Vintage Dirt Bike Q & A

The older vintage bikes call for 20:1 mix ratio but my new MX bikes mix at 32:1.

My question to the board is with the high quality of the newer race oils should I be mixing at 32:1 as I find the 20:1 to rich and can foul the plugs easily.

Comments please as my vintage bikes are all new rebuilds and the last thing I want is a melt down.

Any help is appreciated,

Paul

I have used 20:1 premix in my MR175 with no ill effects, and the only time i have fouled a plug is when i poured penetrating oil into the cylinder to free up a stuck piston(when i first got the bike). I use castrol 2 stroke gran prix oil(blue in color) and have had no problems. Plus, its better to be safe than sorry. Id rather foul a plug or two instead of causing catastrophic engine meltdown, especially when engine parts are getting harder and harder to find for these bikes. But this is my opinion, its your bike, run whatever you feel like you should run in it.

Happy Riding

I run my entire collection at 32:1 Yama R............. did 2 hard race seasons at 40:1 with YZ465 without ANY problems.

A point to remember.......when running less oil your air /fuel ratio will richen up because the fuel is "less dense" without heavy oil and is sucked through jetting in slightly larger quantity........ conversely, pouring more oil in can lean it out and contribute to your catrophic meltdown.

Personally I dont think there is any need to run 20:1 with any modern 2 stroke oils....the factory set 20:1 as a very conservative mixture in first place even with old shitty oils.

We tend to associate old 2 strokes and smoky exhausts / fouled plugs as going hand in hand.
This is not necessarily the case anymore with modern oil mixed at correct ratio.
All my collection run with clear exhausts when warmed up and Zero plug fouling....Always.

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'84 Honda CR500
'84 CR125
'85 KX125
'83 IT490
'82 Maico 490
'80 YZ465
'75 Husky CR360 GP Mikkola
'75 CR250
'72 DT2MX
'91 XR200

Run high-quality synthetic oil at the ratio recommended by the oil manufacturer. This is normally 32:1 through 40:1, but Bel-Ray MC-1 can be run at 50:1 or higher. While it is true that the ratio will affect jetting, I believe this is only about 1/3 of a jet size so altitude and temp are much more significant.

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

I DON'T race. I don't even ride hard compared to most.

That being said, lately I have been buying Husqavarna 2 stroke oil that comes in doses<2.6 oz> for 1 gal of gas at 50:1. It's a bit pricey ~$1 a bottle.

I run it in everything and haven't had a problem. By everything I mean motorcycles, chain saws, outboard motors, line trimmers. It seems as good as Bel Ray which I mostly used before.

Guess I'll throw my 2 cents worth in:

I'm burning Bel-Ray synethic at 32-1 only because I believe that the
synthetic is a higher quality oil thus better lubrication which is one thing an old bike needs for sure.
Back in the day(early 70's) all we burned was Castrol R bean oil and top ends had to be done constantly don't think that would have happened if we woulda had synthetic.
I miss the smell of that old Castrol R!

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Garry Mainer
#33m (retired)
Honda Cr250r 1980
Honda Cr250r 1980
Yamaha TY250C 1976
Arctic Cat 650 H1 2007

I've been running 40:1 synthetic racing oil on all my vintage CR Elsies (1973-1983 125cc-480cc) for the past 5 years with no problem whatsoever.

I run 30:1 with synthetic blend 2 stroke oil in my 1975 Honda MT250 Elsinore.

Your comments are appreciated and I have adjusted my mix ratio as per the feedback.

Thanks

i just keep it simple and do 50/1 that way you can use it in you weed wacker to

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1974/75 Honda MT 250

Rules are put there to be broken.

For my 74 CR-125, I mix Suzuki CCI at 20:1 with correct jetting and have had no problems. For my 74 CR-250, I mix the same oil at 32:1. The Suzuki CCI oil was recommended from a shop doing Elsinore repairs in Littleton, CO over ten years ago. Since I switched to the CCI, I have never burned up a rod bearing again so It's been a good experience.