Horrible backfiring at mid rpms

Hello all. So I put a new motor in my DRZ (last one locked up) and took it on a few rides, all good. Rode it about 500 miles one day then went to take it to work the next day and after about 20 miles it started surging and backfiring really bad. Parked at work and went to ride home and couldn't go over 3000 rpm (estimate) without it backfiring like crazy. Got it towed home and didn't touch it for a while. Just now got to diag on it. Unplugged the stator and it still has the issue. Removed the spark plug and didn't see any marks on the boot indicating it grounding through it. Checked spark and it looked kind of weak(I'm an automotive mechanic so I'm used to real heavy spark). Tried switching tank to prime and no change. The bike runs perfect at idle then just starts backfiring when up above idle. I kind of suspect fuel but I hate installing the fcr39 so I refuse to pull it out until I know for a fact there are no other issues. Any other things to check? I have someone coming over saturday so I can try swapping the cdi box.

My guess is fuel also...what year of DR-Z are we talking about?

1 minute ago, Oldmossyspokes said:

My guess is fuel also...what year of DR-Z are we talking about?

2013. all parts except motor have around 13k on them. Motor supposedly only had 4k. If it ends up being fuel I think I'm just taking it to a shop. I refuse to put that carb in again. I pulled off the top cover of the carb and pulled the main jet and the needle and they looked clean. I'm not going to pull it to check the float. The needle is at clip 3. Its set up just how it comes from the TT store.

45 minutes ago, MoreBassXD said:

2013. all parts except motor have around 13k on them. Motor supposedly only had 4k. If it ends up being fuel I think I'm just taking it to a shop. I refuse to put that carb in again. I pulled off the top cover of the carb and pulled the main jet and the needle and they looked clean. I'm not going to pull it to check the float. The needle is at clip 3. Its set up just how it comes from the TT store.

My guess is an other stator bites the dust. Those are the symptoms when the pickup or ign charge coil acts up, very hard to diagnose. What did you disconnect the three yellow wire connector? 

Just I would hate to see you chasing you tail, replacing a bunch of parts without considering the stator.  I did all the factory tests on mine, they all passed and even used a DSO on all the wires from the stator, couldn't really see the problem, but my stator looked all crispy and burnt. So I closed my eyes and threw a new one in. Problem solved.

If you bring the rpm up till it starts back firing, then add some propane into the back of the carb. That will tell you if it's starving for fuel or not.

Edited by bucket list
17 minutes ago, bucket list said:

My guess is an other stator bites the dust. Those are the symptoms when the pickup or ign charge coil acts up, very hard to diagnose. What did you disconnect the three yellow wire connector? 

Just I would hate to see you chasing you tail, replacing a bunch of parts without considering the stator.  I did all the factory tests on mine, they all passed and even used a DSO on all the wires from the stator, couldn't really see the problem, but my stator looked all crispy and burnt. So I closed my eyes and threw a new one in. Problem solved.

If you bring the rpm up till it starts back firing, then add some propane into the back of the carb. That will tell you if it's starving for fuel or not.

Well I still have my old blown motor with a good stator in it. Might as well toss it in and see I guess because stator was my original thought. I unplugged the 3 wire connector with 3 yelllow wires. The idle came up a little bit when unplugged and seemed a tad smoother, I just attributed it to the slight hp draw from the stator.

9 hours ago, MoreBassXD said:

 I pulled off the top cover of the carb and pulled the main jet and the needle and they looked clean. 

From my experience I never see the problem in jets with my eye. Just clean them with air pressure and it is back to normal again even though there are no visible difference (to me at least).

Then again it seems to be strange to have a jet problem after riding 500 miles in that day. I've only had had problems after longer stay.

On 1/30/2018 at 9:50 PM, bucket list said:

If you bring the rpm up till it starts back firing, then add some propane into the back of the carb. That will tell you if it's starving for fuel or not.

Awesome idea. :thumbsup:

This is the same symptom that several different bikes get when either the cdi , pulse gen. or stator is bad . They'll run perfect till a certain rpm and then hit a wall . With the way the drz is setup and it being a common issue the stator would be a good guess at this point , cdi's going bad isn't a high instance on this model so it leaves the 2 .  There is a way to plumb more oil onto the stator to keep the heat damage down , but it involves knowing how much can be scavenged from the pump to not starve any other parts . 

 

 

.

Edited by jjktmrider
3 hours ago, jjktmrider said:

This is the same symptom that several different bikes get when either the cdi , pulse gen. or stator is bad . They'll run perfect till a certain rpm and then hit a wall . With the way the drz is setup and it being a common issue the stator would be a good guess at this point , cdi's going bad isn't a high instance on this model so it leaves the 2 .  There is a way to plumb more oil onto the stator to keep the heat damage down , but it involves knowing how much can be scavenged from the pump to not starve any other parts . 

 

 

.

Share more of this idea you have for keep or getting more oil to the stator to keep it cooler.

6 hours ago, jjktmrider said:

This is the same symptom that several different bikes get when either the cdi , pulse gen. or stator is bad . They'll run perfect till a certain rpm and then hit a wall . With the way the drz is setup and it being a common issue the stator would be a good guess at this point , cdi's going bad isn't a high instance on this model so it leaves the 2 .  There is a way to plumb more oil onto the stator to keep the heat damage down , but it involves knowing how much can be scavenged from the pump to not starve any other parts . 

 

 

.

Well I swapped the cdi today and it didn't fix it. I'm going to throw a stator in it tomorrow. I'll post back with results. What do you mean by pulse gen?

6 hours ago, bucket list said:

Share more of this idea you have for keep or getting more oil to the stator to keep it cooler.

You have to tap into an oil port and run an external line to the stator , drill through the cover(or inspection cap in center) to feed the oil to the stator . I did something similar on a hybrid motor to feed oil to the topend because I used a different topend than what the bottom end was designed for so the internal ports didn't suffice . A person has to make a banjo bolt with a specific size hole or an squirter nozzle to regulate oil volume so the other parts don't get starved , that's that hard part . 

 

The pulse gen is a hall sensor that send the spark signal to the cdi , it's down in the stator cover . If you swap out the whole cover from the spare it'll be with swapped as well with the stator.

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Edited by jjktmrider
9 hours ago, jjktmrider said:

You have to tap into an oil port and run an external line to the stator , drill through the cover(or inspection cap in center) to feed the oil to the stator . I did something similar on a hybrid motor to feed oil to the topend because I used a different topend than what the bottom end was designed for so the internal ports didn't suffice . A person has to make a banjo bolt with a specific size hole or an squirter nozzle to regulate oil volume so the other parts don't get starved , that's that hard part . 

 

The pulse gen is a hall sensor that send the spark signal to the cdi , it's down in the stator cover . If you swap out the whole cover from the spare it'll be with swapped as well with the stator.

.

Still kind of confused on the pulse gen... It it that hall effect in the cover connected to the stator? That picks up off the flywheel? I replaced the stator today (with the hall effect I assume you're talking about as it was connect to the stator) and The problem is gone. The outside edge of the stator, like if you looked at it as a cylinder it would be rounded outside part, was deteriorating. There seemed to be a coating over top of the metal on the outside edge and it was worn through on most of the coils, everything else looked okay. I'll grab some pictures if I can figure out how to post them.

Yep that's the pulse gen . Seems you found the culprit , stator going bad either from heat or age/hours or both .

 

 

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Edited by jjktmrider
39 minutes ago, jjktmrider said:

Yep that's the pulse gen . Seems you found the culprit , stator going bad either from heat or age/hours or both .

 

.

Kind of odd to me that the one that came in my new motor with only 3000 miles shit out and looked horrible meanwhile my stator out of my 15k mile motor looked brand new

On ‎5‎/‎02‎/‎2018 at 2:53 AM, jjktmrider said:

You have to tap into an oil port and run an external line to the stator , drill through the cover(or inspection cap in center) to feed the oil to the stator . I did something similar on a hybrid motor to feed oil to the topend because I used a different topend than what the bottom end was designed for so the internal ports didn't suffice . A person has to make a banjo bolt with a specific size hole or an squirter nozzle to regulate oil volume so the other parts don't get starved , that's that hard part . 

 

The pulse gen is a hall sensor that send the spark signal to the cdi , it's down in the stator cover . If you swap out the whole cover from the spare it'll be with swapped as well with the stator.

.

They actually are a reluctor pickup. Which is a simple coil of wire (many turns) that runs close to the flywheel.  As a chunk of metal passes close (such as one of the timing teeth on the outer edge of the flywheel) a magnetic field is generated then subsequently collapses as the metal disappears.  The CDI in our bikes looks at the timing of these flying chunks of metal and works out the engine RPM's and  when to fire the sparkplug.  I must admit I was somewhat bamboozled at first when I could not find mention of a separate part number for the pickup but I soon became apparent that is was part of the stator.  An other issue that I have come across that caused a very similar fault was water in the connecting plug, that, however, was on my green machine (KLX450r) that has an intermediatory plug in the wiring harness from the stator to the CDI - behind the radiator of all places.  Preventative dielectric grease now applied.  

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