The last two times we've ridden our '03 Z400, it runs fine for an hour or two, then starts to run really poorly (no power, stalls when you give it gas, sounds terrible). The first time it happened, we were on vacation in Utah, and had filled it with the lower (85) octane regular gas sold there. I was hoping the problem was due to the higher altitude and/or the low octane gas - although our other 03 Z400 didn't have a problem, and they had both run fine for several rides that week.

We took the problem Z for a day's riding last week, and it seemed to be fine for the first couple of hours, then had the same problem. I had drained and replaced the low octane gas before this trip. This time, when it started running poorly I was barely able to keep it going long enough to crawl back to the trailer. I could barely nurse it along - especially if there was any incline, although it would sometimes seem to regain power and run well for a few seconds before it would lose power or stall out again.

The plug was very black when I checked it. I put in a new one, and it seemed to run a little better, but still no where near normal. FYI, it was a very hot (100 degree) day and we rode through creeks several times before the problem started. When it happened in Utah, we had also run though some water, and it had been ridden pretty hard for a couple of hours before the problems began.

FYI, our Z400s both have Yoshimura pipes, K&N filters, and no airbox lids. I believe they were rejetted for these (per the previous owners). They have both run great on numerous trips until this problem.

As you can probably tell, I'm a rookie when it comes to working on these, so any suggestions (no matter how obvious) are welcome. I've spent a lot of time looking through other posts to try to figure this out, and some possible ideas I've come across are:

- Clogged drain hole that traps water around the spark plug and causes problems.
- Fuel filter clogged, or some other fuel line obstruction.
- Debris in carburetor float bowl.
- Gas tank vent plugged.
- Clogged air filter.
- Bad coil or stator may cause this after warmup (I wouldn't know either of these if you handed me one).
- Engine overheating (change/add coolant?).

That last item reminds me, I put a new clutch in this quad a few weeks ago. In the process (rookie mistake I'm sure), I let some of the coolant leak out. I subsequently added water and some automotive coolant when I noticed the overflow was empty. Now the overflow always seems to have some, but I'm wondering if I should drain and refill the whole system. Would overheating cause this?

Thanks for any help you can provide - it will be much appreciated.

Doug

 

definately do that...clean ur carb, its not the plug water thing...maybe your air filter...or a gas line thing but definately clean the carb and when u go into high altitudes you run rich because there is less air up there...

 

This might sound crazy but check your ignition module, and check your t-stat.

First make sure it is not simple a overheating issue. Since the quad has sensors it may have a "limp" mode built in if it gets too hot, to keep you from blowing the engine the ignition will be staggered to cut spark.

Also make sure there are no cracks in your ignition module itself. If any water gets in there it's a problem. That sucker has to be virtuall air tight, even condensation will cause a problem.

Any ignition issues will fry a plug like you described.