Pilot Screw Adjustment

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#1
I understand to adjust the Pilot Screw like this: "Turn the pilot screw all the way in to seat it, do NOT tighten it. Unscrew 2 to 2 1/2 turns and then adjust using 1/4 turns to achieve fastest idle speed." ... "This gives you a rough estimate of where to start tuning for any hesitation / bogging during acceleration from closed to 1/4 throttle opening."

When adjusting the pilot screw... it doesn't seem to change much of anything that relates to any bogging or hesitation when you crack the throttle. (At least I can't feel it if there is any.) Am I okay with just adjusting for fastest idle? I don't want that fuel circuit to be too lean!!

So, do I just unscrew it until the idle picks up and stop there? Or should I unscrew it until the idle picks up and then back in/out a 1/4 of a turn?
(Also, does unscrewing it or screwing it in enrich the pilot?)
 

dirt bike dave

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#7
aphelion79 said:
(Also, does unscrewing it or screwing it in enrich the pilot?)
Turning it in (clockwise) richens. Turning it out leans it out.

Make sure the bike is up to operating temperature before you try to adjust by the 'idle' method. Also, how the bike runs under your actual riding conditions is the true test. With most bikes, 1/2 turn is very noticeable. On some bikes, even 1/8 turn is quite noticeable.

As a general rule, anymore than 3 turns out and you should be running a leaner pilot jet.

BTW, if you are a little lean on the pilot jet it is very unlikely you are going to hurt the motor. Too lean on the mainjet is another story!
 
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#8
Yeah its my '83 RM125 (didn't get any replies in my main topic so I made a separate one)

Anywho yeah I just didn't know what to "feel" for... right now, off throttle at low rpms if I barely just crack the throttle open it works fine but if I get it to around maybe oh, 1/3 throttle it bogs a bit then when it gets to a midrange rpm to high rpm I can twist the grip any which way I want to and it never skips a beat!
I figure it shouldn't bog at the low low RPMS at all right? Is this a product of a needle jet or pilot jet? (Main jet seems to have the plug colored very nicely during WOT chops as far as I can tell, lol.)
 

dirt bike dave

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#9
The airscrew is the easiest to adjust, so you might as well experiment with that first. If it seems to work best at 2.5 or more turns out, go one leaner on the pilot jet.

You could also try putting the needle clip one groove higher, which drops the needle. Also easy to do and free.

Another thing that effects low/mid running is the cutaway of the carb slide. But buying a different slide or modifying the one you have is either costly (new slide) or non-reversable (modifying your old slide).

Finally, your bike has a small motor, old carb technology and it is tuned to run at high rpm (which it apparently does quite well). If the bog is not bad, you might already be jetted as good as it is going to get. If that's the case, abuse the clutch and keep the motor in an rpm range that is above the 'bog'. That's the way to ride an old school 125!
 
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#10
Alright! Yeah it's like a rocket once you get into the revs! :yikes: If thats just how it runs then so be it!

It still does well enough to get me where I want and makes the low speed riding a bit more technical... lol so I guess I can deal with it :)
 
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#11
same deal hear on my 97 rm125... I really need to throttle up and play with the clutch to get up some of the bigger hills

once i get in the high mid rev range its a bullet.. like a light switch being flipped, gotta be ready for it

from what ive been reading this is just generally the way all rm125's have been for like forever... no real low end and tons of top and mid..
 
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#12
Well see I understand that as a 125 thats how they work... but I didn't believe it should bog out during those low rpms, just have a lack of power no matter how much throttle I twisted, you know?

I was just seeing if the BOGGING was normal during low RPMS considering I have a MX pipe from DG the curve is all higher up in the rpms lol...
 

dirt bike dave

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#13
When the motor has insufficient power to pull the gear you have selected, most MX race 125s will bog. They really don't make much power down low, and a large flat spot before the power comes in would probably show on a dyno chart. Stab the clutch or downshift to avoid the bog.

Unfortunately, a bad bog reduces the bike's appeal for trail use, but its not unheard of for MX racing 125s. On an MX track a fast rider would probably never notice it, and that's the guy Suzuki ported and carbed the bike for. A swap to a smaller carb or porting the bike for low end power might help clean the response up at low rpm, but its probably not worth the money.
 
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#14
Yeah exactly what I was thinking, which is just fine I have to realize what this bike was built for which is racing! Its not meant to put around in first gear through a densely forested area. (Heck I can barely go higher than second gear when running the local track this thing gets up and moves so quickly!)
 
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#15
lol you just made me want to sell my bike...

and exactly my sentiment, my bike is totally made for racing and i purchased it thinking I could ride it on the trails... been out of the scene for awhile..

A supercross or MX fanatic would love my bike...

I so badly crave low end