20:1 premix for aircooled 2-strokes?

[Beeza]

My PE175 manual from 1980 says 20:1 is the correct mix. But it seems extreme, seeing as my two-stroke lawnmower has run happily for over a decade on 50:1! In these days of super high-tech pure synthetic oils, is a rich mixture like 20:1 really necessary on what's a detuned motocrosser like a PE Suzuki? Or is it best to stick with the manufacturer's recommendation?

[MSTRS]

My PE175 manual from 1980 says 20:1 is the correct mix. But it seems extreme, seeing as my two-stroke lawnmower has run happily for over a decade on 50:1! In these days of super high-tech pure synthetic oils, is a rich mixture like 20:1 really necessary on what's a detuned motocrosser like a PE Suzuki? Or is it best to stick with the manufacturer's recommendation?

Hard to know since oils have changed a bit, as you say. I had a TE250 for a (little) while...ran that on premix at 30:1 and blew the bottom end. Your choice whether to vary the mix rate...

[Reckless]

My PE175 manual from 1980 says 20:1 is the correct mix. But it seems extreme, seeing as my two-stroke lawnmower has run happily for over a decade on 50:1! In these days of super high-tech pure synthetic oils, is a rich mixture like 20:1 really necessary on what's a detuned motocrosser like a PE Suzuki? Or is it best to stick with the manufacturer's recommendation?

20:1 is what we used to put in our 125 and 250 race karts. So should be good for your PE175.
By the way a few years ago when I was checking what would give me good horse power in my 125 methanol race kart. Every test, study and dyno run I ever read, more oil = more horsepower. I think more oil adds up to a better ring seal, less bore wash. Which means more compression which equals more HP. You just can't put so much oil in, it stops the fuel igniting properly. We used to race 20:1 in 125, cadets ( air cooled) and Rotax 125 while every one else was going 50:1 and we usually beat them. No one ever noticed ours smoking a bit more than the others on the warm up laps.
Hope this helps.

[scott411]

it is a comman misconseption that less oil is better for bikes to run,
if you put more oil in you get more horsepower due to leaner fuel mix, and better rinh sealing, however if you are not getting rid of the oil it can cause fouling or carbon problems,

Race Karts and GP Bikes tend to rev harder than mx or trail bikes due to the nature of the courses they run on, (hard and flat) so they tend to need more oil,

i run my 125's on 32 to 1, and my 250's and above on 40 to 1, mainly to get rid of the oil spooge that forms up on them, i always use fully synthetic oil,

[Reckless]

Scott is right on the button! MX bikes spend alot more time off throttle going into corners and down hills with their idle jets sucking in fuel and oil.
Getting back your original question 20:1 was pretty normal in the PE175 days so Id stick with that unless your good with plug colour and rejetting.

[NZsarge]

Used to run my IT250L and IT175J at 40:1 using Castrol TTS with no worryies.

[Reckless]

Used to run my IT250L and IT175J at 40:1 using Castrol TTS with no worryies.


You know Castrol was the bees knees until all these fancy motuls etc came on the market. We ran some TTS but mainly Castrol R. Smells good and was a fine oil. The caster base made plug colour and tuning easy as well. Shit I've still got a 4 litre container of MSSR I'm using up in the mower at the moment!

[NZsarge]

You know Castrol was the bees knees until all these fancy motuls etc came on the market. We ran some TTS but mainly Castrol R. Smells good and was a fine oil. The caster base made plug colour and tuning easy as well. Shit I've still got a 4 litre container of MSSR I'm using up in the mower at the moment!

Yeah, been out of that scene for a long while I must admit.Still remember the sweet smell of TTS tho

[cheese]

Yeah that is why I changed from Motul. that and cause motul is freaking expensive...

[laRIKin]

My PE175 manual from 1980 says 20:1 is the correct mix. But it seems extreme, seeing as my two-stroke lawnmower has run happily for over a decade on 50:1! In these days of super high-tech pure synthetic oils, is a rich mixture like 20:1 really necessary on what's a detuned motocrosser like a PE Suzuki? Or is it best to stick with the manufacturer's recommendation?


That's what it use to be and if you try to run your bike on that mix with modern oil's.
You will foul plug after plug as the modern oils do not need to be run that think and you poor old girl will not have a strong enough spark to burn off all that oil.

We found that my bother in laws bike (PE175) ran fine on the same mix as my KX's (250 and 500) 50:1 Motul 800.
We try every mix from 20:1 to 50:1 in 5:1 steps.
And use to have to take a pocket full of plugs for a days ride until we went F.I, run your bloody bike on the same mix as me.
And we never looked back after that.

Some times on the side of the bottle or may be on their Web site they do give you a idea of what is a good mix on air cooled bikes.

[B0000M]

You know Castrol was the bees knees until all these fancy motuls etc came on the market. We ran some TTS but mainly Castrol R. Smells good and was a fine oil. The caster base made plug colour and tuning easy as well. Shit I've still got a 4 litre container of MSSR I'm using up in the mower at the moment!

tts still is the bees knees. 14 years of CRs and never a damaged engine it cant be bad.

[Beeza]

Fifty to one?

Radical!

So, why did you guys stop there? Why not progress the experiment on to 60:1 or even further? In Canada they run skidoo race machinery at an eye-watering 100:1

[dammad1]

My KTM manual says to run it at 60:1 so its not that radical, however I still run it at 40:1 with no problems with fouling or spooge.

[Reckless]

Fifty to one?

Radical!

So, why did you guys stop there? Why not progress the experiment on to 60:1 or even further? In Canada they run skidoo race machinery at an eye-watering 100:1

I can only tell you what we discovered in karting. I'm no expert either. It is a very close sport with a lot less variables like different rider skills, conditions, race lines etc that you have in MX. In karting these things are alot lot closer. Within Hundredths, within sections of the track. We used Laptops and computerised track mapping for kart set up, speed and timing. In other words a very controlled environment.
And what we found was that when you leaned off you gained revs (sometimes) and the kart seemed faster and brighter. Which gave the illusion (seat of the pants) you had more horse power and therefore where faster. But what we discovered was that we lost bottom end pulling power. It pulled far less put of the corners. Therefore your terminal speed end of straight may have been as fast (it often wasn't) but it took more time to get there. So your laps where slower because you had more revs but less horsepower. You know what they say 10% gained through the corner is 10% added at the end of the straight. So 10% of 30K out of the corner is 3K which translates to 10% of 140K at the end of the straight which is 14k. If you pass someone 14k faster it looks like they are standing still.
So at 20, 30 or 40:1 your probably OK depending on tuning. At 50:1 the above is not so evident and the bike shops love you cause your buying lots of pistons. But at 100:1 it probably lots like the thing is going like shit even if its revving its guts out. Apart from the heat and wear and tear! I dunno about skiddos but every 2smoker we put on the dyno gave the most horsepower at 20 or 25:1. On petrol , av gas or methanol.
My opinion only! and I hope to hell Robert Taylor doesn't read this cause he really does know what he's talking about!!!
Far out didn't mean to write a book!

[Rupe]

why would a air cooled engine need a different ratio to a liquid cooled one. Sorry if thats a stupid question but I don't know.

Also some of the guys on here would be running around on the old air cooled kdx's. What are they running at?

[clmintie]

Just out of interest... I have some 2.5cc two stroke model motors that run on 4 to 1 methanol/castor. They make stupid hp for their capacity, nearly 1hp/cc at 38000 rpm and the oil is not just there to lubricate, but to cool as well. Most of it is unburnt and takes heat out with it... Messy, but sure works well.

[Reckless]

why would a air cooled engine need a different ratio to a liquid cooled one. Sorry if that's a stupid question but I don't know.

Also some of the guys on here would be running around on the old air cooled kdx's. What are they running at?


They are probably running or should be running a richer mix compared to the modern bike. Because they may/will have steel bores etc vs the more modern Nikasil bores and more modern metals in later engines. Also heat is far better controlled in a water cooled engine. That's not to say they can get away with running a leaner mix due to the better synthetic oils etc they have today. In their day we only had the tts Castrol R and the comparative Castor based 2smoke oils. Remember leaner usuallly means more heat, more revs = More wear. In the old days (air cooled) you had about 5 different piston sizes and you changed them as the steel bore whore out. Then resleaved the bore and started again. To reduce this wear and get good ring seal and compression you ran a richer mix.

[Reckless]

Just out of interest... I have some 2.5cc two stroke model motors that run on 4 to 1 methanol/castor. They make stupid hp for their capacity, nearly 1hp/cc at 38000 rpm and the oil is not just there to lubricate, but to cool as well. Most of it is unburnt and takes heat out with it... Messy, but sure works well.

Your sort of correct, the oil is only there to prevent friction which generates heat. Not really to dissipate heat.
Methanol is another kettle of fish again. Its claim to fame is it runs/burns coooool. So the advantage of running methanol is not so much the fuel giving more horse power. It is what you can do to the engine because you are running methanol. IE much higher compression ratios, advanced timing etc etc. That is why your little engine is producing silly HP not so much because of the methanol itself. This applies from your little 2.5cc engine to drag cars.

Do you get the theme, in all the posts, less heat, less heat.
Air cooled to water cooled =less heat. Synthetic oils =less friction = less heat. Nikasil bores= one ring=less heat. All of the above mean they can raise compression and revs etc to gain HP and performance in a 2smoker.

[Beeza]

Jeez! Looks like that ancient old 20:1 premix really IS the proper way to go on the PE175, then? Even with hi-tech modern fully-synthetic two-stroke oil in the petrol. Whoda thunk it?

Thanks for the advice!

[mc4aregreat]

mmmmmmmmmmmmmm!, ah those were the days.

[Beeza]

Well, I've been known to ride my 850cc Guzzi Le Mans 3 behind someone with Castrol R in his premix for his CZ175 2-stroke just because his blue-haze exhaust fumes smelt so wonderful. And this smell festival went on for 200km at 100km/h and my wrists ached from those Guzzi clip-ons travelling at such a low speed!

[Beeza]

If you're really flat-out racing that 2T motor as hard as it'll go whenever you can, would you perhaps require a 20:1, but if you're a very much meeker sort of trail rider, would you actually be better off with 32:1 or 40:1 of pure synthetic oil mixed in the petrol tank?

[Beeza]

Karters know what works and what doesn't when it comes to aircooled 2 strokes, so your input is very special! Looks like 20:1 premix really is the way to go if you want every last scrap of that low-end pulling power grunt which is always in pretty short supply on a light-flywheeled 175cc stroker! Thanks for the advice!