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After the car has been run awhile and the engine is warm, if I leave it sit for around 20 minutes, it will take a lot of cranking before it will start. I usually have to pump a little gas at it. If you just start it right back up, it will take right off.
I have done about all of the adjustments I can think of. The idle air seems to be perfect, the choke is kicking off, and I did all the adjustments to the timing from Lars write-up.
I've read some about the gas in the carb getting hot and causing this but how can I fix that?
I have seen this issue first hand on my own car. Try this, take her out on a hot summer afternoon and get it nice and hot before you come back to your shop. When you shut it off, give it a minute or two to marinate and let the heat build and then go out and pull the air cleaner off.
You may be able to hear a light bubbling sound coming from the carb. Take a look down the throat with the car off. The fuel will boil and drip down onto the intake floor flooding the motor and depleting the fuel in the bowl which exacerbates the hard start. To troubleshoot this, try to hold the accelerator to the floor next time it happens instead of pumping.
Here are some things I have done to combat this condition.
1. insulate fuel line along frame to pump and from pump to carb.
2. use a thermal spacer between carb and intake
3. advance timing to try and reduce engine heat
4. increase idle mix to try and reduce engine heat
5. adjust float to lower fuel in the bowl (Easier on a Holley than Qjet)
6. be aware of winter and summer blend fuels and try not to get stuck with a tank full of winter blend as the temps warm up outside.
I hope you get it figured out, this was very frustrating to me.
Thanks John. One, I know I need to adjust my float level down for other issues. That is one thing I'm going to do first. I have some cooling issues to work on as she tends to run around 200 degrees or slightly above it.
I didn't know about the summer/winter blends. Now I reading that the different octanes have different boiling points. Some are as low as 100 degrees! I run the higher octane in the car only to keep out the ethanols and they are supposed to have the lowest boiling points.
I wish I could use a thermal spacer, but I am maxed out on height already.
I had to get medieval on the insulating, I was desperate. Sometimes I think about removing because of how it looks, then I think back to the days of hard starts at the gas station. I justify it to myself as fuel as changed since these cars were designed. Todays fuel is optimized for fuel injected motors with higher pressure fuel systems.
Here was my first attempt.
Then went to this.
My car has headers and is run in Texas. I also use a 180* thermostat.
I was think about how come the new engines with compartment temps so much higher don't have any problems, and then it dawned on me that it's because of the higher pressure.
I was think about how come the new engines with compartment temps so much higher don't have any problems, and then it dawned on me that it's because of the higher pressure.
Holleys have a tendency to leak into the engine after warm up. Its Holleyitis. Its flooding, and the proper starting technique would be to open it up and hold it until it starts.
I agree with Johnt365 - I had the same issue with my Holley 4150. It manifested with the QJwt but just not as badly. I fixed it by adding a heat shield and running a fuel return from the carb inlet (vs just relying on the stock pump return.
The heat shield helped with the fuel bowl temps, and the return line allowed any boiling fuel in the feed from the pump to release back to the tank.
Search the forum on the subject and you'll find other examples and probably potential solutions.
Holley-type carbs have a hot-start problem that works as follows:
The accel pump wells hang out over the intake manifold, since they are located on the bottom surface of the float bowls. When you shut down the hot engine, radiant heating (not conduction or convection) from the hot manifold hits the accel pump well, and the fuel pressure in the well increases. This causes the accel pump checkball to seat, and the pressure in the well will quickly get high enough to cause the fuel to squirt out of the accel pump discharge nozzle. As soon as it has squirted out, the accel pump will re-fill itself, and the cycle starts again. On a hot engine, it will actually look like someone is pumping the gas pedal at regular intervals: fuel will dribble out the discharge nozzle until the engine cools down. This fuel will hit the closed throttle blades, wick out the ends of the throttle shafts, pool on the intake, and dribble down into the intake to flood out the engine. There is nothing wrong with the carb, the float setting, or the needle/seat.
The solution is to install a reflective heat shield (not a thick insulating spacer) between the accel pump/float bowl and the manifold. GM actually used them on their Holley-equipped cars for this reason. You can get part numbers and fabrication ideas from my "BG Carb Installation" paper, available by e-mail request. Running a return fuel line also helps with fuel supply and boiling issues in street-driven cars.
Holley-type carbs have a hot-start problem that works as follows:
The accel pump wells hang out over the intake manifold, since they are located on the bottom surface of the float bowls. When you shut down the hot engine, radiant heating (not conduction or convection) from the hot manifold hits the accel pump well, and the fuel pressure in the well increases. This causes the accel pump checkball to seat, and the pressure in the well will quickly get high enough to cause the fuel to squirt out of the accel pump discharge nozzle. As soon as it has squirted out, the accel pump will re-fill itself, and the cycle starts again. On a hot engine, it will actually look like someone is pumping the gas pedal at regular intervals: fuel will dribble out the discharge nozzle until the engine cools down. This fuel will hit the closed throttle blades, wick out the ends of the throttle shafts, pool on the intake, and dribble down into the intake to flood out the engine. There is nothing wrong with the carb, the float setting, or the needle/seat.
The solution is to install a reflective heat shield (not a thick insulating spacer) between the accel pump/float bowl and the manifold. GM actually used them on their Holley-equipped cars for this reason. You can get part numbers and fabrication ideas from my "BG Carb Installation" paper, available by e-mail request. Running a return fuel line also helps with fuel supply and boiling issues in street-driven cars.
Thanks Lars! This answers why I noticed old pools of a dirty brown liquid that has thickened in the depressions of the intake. When rebuilding the carb, the throttle plates shafts were extremely sticky and caused the throttle to hang if it were not for the heavy return springs. In addition the one throttle shaft had a terrible bend in it causing it to bind.
I do need to lower the float level for the stalling under hard braking, so I will lower it some to see if it helps that.
I can see how the heat shield should help the problem. I was also thinking about doing the return line, but I knew that would do little for the fuel already in the carb.
Please try a insulated spacer between the carb and intake this will keep the carb cooler.
Gas might be boiling- I had this and installed a electric fuel pump with a bypass regulator to keep a cool fuel supply.
Gas might be leaking into the bowls after sitting- Good luck
06-16-2014, 07:19 PM
Hard Starting When Hot
