running avgas in 338 gpx

338gpx

338gpx

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is there good and bad to using avgas in my gpx and do i need to change the jetting if i use it.

Thanks
 

I've used it with good results. I heard it doesn't go Bad like regular Gas. It burnes slower than 93 octane so burning pistons is less likely. I think Yamaha recommended 100ll avgas for the 77 SRX so it sure won't hurt your GPX.

Mark
 
Ive raced karts and sleds on 100LL for many years. I store EVERY motor with av gas and never had a material storage issue. You will need bigger gets with AV gas
 
should a person try 2 sizes larger or what would you recommend
 
thats a good starting point. Av gas is not a heavy or dense as pump gas so you need more volume to make up the difference. You will also note that your motor will run a little cooler also
 
NOT STARTING A PISS MATCH HERE. BUT, SORRY GUYS, I DISAGREE WITH YOU MUST JET UP TO RUN AV GAS. SO YOUR SAYING YOU MUST JET UP IF YOU USE RACE GAS WITH OCTANE HIGHER THAN 100 ? DON,T THINK SO. FOR GRASS DRAGGING RUN A GOOD SYN OIL LIKE AMSOIL AND DROP JETTING AND MAKE HORSEPOWER. FOR ICE YOU BE FINE WITH STOCK JETTING 3:16 (yammie tony)
 
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Tony
We had to run larger jets due to the specific desnity of AV gas being lighter than pump gas. AV gas weights aroung 6lb per gallon and pump gas is something like 6.25lb per gallon. The lighter the fuel, the more you need to avoid lean conditions.
This has nothing to do with octane levels
 
OK I CAN UNDERSTAND THAT, BUT IF IT HAS NOTHING TO DO WITH OCTANE, THAN WHATS THE POINT RUNNING AV GAS OVER RACE FUEL BESIDES AVAILABILTY IN YOUR AREA. WITH RACE FUEL YOU SHURE TO NOT NEED TO JET UP. UNLESS YOUR USEING A QXYENATED FUEL. NOW LIKE 94MAX POSTED UP, THE 77 SRX SERVICE MANUAL AND TAG ON GAS TANK CALLED OUT FOR AV GAS, BUT I DON,T BELIEVE ANYWHERE DOSE IT SAY INCRESE JET SIZE. 3:16 (yammie tony)
 
Hi Tony! He said "jetting" had nothing to do with octane. The reason the 77 SRX didn't say anything about jetting for using AV gas is because the specs listed ARE for using AV gas. Also the fuel mentioned in the 77 manual is way different from the 100LL you buy today. A stock GPX will run great on 100LL and the stock jetting will be very close depending on temperature. (air density conditions)
 
AND I,LL TELL MORE 77 SRX,s RAN 110 RACE GAS THAN AV GAS!!!! ALRIGHT, ONLY WAY TO KNOW FOR SHURE IS NEXT TIME I SEE JIM FROM C&H DYNO HERE IN NY I AM GONNA ASK HIM WHAT HE HAS SEEN ON PULLS USEING AV GAS AS FARR AS JETTING. RICK, WHAT IS THE BENEFICT THAN USEING AV GAS IF IT HAS NOTHING TO DO WITH OCTANE ? just run 93 if that the case. whats are you looking for. 3:16 (yammie tiony)
 
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