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What type of fuel do you put in your cj2a?

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ajax25 View Drop Down
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    Posted: 08 Aug. 2022 at 2:26pm
So when I first got my jeep from my grandpa someone recommended to me that I run premium fuel in it as it would be the “cleanest” and “help my engine run at its best”. However as I read on here and in the manual it says “low octane fuel” and it sounds like running higher octane can cause timing issues? What do you guys recommend?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dasvis Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug. 2022 at 2:28pm
Non ethanol, whatever octane you can get.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldscot3 Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug. 2022 at 2:49pm
Same for Chigger; local non-ethanol.
James 4:6 God resists the proud, but gives grace to the humble.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jeeper50 Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug. 2022 at 2:50pm
X2,  non ethanol is your friend in all your off road and yard equipment too. 

Belleview ol skool winch soon.
'48 CJ2A 283 V8 sm 420 granny low, tera low D18, overdrive,lockers

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 3A Steve Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug. 2022 at 2:52pm
Don't know about WA but the high test I get in Colorado is non-ethanol. I only use the non-ethanol (unless flat empty with none available) even in WV. Don't have vapor lock issues with the non-ethanol.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldtime Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug. 2022 at 3:10pm
Absolutely no advantage to use octane greater than minimum available. 
If at all possible do shy away from any ethanol.
These low compression engines were designed operate on uncracked 69 octane gasoline.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WKWillys Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug. 2022 at 3:16pm
X? ETHANOL free is what I do. High octane is a waste, but you get what you can.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote ajax25 Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug. 2022 at 3:19pm
Alright non ethanol as much as I possibly can from here on out. Thanks guys, I wonder if running premium has caused some timing issues. Going to fill it up with non ethanol next time and see if it helps. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jeff J Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug. 2022 at 3:28pm
Originally posted by ajax25 ajax25 wrote:

Alright non ethanol as much as I possibly can from here on out. Thanks guys, I wonder if running premium has caused some timing issues. Going to fill it up with non ethanol next time and see if it helps. 

I don’t see how. A lot of airplanes swapping between 87 octane car gas and 100 octane avgas in a wide variety of conditions and altitudes without issues. Airplanes have fixed timing so I think if there would be an issue it would show there before anywhere else. A lot of the older engines, like the one on my Cub, was designed for 80 octane and it runs on 100 octane exactly the same as it does car gas. 


Edited by Jeff J - 08 Aug. 2022 at 3:29pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldscot3 Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug. 2022 at 3:58pm
Premium (high octane) is the opposite of what our low compression flathead engines need. High octane was developed for high compression OHV engines to prevent pre-ignition (engine knock) under certain load conditions. 

The non-ethanol I find in my area is around 86 octane (if I remember correctly.)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 3A Steve Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug. 2022 at 4:12pm
Octane varies at different altitudes. Premium grade gas in WV is 92 octane. The stuff in Colorado is in the 80's. The reason I mentioned high test non-ethanol is that it is the only grade I have found in Colorado that is non-ethanol. Here in WV I buy regular grade non-ethanol. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ajax25 Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug. 2022 at 4:35pm
Originally posted by Jeff J Jeff J wrote:

Originally posted by ajax25 ajax25 wrote:

Alright non ethanol as much as I possibly can from here on out. Thanks guys, I wonder if running premium has caused some timing issues. Going to fill it up with non ethanol next time and see if it helps. 

I don’t see how. A lot of airplanes swapping between 87 octane car gas and 100 octane avgas in a wide variety of conditions and altitudes without issues. Airplanes have fixed timing so I think if there would be an issue it would show there before anywhere else. A lot of the older engines, like the one on my Cub, was designed for 80 octane and it runs on 100 octane exactly the same as it does car gas. 

It was mentioned it my other thread about timing. Someone mentioned possibly needing to advance the timing slightly because these engines were designed for low octane fuel and todays fuel can throw it off a bit 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jeff J Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug. 2022 at 6:22pm
I suggest a little research. There are an unbelievable number of myths floating around backyards and the internet forums. 90% of what I thought I “knew” 30 years ago is nothing but 100% grade A BS but not very many days go by where I don’t see it spread around anyway. 

By research, I mean nearly everywhere except the favorite  watering hole, social media site and/or forum. 


Edited by Jeff J - 08 Aug. 2022 at 6:25pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldscot3 Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug. 2022 at 6:46pm
Here's a little story from personal experience, not from the internet or local watering hole. 

Years ago, mid-eighties I think, my mom had a Lincoln with a 302 (might have been a 351W but same engine family). The owner's manual specified regular, but she thought she would do it a favor and buy the good stuff. It ran the same and got the same milage, for several years. Then performance dropped off and she eventually took it to a local shop. He found massive amounts of carbon buildup. The premium gas just wasn't fully burning and left carbon behind. He chiseled as much out as he could, and she ran regular from then on. 

The point is, I can see how advancing the timing a couple degrees might help promote a more complete burn of high-octane gas, but if ajax25 can get non-ethanol regular, that would be better IMO.
James 4:6 God resists the proud, but gives grace to the humble.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jeff J Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug. 2022 at 7:43pm
Or the buildup could have been from a bad mixture or even the brand of fuel too. We lost 2 chickens this week. Game camera took a picture of a raccoon outside the pen after the first one disappeared. I caught a opossum near the patched hole in the barn after the second one disappeared. Both will kill and eat chickens along with a host of other critters in this area. From the evidence presented here I think it was a fox that killed the chickens (not really). 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ajax25 Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug. 2022 at 7:57pm
Yeah I’m going to make sure TDC is correct and try non ethanol on my next fill up and see how that works out for me. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hawkeye283 Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug. 2022 at 10:47pm
I use 100 LL av gas. Not for the octane, but it doesn't varnish up like auto gas.  I use it in my tractor (MF 235), AC forklift, 1929 Taperwing Waco, dixie chopper, pony motor in the D4 cat dozer. None of those run on the highway, so I don't have to worry about highway taxes. Haven't had any issues with the carbs after setting. I haven't had to adjust any timing.  I may try it and see if it makes any difference. 
Tom
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark W. Quote  Post ReplyReply Direct Link To This Post Posted: 09 Aug. 2022 at 12:26am
87 octane E-10 I built CHUG to drive long distances. So its built for commonly available fuel. I have had E-10 sit in the tank 5 months with no issues.
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