Petrol/oil Mix

[greenlaner1]

is this specific to each bike, i have a montesa 311 and been told to mix 50-1

but this seems very weak, do different mixtures give different performance? what would you advise?

thanks in advance

GL1

[woody]

If you run fully synthetic at 50:1 in the Mont it will be fine, no problems at all. That mixture is ok for old steel liners or modern plated liner. On plated liner you can go as weak as 70-80:1 on fully synthetic without a problem.

Which brand oil is personal choice but Castrol TTS runs very clean, doesn't gum up piston rings or silencer like some other brands can do. I've used TTS at 50:1 in Yamaha TYZ, Bultaco Sherpa, Ossa and KTM 300. No problems with any of them.

[motojojo]

If you run 50 to 1 you will smoke everybody out thats parked behind you. I would run 70 to 1 in any trials bike old or new, but I don't like breathing smoke from other peoples bikes.

[jse]

If you run fully synthetic at 50:1 in the Mont it will be fine, no problems at all. That mixture is ok for old steel liners or modern plated liner. On plated liner you can go as weak as 70-80:1 on fully synthetic without a problem.

Which brand oil is personal choice but Castrol TTS runs very clean, doesn't gum up piston rings or silencer like some other brands can do. I've used TTS at 50:1 in Yamaha TYZ, Bultaco Sherpa, Ossa and KTM 300. No problems with any of them.

My current favorite is also the Castrol TTS, although I've tested a bunch of other oils with favorable results like Silkolene Pro2, Rock Oil etc. Just make sure it's a "full-synthetic" and not a blend. I run 50:1 in my air-cooled TY and 70:1 in my Pro but I agree with Woody, if you have a smoking problem and you're running a full-synthetic, it's probably not the slight amount of extra oil that is causing the problem. I've run 50:1 in my Pro, when I was too lazy to mix another batch and used the TY can (I like to mix in small 1 gal. cans to keep it fresh) and didn't notice any excess smoke with the TTS. As I remember, the 311 is water-cooled so cylinder distortion is not a problem and a 50:1 premix ratio, provided it a full-synthetic, is actually a "rich" mixture for Trials use. 50:1 is a 2% mixture and in checking the GasGas factory website I see they recommend a 2.5% premix (and a 3% for the 2005 models!) for the larger Pros, but I'm assuming that is for the possibility of the rider using a mineral-based oil, but synthetics seem to work well at leaner ratios.

Jon

Edited April 6, 2008 by JSE

[t-shock 250]

50:1 would actually result in a weak mixture, more oil = less fuel.

Though would hardly be noticable on a trials bike.

[Guest majestyman340]

Never been able to figure why people have such strange ideas about amount of oil to use? Maybe it has something to do with the old days when you couldnt get fully synthetic 2 stroke oils, which are in fact ok to use at ratios of up to 100:1 on pretty much any trials engine you care to think of.

[jse]

50:1 would actually result in a weak mixture, more oil = less fuel.

Though would hardly be noticable on a trials bike.

It does get a little confusing, this "weak"/"rich" thing, kinda like talking about raise needle/drop clip or the air/fuel screw adjustment.

He had framed the question in fuel/oil ratio, i.e. "is this specific to each bike, i have a montesa 311 and been told to mix 50-1 but this seems very weak, do different mixtures give different performance? what would you advise?" so I answered in kind, but you're correct on both counts, additional premix oil would have probably resulted in a slightly "weaker" air/fuel ratio and it probably would be hard to measure exactly.

Jon

[greenlaner1]

cheers fellas, i was wondering as my scramblers used to be between 25-1 and 35-1 and didnt wanna run the risk of siezing[sp] the engine with a weak mix, but 50-1 sounds good

GL1

[jse]

Never been able to figure why people have such strange ideas about amount of oil to use? Maybe it has something to do with the old days when you couldnt get fully synthetic 2 stroke oils, which are in fact ok to use at ratios of up to 100:1 on pretty much any trials engine you care to think of.

I haven't figured it out either. I know I've run into riders who boast how lean they run their premix ratios (I guess thinking they are getting more power by using less oil, unaware of lubricity and ring sealing issues) and how cheap the oil is they are using "yea, well, I pick up dis here Dino-Squeezings Premix Oil for almost nothing and I run it at 130:1 and my bike runs great!. It doesn't matter what kind of oil you use, it's all the same".

We run the Pro MX and SX'ers on 32:1 (Roadracing is a different issue) with no problems ( and Honda set their jetting for their two-stroke production MXers at 20:1), but in the relatively understressed engines in Trials use, a high-quality full-synthetic should be able to run fine at up to 100:1. For my personal use, I've weighed all the variables and decided that 70:1 makes me most comfortable, but it amazes me how premix ratio is such a "personal" thing with riders, I guess myself included.

Jon

[t-shock 250]

Everyone will tell you their own stories on this, a couple of ex-professional riders both told me never to use fully synthetic oil in an air-cooled trials engine, but i can't bring myself to use semi-synth after the silkolene comp 2 episode which cost me an engine rebuild.

[jse]

Everyone will tell you their own stories on this, a couple of ex-professional riders both told me never to use fully synthetic oil in an air-cooled trials engine, but i can't bring myself to use semi-synth after the silkolene comp 2 episode which cost me an engine rebuild.

True. I've also heard a lot of stories that promote either side of the synthetic "controversy". I think that there are so many other variables that contribute to the end result that it's difficult to effectively evaluate causal factors. I've run my bikes exclusively on full-synthetic and my air-cooled TY has over 23 years of use on the lower end with no signs of a problem and less than normal top-end wear.

I would guess that if a rider takes reasonable care of their engine and uses a ratio appropriate to the type of oil and riding conditions encountered, it shouldn't matter much what they use.

Jon