Vintage Dirt Bike Q & A

I'm about to fire up my '74 MT125 after an extensive rebuild, and need a recommendation on what brand/type of oil to put in the oil tank, and what (if any) treatment should be added to the unleaded 87octane fuel we're stuck with. Any advice on fuel and oil for this old bike would be greatly appreciated!

I recommended Bel-Ray Si-7 injector oil for my friend's MT250, but he hasn't exactly put a ton of miles on it since so I can't really give a performance report. I've always had excellent luck with Bel-Ray, though.

If your motor's stock, and you don't plan on tweaking it much and/or setting the jetting & timing for max power, pump premium should be fine.

When I first got back into riding I used 93 octane pump gas 1n my stock 2-stroke motors, and they seemed to run OK. When I started trying to get more performance out of them via jetting, timing, and compression changes, though, the pump gas didn't cut it (detonation, and variability from one tank to the next). I tried using Turner Labs octane booster for a while, and while it helped with the detonation the variability was still there. Now I only use 104-octane Sunoco race gas, all problems solved - plus I can now tune for even more power than before.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Jammin,

Modern fuel won't really affect much. The only thing I would suggest is to run your oil a slight bit richer. 50:1 is the norm, but 32:1 is about as rich as you can go without hurting anything.

You could simply disable the oil injection and pre-mix. Or, there should be an adjustment on your pump to increase flow.

Even dribbling a couple of cap-fulls of oil into your gas tank each fill-up can counter the wash-out affect of ethanol.

Run 93 octane ALWAYS in small motors as well... Don't get skimpy and run 87.

Try AmsOil synthetic injection oil.

Dan

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I drink your milkshake!

I run Yamalube 2S injector oil and 87 octane gas in my MT125 and it runs great. But I would stay away from Walmart gas or other stations that have alot of ethanol in there fuel.