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  #1  
Old 06-05-2011, 01:05 PM
meg meg is offline
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Default RM 125 Timing Question

     

I have a question about timing on a RM 125 hopefully someone can help. I will first give some history.......
I recently bought my son a 2001 RM125. I bought it knowing it needed a new top end. Previous owner said it had run lean. No compression. Pulled the cylinder and found the needle bearing had imbeaded pieces into the piston and head.
I did a bottom and top rebuild. New Hot Rods crank, new Weisco piston (bored 1mm over), checked ring end gap, new VForce3 reeds, new cylinder head. Rebuilt carb and moved needle clip to stock setting (middle). Previous owner had it full lean with clip in top position. All jets are stock. Did a leak down test through the intake. It held good at 5 psi.
The bike started fine but just doesnt run right. It sputters just off idle till it gets into powerband. It has good bit of oil from exhaust, actually runs down the silencer. I have taken it through break-in period with several heat cycles and then been riding normal.
As a precautionary measure I removed the head for inspection to see how the bike was running. I found what looks like overheating. There is pitting on the top edge of the piston on the intake side. I have double-checked cooling system.
Finally (after much reading) I checked the timing. I found TDC and marked the flywheel and a reference mark on the case. Using a timing light with advance dial it says the timing is WAY advanced - like 55 degrees!! (I could'nt believe it so I double checked TDC mark and bought a new timing light) I adjusted the stator as far retard as it would go and timing is around 45 degrees advanced. With the timing light on and the bike running, I noticed the timing would jump from 5 degrees to 45 degrees. You could hear the engine change idle when the timing changed. Does the timing advance on these 2 strokes? Spec is 5 degrees BTDC. If there is an advance, how much is it?
This has me puzzled?? I'm assuming it is a bad ignition? Is there a way to tell what is defective?
Sorry for the long post but wanted to give as much info as possible. Thanks for any help.
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Old 06-05-2011, 06:38 PM
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Sounds to me like detonation, look at the stator plate, should have a few marks on it. Also on the case it should have a pointer "arrow" Should be set in the center if I remember right. Also what kind of gas are you running in it?
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Old 06-05-2011, 09:16 PM
meg meg is offline
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Yes, the stator plate has a center mark on it and a line on the case to center it. There is a little adjustment left and right to change the timing. With the marks lined up center the engine timing was 55 degrees BTDC. I moved the stator plate counter-clockwise to retard the timing and it was still way off at 40 degrees. That would explain the detonation.
I'm wondering if anyone has had experience with timing being that far off and what could cause it?
Oh yea, I'm running premium pump gas with Castor 927 at 32:1.

Last edited by meg; 06-05-2011 at 09:23 PM.
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Old 06-05-2011, 09:48 PM
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I have no idea what it's supposed to be at degrees wise but i don't see how it could be out of wack if you have the plate in the correct spot. 55 degrees advanced that bike shouldnt even run I wouldnt think. You are using a lite for high rpm 2strokes ill assume? From what I have seen it should be 5degrees advanced

Last edited by bbrmotosports; 06-05-2011 at 10:01 PM.
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Old 11-22-2018, 10:19 PM
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Did you ever figure the timing issue out? I am having the same issue.
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