race gas question

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#1
Im considering using race gas in my 2000 cr500 motor, but I really only want to do this if it will significantly reduce engine wear. The reason I ask is when I got the bike it had race gas in the tank, I ran it mostly out and switched to pump. The carb was still full of race gas, and when I rode it I was able to notice when it got to the pump gas. I noticed a little extra "engine noise" during deceleration, and maybe a tiny bit more vibration from the motor, and of course it no longer smelled like race gas. Now the first two were not major changes, in fact they were probably barely noticeable, but it was enough to make me wonder if race gas could reduce wear on things such as crank bearings, etc. I was kindof assuming that pump gas would be ok for a low tech big bore, but the motor did seem to run a little tighter with the race gas. Im asking because this is the closest thing Ive had to a brand new motor, and if using race gas would keep it that way significantly longer than using pump gas I might have to switch. Thanks!
 
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#2
That's probably one of the hardest issues to tackle, but, pump gas generally burns hotter and faster than race gas and is far less consistent in its makeup. If your bike is jetted correctly, it shouldn't need race gas - but it's hard to jet for gas that changes every time you go to the pump. I run race gas because (1) I got used to it when I rode KTM's and they wouldn't run on anything else without pinging; and (2) I kept doing it in my '03 CR500AF because I don't like to fiddle with jetting. Plus, it's expensive on a per-gallon basis but I can get it right down the street and I don't burn enough gas so that the cost is an issue. Bottom line, you really shouldn't need race gas but it may be more convenient because it's more consistent.
 
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#3
Originally posted by WhKnuckle
pump gas generally burns hotter and faster than race gas
For the 10000000000th time, No it doesn't :silly:

Keith the only way race gas can help engine life is in the situation where it reduces engine knock (pressure spikes from knock can erode the piston and beat the lower end bearings out), or in situations where it makes it more tolerant of pre-ignition (effects similar to overly advanced ignition timing). If you aren't running into the above combustion issues you won't see any measurable changes in engine life.
 
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#4
Thanks a million Rich, thats exactly the kind of answer I was looking for and I appreciate you taking the time to answer. I am completely satisfied with the way the motor runs on pump gas, and I havnt seen any of the issues you described so im stickin with pump gas for now. thanks to DRN and Rich!!
 

motometal

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#5
are you sure that extra "engine noise" on the pump gas isn't ping?  If nothing else, you may want to mix up another small batch to swich back and forth to listen for the noise again?  Some mx bikes will ping on 92 pump gas even when stock.  This gets worse when the jetting is leaned out as appropriate.  I seem to remember the old open class Yamahas were notorius for pinging.

If you even suspect at all that it's pinging, you need to run race gas, or richen the mixture (here comes spooge and sluggish response), or retard the timing a bit.  Assuming the timing is already proper, that last idea is probably not the best option.
 

bclapham

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#6
i think motometal is right- if the bike was setup well (jetted) for race gas, maybe its pinging all over the place with the pump gas and it neeeds richening a bit?
 
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#7
Keith - If you are experiencing trace knock on pump gas you should be able to see it on a new plug. Look for evidence of what appear to be little flakes of dirt (or carbon) on the insulator. Gordon Jennings always described it as looking like specs of pepper.

But as MM pointed out, a back to back test using pump fuel and a non-oxygenated race fuel should be the easiest test.
 
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#8
hmm. I cant say that ive heard a bike that was pinging before, so I dont really know what the pinging sounds like but the sound of my bike is smooth and consistent, no surging or rough running or anything like that. When I noticed the noise I was coasting down a hill in gear, the noise of the motor revving is what slighly increased. I never heard anything different when accelerating. I think im worrying over nothing, because it wasnt a major change but I'll check the plug and see about finding some race gas locally, it wouldnt hurt to make a 2nd comparison.