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DRZ Runs, Backfires and Dies

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First off, thank you everyone for your input to this site, it took an issue for me to make an account but I have been getting info off of this site for well over a year.

So I have an ongoing issue on my '01 DRZ400S. The bike on two occasions now will run fine, then after 10-40 miles start acting as if low on fuel, backfires several times and finally dies. It will take a few minutes, but then will start fine and once again dies after a mile or so. After the first time, I took off the tank, petcock, carb and lines, cleaned them out with no obvious issues found. I took it out for a 27 mile ride with no issues. Then took the second trip where it died after about 40 miles.

This bike has had the CA emissions removed, free power mod completed, and I had put in a new stator before this issue came up with loctite fixes. Otherwise the bike is stock. After the second time it died, I have checked the spark plug, cap, ignition coil resistance, stator resistance, pickup coil resistance and signal coil resistance. Everything is within specs. I have been told it may be the CDI, but then saw here its not an issue on this bike.

Just need some input as to where to go from here. I don't want to start throwing money at it if I don't have to.

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1 hour ago, Backwoods-Bomber said:

Fuel in oil. Carb float seat o-ring needs to be replaced.

The first time it happened was after I had filled up with gas and may have put in too much. Would this have cause the fuel to go into the oil?

I'm not sure what o-ring you are referring to. Is it the needle valve o-ring?

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The first time it happened was after I had filled up with gas and may have put in too much. Would this have cause the fuel to go into the oil?
I'm not sure what o-ring you are referring to. Is it the needle valve o-ring?

Overfilling would not cause it. This is a very common problem.

The float needle seat o-ring fails, allowing fuel to flow past the float valve even when it is closed.

This is the o-ring that seals the brass float valve seat against the carb body. Most folks replace the stock rubber o-ring with a fuel resistant vitron o-ring. These are available in multi-packs at most auto parts stores.
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Sorry it took so long, but family business has had me busy.

After changing out the oil and the o-ring, the bike still dies after ~30 miles. Bike restarted after about 10 min. and died after a few hundred feet.

I was given the idea that the CDI could be overheating by my father in law. I moved the CDI to the side of the bike for better airflow and went for another ride. I got to 34 miles, after which I placed some ice in a bag on it for a few minutes. The bike started up after 3 min. I only was able to go for another 2 miles, but this was better than the last time.

At this point I am looking at a new CDI, unless there is some other ideas I could try. 

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It isn't common for the cdi to go but as with all electronics there will always be some . It would be nice to borrow one before buying to know for sure . When it dies , you can quickly test for spark . The coil can also become hot and fail.

 

Gas in the oil shows itself as soon as the motor is getting up to full temp and will run under heavy throttle but die at idle and not want to restart . It won't wait 30-40 miles to cause trouble . You should look into replacing the o-ring under the needle valve anyways and possibly replacing the petcock with a manual one or rebuilding the stock one , they both fail which causes the gas in oil issue, nice to replace/rebuild early before it suddenly lets you sit and do it at a time that's convenient, depending how old the bike is .

 

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Edited by jjktmrider

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1 minute ago, jjktmrider said:

It isn't common for the cdi to go but as with all electronics there will always be some . It would be nice to borrow one before buying to know for sure . When it dies , you can quickly test for spark . The coil can also become hot and fail.

 

Gas in the oil shows itself as soon as the motor is getting up to full temp and will run under heavy throttle but die at idle and not want to restart . It won't wait 30-40 minutes to cause trouble . You should look into replacing the o-ring under the needle valve anyways and possibly replacing the petcock with a manual one or rebuilding the stock one , they both fail which causes the gas in oil issue, nice to replace/rebuild early before it suddenly lets you sit and do it at a time that's convenient, depending how old the bike is .

 

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Unfortunately I don't have one to borrow. Seems like all of the aftermarket ones are garbage. I'm considering getting a used one from ebay.

Is there any way to check the coil?

The oil in the gas idea was just something to try. This last test ride i noticed the bike dies faster the more the throttle is applied. In neutral it will idle, but after some throttle it dies. I've been dealing with this issue for months and I'm willing to try anything within reason at this point.

As a side note, I did have a bad stator before, which I replaced. It was several months between this issue and the bad stator though. I've checked the battery each time after these test rides. I'm at around 13 volts at the end of the ride at the battery terminals.

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Many of the cdi failures I've found has shown up by either running fine up to 3500-4k rpms then hitting a wall and backfiring , or simply no start issues often ok when cold but trouble once warmed up , probably the reason your father-in-law suggested it . It doesn't sound like it if the motor will idle but then die when giving gas ,that acts like a carb thing more than cdi(ecu in this case)or even coil , but with this type of ecu anything is possible. Have you opened the gas cap when it won't run right to see if there is a vacuum being created ? that would be one test to try or run with the cap loose (and low'ish fuel level ,watch for leaking). Also when it shuts down , quickly open the bowl drain screw to see if there is good and consistent flow .

 

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Edited by jjktmrider

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1 minute ago, jjktmrider said:

Many of the cdi failures I've found has shown up by either running fine up to 3500-4k rpms then hitting a wall and backfiring , or simply no start issues often ok when cold but trouble once warmed up , probably the reason your father-in-law suggested it . It doesn't sound like it if the motor will idle but then die when giving gas ,that acts like a carb thing more than cdi(ecu in this case)or even coil , but with this type of ecu anything is possible. Have you opened the gas cap when it won't run right to see if there is a vacuum being created ? that would be one test to try or run with the cap loose (and low'ish fuel level ,watch for leaking)

 

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The initial 30 miles worth of riding the bike runs fine through the RPM range. The 3.5-4k RPM mark is where I am at when it backfires after those first 30 miles. I opened up the gas cap the first time it happened, it didn't help.

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