Re: Chasing Rough idle...compression?

Posted by PackardV8 On 2011/5/24 22:22:45

Now that we have everyone up to speed on the basics of engine operation lets get back to the rough idle problem:

At this point i don;t even remeber what engine we're talking about. But it doesn;t matter. One possible source of a rough engine idle is carburetor jetting. Not sure if this particular carb has a removeable jet for idle circuit or not but if it does that mite be one source of the rough idle problem.

Since there was some evidence of high speed 'breathing' problem it could also be that any high speed circuit jets of the carb need to be larger.

Some carbs have a certain balance between high speed and idle circuits so changing one could effect the other.

During the mid 70's there was the so called "oil crisis". Many owners changed carb jetting to smaller jets for the purpose of obtaining better gas mileage. Fast forward to the ethanol and other gas additives of today it is quite possible that any economy measures that were taken during the mid 70's could be producing negative engine operation characterists today.

So carb jetting mite be a good place to start after all other diagnosis and repairs have been made.