Avgas - Jetting Changes?

Tom711
Posts
202
Joined
2/20/2015
Location
GB
4/11/2018 10:10am
I ran Avgas (100LL) mixed 50/50 with super unleaded pump fuel today in my sons KX 85 and it spluttered/popped pretty bad on top end, I’m guessing (hoping) it’s a lean main? It was unusually cold today and we were riding a deep sand track so these could have always contributed.
Is it common to have to richen the jetting up with Avgas?
I went up one size on the main and the problem still seemed to be there although maybe not quite as bad (it’s quite difficult to hear when it’s someone else riding and there are other bikes going round as well). The only other bigger jets I had with me were quite a lot bigger so that’s where I had to leave it for the day.
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4/11/2018 11:05am
I run AvGas 100% in my KX125. In my experience it runs richer on the same jetting compared to pump gas. Stock jetting on a KX125 is 40 pilot and 420 main. I run a 35 pilot and a 400 main using AvGas 100% in the same temperature and altitude, and I actually think i can go a little leaner (32.5 pilot and 390 main).
Tom711
Posts
202
Joined
2/20/2015
Location
GB
4/13/2018 2:15am
I run AvGas 100% in my KX125. In my experience it runs richer on the same jetting compared to pump gas. Stock jetting on a KX125...
I run AvGas 100% in my KX125. In my experience it runs richer on the same jetting compared to pump gas. Stock jetting on a KX125 is 40 pilot and 420 main. I run a 35 pilot and a 400 main using AvGas 100% in the same temperature and altitude, and I actually think i can go a little leaner (32.5 pilot and 390 main).
Thanks. I’ll have a little more time at the track this weekend so going to take a bunch of jets and have a play around with it. How long have you run Avgas? Have you found any negatives?
I can get it around the same price as premium pump fuel so it seems a little too good to be true at the moment.
dmm698
Posts
912
Joined
6/24/2015
Location
NY US
4/13/2018 6:12am
I run AvGas 100% in my KX125. In my experience it runs richer on the same jetting compared to pump gas. Stock jetting on a KX125...
I run AvGas 100% in my KX125. In my experience it runs richer on the same jetting compared to pump gas. Stock jetting on a KX125 is 40 pilot and 420 main. I run a 35 pilot and a 400 main using AvGas 100% in the same temperature and altitude, and I actually think i can go a little leaner (32.5 pilot and 390 main).
Tom711 wrote:
Thanks. I’ll have a little more time at the track this weekend so going to take a bunch of jets and have a play around with...
Thanks. I’ll have a little more time at the track this weekend so going to take a bunch of jets and have a play around with it. How long have you run Avgas? Have you found any negatives?
I can get it around the same price as premium pump fuel so it seems a little too good to be true at the moment.
I run 100% AVgas for about 4 seasons straight in a yz250 2 stroke. No issues.

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