1981 YZ125H backfires and dies right off of idle.

dcfitz
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dcfitz
Just put a new stator on my 1981 YZ125H and it starts and idles fine, but when I begin to open the throttle it backfires and dies. It was running fine a month ago, before the stator meltdown episode. Iv’e tried two different CDI units on it with the same results. Is it a timing issue, or is it flooding when I open the throttle a bit?
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newmann
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newmann 10/12/2018 5:18pm
10/12/2018 5:18pm
Timing good? Reeds okay? My 81 YZ250 would backfire when starting and I found the new VForce carbon reeds were shattered. Put the stock Reed cage in and all was well.
dcfitz
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dcfitz 10/12/2018 5:31pm
10/12/2018 5:31pm
I just restored the bike. New top end, fiber reeds, etc. The first time out, the stator melted down. A dumb assembly issue, so I put in a brand new stator. All was good, before the stator meltdown. Not sure what the issue could be. I guess the fiber reeds could have shattered. I’ll have to bust it down and inspect, I guess.
dcfitz
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dcfitz 10/12/2018 5:37pm
10/12/2018 5:37pm
Oh, and the timing should be fine, as I set it to the factory specs with a dial gauge.
MaxPower
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MaxPower 10/12/2018 11:48pm
10/12/2018 11:48pm
could that stator be bad? I know you just put it on. But it sounds like a bad stator

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dcfitz
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dcfitz 10/13/2018 11:21am
10/13/2018 11:21am Edited Date/Time 10/13/2018 11:21am
The ohm readings look good on it. Plus it starts and idles fine. Just when I crack the throttle open, it huffs and dies. I’m going to recheck the timing and check the pilot jet on it.
dcfitz
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dcfitz 10/13/2018 1:43pm
10/13/2018 1:43pm
I pulled the carb and checked the float level. It checks out. Also cleaned some crud from the carb and blew all the jets and passages with compressed air. I reset the timing and it’s still doing the same thing. Also pulled the reed block and the fiber reeds are like new.
dcfitz
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dcfitz 10/13/2018 2:31pm
10/13/2018 2:31pm
Correct me if I’m wrong, but when you roll on the throttle from an idle, the pilot jet kicks in, right? I thought it might be clogged, but it’s not. One of you suggested the new stator might be bad, but all it does is generate voltage and send a signal to the CDI to fire. If it’s starting and idling, I would think the circuitry is working fine, there. The only thing I haven’t swapped out is the ignition coil. Although, the ohm readings are good on it.
project racer 10/13/2018 4:36pm
10/13/2018 4:36pm Edited Date/Time 10/13/2018 4:50pm
dcfitz wrote:
Correct me if I’m wrong, but when you roll on the throttle from an idle, the pilot jet kicks in, right? I thought it might be...
Correct me if I’m wrong, but when you roll on the throttle from an idle, the pilot jet kicks in, right? I thought it might be clogged, but it’s not. One of you suggested the new stator might be bad, but all it does is generate voltage and send a signal to the CDI to fire. If it’s starting and idling, I would think the circuitry is working fine, there. The only thing I haven’t swapped out is the ignition coil. Although, the ohm readings are good on it.
Where is the air screw setting ? More than 3 turns out, pilot is too big. Less than 1 turn out, pilot too small. Crank the air screw in and see if it has any effect on the running. It should richen the low speed jetting noticeably if the pilot circuit is clear.

If no change, back the screw out 3 turns ,and try again. Basically trying to see if richening or leaning the mix has any effect. Can even move the needle clip a spot each way if needed.
dcfitz
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dcfitz 10/13/2018 4:49pm
10/13/2018 4:49pm Edited Date/Time 10/13/2018 8:28pm
I’ll check. Here’s the thing. My son and I did a partial restoration on it. It was running fine before the stator meltdown. So, I’ve made no changes to the carb settings since then. I would think it would run the same now that it has a new stator. Thanks for the idea, though. I’ll check it out.
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dcfitz
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dcfitz 10/14/2018 8:33am
10/14/2018 8:33am
The stator is From Ricky Stator and is new. The two CDI units I have are the original one from the YZ and a used one from a running bike, same as mine. Both the CDI’s have been used and they make no difference.
riv187
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riv187 10/16/2018 6:51am
10/16/2018 6:51am Edited Date/Time 10/16/2018 7:07am
I saw a 1986 cr125 couple years ago on here with fellow suffering like you. Total engine rebuild, done right. The thing backfired didn't run right. Owner was requesting a carb to try. I suspected the stator...No he said- "it's new,,coil under tank is new as well". I was going to send him a carb(even though I believed it wasn't problem) but offered to save the fellow more headaches and buy the bike...on arriving I seen the new coils,,and immediately took off the stator plate and put on a stock old one. It fired right up and ran great. To prove which coil was bad,,I swapped the trigger one with new one and guess what..ran crap and sputter. The 'new' trigger was not timing bike same as OEM.
On another bike 79 RM125,,I got one rewired and the bike did same thing...the shop installed and soldered the coils on upside down...putting bike out of timing...When I spun the stator on that one 180* it ran...problem was now wires on wrong side to reach out of cover correctly...
dcfitz
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dcfitz 10/16/2018 8:41am
10/16/2018 8:41am Edited Date/Time 10/18/2018 3:49pm
Thanks for the input. I believe I am just going to order a complete HPI system to replace everything electrical. This should solve my problem, all together.
dcfitz
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dcfitz 10/21/2018 4:07pm
10/21/2018 4:07pm
I installed the HPI ignition system and the YZ runs like a bat out of hell!!! I should have ordered this kit, a long time ago!!!

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