Fuel/Oil ratio

[vlxk]

I don't mean to start a big long conversation about what oil is best etc. I left my cylinder at the machine shop Tuesday morning to be bored to fit the .50mm oversize Wiseco piston. 78 1/2 C2.

I have bad history with an RM250A back in 1975/76. In retrospect, it was my fault, but that bike would seize at will. I raced it about a season and a half and was at the largest overbore when I got ride of it. Come to find out the first A models imported to the lower 48 were jetted very lean. At about the time I was selling the bike Suzuki came out with a fix that included a different needle jet (Q0 to about an R4 or something) and a larger pilot I think.

Back to today. The cylinder has been mildly ported, intake side cleaned up and the round castings sharpened. It was on the std bore but worn about to the limits. My question is about mix ratio. The 95 KDX I just sold was running at 40:1 on Yamalube 2R. The manual states 20:1 is the recommended ratio for the C2. Are you guys running those ratios?

When I got the bike I went through the carb to get it cleaned up, replaced the pilot jet, it was a #25, book says #45 or #50 was stock. I went with #45 to start. I am at roughly 1000ft above sea level and I noticed several layers of Florida Offroad stickers on the fork legs that would indicate much closer to sea level. I'm no jetting expert but that seems very lean to me. Anyway, is 20:1 with Yamalube 2R a reasonable starting point? 

I know oils are better now than 35 years ago, and I absolutely do not want to repeat the horrors of my first RM250.

Thanks for your input, and please, I don't want this to turn into a "what oil is best" thread!

Thanks guys.

[sleepy]

Best to do a search on oil fuel ratios on this forum and try and work out what to run. It will be difficult to get an answer with so much BS on the subject.

[Slakewell]

This is the research done by the Lewis Brothers so credit really goes to there hard work. This is their findings nothing more. After melting piston tops and blaming the new fuels these days it was decided that more information was needed. There was also some evidence that the new synthetic oils dont work well on AIR cooled motor because they burn to clean to transfer heat.
A heat sensor was placed in the header pipe and a number of test with different fuels and oils were done.
The conclusion was that normal 98 pump fuel with old school mineral oil ratio 25 to 1 / 20 to 1( Like super TT or Maxima ) ran the coolest. Worst was race gas and full synthetic oil.
 
If this works for you buy them a beer as they did the hard yards.

[Lozza]

This is the research done by the Lewis Brothers so credit really goes to there hard work. This is their findings nothing more. After melting piston tops and blaming the new fuels these days it was decided that more information was needed. There was also some evidence that the new synthetic oils dont work well on AIR cooled motor because they burn to clean to transfer heat.
A heat sensor was placed in the header pipe and a number of test with different fuels and oils were done.
The conclusion was that normal 98 pump fuel with old school mineral oil ratio 25 to 1 / 20 to 1( Like super TT or Maxima ) ran the coolest. Worst was race gas and full synthetic oil.
 
If this works for you buy them a beer as they did the hard yards.

W... I don't see how oil burning "clean"and transfering heat relate? Exhaust Gas temps are indicative of jetting, compression and ignition timing not oils or ratios. Under plug temps are more reliable an indicator of the engine running hotter or colder. Melting pistons are overheating likely would be too much timing with unleaded fuel. Gordon Jennings did all that years ago.

When I got the bike I went through the carb to get it cleaned up, replaced the pilot jet, it was a #25, book says #45 or #50 was stock. I went with #45 to start. I am at roughly 1000ft above sea level and I noticed several layers of Florida Offroad stickers on the fork legs that would indicate much closer to sea level. I'm no jetting expert but that seems very lean to me. Anyway, is 20:1 with Yamalube 2R a reasonable starting point? 

25 is a awfuly small pilot at sea level you would be running richer jetting than 300m Air cooled engine @20:1 is a ideal start. I have yet to see todays oils are "better" just different. The aim of todays oils is low smoke. For your reading pleasure 

http://www.bridgestonemotorcycle.com/documents/oilpremix6.pdf

the highest oil ratio I've heard of is 8:1 in a outboard run 16:1 in chainsaws (with ULP and synthetic)

[Slakewell]

Ok I know some of this goes against current thinking so Ill try explain a little better.
When the Horwood brothers race some of our bikes they raise issues that normally dont get raised but you get that with very fast A grade riders who win Championships. Not normal guys like us who ride around at best in the top 10ish.
Old school oil and cooling. The theory goes like this. That older mineral based oil don't burn completely away and leave a film that helps transfer heat from the piston out thou the fins on the cylinder. The new synthetic oils burn too well and leave an air cap that heat doesn't cross as easy.
 
This was the results of the testing done with the heat sensor backed this up. The bike was the same , same jetting etc the only change was oil ratio's and mixtures. Old school mineral oils and good pump petrol ran the coolest by a fair margin.

You guys make up your own mind but Ill be running old school oil at 25 to 1 and using the synthetic stuff in my modern water cooled bike.

Now Lozza if you run some testing that disproves this and post up the results I really like to see that , all information is good an all ideas need to looked at. Also if can tell me how to measure plug temperature whilst riding that would also be good. I think a good heat sensor right near the exhaust port is a good measure but I'm happy to listen to better ideas that can be done on small budget.

[skypig]

I found some interesting info that made sense to me.
I re posted here. http://forum.ozvmx.com/index.php?topic=38180.0

[vlxk]

I really appreciate the comments and thanks to you guys I have a better idea of what to do.

I think I am going to try the Motul 710 and see what happens. I will be riding MX at less than hyper speeds so I'm thinking that product will work fine.

A little more history with the A model 250 I had back in the day if you don't mind a short story. My dad picked the bike up for me, it was one of the first RM250s in Arkansas. I lived in St Louis MO, another long story, no my parents were not divorced or separated. Anyway, the first thing that happened with it was on a break-in get to know what it was about ride, I had moved up from a TM100, the front wheel basically fell off! When the Suzuki shop assembled the bike the sleeve that went on the pinch bolt side of the fork was rotated so the pinch bolt didn't clamp down on the axle which allowed the axle to back out and land me on the ground pretty hard!

On one of the next race days I experienced a nice electric shock when I would scoot up on the tank in corners. Took everything apart during practice and found nothing wrong. Apparently whatever was happening to cause the shock was fixed when going back together???

After that when I moved to Arkansas, the track I raced on was the St Peters Cycle World track, going from nice black bottom land dirt to the hard pack red clay was an awakening! That's when the seizing really started. Suzuki eventually sent a repair kit which included a pilot jet and a slide. The slide was heavier because of a few throttle hang ups from the very light original slides I guess. My dad and I had no real experience with jetting from my TM100 days. That bike just ran and ran. The 250 was more fickle and not knowing any better I/we replaced the cylinder head with a porcupine style, the pipe was swapped for an FMF both of which made the seizing worse. That's a lesson on learning what is causing the problem rather than throwing parts at it to see what happens.

Down in Arkansas I met a guy named Tony Wynn. His shop was less than a block away from my dad's business. I ended up buying an RM125B from him, I had already been riding an A model 125 with the 250 forks on it. The 125B from Tony Wynn was a rocket. From there I went to a 125C and then street bikes for a while.

The current 250C2 I am building will have some throwback parts to my days with Tony Wynn. I'm going with the old duckbill front fender and he had a replacement set of side panels that I thought were pretty cool at the time. Once I get things settled I'll put up pictures of the 125 I bought from him and the 250 from today.

Thanks again for the input on fuel/oil ratios, I really enjoy the posts on this site even though I sometimes don't quite get the lingo

Kenny

[skypig]

Nice history and memories in that story.

A little from me.
Moved up from a YZ80G (a lemon, compared to the perfect "F" model I'd won the A grade club champs on the year before)

The first water cooled RM125. What a bike! (Second one to arrive, the first to the local sponsored rider)

The first rebore didn't feel crisp. I had to go to the next oversize and educate/convince my excellent machinist that I really wanted it "that tight" (as specified in the manual).
The clearances were different from the air cooled bikes we were all used to.

More than one RM cold seized that year. (Not mine) Warm up was slower...

Water cooling was a learning curve.

Prior to reading all the info on this and the linked thread I was going to run full synthetic at 40:1 (thinking this conservative.)
Now I intend to run 710, (or 510 until it's used up), at 25:1.