CarburetorHey Ole Mechanic;

For about the last month I've had trouble starting my truck.  It starts just fine when it is cold, but once it warms up it doesn' want to start.  It turns over good, but once it's hot it cranks and cranks like it is flooded.  It starts best if I just floor the throttle right from the git-go.  Even then it still cranks and cranks before it starts.  One time when I shut it down to go into the store, I could smell gas when I came out.  I opened the hood to look things over and the area around the carburetor throttle shaft was wet with gas.  I'm no mechanic, but I do know that gas around the throttle shaft isn't right.

What do I need to do?  Have the carburetor overhauled?  Replace the carburetor?  The truck is a 1983 GMC ton with a 350 V8 and automatic transmission.

Don’t tell me to trade it in on a new one.  I won’t buy one with a computer if I can help it!  The driver should have the brain, not the truck.



Dear Stubborn;

I can relate to your feelings concerning computerized vehicles.  A carburetor and points ignition can be enough of a problem, but to really foul things up, just add an emission computer.  However, when the computer is working right, it can deliver more power and better fuel mileage.  OK, so much for the soap-box opinions. 

Your problem could be one of two things.  With the gas leaking at the throttle shaft, the first and most likely cause is the float in the carburetor.  It controls the gasoline level in the carburetor.  If the float is set too high, raw gas can spill over and get down on the throttle plates, whee it would normally be drawn into the engine and burned.  When the engine is shut off, the gas on the throttle plates can leak out around the throttle shaft.  Since the float is inside the carburetor, it's not likely to get out of adjustment and since your problem just showed up “…last month,” it's most likely still in adjustment.  What could have happened recently is that the float has gotten a crack or pinhole in it and gas has gotten inside of it and made it heavier.  Because the heavy float now does not float as well, more gas is required to get the float high enough to control the gas level and the gas level is now too high.  More gas means that it can leak onto the throttle plates and out around the shaft when the engine is shut off.  When this happens, it is time to get the carburetor overhauled and while it is apart, to check the float to see if it has gas inside of it.  Replacement floats are available but are not included in the overhaul-kit.  How does a float get a crack or pinhole in it?  Vibrations and age are the most common causes.  A crack or pinhole can be caused by age and ny some of the stuff added to gas today--like alcohol and other additives. 

The other thing that could be causing your problem is the winte- blend of gasoline.  The refineries adjust the volatility or evaporating point of gasoline depending on the season.  To get gas to vaporize in cold 30-degree weather, the evaporating point must be lower.  Did the refinery plan for 70-degree days in January?  I doubt it. They probably planned for 6-degree cold starts like we had last winter.  What happens when you get the engine warmed up and then shut it off?  That low evaporating point gas is sitting on top of that nice hot engine.  You did put a 195-degree thermostat in the truck so that the heater would keep you warm, didn’t you?  With a hot 190-degree engine under the carburetor, the low evaporating point gas is going to boil off and some may bubble over onto the throttle plates and leak out around the shaft.

At this point, overhauling or replacing the carburetor will not help one bit.  About all you can do is sit by the fire and wait for summer-blend gasoline.  That’s  what I'm doing.

Herr Professor Nuzanbolts