rm 125 powerband issue

[2stroker144]

so i just bought a 2001 rm125, when i bought the bike it ran amazing, for a 125 the powerband was fanstastic. however when i ran out of the gas that was origionally in the bike and put in my own, the powerband became a peice of crap. it wouldnt hit and be smooth it would just be really choppy and loud. so my question is, is my gas mixture off? do i need to be richer or leaner? i mixed the gas i put in myself at 32:1. should i be at 40:1? im going riding tomorrow so anyhelp would be greatly appreciated. thank you

 

[whenfoxforks-ruled]

Start by trying 20:1~24:1. Leaning the premix ratio reduces the 125's ability to make good horsepower, oil protection and good compression at the top of the list. I would recommend pulling the top end off and doing an inspection. Figure at least a rering and gaskets. Look and measure with a feeler gauge and bore gauge. I sure hope you have a shop manual, by the book you will need to do this every 7 to 15 hours or so. Depending on your habits. a little to read by, Vintage Bob .www.dirtrider.net/forums3/showthread.php?t=167446&highlight=spankys+jetting ,www.dirtrider.net/forums3/showthread.php?t=179073&page=3&pp=20&highlight=spankys+jetting , and ,www.dirtrider.net/forums3/showthread.php?t=179821

 

[RM_guy]

Can you contact the original owner to ask what oil mixture and octane gas he was using?

 

[_JOE_]

RM_guy has a great suggestion. It could be set up to run a funky mix ratio or could've had some motor work and need race gas. Any time you buy a 2 stroke you should find out what fuel/oil they've been running, it has a big impact on tuning. Then study that jetting guide Bob gave ya.....

 

[robertmoto10]

My rm 125 ran weird with 32 1 I works a lot beter with 36 1

 

[jb_dallas]

The correct mixture depends on jetting. You can jet a 2 stroke to run 20:1 or 40:1. As mentioned, engine mods also could be a big factor. Personally, I always thought the sweet spot was around 32 or 34 to 1...enough oil for proper lubrication, but doesnt break the bank with todays expensive mix.

 

[whenfoxforks-ruled]

The correct mixture depends on jetting.

That is backwards. Use and design dictate oil ratio. Fools with tools take it from there. Vintage Bob

 

[jb_dallas]

It is backwards only if you care to take the time to experiment with jetting. If the jetting was close, one might just tweak the mixture slightly. I have actually found this useful in cases when time didnt permit experimenting with jetting. WFFR, you seem to be happy with 20 or 24:1. Of course, there are numerous threads on here debating mixture. I know people that trail ride 2 strokes that run 40:1 and they dont rebuild their engines every 30 hours. So, it could be debated if use and design really dicate oil ratios as it comes down to personal opinion more than anything.

 

[IndyMX]

So, it could be debated if use and design really dicate oil ratios as it comes down to personal opinion more than anything.

I would suggest that an engine ran at WFO or near it for long periods of time would require more oil than an engine that's run at lower RPM's for long periods.

It's probably also a better idea to use as much oil as you can get away with, and jet accordingly.

There is evidence that an engine will actually run better with more oil than less.

 

[jb_dallas]

Indy...that is why I run low rpms on my KDX with 32:1 mix. I am not advocating running a thin mixture. I will say that I know several folks that have never ran anything thicker than 40:1 synthetic and their bikes have ran 60+ hours between pistons, so I dont buy into the thought that one must run 20:1 for longevity.

Back to the topic, my old RM125 ran great at 32:1.

 

[pesky nz]

A 2stroke gets better port sealing/timing when it has enough residual oil on the cylinder wall and piston skirts (meaning more power). The hotter it gets inside your motor the more oil is burned away so hard use needs more oil than idling. Diferent types of oil are better at staying on the crutial parts. My preference is Motul 800 2t and will need 40:1 for hard riding and 60:1 in my trials bike. In general cheaper oils burn away easier

 

[whenfoxforks-ruled]

I have seen fresh top ends scatter on a 125 at 32:1. It depends on the use and user. Rode at wfo the engine knows the difference? I think not. I do wish it was not so, I love the 125's. I know what the proper maintenance would be for me to ride it also. Basically I double the top end on the 250, and double that for that 480 monster. A set of rings a year. Its all about the maintenance, riding is the treat. The 97 CR250 at 20:1 runs way better jetted for it than 32:1, try it? Its not a rich premix that is your enemy, its a rich mixture that kills the plug, and not able to get the plug hot enough to run clean the entire throttle range. Throttle response to scare the hell out of you! Vintage Bob