^this. I bet that thing would run on anything. Most low compression engines would. If you readjusted the carb, that stumble could be completely gone.

 

Agreed, I would add a proper amount of Sea Foam* in the gas & let it clean the carb too...

 

Well if you want to come up and adjust it be my guest. But I've had more than 1 carb on the engine since I bought it, and they were all the same.

 

Carburetors do not like alcohol. It causes corrosion in the aluminum and steel parts will rust. A carburetor has to be specifically designed and plated to work properly with even 10% ethanol. Adjustments won't help. The jets would have to be changed for slightly larger ones and a higher volume accelerator pump is needed to prevent stalling on acceleration.

Modern fuel injection systems use oxygen sensors to adjust the fuel mixture for optimum performance. Still the HHR with a 2.4 is designed to use fuels of 91 octane or higher according to the owners manual.

My lawnmowers specifically state NO ALCOHOL in minimum 91 octane gasoline to prevent fuel system damage and to supply full rated power.

 

Ethanol has lower BTUs per gallon than gasoline, which is why I think there is the difference in fuel economy when I run pure gas and the stuff that has ethanol in it. I got 23.1 mpg last tank with my normal driving after filling up at a BP with ethanol containing gas. I didn't pay attention and was almost out of gas, so had no choice. I filled up yesterday with gas from a place 3 miles from where I live that has no ethanol, and with the same driving I am at 27.6 mpg. I reset it each fill up to see how it does. I think I will stick with the ethanol free stuff as much as I can, and I will pay attention to here my gas level is so I don't get ethanol in there again. I really think they are doing more than 10% ethanol to throw the mileage off that bad.

 

I have used 93 octane E10, 91 octane, pure gas, and 87 octane E10 and have never seen a difference with mpg. The only differences I saw was in the price of the various grades of gas.93 octane being 20-25 cents more per gallon than 87 octane and pure gas being about 30 cents more than 87 octane. Mpg is very dependent on driving techniques that is all. Statisticall my HHR obtains 30.6 mph average +/- 3 mpg for 76K miles.

 

This is logical, ethanol will reduce your MPG. That is why E85 really isn't what it's cracked up to be.... Less $ but much less MPG. Not enough $ savings to make up for the reduced MPG

 

Ethanol Free Gas Stations - By State

http://www.pure-gas.org/