All,

My 99 F4 has been fouling plugs ever since I started working on it after being idle for a couple years. This particular bike used to be my track only bike around four years ago. Since I moved to a different state I haven't rode it almost at all and decided this year to put it back on the street.


Upon starting, the bike will only start when the choke is on fully. It takes about 1 minute to get the bike able to idle without choke, however idle is very rough.

Upon further inspection certain cylinders aren't firing. So far, this seems to be random, however last night I think I was able to make some headway on that front by swapping coil sticks from the offending cylinders with the running cylinders.

What I've done so far:

Before I tried starting the bike up a couple months ago, the carbs were cleaned thoroughly. All gas and air passages were cleaned with cleaner and compressed air where necessary. I've done this three times now. I am confident that the carbs are 100% clean.

When I inspect the spark plugs from the cylinders that aren't running, they are wet with gas. This leads me to believe that each cylinder is getting fuel.

The spark plugs were changed before I started working on this issue so they are effectively new.

The A/F ratio when I was racing this bike was at 2.5 turns out. When I started diagnosing the problem the A/F was at 2.5 turns out. I've since tried it at 1.5 and 1 turns out with no luck.

I am getting great spark when I pull the coil stick and the plug to test it at a ground point. Each coil stick/plug has consistent blue/white spark. One thing I've noticed is that if I put the coil stick without a plug next to a ground and move the coil stick around, I can get it to arc at the edge of some insulation. As an electrical engineer, I suspect this to be a normal phenomenon due to the high voltage present at the tip of the coil stick, even though it is designed as a high voltage insulator.

Some results:

Last night it was running on cylinders 2 and 4. When I swapped coil sticks, the issue seemed to follow the coil stick. But in the recent past, I've had any/all of the cylinders not fire properly, so I can't say without doubt that the coil is the problem.

At this point, I'm nearing the desperation of starting to just purchase parts and throw them at the motorcycle to see what sticks. New coil sticks are a little over $100 but I'd like to avoid that until I try everything to diagnose the problem.


So...any thoughts? Any places to look besides the spark plug end of system? If I'm getting good spark outside of the cylinder, is it possible that the coil insulation is breaking down and arcing on the wall?

 

For posterity...

I figured out the issue last night.

While doing the multiple carb cleanings over the past few months I overlooked the importance of resetting the throttle position sensor correctly. The TPS has a standard resistance at 0% throttle of around 500ohms. Mine was reading around 260ohms. So I unscrewed the little security screws that hold the sensor in position and repositioned it while reading the resistance to make sure it was in the correct position. After repositioning it I put the carbs back on, put some gas in the pump and she fired right up.

 

Nope!!!!!

I tried to start the bike back up the next day and it was only firing on three cylinders.

Day after that it was firing on only two cylinders. The cylinders that weren't firing had plugs that were wet with gas.

So, still looking for hints before I buy new coils.