Fuel

[madmax-im]

I am fortunate to live in a state that has independent retailers that sell Non-ethanol gas...in fact theres a station right in my town...about 5 miles from me.
Its simple...ethanol is crap...engines are less powerful...run less efficiently...and get poorer gas mileage... Some people claim they notice no difference in performance but I sure do...when I am travelling away from home I carry a list of Pure-Gas stations where I am heading...

http://www.pure-gas.org/

[mack]

update

So I’ve done some more research on ethanol. Apparently it is powerful solvent that will break down any crud in your tank or filters and allow it to pass into your carbs. It also attracts moisture from the atmosphere but will only hold it in suspension up to a very low percentage then everything breaks down rather quickly and you lose it’s already low octane value and combustibility. Considering how our carbs are vented, this is not a good thing. In general, ethanol fuels burn with lower energy than the traditional fuels did, and will leave behind excessive residue, foul your plugs and valves over time. Despite government claims, this fuel is junk. It doesn’t help the environment because it decreases fuel economy by not completely burning everything in the cylinder and pushing it past the valves into the atmosphere. What a sham. Unfortunately up here the price of gas is already too high and using high test is not really an option. Our only alternative is to frequently use fuel additives like sea foam or star tron to limit the damage being caused by this junk.

[Rich*11sg]

I'm not too lazy to seafoam the motor, just too lazy to resync the carbs afterwards.

Although I have to after the valve adjustment, i'll just do it all at the same time.

[DiverRay]

If you pour some B12 Chemtool or SeaFoam into the carbs when the engine is running AND warmed up, let it die from the mix, and then start again after about 20 minutes it should take off a LOT of the carbon. An easy way to do this is put four tubes on the carb boots, and put them into a can with the seafoam. It should be sucked into the system that way.

[Rich*11sg]

I run 93 in my bike as it has over 64k miles on it and the carbon build up on the pistons raised the CR high enough to need it. although i probably should just fix that, but you know, i'm lazy.

[Bonz]

Just got back from Kansas, looking forward to the Colorado '14 Rally starting tomorrow!

I don't know two strokes all that well but the same principles should apply as a 4 stroke... If the comp ratio warrants higher octane, then it will produce better power because the fuel burns optimally/at the correct rate for the engine design. Thus your better performance, in all likelihood, rdmcguy.

The XS produces best power on lower/standard grade. Because higher octane burns fractionally slower, it finishes burning going out the exhaust, thus not giving all it can to push the piston, and has been proven to carbon up exhaust valves as a result.

If an RD had a high enough CR for a two stroke that more octane was actually needed than low test could provide, it would make more power all else equal, IMO.

For example, my ZRX1200 is a relatively mild 10:1 CR for a modern 4 valve engine and I run low octane with no issues, even with a +4 degree timing advance rotor.

The ZZR1200, which was/is probably the fastest carbureted bike in the world to this day is the exact same engine as the ZRX other than .5 CR higher pistons and larger downdraft carbs. It has a 10.5:1 CR but calls for high test due to the ram air system it uses, thus effectively boosting the CR by force feeding the equivalent of a couple psi like a turbo at higher speeds, and thus the higher octane is called for, at least that's my take on it.

Normally boosting a CR by .5 on an engine that was not already on the edge will not need much, if any change in fuel.

I have ZZR 1200 pistons ready to go in the ZRX and everyone that has done that says it does not change the octane needs.

Guys that "treat" their engine to higher octane if the engine does not need it are absolutely doing their bike NO favor and could lead to carbon'd exhaust valves and will have lower power output vs a lower octane.

For Colorado riding, lower octane is even more agreeable to engines because less dense air (lower oxygen to burn the fuel being drawn in as well) takes up less space in the combustion chamber in a naturally aspirated engine, and CR is effectively reduced because there is less air being compressed and no way to pack more in and make up for it since it is being drawn in and not forced in.

Dragsters at Bandimere speedway run higher boost compared to lower elevation, as another example, because they need to re-gain the packing of the combustion chamber to offset the less dense air to get back to the effective crazy high CR they run at lower elevation.

[rdmcguy]

Gas

I don't know the chemical makeup of old school gas versus modern but in the early 70's but Sunoco 240 versus the lower grades would give you enough of an edge to beat a similar machine..in my case rd 350's ...also you could wheelie one gear lower with the better gas/higher octane...
I think modern era gas is trash...but what are the options?

[jetmechmarty]

On this side of the border, we've been using the same rating system, (R+M)/2, since before these bikes were born. Lead was being phased out by then as well. I remember mixing my fuel at the pump if I could. I'd get half full with leaded and top up with no lead. 89 leaded was as high as I could find as I recall. Unleaded used to be 91 where I shopped. Seat of the pants, I don't think there's really much difference. My bike runs fine on corn gas even though I do my very best to avoid it.

[mack]

Anyone know what the octane comparison was from 78 to now for regular gas. I suspect it was the same but it was pure gas back then with a bit of lead in it. But now we have corn etc added to make up the volumn. I read recently that todays gas burns cleaner, but does it compress and combust as well as the gas did back in 78/79?