Low-end bog on RM125 w/ fresh top end

queen of spodes
Edited Date/Time 1/27/2012 8:52am
My RM125 has started hesitating off idle in the past few months. It feels lean, because when the choke is pulled up just a smidge, the hesitation goes away. On the track I don't notice it, since it's either wide open or chopped.

The top end was replaced about 15 engine hours ago, it has the correct (expensive) factory recommended plug, stock reeds and Pro Circuit pipe. The jetting is also stock. I run pump 93 octane with Super Techniplate at 45:1.

Finally -- I am thinking about sending the cylinder off to Gorr for mid/top porting (w/ pump gas).

Should I clean up the jetting before I let Eric work his magic, to have a clean slate? Or should I wait till the cylinder is finished? How does pilot & main jetting normally change after porting a 125?
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scooter5002
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scooter5002 2/1/2011 7:12pm
2/1/2011 7:12pm
In the last few months, as in when the cooler weather set in? Play with the air screw and see if that cleans it up. If the choke straightens it out, sounds like you need to richen the air screw. Turn it in. Are the reeds in good shape, none cracked? Check that too, if air screw doesn't change it. Could be a choke issue as well, if the rubber seal on it is torn. Straighten it out before you send it off, or you will be tearing your hair out chasing gremlins later, and very angry. Changes will depend on how badly the jetting is off from the factory if you are still running it. Monsieur Gorr should be able to suggest baseline jetting for you.
xnationalwrench 2/1/2011 7:15pm
2/1/2011 7:15pm
You might double check the slow speed jet, if it is blocked you can see problems like what you are getting. Also make sure there isn't a aiir leak at the LH crank seal or at the carb mount.
queen of spodes 2/2/2011 4:28am
2/2/2011 4:28am
X, how would I test for a leaky LH crank seal? Simple as pulling the ignition cover, starting the bike & spraying some stater fluid?
xnationalwrench 2/2/2011 9:12am
2/2/2011 9:12am
queen of spodes wrote:
X, how would I test for a leaky LH crank seal? Simple as pulling the ignition cover, starting the bike & spraying some stater fluid?
That will work also if that seal is leaking remove the LH engine side cover and you would see a dribble of fuel in the bottom of the case. You can also do the same spray trick to see if you have a air leak were the carb mounts. Good Luck and take your time and be safe.

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CamP
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CamP 2/2/2011 10:41am
2/2/2011 10:41am
Make sure you can see light through your pilot jet.
queen of spodes 2/27/2011 12:05pm
2/27/2011 12:05pm
Replaced the stock pilot 27.5 with a 25, and dropped the main from 460 to 450. No more bog in a little backyard testing just now. Starts MUCH easier too. Heading to the track in a bit (with my jet box in case I want to swap back to the 460 main).
queen of spodes 2/27/2011 5:35pm
2/27/2011 5:35pm
Yeah, much better on the track. Feels more snappy & crisp. It wasn't noticeably faster, just cleaner running.
OldTiddler
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Longwood, FL, USA
OldTiddler 3/9/2011 5:45pm
3/9/2011 5:45pm
What yr is your bike? stock rm 125 has 42.5 pilot and 370 main jet...

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