Tried 50/50 110oct/91oct. Hard cold starts?


9 replies to this topic
  • johnny6speed

Posted August 20, 2011 - 03:17 PM

#1

The bike would start 1st-2nd kick with Grey's starting method before I did this. I let myself be "peer pressured" into trying 50/50, 110/91 from a 11' kx450f owner. "It will run much better and stall less" he said. Stall less? Sign me up! Well it didn't change its operation except, since then, its a BEAR to start cold 15-20 kicks. (Hot starting, business as usual.)

I drained all the fuel in the tank, refilled with 91 from the per usual gas station, and it started like a bear again. Ran 3 gallons through it today doing some woods riding/sand track. Going to let it sit tonight, hopefully this cold start issue will go away.

Any ideas on what has happened?

Thanks :eek:

  • grayracer513

Posted August 20, 2011 - 07:32 PM

#2

If the 110 came from a pump available for highway driven vehicles, it's entirely possible that that could have been the culprit. Quite a few of the current street legal high octane fuels use low cost chemical shortcuts to get the octane at the expense of cold starting and driveability. Tech in car dealers see this when someone with a car that was built for regular fuel falls for the hype that premium fuel equals more performance.

But you say it's acting up on it's normal favorite food, so then what? If the temperature has dropped since you last trimmed the pilot screw, that could be a cause. Starter jets (the one the "choke" uses) can get varnished from sitting around for a few weeks, same as pilots, although it's not as likely. Flaky spark plugs will foul things up, too. Mine just gets cranky once in a while and ends up liking a LOT of priming when cold.

  • RocketRoss57

Posted August 21, 2011 - 07:16 AM

#3

someone talked me into the 110/91 also but i never noticed any difference so i just quit throwing out the extra 3 to 4 dollars per gallon and just went back to 91

  • johnny6speed

Posted August 21, 2011 - 03:33 PM

#4

Rode some woods this afternoon. 3rd kick, fired right up! WOHOO! I was so frustrated that my laying down to peer pressure had cause some sort of minor damage. Phew. Business as usual once again. :eek:

Oh and, I have whatever jetting/fuel screw settings that was setup from the dealership currently and have never touched it. I have fiddled with the idle screw a bit but, thats bout it.

0-500ft of elevation. 60f-90f. If you don't like Maine's weather, just wait a minute. :smirk:

But, while riding some of this...
Posted Image

I did this...
Posted Image

  • gyd

Posted August 21, 2011 - 03:47 PM

#5

You don't need fuel with near 100 octane in a stock bike. Pump will run better than high octane race fuel because it burns to slow. You only need enough octane to prevent detonation and unless you have some super dome piston, flat valves and shaved head you should never even need more than about 96 octane. Some of the best race fuels for 4 stroke mx bikes are less than 90 octane. The key is oxygen content. We used to run straight MR 9 in stock class 250f's and it was 86 octane, when jetted properly you would swear the bike had motor work compared to most stock 250f's.

Try running 50/50 premium non-ethenol pump gas with one the following:

Renegade sx4, Renegade Mx4, or Vp MR 12, all are first rate fuels made for perfomance 4 stroke mx bikes.

If mapped or jetted right you will notice a difference.

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  • johnny6speed

Posted August 21, 2011 - 03:57 PM

#6

I would love to get some non-corn fuel up here in Maine but, alas it doesn't exist. And until I meet a fellow 06-09 yz450 up here in the northeast at an offroad race or on the trails and he says (your bike is running like balls, here lets change jetting) I'm not touching it. 91 from my local station and seat time for me. :eek:

  • grayracer513

Posted August 21, 2011 - 04:33 PM

#7

I did this...

Minor problem. Pull the header off, stand it up like a U and nearly fill it to the top of the short end with water, Then stand it in the freezer like that overnight. The freezing water will push the dent out. Might take two ro 3 times, but it will work.

You don't need fuel with near 100 octane in a stock bike.

True. You need 95 Research Octane, 86 Motor Octane, or a U.S. "anti-knock index" (Research + Motor divided by 2) of 91.

You only need enough octane to prevent detonation and unless you have some super dome piston, flat valves and shaved head you should never even need more than about 96 octane.

True, mostly.

Pump will run better than high octane race fuel because it burns to slow.

False. Octane number measures a fuel's resistance to ignition by heat and pressure, and thus its resistance to detonation. It does not measure the rate at which the fuel burns, the temperature at which it burns, how readily ignitable it is, or any other aspect of the fuel's chemistry. Some very high octane fuels burn very rapidly, in fact.

Some of the best race fuels for 4 stroke mx bikes are less than 90 octane. The key is oxygen content. We used to run straight MR 9 in stock class 250f's and it was 86 octane,

VP MR9 was 86 MOTOR Octane, roughly the equivalent of 95 to 96 Research octane, or an AKI of 91-92.

Oxygenation is not the key to power. If it were, contemporary pump fuels would be like running nitro. "Low emissions" gasolines are virtually all oxygenated by some means, either MTBE or ethanol, typically, and while they have gotten better than they were 10 years ago, they still are a long way from being optimized for power production. What makes racing fuels a better source of power is the chemical components used to blend the fuel, and the energy value of the complete formula. You should note that some of the highest octane fuels available are not oxygenated at all.

  • Polar_Bus

Posted August 22, 2011 - 04:20 AM

#8

The bike would start 1st-2nd kick with Grey's starting method before I did this. I let myself be "peer pressured" into trying 50/50, 110/91 from a 11' kx450f owner. "It will run much better and stall less" he said. Stall less? Sign me up! Well it didn't change its operation except, since then, its a BEAR to start cold 15-20 kicks. (Hot starting, business as usual.)

I drained all the fuel in the tank, refilled with 91 from the per usual gas station, and it started like a bear again. Ran 3 gallons through it today doing some woods riding/sand track. Going to let it sit tonight, hopefully this cold start issue will go away.

Any ideas on what has happened?

Thanks :)


The key to getting a 450F to fire right up in colder temps is give 2 or 3 good twists on the throttle prior to kicking. This introduces a bit of raw fuel. My '07 likes a tad bit of raw fuel when stone cold. lastly, forget race fuel in a stock YZF, totally unnecessary.

  • josh8811

Posted August 23, 2011 - 05:18 PM

#9

I just shake my head when I read about clowns putting race fuel in a stock 4 stroke.. Johnny... Please.. Put the race fuel down and do your home work.. Thanks, Dad

  • johnny6speed

Posted August 23, 2011 - 05:35 PM

#10

I just shake my head when I read about clowns putting race fuel in a stock 4 stroke.. Johnny... Please.. Put the race fuel down and do your home work.. Thanks, Dad


As of Sunday, the race fuel was out with 91 cycled in. Rode today at a new spot with some older guys that broke me in good on their harescramble loop. They were flying. Can't wait to go and ride with them again. Next time with less mudhole bathing, and keeping more material on my skid plate.

Oh and it started 2nd kick today. All is well. :)





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