100 Octane LL AV Gas

[sixt9rsx33]

Yesterday was the first time I have used the above. At first my car ran great then started acting as if the carb had trash in it. Would not idle well just generally ran crummy. I then went and put in an equal amount of 93 octane from the pump drove it around and it cleaned up ran well. I did run it up to around 5 grand a few times because I was suspect that the carb had perhaps loaded up or I was fouling a plug. Not sure what was going on. Anyone have similar issues with running straight AV Gas?
I was driving my 67 Vette L79.

[COPO]

I've read AV Gas is formulated for lower oxygen content experienced at higher elevations. Not sure if that is true, but would explain it not running well at lower elevations. Seems a mix like you did of pump and AV Gas is more appropriate given you don't need that octane level for a typical high compression street car. Too much octane is not a good thing if you don't require it

[JRSully]

I use AvGas quite a bit for the high compression BB. It is relatively cheaper compared to race gas, lasts forever (no ethanol breakdown). What I find is that when it is very warm out, it can idle a bit wonky (I have a stock 11:1 L78, all timing in at 3k). A splash of 93 can help there as you did. I also find that if you are running a stock Holley, it needs to be squeaky clean. I regularly pull the idle screws on the metering block and blow the idle circuits out with an air blast (Thx to Eric Jackson for that tip), change the brass filters regularly as well. With all that, my engine responds pretty well with AvGas

[Lynn]

I use 100LL in my Z and it runs great. Have had not idle issues at all since using it.

My home is at 981 feet and my office (only 18 miles away) is at 1204 feet.

[MarcDant]

Av fuel is lighter than pump gas ( more liquidy) meaning more fuel entering & larger jetting needed if used pure. Lower gravity than pump fuel (density) means you actually run leaner with same jetting.i used it a lot mixed 50 50 with shell & worked good for me as witnessed by checking burn on spark plug. My experience any way.

[WILMASBOYL78]

Originally Posted by JRSully

I use AvGas quite a bit for the high compression BB. It is relatively cheaper compared to race gas, lasts forever (no ethanol breakdown). What I find is that when it is very warm out, it can idle a bit wonky (I have a stock 11:1 L78, all timing in at 3k). A splash of 93 can help there as you did. I also find that if you are running a stock Holley, it needs to be squeaky clean. I regularly pull the idle screws on the metering block and blow the idle circuits out with an air blast (Thx to Eric Jackson for that tip), change the brass filters regularly as well. With all that, my engine responds pretty well with AvGas

I started using this stuff about 15 years ago in snowmobiles...had to increase the jet sizes in both sleds. AV gas is designed to not absorb moisture...water in an airplane fuel system will hasten the use of parachutes.

Blending it with some 93 non-ethanol high test is a good idea...or if you feel wealthy a little high octane race gas.

Our L78 cars seem to run pretty good with it...of course all big block cars go faster on the flat roads of Long Island

[JRSully]

Ditto on what Tommyboy stated, and advantage to AvGas is minimal water absorb and NO ETHANOL, wont rot rubber that is not compatible with the Ethy garbage. If anybody on Long Island needs a steady supply/readily available at any time, ping me

[RALLY]

Agree with the mix with AV gas. Use Shell V-Power Nitro 93 octane. No ethanol garbage in this gas.

[oldstv]

Just a thought but could it be that you don't have enough compression for the higher octane?

[sixt9rsx33]

I am at sea level and based on what you guys have said above, I think it was more of a carb setup issue for this fuel. You guys confirmed too that once I added the pump 93 things straightened out. Compression is 11.1 so may have enough compression? Can't answer that one.