Thinking of a Jawa 350 - 640... with possibly 32:1 premix; Will it Smoke a Lot on a Synthetic 2 Cycle Oil?

Sep 30, 2017
Vancouver, BC Canada
Jawa's are Czech made motorcycles... back from the Eastern Bloc era... and they are still produced to this day (I think now owned by Mahindra)... still with a Czech Republic factory, I believe. Well, in Canada, a person can import and run a 15 year old- or older motor vehicle... without the need to be emissions or safety equipment compliant, if, however, it was made by a legitimate producer.

I have a bit of a perverse love affair with 2 strokes... and the Jawa is possibly the ONLY one out there that has a ready supply of spare parts being manufactured, to this day. On a 2 stroke, you would want to be able to find spare crankpins, big and small end bearings, conn rods, oversized pistons and OS rings, crankshaft main bearings (typically ball bearings), and crankshaft seals. All of these components are readily available for Jawa's... and cheap. And the Jawa design has changed ever so little over the years. It apparently is reasonably durable.

Now, it is NOT sophisticated. Only 4 speed gearboxes... and though they had a Czech made oil injection pump, and then latterly a Mikuni one... they NOW have none... and require premix. They have a labyrinth centre-seal and two centre-bearings. The case split line is a vertical plane... not as nice as the Suzuki T500 (which has a horiz. plane split line and bearing anti-rotation dowels). Oh, the Jawa has a fully enclosed non-o-ring chain... and I THINK they may have an automatic chain oiler... ?

So, my question is... if a person does have to run pre-mix... and for the Jawa, 32:1 is probably best (for middle crankshaft bearings longer life expectancy) - can I expect a bike running 32:1, though running a high quality synthetic, to smoke a lot?

The other bike I am considering is a Suzuki T500 (or GT500)... last made in 1977. A bunch of parts are, understandably, NLA. However, it is clear that the Suzuki has a superior crankshaft lubrication system, and is 'way more sophisticated in terms of drive-quality. But NLA parts means a whole lot of workarounds to be able to run them. This gives me pause. And they are very, very expensive!

Any ways.... your thoughts re the Jawa... and smoking?


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I haven't seen a Jawa 350 for a long time. Great they are still making them, and should be well sorted by now. It will hardly smoke at all on a synthetic FD oil...I'd go to 40 or 50:1, but it won't make a lot of difference. Have fun with that kickstarter/gearlever, it was common on their other 2 strokes too.
Actually it is a nice looking M/C I remember Jawas from reading motorcycle magazines then I was young . 2 smokes are fun.
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Looks like czech version of an RD350.

If you are running really good 2 stroke oil you can lean the mixture out a bit more - take it to 40:1 it will cut any smoke even more.
I can appreciate that the quality of the 2 stroke oil makes for the ability to lean-out the oil ratio. Also, a bunch of oil effectively leans-out the fuel/air ratio. Having said that - lubrication of the two centre bearings, especially, is impacted by lean oil ratios... and as the crankshaft is a built-up one (requiring jigs + a stout-enough hydraulic press to renew all of the main bearings) - it gives me pause to run too little oil.

Then there is that whole thing like "political correctness"... which is contrary. Can you imagine the green-oriented folks who see you smoke down the street on your i) gasoline powered; and ii) oil-smoke-polluting 2 stroke. I am not one for political correctness... but I would want to minimize the backlash...
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they make low smoke oil, in 32 to 1 you will never see any smoke and little smoke at 24 to 1. It does wear a bit more, but so does 40 or 50 to 1 over 24 to 1 Probably a wash. And there is castor oil, great smell and little smoke.
they make low smoke oil, in 32 to 1 you will never see any smoke and little smoke at 24 to 1. It does wear a bit more, but so does 40 or 50 to 1 over 24 to 1 Probably a wash. And there is castor oil, great smell and little smoke.
So if I read you correctly, so-called "smokeless" 2 Stroke oil (presumably both for pre-mix or for oil injection use) wears more than non "smokeless"? Now I was contemplating a JASO FD oil... that, compared to JASO FB oil has a lot more detergency but about the same capability to lubricate. Now I don't pretend to know why detergency matters in a pre-mix 2 stroke, but it may have something to do with the tenacity of the spooge???

Any comments to elucidate this would be much appreciated!
I always ran my DT230 on FD, it had an injection pump, and there was a little smoke on warm up, and none up to temp. I ran my Piaggio Zip 50 on FB, FC, and FD (it was supposed to use FD) with an oil pump, and at times on 50:1 premix with no pump. It had a cat, and again, smoke on start up, and zero when warm.
i owned/rode a jawa moped in 1984 ;)

i'd suggest 32:1 if you keep the rpms under 8000ish, 24:1 above that

the amount of smoke/spooge is all dependant on jetting, not ratio
The Jawa 350 really wants moderate rpm's... like 3000 - 5000 rpm's. Apparently quite unlike a "pipey" 2 stroke. More torque / low rpm focused. Undersquare bore stroke relation. Heavy flywheel disks. 'Been made for donkey's years more or less in the same configuration, and only minor changes all along. 'Lotsa spare parts available which i like. Fully enclosed and lubricated non o ring chain.
Oil is good for 2 strokes. Lowering the ratio is poor advice given by people that keep the oil on their cars engine always to the full like on the dip stick.
VP makes a 2 stroke oil that is JD spec. I run it at 40:1 in all my Stihl stuff and there is no real smoke. I run it at 32:1 in my kid's Blaster and KX100, there is a little smoke under hard acceleration but not bad at all.