Poor acceleration when hot

[AustinJim]

I have a 78 Spitfire with a ZS carb. After driving it for 20 minutes or so (with ambient temp around 70) the car begins to sputter and hesitate when accelerating. This happens from a stop and when accellerating while already driving. I think the car is running rich and I will adjust that as soon as I can find someone local with the tool but I'm not sure that would cause this problem. Any hints on what to check?
Thanks!

 

[ALLAN]

Jim, sometimes when you push your choke cable in the chokes on the carb will not completly shut which would cause a rich condition when hot, make sure your cable is working freely and not hanging up at the carb end of it. othere than that you may need a carb adjustment or rebuild.

 

[AustinJim]

This car as the automatic water choke so no cable problem. One thing I did check a while back was the throttle bushings. I sprayed starter fluid on the outside of the carb where the throttle rod comes out and the engine sputtered. I'm pretty sure this indicates the busings and/or shaft are worn. Could the sputtering when hot be caused by work bushings/shaft?

 

[ALLAN]

That could be causing a miss or stumble from a vacume leak around the throttle shafts, but that would give you more of a lean conditon instead of rich, with a rich condition it is starting to sound more like a worn needle and seat/and you might have worn shaft bushings also. If this is the case it sounds like your ready for a carb rebuild.

 

[Geo Hahn]

[ QUOTE ]
I...After driving it for 20 minutes or so (with ambient temp around 70) the car begins to sputter and hesitate when accelerating. This happens from a stop and when accellerating while already driving. I think the car is running rich and I will adjust that as soon as I can find someone local with the tool...

[/ QUOTE ]

Bear in mind that many 'carb' problems are resolved only after working on the ignition system. In your case I would suspact the coil or condensor as both may suffer with heat.

 

[Andrew Mace]

I agree that around 95% of carburetor problems are electrical; however, it's worth taking a look at the rubber diaphragm in the carb. Pinholes or tears can cause problems similar to what you describe.