Jetting- early warning of lean condition?

[SULLY]

Having gradually jetted leaner and leaner on my son's 03 RM125, I am pretty close with 440 main, 37.5 pilot and second clip. Bike runs great with much increased crispness, repsonse and power, with no fouling or spooge. A huge difference from the way rich standard settings.

As ever though it's always a quest, and am keen to go to 430/420 to see if we get still further improvement, but I would like to know - What is the most likely first indication of a lean condition?, plug colour, pinking, detonation, lost power etc...which symptom is likely to exhibit first so I can look out for it when testing. Thanks Sully

 

[reelrazor]

Heat, excessive heat is your first indicator.

Power loss when full hot may be noticed. Pinking(that's Brit for pinging or spark knock, correct?) may occur, may not be hearable and may cause damage by the time it is noticed.

I am a big fan of EGT gauges and/or infrared thermometers and checking piston wash and plugs.

Thing is, get it right on that leeeeean edge and then an overnight drop in air temp and you are ordering parts and booking machine work. If it is a racing effort it may be worth that, but otherwise you say you have gotten benefits; "..runs great with much increased crispness, repsonse and power, with no fouling or spooge. A huge difference from the way rich standard settings..".

I would say you have done well and if the engine is happy like that, enjoy it.

 

[Can Can Kev]

i agree w/ real razor i wouldnt be on the fine line, if your looking for added crispness go with a good quality race fuel like VP either C-12 , or if u can afford it Ultimate 2 , or if anything regular 110 if the prices are gonna effect u u can delude it with pump gas 50/50 with 91 octane and it will last longer and still give good effects....

 

[marcusgunby]

Your already leaner than most run in the UK-we went to a 480 on a friends 03 rm125, i would be very careful on going any leaner.

 

[Chili]

We are currently at 460 main, 35 pilot, and 2nd clip on my son's 03. I know it's completley different environment setting but we are still somewhat rich but I am reluctant to drop the main much more until I get time to do some plug chops.

 

[SULLY]

Hmmm..thanks for the input Marcus and Chili. We have had no pb's at the setting I describe, am loath to go any leaner without evidence of previous experience at similar geo conditions so will be content to stick where we are. We have good perfromance, with no discernable damage/ wear/ ill affect apparent at the last rebuild. cheers all, Sully

 

[Chili]

As a follow up we just did the top end on Troy's bike last week and there was some evidence of a very minor amount of detonation on the piston crown. Not sure what your running for fuel but we were running on 93 premium pump and it looks like we will have to bump the octane up a tad.

 

[SULLY]

OK thanks Chili, we too will be due for a re- ring soon, I will check for det. then. What were you seeing?, metal deposits/specking?, did you have the 'BLAAACK SPAAAAAT' (spot) underside the piston crown? etc...

 

[Chili]

I'll post up some pics of the piston if I can this weekend. It all looked very good with the exception of a slight rough area (slight pitting/rough feel) around the top edge of the crown.