11 pro av gas makes bog???

[Rmk_RDR]

hey guys im having a bogging problem with my 11 pro. I put a rk tek drop in kit in it and I hit det once so I started to put alittle 100 av gas in (1 gallon) and I keep having this bogging issue where one cylinder wont fire and if I let off the throttle and get back on it the bog is gone ive got it narrowed down to the gas I think. Does this make any sense? Thanks

 

[hoov165x]

hey guys im having a bogging problem with my 11 pro. I put a rk tek drop in kit in it and I hit det once so I started to put alittle 100 av gas in (1 gallon) and I keep having this bogging issue where one cylinder wont fire and if I let off the throttle and get back on it the bog is gone ive got it narrowed down to the gas I think. Does this make any sense? Thanks

As a pilot I can tell you that 100LL AvGas is a poor choice for high performance 2 stroke engines. Our GA aircraft engines run at very low RPM in comparison to 2 stroke engines and that is where the majority of the issues with AvGas lie. I know it sounds glorious and cool to use aviation fuel, but you need to get rid of it and buy a fuel designed for your application. There is plenty of info on the web regarding the physics involved with this- you just have to sift through the BS to find it.

That said, I don't know if this is causing your issues, but it is a good place to start.

 

[hankohlson]

Any links to this information?

I am by no means an expert on the different fuels and compositions. I've never heard of an RPM issue with AV gas. Lack of top end lubricants in the AV fuels I have heard, but in a 2 stroke that's burning oil I don't see that being an issue.

There are a lot of turbo guys out there running AV fuel with no ill effects. Too much octane can hurt performance. If in fact he was hitting DET I doubt a bit of AV gas would cause a bog from over octane.

 

[Murph]

If it is fuel it should be effecting both cylinders.

Are you clutched too light? Is the crank sensor thinking you broke a belt because the light clutching is spooling up too fast?

Have you tried putting in heavier weights (or a slightly lighter finishing rate spring) and see if the bog goes away?

 

[Scott]

As a pilot I can tell you that 100LL AvGas is a poor choice for high performance 2 stroke engines. Our GA aircraft engines run at very low RPM in comparison to 2 stroke engines and that is where the majority of the issues with AvGas lie. I know it sounds glorious and cool to use aviation fuel, but you need to get rid of it and buy a fuel designed for your application. There is plenty of info on the web regarding the physics involved with this- you just have to sift through the BS to find it.

That said, I don't know if this is causing your issues, but it is a good place to start.

Thank you for bringing this up.
Back about 15 years ago on here a LOT of people were using AV gas in their high compression aftermarket heads and port/polish jobs.

A small group of aviation guys began to educate the masses on here that AV gas is a poor choice for 2-strokes that turn 8000+ RPM.
AV gas is designed for much LOWER RPM and it has additives in it for MUCH HIGHER altitudes than sleds run (obviously for flight applications).

I bought into that and listened.

Now we have people on here saying it's all hogwash and not true.
"AV gas is fine"...etc...


What gives? Why are they saying that?

 

[hoov165x]

Oh Good Lord, here we go again.....

A Quote released from SUNOCO

Aviation gasolines are leaded and not taxed as road fuels, either of which make them illegal for use on public highways. Aircraft engines are also essentially low engine speed, constant throttle applications that must work well at very low atmospheric pressure and temperature. Aviation gasolines are blended to work well only under these very specific circumstances, and do not perform as well under high rpm and high load applications.


I will find the actual scientific explanation if I can. I am going to keep it safe in the bowels of my server so when this comes up again, I can provide the info...again

 

[hoov165x]

We asked Sunoco's Wurth about using aviation fuel in an automobile engine. He was emphatic when he said, "Don't do it. Even though Sunoco is a major producer of aviation fuel, this fuel is specifically blended for aircraft engines. Aircraft operate under very different conditions than automobiles, and the fuel requirements are quite different as well. Aircraft engines generally.... run within a very narrow rpm range. There's no need for transient throttle response in an airplane because after the pilot does the initial engine run-up, the throttle is set in one position and the rpm doesn't normally change until landing. Also, airplanes fly where the air is cold and thin, and the atmospheric pressure is low. These are not even close to the conditions your street machine will see on the ground. Also, since most piston-driven aircraft cruise at 3,000 rpm or so, the burn rate of aviation gas is much too slow for any high performance automotive applications."

I know this references automotive use, but the general idea is that the fuel burn rate is too slow.

I need to find the engineering write up I used to have regarding AvGas in high RPM engines. When I have more time to search.....

 

[sledheadd]

I've burned many barrels of av through my sleds with no ill effects.
Actually my engine builder recommends that I run av gas in my ported pro. 100% @ 2000' and 50-50 above 4000'. He's a very knowledgeable guy and well respected in the industry.

 

[4strokeperformance]

Avy

X2.

 

[ditch1000]

If it is fuel it should be effecting both cylinders.

Are you clutched too light? Is the crank sensor thinking you broke a belt because the light clutching is spooling up too fast?

Have you tried putting in heavier weights (or a slightly lighter finishing rate spring) and see if the bog goes away?

X2!! Add a gram or two to the primary.... I have the same setup and had to do that!! I added 1.5 grams to the tips on the Team Rooster Weights and that solved the problem!!

 

[Scott]

Oh Good Lord, here we go again.....

A Quote released from SUNOCO

Aviation gasolines are leaded and not taxed as road fuels, either of which make them illegal for use on public highways. Aircraft engines are also essentially low engine speed, constant throttle applications that must work well at very low atmospheric pressure and temperature. Aviation gasolines are blended to work well only under these very specific circumstances, and do not perform as well under high rpm and high load applications.


I will find the actual scientific explanation if I can. I am going to keep it safe in the bowels of my server so when this comes up again, I can provide the info...again

We asked Sunoco's Wurth about using aviation fuel in an automobile engine. He was emphatic when he said, "Don't do it. Even though Sunoco is a major producer of aviation fuel, this fuel is specifically blended for aircraft engines. Aircraft operate under very different conditions than automobiles, and the fuel requirements are quite different as well. Aircraft engines generally.... run within a very narrow rpm range. There's no need for transient throttle response in an airplane because after the pilot does the initial engine run-up, the throttle is set in one position and the rpm doesn't normally change until landing. Also, airplanes fly where the air is cold and thin, and the atmospheric pressure is low. These are not even close to the conditions your street machine will see on the ground. Also, since most piston-driven aircraft cruise at 3,000 rpm or so, the burn rate of aviation gas is much too slow for any high performance automotive applications."

I know this references automotive use, but the general idea is that the fuel burn rate is too slow.

I need to find the engineering write up I used to have regarding AvGas in high RPM engines. When I have more time to search.....

That's the way I remember it explained years ago.
I don't run AV gas in my sleds because of that very explanation.

 

[kanedog]

So we should stop using avgas and buy Sunoco 100 octane?

 

[JonezyBones]

I think big fuel companies might be obligated to make statements like that. Most Avgas that you buy is 100LL. LL means low lead. Running leaded fuels is illegal in automobiles on public roads and highways.

100LL avgas actually is a very good quality fuel. They dont actually test it the same as they do your typical automobile fuels. However they use Aviation Lean which is comparable to Mon and Avitation Rich. 100LL avgas has an aviation lean of 100 and an aviation rich of 130. The Mon value is what your looking for here. If you dont know about ron and mon values of fuel then a quick wiki search will guide your way.

So even though airplanes are run at lower RPM's that doesnt mean that 100LL avgas wont perform under high RPM applications. The only thing you might have to worry about here is the lead maybe wrecking pipe temp sensor? Plenty of people use avgas in turbo/high compression applications with no problems.

OP I agree that I dont think its a fuel issue if its only happening to one cylinder

 

[rick5150]

Oh Good Lord, here we go again.....

Exactly what I thought when I saw you post .....Oh Good Lord here we go again even better your a pilot and talked to a race gas rep LOL I was going to stay quiet then you had to bust out the scientific explanation. So just to set the record straight for future readers...........


Here's the BOTTOM LINE if avgas meets your octane requirement it is 100% acceptable/a great choice! (bonus!!!! its cheaper!!)
I personally have used it for 15 yrs and my father a motor builder and owner of a race shop for over 40 yrs has as well.
We've got a lot of trophies on the wall using avgas, 7 yrs in a row even at the world finals pro-mod class watercraft racing using AVGAS 210#'s of compression at 400 ft (lake Havasu) 2 stroke motors.


So do all the scientific research talk to some chemist maybe throw in a rocket scientist just for fun none of what they tell you means jack because race shops EVERYWHERE and for a LONG time have been using AVGAS in motors where it meets there octane requirement they're looking for


I just really don't understand how this is still a debate for anyone besides new people to motorsports the sheer numbers alone of people using it over the decades puts to bed what any company, scientist, rep, salesman, chemist would say against using it.

 

[mountainhorse]

AV Gas works well, like 5150, said if you engine can use the octane... which equates to about 103 or 104 motor octane.

It is a high quality, non ethanol, non oxygenated, fuel with tetraethyl lead added.

That lead will foul O2 sensors fairly quickly and can also lead to plug fouling... but that is manageable, IMO.

IMO... if you have the sled set up to run it (more compression/more timing or boost)... it can be a plus.

Is not an across the board fuel though, IMO, there are throttle response differences compared to most race fuels of the similar octane.

The high endpoint can be a benefit with combustion chamber cooling.

I do believe however, that the advantages outweigh the disadvantages when you need the octane.

If the octane requirements of your engine are lower than the 103 MON of 100LL... then you will need to find the blend that will work the best for your application.

DET could come from other things than the fuel.

The Primary weights are a big place to look as Murph & SH point out.

But... that said... have the injectors been changed out on your sled?
Fuel filter? Spark Plug caps tight and corrosion free on the plugs?

What exhaust are you running?
Have you checked the TPS setting?

What clutching are you running?


.

 

[fast8seccamaro]

3 years on my 925BB with av gas, no problems. Engine builder has been running it on his sleds and dyno for years, no problems. I can buy it from the Husky bulk station 6 days a week, no ordering like the race gas from dealers. Im only paying $0.15 more per litre than preminum pump gas where I ride and the av gas comes in a sealed drum with no ethanol. Yup....i`ll keep on running it!

 

[kanedog]

Exactly what I thought when I saw you post .....Oh Good Lord here we go again even better your a pilot and talked to a race gas rep LOL

So true.

 

[gopher-it!]

av gas

Running 3 seasons now on 50/50 av premium.
Still same pipe and 02 sensor.
Exceptional throttle response.

 

[mountainhorse]

Gopher... what mods requiring 95 MON octane? (compared to 87 MON for pump premium)


.

 

[gopher-it!]

av gas

also ran 100 % av for first couple months and throttle response is the same.