AV GAS

[ianscr250]

Ok guys i need some help ideas or info
can i run av gas in my CR'S to get the octane boost or is it a no no

im thinking mabye run it in my hpi baja 1/5 scale buggy as well since it runs the same mix as the Cr's

[Gerard De Ruyter (Twistandshout)]

ian, you're my main man on advice related to anything CR, so getting a question from you as opposed to answered by you is a bit disconcerting.  and no, no idea if can run avgas.  but if others say its the go, then i'll be asking where d'ya git it?  did you sell the '82?  how's pre-85 going over there?

[jimg1au]

hi
we used to run av gas in the tz yamahas in the lat 70s(wish istill had my c)no jetting change i think it was 115 oct you also use to be able to buy 122 oct but you will need to rejet if you use this.guys in the states run av gas in there yz490s this helps it to run properly no pinging.the reason for using av gas is for better burning of fuel so the motor runs smoother and also cooler.try it and see what happens do a plug check and remember use good oil in the fuel.
cheers
jimg

[Lozza]

Ian,
I am hoping to start another 10 page thread here,so to kick it off I'll ask some questions
1) Is your engine standard?
If it is then you really don't need no ping avgas, 98 will suffice.Avgas has been forumulated to provide a stable fuel for piston engine aircraft that point blank refuses to detonate, it takes a lot of compression and advance to make this happen.
As far as octane is concerned it is 100/130 RON or MON but unless you have sky high compression you won't notice any difference to performance,HOWEVER the lead in avgas gives better plug readings which allows finer tuning.Avgas is less dense than the 98 pump fuels(0.73 v's 0.78).Pistons need more clearence with 98, less with avgas not because avgas runs cooler it's because the 98's burn faster and hotter.Rule No.546 is if you set up for a fuel, tune to that and stick with it (applies to methanol as well)
HTH

[Tim754]

Lozza thank you. How many times have I said basically (OK exactly) the same to inquiring people. The people usually ask why I run Avgas in the 754s is it to "make um go like stink dat specool racen fool" After I explain in detail that the way the engine is set up it will not run correctly and may damage itself with out the increase in RON , They think I am pulling there leg and trying to hide some super secret witch craft go fast brew. Then I get the old but gees it smells like shit hot stuff.... (Two cap fulls of R30 in the tank cause I like the scent  ;.....)Look if I could run 98 RON pump fuel I would ,if you can do so do that. Tim
 

[ianscr250]

ok to answer a couple of questions  these bloody cr's of mine tend not liking starting and both ping a bit
the 250 doesnt like comming on pipe until the very top of the rev range i have leaned it out a bit to try to aleviate this but to no avial
the reason i thought of av gas was through working in the hoby industry the higher the octane the cleaner the burn the cooler the burn and the better the rev range like using the nitro we run in rc cars

now one thing i didnt ask im used to the nitrofuels and mix;s but would you still mix at say 40 to one if using the av gas to keep the cylinder lubed  if not what would you recomend


cheers ian
hopefuly having my hands on a 78 red rocket soon

[Nathan S]

....the higher the octane the cleaner the burn the cooler the burn and the better the rev range

This may work with certain fuels, but just because a fuel has a high octane number doesn't automatically make it burn cleaner/cooler/anything else - Octane rating quantifies how well a fuel resists detonation and SFA else. People talk about octane rating numbers like they're the only aspect of a fuel that matters, but this is not the case - sadly, reality is far more complex.
They banned AvGas from rally cars a few years ago, and amongst all the groaning and bitching, some people decompressed their engines and got them tuned properly to run on 98 octane pump fuel. In every case, the cars made more power and had better throttle response than they did on AvGas (remember that we're talking 4-strokes there, so not a true apples-with-apples comparision with a 2-stroke dirt bike).

AvGas burns slowly, and has marginally less energy/gram than 98 octane pump fuels. The slow burn is basically the trade-off that you have to make for the excellent detonation resistance.
So unless you bump up the compression and (probably) screw in some more ignition advance, then it's basically a waste of money - in my bikes, I found that it made them flat off the bottom, flat in the midrange, and flat in the top end... Never pinged though!

Oh, and I'm told that the 81 CR250 is a peaky bugger "like a big 125"... Maybe the 82s are just like that too?

[Lozza]

Ian,
I think your CR problems are nothing to do with fuel.Those sort of problems are port,pipe and ignition related.

[ianscr250]

the porting and pips on both bikes are originals but both have been taken out to .05 on piston and rings


this was partly the reason on wanting av gas as i know when i had the 250 back in 82 it ran leaded and seemed to hit the pipe straight away
i dont now wether fuels have changed a lot other than the lead   

[Rossvickicampbell]

Ian - AVGAS isn't going to help - as Lozza said not much difference between what we can buy (with a licence) and BP Ultimate at 98.  Speak to somebody like Rod as he is fairly cluely with regards jetting etc.

cheers

Rossco

[fsc]

Ian
I maybe able to help you out. I have had and still have a number of CR's which I run on Av gas. First of all the only difference I have notice when I run Av gas in my 250's (1981, 1983) is that they start easier. I have noticed no other difference at all in the way the bikes run other then that. However in my 125 (1982) it was like the motor had just been rebuilt it just was that fresh and went a lot better across the whole rev range. The difference in the bike was worth the extra trouble of getting AV gas. One thing I have noticed about this fuel is the fuel and oil seem to separate, if left to sit in the tank for to long. The pilot jet in the 1983 CR250 was always blocking up after sitting for a while.
If you have any other questions, just reply and a will give you a call. 

[TonyB]

If a person wants to use avgas where would they get it in brisbane. I would like to get hold a a fuel which has a rating of aprox 110 octane. I think the cost of bp100 is silly when you can run 98 and add booster to get 100?? let me know if that thinking is wrong. But i would appreciate it if someone could tell me how i could get some.

[Lozza]

Tony I have some leaded booster that will take you to 110 octane from 98PULP.Works best if you have upped compression, but as a rule will lift throttle response a hell of a lot.1 bottle makes 60l of 110 octane.

[Freakshow]

i was listening to neville lush tell one of the guys at the last race meet he dosnt take too much notice of the colour of plugs too much any more as the unleaded doenst leave the same signs as the old lead petrol, and it seems all the additives in it change the way your plug can look.  Basically if i heard correctly he said it was a quick check to see if it was very lean or very rich other than that dont put your nuts on the colour etc as its moved away from what it used to be. 

I used to run what they called bp 100 pumpavgas on my 100cc superlight , the reason i did was because it always seemd to be even, when i say even, every race i would write in my race diary temps etc etc. and every plug chop and jets would always come up the same.  when i used av gas it never seemed to vary much - and thats on such a small high reving, ported motor you would notice every little thing.   After a lot of trial and track time in the end i used a 70 /30 mix i could have been on drugs at the time but for what ever reason i found my little 2 smoker would run fasted and hardest on a a mix of 70% avgas and 30% leaded super - dont ask me why but after years of testing this, race after race on the road circuit i swear it was fact, any time i didnt mix it the same way it would run less or feel less i have a agricultural 5lt measuring jug that i would get it to the mm3 same with the oil premix.   Currently in MX bikes i run pulp @ 32:1 oil, but i have never taken much notice, with all the bumps and dirty filters etc it would be near impossible to rule out all the variables to exact the fuel now as i did in the late 90's.  But im guessing the rule of thumb would still stand,
1. buy the same fuel every time
2. from the busiest server you can find and always only buy it from there
3. use a funel with a strainer
4. and run a plastic car fuel filter in line. 

other than that jet the thing to an inch of its life on the pilot and get the main rich enough for the main straights. if its still crappy start looking at your cdi or something poxy like that cause it aint the fuel then.