QJet Hard Starting After Being Off For 10+ Minutes

Discussion in 'The Venerable Q-Jet' started by MrSony, Jul 11, 2018.

  1. MrSony

    MrSony Well-Known Member

    Start it let it get up to temp, shut it off, and I can start it back up immediately.

    But if I let it sit for 10 minutes or more, it acts like there's no fuel in the bowl (confirmed there is) or is flooding itself out.

    I've heard the float level being too high can cause this issue, with heat soak after an engine sits (90* around here, engine runs at 195, gets to about 210 after sitting for 20 minutes off, goes back down after that).

    What say you guys?
  2. 436'd Skylark

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

    It's probably leaking fuel out the plugs on the bottom of the carb. Pull the carb and inspect.
  3. Cliff R

    Cliff R Well-Known Member

    There are several things that can/will cause difficult hot re-starts. Some are very easy fixes, others are not.

    The first thing to do is to remove the carburetor and strip it down and pressure test the main casting. You must confirm that it isnt' draining any fuel from the bowl when sitting as this will make restarts, especially after a half hour or so very difficult.

    Don't by disillusioned by any efforts to dab JB Weld over the plugs, 99.9 percent of the ones we test here leak right thru it. The only effective repair is to remove the plugs and tap the castings for screw in plugs coated with Marine Tex or fuel tank epoxy.

    One you have determined the main casting is not leaking there are other things that can cause difficult hot restarts, which include flooding caused by fuel pressure pushing some fuel past the N/S assembly, or getting things hot enough to evaporate fuel from the fuel bowl, but that problem usually doesn't manifest into a difficult hot restart after a short time period.

    Something else I've ran into that few folks look at is running manifold vacuum to the advance. With some set-ups it is used to increase timing at idle speed to help with big cams or poor carb tuning. When MVA is used the throttle plates are typically much lower than if ported VA was used, which can cause restarts, especially well heat soaked to be a little more difficult as the timing is retarded some and the throttle plates are closed further.

    I have ran into a few defective castings which leak internally between the main fuel and idle fuel passages, but that's pretty rare.

    Another problem I've seen is a very small leak under the fuel inlet seat at the gasket. A very small leak may not cause a running issue, but will cause a higher fuel level after shut down if fuel pressure is still present at the carb inlet.

    Don't rule out electrical/ignition either, as hot restarts often tax the system more and can rob voltage from the coil, plus slower cranking speeds.......Cliff
    lemmy-67 likes this.
  4. lemmy-67

    lemmy-67 Gold Level Contributor

    If the hood is down on a hot day after driving for a while, the fuel can boil out of the bowl and load it up, making starting harder until some airflow starts to lean it out. If your carb has not been properly rebuilt, leaking well plugs and vacuum leaks at the primary throttle shaft will happen at hot temperatures when the metal pieces get hot & expand.
  5. MrSony

    MrSony Well-Known Member

    I can say with 100% certainty it has fuel all the time. I left it for a week last month (in preparation for Good Guys) and it started up after a pump and ran great. Only since it's been steady 90s here in Iowa it's been doing this, about the past 3 days it's been annoying. It starts if I hold the pedal halfway and its good from there. I do think just out of my own curiosity I will check the float level (stock be fine in my case? '70 SP, stock except crower lvl3, daily driven car), carb is a 17058241.
    Last edited: Jul 11, 2018
  6. 436'd Skylark

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

    There is a chance the float has lost some buoyancy and allowing fuel to leak into the intake. That's fairly common.
  7. TORQUED455

    TORQUED455 Well-Known Member

    Are you using E10 fuel? If so, do you have access to non-oxygenated fuel?
  8. Dwayne B

    Dwayne B Well-Known Member

    I had A similar problem, my skylark was hard to start and it smelled flooded when hot, Larry suggested A metal heat shield. I put one on and it helped A lot. I'm running 10% ethonal gasoline and think it is making the car get heat soaked easier .

    I have had problems with my old chevy with A elderbrock carb getting heat soaked ,I put A 1/2 in wood spacer on it and helped ,but thinking about using A metal heat shield on it to.The heat shield helps isolate the heat from intake to carb bowls.
  9. shiftbyear

    shiftbyear Well-Known Member

  10. MrSony

    MrSony Well-Known Member

    I have a 1/2" phenolic/wood spacer on there.
  11. Dwayne B

    Dwayne B Well-Known Member

    Here is A heat shield I installed on my car ,and it helped A lot with stopping my heat soaked problem. 20180712_054114.jpg

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