PDA

View Full Version : Need some insight..



SOUN1
Jun 2nd, 2014, 08:49 AM
I have a CR125R (2000) 2 stroke. it boggs and loose power when trying to climb..current it has -2 (or -1) front sprocket.. 45 jet and the last notch on the needle..
I took it out to 007 yesterday and ran like a POS!! Any suggestion?

aaw749r
Jun 2nd, 2014, 09:25 AM
I have a CR125R (2000) 2 stroke. it boggs and loose power when trying to climb..current it has -2 (or -1) front sprocket.. 45 jet and the last notch on the needle..
I took it out to 007 yesterday and ran like a POS!! Any suggestion?

If it is not setting on the rev limiter you don't have enough RPM.

MadKaw
Jun 2nd, 2014, 11:11 AM
what does the spark plug look like?

SOUN1
Jun 2nd, 2014, 12:10 PM
Last week was fine but I'll pull it tonight and post up pictures. I'll try moving the needle down 2 notch.. I just hate going up to the mountain and have to take it apart there..

aaw749r
Jun 2nd, 2014, 12:53 PM
How much time is on the motor? Compression could be dropping and time for a new top end.

SOUN1
Jun 2nd, 2014, 01:49 PM
it's not the top end.. It runs great stock in the valley.. just the elevation change that's giving it a issue.. I'm a NOOB to dirt bike so what I think is not valid ;)

SF Boyz
Jun 2nd, 2014, 04:05 PM
it's not the top end.. It runs great stock in the valley.. just the elevation change that's giving it a issue.. I'm a NOOB to dirt bike so what I think is not valid ;)

It's jetted wrong because of elevation

SOUN1
Jun 3rd, 2014, 08:16 AM
plug look like

aaw749r
Jun 3rd, 2014, 09:07 AM
go down 3 jet (main) sizes at a time and try again, take one another -3 with you if you are still running fat. One of these will get you close for the elevation, then you can fine tune for the elevation. BUT, you will have to change it back when you ride in the valley or it will be way too lean.

SOUN1
Jun 3rd, 2014, 09:21 AM
On the jet went from 50 to a 45 and top notch on the needle. just change to 3 notch down but have not test it out yet. I'll have to take it up there and just do the combination until I get right..
The valley setting is 50 on the jet with 2nd. notch on the needle..

aaw749r
Jun 3rd, 2014, 11:09 AM
You can make jumps of 5 sizes at a time to get in the ball park and then fine tune, either way, it is trial and error and you can only do it properly at whatever elevation you are riding at.

MadKaw
Jun 3rd, 2014, 01:19 PM
you need to do the pilot jet first.

on the Mikunis you are only on the main jet when the throttle is open 3/4 to full


for most riding you do, you will be only on the pilot and the needle.

MadKaw
Jun 3rd, 2014, 01:22 PM
see here, you are not even on the main jet unless you are really on it.

SOUN1
Jun 3rd, 2014, 02:12 PM
Changed the pilot jet from a 50 to a 45 and moved the top needle slot= ran like POS

pilot jet at 45 and moved needle 2 slot down= need to test

(next) pilot jet at 45 move up one slot from above setting

(if necessary) pilot jet at 45 them move to the 3rd. slot the 4th. if need be.. if that don't work.. it's back to the valley setting and sell the POS!! :popcorn:

aaw749r
Jun 3rd, 2014, 05:03 PM
When tuning a motor only make ONE change at a time, that way you know how each change affected the bike. If you make multiple changes at a time you have no idea what change did what.

change
45 jet needle 1
45 jet needle 2
45 jet needle 3
45 jet needle 4
40 jet needle 1
40 jet needle 2
40 jet needle 3

MadKaw
Jun 3rd, 2014, 05:38 PM
Changed the pilot jet from a 50 to a 45 and moved the top needle slot= ran like POS

pilot jet at 45 and moved needle 2 slot down= need to test

(next) pilot jet at 45 move up one slot from above setting

(if necessary) pilot jet at 45 them move to the 3rd. slot the 4th. if need be.. if that don't work.. it's back to the valley setting and sell the POS!! :popcorn:

are you tuning it up there, or down here?

If you are trying to tune it down here in the valley for high altitude, it cannot be done. You are just guessing. You need to take a handful of pilots and some mains up to the top of the 4 lane and do the tuning up there.

ALso dont forget the adjustment of the pilot air screw. The pilot air screw is an indicator of whether you have the correct pilot jet.

MadKaw
Jun 3rd, 2014, 05:55 PM
FIRST FIRST FIRST....what you must do to properly establish the correct pilot air screw (from a Mikuni manual and lots of practice on my 2 strokes)-

1. set the jets in the carb, put it together, get it running and let it warm up
2. start with the pilot air screw at 1 1/2 turns out from seated, get it to idle at about 1000 rpm with the idle speed set screw
3. slowly close the pilot air screw, cutting off air; the idle should get slower and run rougher. set it back to 1 1/2
4. now slowly open the pilot air screw, and at about 2 to 2 1/4 turns the idle rpm should increase, then as you keep turning it past that point it wont increase any more.

Desired effect: The above would be an indication that the pilot jet is correct. You are wanting to see that the RPM rises as you go up to 2 turns or so, then stops rising. Optimal performance is with the pilot air screw at 1 1/2 turns out. you would have effective leaning or richening within about 1/2 to 3/4 turns in or out

Undesired effect: If you keep turning it past 2 or 2 1/4 and the idle RPM keeps rising, this indicates you are waaaay too rich still and its asking for more air. You should try going 1/2 pilot jet size smaller. say from a 45 to a 42.5, not jump to a 40. Repeat the above pilot air screw tests with the new pilot.
If you turn the pilot air screw open to 2 or 2 1/4 and there is no rpm rise then its probably too lean already. Try closing the pilot air screw and most likely as you close it and add fuel, the RPM will start to rise. If the RPM rises as you add fuel then you are too lean and need to go UP on the pilot jet.

Always remember, the pilot air screw is an AIR screw not a fuel screw. So closing it adds makes the pilot circuit richer, opening it makes the pilot circuit leaner.

NEXT When you have the desired response from the pilot, then move to the needle. try riding the bike and as you open the throttle it's either going to sag, or burble rich. Go ONE needle clip at a time until you can satisfactorily open the throttle half way without a stumble and no sag or burble. If needed you can get RC car gearbox spacers from hobby town. THey are 1/2 the thickness of the needle clip. And you can get a 1/2 needle movement by putting it under the clip.

LAST -only when the above are good, you can then run it hard, gradually open to full throttle and see if it either sags or burbles when the throttle is WFO


Fine tune the off-idle stumble. You might get an off-idle transition stumble as you first open the throttle. You might need to add just a bit of fuel to the pilot circuit or take a little away. The pilot air screw is actually sensitive and 1/8 turn rich or lean will help you eliminate that

you have to be patient

MadKaw
Jun 3rd, 2014, 06:06 PM
the red #1 is the idle speed setting screw. Once mixtures are adjusted this screw just pushes the slider up or down so you can set the idle RPM speed you want.

the green #2 is the pilot air screw used to adjust the pilot circuit mixture. Hint- the screw is on the airbox/filter side of the carb so it adjusts air not fuel

montibank
Jun 3rd, 2014, 06:09 PM
I love playing devil's advocate... Prolly what I do best.

Could his symptoms all be actually the difference he is noticing going from a between a 250cc 2 stroke known to have less torque, and a 400cc 4 stroke known for considerably more torque?
Could it be he just needs to use the clutch more?

MadKaw
Jun 3rd, 2014, 08:31 PM
could be, but thats a big altitude difference and not properly jetted its killing that little 2 stroke

SOUN1
Jun 4th, 2014, 08:43 AM
I love playing devil's advocate... Prolly what I do best.

Could his symptoms all be actually the difference he is noticing going from a between a 250cc 2 stroke known to have less torque, and a 400cc 4 stroke known for considerably more torque?
Could it be he just needs to use the clutch more?

Dear sir..... THAT'S A NEGATIVE.. :p

Started a saving account to get me a WR250R plated !!!

SOUN1
Jun 9th, 2014, 07:58 AM
Made it up to Shut eye and came down the back way (never doing that again, well maybe) the bike ran way better now, just got to mess with the air screw..
It was freaking mega hot!!

MadKaw
Jun 9th, 2014, 12:37 PM
what did you adjust or change to make it run better?

SOUN1
Jun 9th, 2014, 12:49 PM
I left the jet at 45, I'd change the needle slot back to stock at 2nd. slot.. Next I'll play with the air screw, and the idle.. It doesn't want to stay on when it's in neutral..

MadKaw
Jun 9th, 2014, 05:38 PM
well we know it's too rich. so Open the air screw. I'm sure you 'll have to change that pilot at least one size

chromefonica
Jun 13th, 2014, 12:18 AM
Don't forget about fuel mixture. What mixture are you running?

aaw749r
Jun 13th, 2014, 06:16 AM
Oil to fuel should not change due to altitude, you are only trying to balance air to fuel due to the change in altitude.

SOUN1
Jun 13th, 2014, 07:38 AM
Don't forget about fuel mixture. What mixture are you running?

38-1

aaw749r
Jun 13th, 2014, 01:14 PM
What ever happened to 20-1? Everything 2 stroke used to be 20-1. Does anything use this ratio any more?
Maybe I'm just a dinosaur.


Cause you see I'm a dinosaur
I should've died a long time before
Have pity on a dinosaur
Hand me my hat
Excuse me man
But where's the door

Hey man them ain't high heeled sneakers
And they sure don't look like cowboy boots
And that ain't rock and roll you're playin'
And it sure ain't country or rhythm and blues

You're singin' a song about makin' love to your drummer
Well gay guitar-pickers don't turn me on
And we don't all get into Donna summer
Do you happen to know any old hank Williams songs

SOUN1
Jun 13th, 2014, 01:43 PM
Get yourself "MODERNIZED" pop!! ;):evilgrin0013::popcorn::weirdface::p:rolleyes:

MadKaw
Jun 13th, 2014, 05:37 PM
I run 45:1

hippylong
Jun 14th, 2014, 01:48 PM
gold spectro 50 to 1
I went from 320 ' above sea level to 6000' feet on my 1986 500 ktm
never had an issue. some loss in hp.
rejetted for 5000' (new mexico)
it ran xtra good.
the issue is ......
by far .....
riding a 125....
big bore or bust !!!!

MadKaw
Jun 14th, 2014, 03:46 PM
with a synthetic like Castrol TTs you can go 50:1. way less smoke that way too