Leaded fuel in four strokes

20 replies to this topic
  • mywifefarts

Posted April 07, 2009 - 09:33 PM


Will running leaded fuel in my four stroke hurt my valve train? My YZ450f manuel says you must run unleaded only and not doing so will cause engine damage, or something to that effect. I was under the impression that leaded fuels helped cusion the contact between valve and seat. For example back in the 60's when auto manufacturer's used cast-in iron seats.

  • wondermuscle

Posted April 08, 2009 - 07:34 AM


I would not use leaded gas if you can avoid it.

The valves have a very hard thin, a few microns, coating. If you compromise that coating your vavles will start to tulip very fast. I'm not saying that leaded gas would do this but you never know.....

  • grayracer513

Posted April 08, 2009 - 07:40 AM


Some of the lead in leaded fuels ends up being deposited in the combustion chamber, and that just adds to the carbon buildup. Being metallic, it can contribute to the shorting of spark plugs, and create hot spots in the carbon deposit that can cause pre-ignition.

And it is also deposited on the valve faces, as noted already. In an engine with steel valves, this can actually reduce wear at the valve face, but for the reasons given above, the "benefit" to Ti valves is very questionable.

  • harrperf

Posted April 08, 2009 - 08:29 AM


What fuel is in question? Most fuels you would run have some lead content....

It's pretty common to run say C12 mixed with pump on many mod four strokes....mostly for added octane, but also seems to really help ti valve life....(a lot of honda's seeem to last MUCH longer with a leaded fuel) so yes, you can run leaded fuel within reason.

  • erprob

Posted April 08, 2009 - 07:36 PM


I run jet fuel in my YZ450f. Work Great. Start Great too.

  • grayracer513

Posted April 08, 2009 - 08:39 PM


I run jet fuel in my YZ450f. Work Great. Start Great too.

Unless you have the only diesel YZF in captivity, you do not run jet fuel in your 450.

  • Kawirider37

Posted April 08, 2009 - 10:40 PM


maybe he ment to say avgas. I wonder how much torque a diesel yz450 could produce..

  • spark250

Posted April 09, 2009 - 10:32 AM


I run jet fuel in my YZ450f. Work Great. Start Great too.

sounds like a waste of time. avgas was popular when there wasn't a lot of high octane fuels available. You can buy fuels specifically designed for four stroke bikes and probably at a more convenient location.

  • TIG88

Posted April 09, 2009 - 12:32 PM


Or you could just run 93 octane and save yourself some money and trouble!

When do you need race fuels on a yz? Seems even with 13.5:1 pistons you dont need it. Igniton box or something?

  • grayracer513

Posted April 09, 2009 - 12:49 PM


When do you need race fuels on a yz?

13.5:1 at sea level in the winter at night.

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  • 642MX

Posted April 09, 2009 - 03:29 PM


I ran leaded race fuel when I was running a 13.5:1 compression piston. I rering every year and when I would rebuild the top end after running leaded fuel, I would have a little white dust on top of the piston, but no deposits on the valves or anything. The white stuff wiped off with carb cleaner and a shop towel.

I saw no problems with running it, but the price got pretty high on it.... so I switched back to 12.5:1 and now use 92-93 octane.

  • 642MX

Posted April 09, 2009 - 03:32 PM


sounds like a waste of time. avgas was popular when there wasn't a lot of high octane fuels available.

Actually, av-gas works pretty darn good in the YZF's. I've used it before with very good results. I also used it in my KTM 2 stroke that I use to have and it worked well in it too.

  • grayracer513

Posted April 09, 2009 - 05:00 PM


AvGas is not formulated correctly for use in motorcycles. The vaporization rates are blended for slow turning engines with long intakes operating at low air temps and high altitudes. It will burn, and run cleanly, but a significant amount of it will be burned outside the combustion chamber in the exhaust stream, and to get the same power from it as other non-oxygenated fuels will require richer jetting.

It may "feel" good, but it won't be as efficient.

  • tcuda499

Posted April 09, 2009 - 05:14 PM


Thanks Gray!!! Finally someone who I DONT have to explain why avgas is a waste of money in bikes and cars. Got to admitt though, it was pretty big in the 80's... or at least around CT.:thumbsup:

  • 642MX

Posted April 09, 2009 - 05:45 PM


I wouldn't call av-gas a "waste of money in bikes". It does work. I do agree that av-gas is not as great as the VP products that are designed for the new 4 strokes.

  • grayracer513

Posted April 09, 2009 - 07:15 PM


If you ran a dyno test on the same bike comparing a good quality pump gas vs. avgas, jetting for optimum output in each case, you would find no advantage to avgas except in those areas of the country where pump gas just totally sucks. As bad as California's fuel is reputed to be, it's not that bad. The bike running avgas would end up burning quite a bit more fuel/hr.

The only thing one would have to gain from it is in the rare case where more than a 93 octane AKI was actually needed. In that case, 100/130 is cheaper than some racing fuels, but not by much, and racing fuels would provide considerably more power.

  • 8upnmx

Posted April 10, 2009 - 09:45 AM


Why not just run 105 UNLEADED race fuel, mixed with 93 of course. Here in KY its at every race track. Then you dont have to worry about the possible damages of lead.

  • mxdude1986

Posted April 10, 2009 - 02:27 PM


We run 112 mixed with 50/50 with 93 here

  • 8upnmx

Posted April 10, 2009 - 05:34 PM


We run 112 mixed with 50/50 with 93 here

leaded or unleaded?

  • diegox450

Posted April 10, 2009 - 05:41 PM


Gray is right... more octane = slower combustion = less power...

if your engine isn't detonating (Off course, correctly jetted and perfect timing) it's a waste of money and power

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