum advance? If you are using ported, try manifold.
     
  9. LARRY70GS

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

    A 1968 430 should be using manifold vacuum. Have you checked the vacuum advance canister, that it actually works. If you have it connected to ported vacuum OR it isn't working, the initial timing will stay at 0*. Not only will the engine not like idling there, but it will have a tendency to run very hot from the retarded timing.
     
  10. 436'd Skylark

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

    If the underhood space allows it you may consider a wood carb spacer.
     
  11. bostoncat68

    bostoncat68 Platinum Level Contributor

    Bob @TORQUED455 I used carb cleaner to look for leaks -- I got so frustrated that I took it to someone else (fresh eyes) and they used brake cleaner. Checked 3 or 4 times now between us carb and intake. I agree that's not likely fuel delivery it feels more like a vac leak. If it were ignition I think it would be an issue at all speeds. I have checked, it's not one specific cylinder. (and Larry timing is not set to O degrees for the reasons you state -- 8 to 10 degrees advanced - and on ported vacuum for advance-- Vac advance canister seems perfect and I have plugged it off just to be sure). Bob -- how do you use the smoke machine to test? Do you use the manifold vacuum port as a feed for the smoke?? I like that idea.

    I know modern fuel is an issue but this is extreme, I can't drive the car like this -- it's not safe to be stalling out. It's total BS. I'm going to try a thicker gasket partly to see if maybe I have a leak that I'm missing. It's that or a baseball bat ;-) ;-)
     
  12. LARRY70GS

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

    So I am guessing you don't have the stock distributor (1111285), because at 8-10* initial, that will get you over advanced at higher RPM. Vacuum canister either works or it don't. Best way to check it is with a timing light. The 68 engines did not use ported vacuum, they used manifold.
     
  13. bostoncat68

    bostoncat68 Platinum Level Contributor

    Thanks much Larry. Larry you are correct, I have to be careful with not going too far with the initial timing or I get a knock under very heavy acceleration. I think in my service manual the disti advance is shown coming from the right front port. I believe that is shown as ported. This is where I have it connected now. FYI I do not have the thermal vac switch connected since I have the timing advanced (and the air cleaner thermo gizmos would just leak vacuum anyway). vac canister doesn't leak.
     
  14. LARRY70GS

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

    The passenger side port is usually manifold vacuum. Just pull it off with the engine running at idle. If it hisses, it's manifold vacuum.
     
  15. TORQUED455

    TORQUED455 Well-Known Member

    A smoke machine is not something a DIYer typically has access to. You can smoke test through any manifold port. PCV hose is a good place. It will also ferret-out leaking throttle plate bushings. They will always leak somewhat, like EGR valves do, but it shouldn’t be excessive. “Excessive” is certainly subjective, and that’s why driveablity on old vehicles is a lost art. Newer vehicles are a science and more black and white.

    Have you pinched-off the PCV hose and the brake booster hose (if equipped) to rule those out as vacuum leaks?

    If your vehicle was in front of me, I would introduce propane into the carb to see how lean it may be. If it’s extremely lean, the idle speed will increase and smooth out. You can also introduce propane into a valve cover with the PCV hose pinched-off to check for intake gaskets leaking from the bottom side. I actually use acetylene and have for 35 years only because it’s readily available to me and I like the small tip. If you are uncomfortable using a flammable gas around a running, hot engine, that is certainly understandable. If there are no vacuum leaks “downstream” from the bottom of the carb, then you likely know where the problem lies.

    How about a couple of under hood pictures with the air cleaner housing off?
     
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  16. 436'd Skylark

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

    You have verified the engine is not running hot?
     
  17. Dwayne B

    Dwayne B Well-Known Member

    My car was getting heat soaked A couple of years ago. My problem was when I turned it off when it was hot and waited A while it was hard to start.Larry should me A link to A metal heat shield with A gasket on the top and bottom, I think I bought it on Ebay,it basically shielded the carb from the heat coming off the intake. I installed the shield and took care of my problem.
     
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  18. bostoncat68

    bostoncat68 Platinum Level Contributor

    Bob thanks for the excellent points. I always appreciate your insight as I know you run a large shop with both old and the newest tech. I'm familiar with smoke machines for evap leaks but never thought of one for this. As you know, I don't have one but I know a good shop that could assist. It seems like a more scientific way to look... cool idea.

    I will not be the guy using the propane... I like to learn but that might be too effective a lesson for me....haha. However what you suggest makes perfect sense in terms of lean behavior. I have plugged the pcv valve but not the brake booster. I have replaced both of those hoses in the past few years (no old rubber on the car) and I replaced the old valve on the booster. You also inspired me to try to use the parking brake to let the car sit in drive after it's warm, without the brake being applied. That might explain the traffic behavior as that involves lots of stopping ... I'll get a few pics.

    Larry disti is on ported, I looked.
    Joe no sign of overheating. I have new aluminum radiator, fresh water pump, t-stat and hoses. I freshened that all up when I did the timing chain 3 years ago. My little laser t stat shows everything nice and cool.
     
  19. LARRY70GS

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

    It's supposed to be on manifold. Try it, what do you have to lose? Switch it back if you don't like it.
     
  20. TORQUED455

    TORQUED455 Well-Known Member

    How about points and dwell?

    Keep in mind that just because you can’t find any vacuum leaks, doesn’t mean it’s not lean. You can unlock the choke after it’s warmed-up, close it a bit and see what happens, as an alternative to propane/acetylene enrichment. Using the choke isn’t as precise vs p/a enrichment IMO, but it may tell you what you to know.
     

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