Author Topic: FEUL - premium unleaded v's unleaded  (Read 19543 times)

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Offline vandy010

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FEUL - premium unleaded v's unleaded
« on: August 07, 2007, 12:20:03 pm »
here's my problem,
mx125a yammie,
jetting on the main and needle is what i'd call ever so slightly rich with the pilot being a touch richer.
on the track at full noise i'm happy with how it goes but when i swing back into the pits and back onto the idle circuit i usually foul a plug.
this has happened with both a ngk B9ES and B8ES and also again with both a points ignition and cdi set up. {saving the EGV series plugs till i get it right}
thinking it's time to lean off the pilot, thinking thats my problem, a wise old guru asked what feul i was running.
i've always run premium unleaded at 30/1 with shell oil in all my 2 strokes both modern and classic.
now for the guru's theory,
he says premium is a more "dense" feul and is therefore harder to jet correctly and suggested using normal unleaded as it's less "dense" with an octane booster if required.
i have no interest in avgas or methenol as i enjoy the simplicity of pump feul.
so c'mon fella's!
standard unleaded with a booster?
or
premium unleaded?
or do i just play with the pilot till i get it right?
« Last Edit: August 07, 2007, 12:24:38 pm by vandy010 »
"flat bickie"

Offline Nathan S

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Re: FEUL - premium unleaded v's unleaded
« Reply #1 on: August 07, 2007, 12:35:34 pm »
...back onto the idle circuit i usually foul a plug.

Shell fuel, yes?
Ditch it and try one of the other brands of 98 octane fuel.
(but make sure you avoid ethanol)
The good thing about telling the truth is that you don't have to remember what you said.

Offline cyclegod

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Re: FEUL - premium unleaded v's unleaded
« Reply #2 on: August 07, 2007, 12:51:08 pm »
One "premium" does not equal another, most so called premium unleaded is rated at 95 octane (about what the old lead fuel was) regular unleaded is about 91 or 92 octane (depending on which state you reside in). Here in W.A ALL petrol is produced by B.P, so when you go to a Caltex,Shell,Gull,Mobil petrol station you are just getting B.P fuel (and its not always their best either  >:()

So my advise is to try B.P ultimate98, wind your air-screw out another 1/4 turn and stop using shitty shitter N.G.forking .K plugs THEY"RE RUBBISH  >:( >:( >:(
Ban BLACK rims NOW

Offline Nathan S

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Re: FEUL - premium unleaded v's unleaded
« Reply #3 on: August 07, 2007, 01:15:45 pm »
Here in W.A ALL petrol is produced by B.P, so when you go to a Caltex,Shell,Gull,Mobil petrol station you are just getting B.P fuel ...

Only partially true. You are getting BP base stock, but the big brands each add their own "additive packs" to it (dunno what Gull etc do - they don't ofer 98 octane over here).
There's something in the Shell 98 that seems to make it particularly prone to fouling plugs on light/trailing throttle, especially in carbied engines.
The good thing about telling the truth is that you don't have to remember what you said.

Offline vandy010

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Re: FEUL - premium unleaded v's unleaded
« Reply #4 on: August 07, 2007, 01:31:32 pm »
i always get my feul from the local caltex so it's always the caltex vortex feul being used.
lets get away for a moment from this octane bizzo as what i'm interested to know is this "density" factor as described by said guru. an old bugger i have come to trust.
as for NGK plugs, i've used them for years with zero problems till now.
so whats the goods on plugs whilst we're here?
and "density" folks, density.
"flat bickie"

Offline cyclegod

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Re: FEUL - premium unleaded v's unleaded
« Reply #5 on: August 07, 2007, 01:49:24 pm »
I don't know about the fuel density thing, it probably has something to do with the vaporization point of the fuel, with the denser premium fuel tending to stay as droplets rather than vaporize at low throttle/low pressure.

As for the plugs DON"T GET ME STARTED ARRGGHHHH......... My NGK experience is a hate/hate one at best as in I HATE how they are built down to a price not up to a standard/ I hate how much they have cost me both in race wins/finishes and being stranded in the middle of nowhere (I went through 6 plugs on one 108km trip  >:( >:( >:( >:() They were crap in dirt bikes and road bikes and I will never EVER use them again. I use Nippon Denso or good old Champions (the bike that went through 6 plugs (an RD350LC) ran for two and half years on a used set of Champions without fault until replaced with new Nippon Denso's) While I will concede that some people have no trouble with NGK's I have met quite a lot of people who will happily rubbish them as much as me. Trust me when I say try a few different brands and when one works reliably stick to it and buy plenty of spares.
« Last Edit: January 23, 2009, 10:56:08 pm by Graeme M »
Ban BLACK rims NOW

Offline Nathan S

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Re: FEUL - premium unleaded v's unleaded
« Reply #6 on: August 07, 2007, 02:48:31 pm »
Denisty should refer to exactly that - how much a given volume of something weighs. IE: Petrol is less dense than water is less dense than mercury.

But many people say 'density' to talk about 'energy density' when it comes to fuel.
This relates to how much bang you get out of a given volume.
For example, methanol has a lot of things going for it, but is quite poor in terms of energy density - you'll probably pour twice as much into the engine to make 25% more power (these are made-up figures, don't sweat their accuracy).

A lot of the 98 octane fuels are mildly oxygenated - this means that they contain some oxygen within them, that is released as the fuel burns.
Nitromethane is a highly oxygenated fuel - when it burns in an engine, it releases more oxygen into the combustion chamber. So you run a very rich mixture as a fair bit of the oxygen required for combusion is brought into the engine by the liquid fuel.
Obviously this requires less air (which takes up a lot of physical room) to give a bigger bang - so you get more HP (everything else being equal).

WRT harping on about "98 octane fuels" you're right - the octane rating is almost irrelevant if the engine isn't pinging... But in the world of simplistic mass marketing, it's the "high octane" fuels that get all the good stuff. In other words: the octane rating is only one of it's attributes, but it's one that's does have some advantages, is easily sold to the punters, and the punters think they understand.
It's like comparing a YZ to a DT and only talking about how much power they make - the YZ is faster around an MX track because it does everything better, but it's easiest to say "Look at that! The YZ125 makes twice as much power as the DT! Bet she honks! Hooooeee!".

PS: I love NGKs - never had an issue with them, but have had dramas with other brands. Go figure.  :)



« Last Edit: August 07, 2007, 02:53:43 pm by Nathan S »
The good thing about telling the truth is that you don't have to remember what you said.

oldfart

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Re: FEUL - premium unleaded v's unleaded
« Reply #7 on: August 07, 2007, 04:49:09 pm »
Explain this then ....I ran the Pe 400 and the mighty Ts 400 on that (shitty shell shit) high octane with motul oil ( 800 racing 2T ) mixed at a ratio of 200 ml per 4.5 litres of fuel running NGK plugs . They both idled ok had no flat spots reved their arse off all weekend  ( Conondale )
« Last Edit: August 07, 2007, 04:52:35 pm by oldfart »

Offline cyclegod

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Re: FEUL - premium unleaded v's unleaded
« Reply #8 on: August 07, 2007, 04:51:47 pm »
Isn't it obvious oldfart THEY"RE SUZUKI'S  ;D ;D ;D the troubled bike in question is a yamaha  :( :( :(
Ban BLACK rims NOW

Offline Lozza

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Re: FEUL - premium unleaded v's unleaded
« Reply #9 on: August 07, 2007, 09:38:08 pm »
Ahh my favorite subject ;D
Vandy I almost reckon your problem is simply a to big pilot/air screw to far in problem or ignition related.I would very much doubt the validity of any opinions of density of the fuel affecting jetting.After all F1 teams have no problems getting mega HP from 91 pump fuel*
Oldfart's been up at his V8 team owner's house getting some of the 'not for public' Shell stuff :D,which seems to be much better quality than from the pump.
As for density bit like lead,steel,aluminium and magnesium, for a given volume (say 1 cc) lead will be heavier thus most dense and magnesium the least dense/heavy. Same for fuels except that the difference is much less the 98 octane fuel are about 0.78kg/litre and the 91 about IIRC 0.72 kg/litre.Not much to it really.
If you run 91 with a booster you'll just drag it up to about 94 octane ::) why not just buy 98 and do lots of plug chops?????
*NB you'll need a lab,chemists and lots of geeks with computers but they do it each week
HTH
Jesus only loves two strokes

Offline gorby

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Re: FEUL - premium unleaded v's unleaded
« Reply #10 on: August 08, 2007, 12:03:45 am »
NGK= :)
Nippon Denso =  ;D
Champion = >:( + $
in my experience over 30 years

I have found the humble spark plug cap to be the culprit on many ill behaving bikes.

Most later model ones have a screw in resistor that can come loose or corrode and are usually the ones
that are purchased new from the bike shop and find their way onto the older bikes.
Always worth a look inside them and not sure how the extra resistance figures into the early model systems.

Offline vandy010

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Re: FEUL - premium unleaded v's unleaded
« Reply #11 on: August 08, 2007, 02:32:10 am »
thanks heaps fella's!
i guess it's kind of reconfirming my idea's a little by reading all this stuff.
i think step 1, i'll stick with the feul/oil/plug i'm using and do the pilot/air screw thingy.
and Lozza, ignition wise, she runs a dt175 87ish lightened flywheel,stator,cdi set at 3mm btdc with a known coil.
when she's on the pipe in the lower gears it works well for what it is.
reading oldfarts post about conondale, us 125's were out first on the sunday and that crisp morning air she went even better all round leading me to think i could even go 1 more leaner on the main and or needle.
1 step at a time i guess.
she won't get ridden for another couple of weeks but i'll try and update how it all goes just for the feedback.
thanks again.
"flat bickie"

Offline fatboycrash

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Re: FEUL - premium unleaded v's unleaded
« Reply #12 on: August 08, 2007, 07:32:58 am »
Speaking of fuel, has anyone had any experience with the new shell "v-power racing" fuel available at the pump here in Brisvegas?  Meant to be a minimum of 100 octane.
I do remember a friend having trouble jetting for  Optimuck when it first appeared.....    It was a density thing then too.
FBC

Offline Lozza

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Re: FEUL - premium unleaded v's unleaded
« Reply #13 on: August 08, 2007, 07:58:40 am »
Static timing of 3mm on a 125 is a hell of a lot of advance,although I haven't seen the advance curve.
IIRC the V-Power has a lot of ethanol in there something to steer well clear of IMO.The  jetting problems with Optimax seem to because of how 'gummy' it is and the deposits it leaves., nothing to do with density.
Plug cap should be 5k ohms
Jesus only loves two strokes

Offline vandy010

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Re: FEUL - premium unleaded v's unleaded
« Reply #14 on: August 08, 2007, 09:20:08 am »
Static timing of 3mm on a 125 is a hell of a lot of advance,

well i'm kind of stumbleing through some of this stuff as i go. when i got the cdi set-up, i made a quick phone call to the local shop/mechanic for advice and i'm pretty sure he plucked the figure out of his head so 3mm it was.
so if i backed it down to say 2.5mm or where do you reckon?
as i say, when on the pipe she goes great but sometimes it can take a little bit to get it there. maybe this could be included in the step 1 solution.
"flat bickie"