91 octane

[tundrabeagle3]

is any one running 91 octane in their briggs? if so what steps did u do to make it work? i tried it and it ended up fouling my plug but i did notice a huge difference in performance. im trying to get my minibike to hit at least 50 mph would i be better getting a clone and gearing it higher?

 

[mckutzy]

why not regular 87, usually the cheapest.

 

[tundrabeagle3]

i want to do it to increase the performance.

 

[mckutzy]

As i understand it gas alone is going to do much, as you can see. Gearing and then actual parts for performance is what I reckon you'll need to do. Easy ones are a new air filter(k&n style) and and free flow exhaust header.

 

[devino246]

Not this again...

OCTANE is a rating which describes the temperature at which a substance ignites. There are several rating systems, but here in the states, we use the Anti-Knock Index (AKI). The OCTANE rating has ABSOLUTELY NOTHING to do with the energy content of the fuel.

If you don't believe me, let's look at an example:

Regular (87) unleaded has an octane rating of 87 on the AKI scale. One gallon of this fuel contains 114,000 BTU.

Pure ethanol has an octane rating of 99.15 on the AKI scale. Although the octane rating is higher, one gallon of ethanol only contains 76,100 BTU.

Se the difference ? See the lack of a relationship?

 

[tundrabeagle3]

i have a uni filter, straight pipe with screw in muffler, e3 spark plug, ported intake, governor removed and intake eye brow slightly shaved. i have 6:1 ratio and have another sprocket that will bring me up to a 4.5:1 but still need low end to take me up the hills around my house.

 

[tundrabeagle3]

i did noticed that it made the engine idle deeper kinda like a diesel and gave me alot more top end

 

[Doc Sprocket]

Yes, this again! LOL

If I may add a few personal notes-

The only possible benefit I can think of for using high-octane fuel in a low-compression OPE engine is that (around here, anyways) the high-test has little or no methanol, whereas the low-grade has up to 10%. This appears to result in a fuel that does not break down as quickly, so is preferable for applications wherein a tank of gas needs to last a longer period of time (months). As I tend to practise "Safe Storage", this does not matter at all to me.

One other point worth debating is whether under the WRONG circumstances, high-octane fuel will actually cause a performance LOSS due to it's increased resistance to ignition... Theory only, I have no reliable means of testing this. That and, I think the circumstances would have to be pretty wrong, and the results would probably be near-undetectable in the seat of your pants.

Tundra- if it fouled your plug, something else is off.

 

[tundrabeagle3]

i have a fixed carb... what could have gone wrong?

 

[Doc Sprocket]

i have a fixed carb... what could have gone wrong?

i have a uni filter, straight pipe with screw in muffler, e3 spark plug, ported intake, governor removed and intake eye brow slightly shaved

Did you alter your stock jetting for all this?

 

[tundrabeagle3]

no i didnt not alter the jetting

 

[devino246]

no i didnt not alter the jetting

With all that done, you probably need to go up a few jet sizes.

 

[tundrabeagle3]

what would be signs of running lean?

 

[Jcotz]

Check your spark plug. Black/very dark is rich, Tan/brown is perfect, lighter is lean.

 

[tundrabeagle3]

my spark plug is a little tan on the top and the rest white... so i guess im running lean what size drill bit should i use to make the jet a little bigger?

 

[bighead]

IMO K&N filters are junk and should never be used.

 

[tundrabeagle3]

im using a uni filter

 

[tundrabeagle3]

what mods do i need to run 91 octane ?i just finished sanding my head down

 

[mckutzy]

Not to be controversial, but why 91 again. Is that the only gas available in your area? seems kinda of odd if that is so. I could understand if this was talking about alky but?
As for the jet size, a size or two up( as in wire size drill bits 'afaik) guage with the size that fits and move up till it works fine.

 

[tundrabeagle3]

i know every body keeps telling me the same thing but i know i felt a huge difference in performance when i ran 91 octane. i even had to let go of the throttle because every thing started to get blurry