Rough idle when hot (only when the fan comes on)....WTF!!

So, I've been commuting to work on my '93 VFR last week and this week and traffic has been fine and the bike has been running great. Getting between 42-48mpg. Great ride.

Yesterday morning and this morning traffic going on base was backed up so I would end up waiting in line for a few minutes. Once the temp. gauge gets to the halfway point and the fan kicks on the idle gets really rough and eventually drops too low and it dies. She fires right back up though and the rough idle process starts all over. Once I get the bike moving and the fan shuts off she idles fine at stop lights until the temp rises and then the process starts over.

At first I thought the carbs needed sinking but I ruled that out since she starts up fine when cold and idles fine when warming up. I'm thinking it has something to do with the fan since it starts when the bike gets warm enough for the fan to kick on. I don't know why that would happen though since the fan doesn't pull that much juice does it?

Suggestions? Ideas?

 

Do you have to use the choke to start it when the engine is cold? If not, what is your idle speed?

What is the battery voltage right now with everything off? What is the voltage when at idle, and at 4000 rpm?

 

My bet is either a weak battery or the alternator or voltage regular needs to be replaced.

 

Hmm, interesting. The issue has been happening for the last 1000 miles though and I have not put the battery on a tender. Would the battery have held out by itself for the last week (1000 miles)? I'll check voltages tomorrow when I have some time I'm thinking the battery is getting charged.

I use a lil choke when cold but only for a second. My idle speed is right at 1100.

 

If the bearings in the fan are going out, then the additional friction is keeping the fan from spinning up to full speed. This would create a high current draw situation that just might be enough to pull the battery voltage down while idling such that the bike cannot keep running. Get your hand in there to feel how much resistance to turning the fan manually.

If the carbs/pilot jets were clogged then you would likely need lots of choke to start it and it would be running very lean at idle, maybe too lean to keep running, but that would be all the time, not just when it gets hot.

The mixture screws might be set on the lean side, but it would probably be backfiring and popping quite a bit while accelerating and decel all the time and even worse when hot.

It may be an air leak that opens up when the bike gets hot that leans out the mixture and causes the rough idle and stalling.

 

I'll check the fan. I'm also going to check vacuum lines. I was thinking about just de-pairing it but I don't have a block off plate. Anyway, some recommended checking voltages. I checked the battery this morning with the bike off and it's at 12.7 volts. That's after 1000 miles in 7 days and no charger or tender hooked up.

The carbs and mixture screws should be fine since. There is not back firing or popping.

I'm leaning towards something with the fan but a air leak somewhere might be it also. I'll do some more digging later this afternoon.

 

De-Par! You can take off the plates after you cut off the metal tubes and plug weld them. Once thats done, simply re-install using the old gaskets, no sweat. You may wana get a Dremel cut off tool to get to the rear cylinders, its a :bs: system and makes everything much more sanitary. My bike runs better since I axed that crap. Far as the plenum plugs, you can use an appropriate screw with crush washer and everything should be good.

I think you need to look at your plug from your stator (three yellow wires from right side of bike) makle sure nothing is burned out/ should check battery voltage while its not running, battery voltage while its running, then rev it top 4500 and measure battery volts.

 

Disconnect the fan and go for a ride to see if the problem goes away or remains--plus it's more fun than surfing the web looking for porn...

 

Once the temp gauge got to the half way point the same issue came up. Rough idle and it was starting to die. I noticed the fuel filter (clear FRAM) was nearly empty and a lil foggy. I then remembered on my VF1000R that I was using that same type filter on, once the engine got up to temp the fuel wouldn't flow through the filter.

I pulled the fuel filter off, re-routed the fuel line and let it warm up to temp again. The fan cycled 4 times and the idle never got rough. I'm pretty sure the problem is fixed. The culprit, fuel filter......again. I'll now for sure when i sit in traffic at the navy base gate on Monday. Thanks for the suggestions though everyone.

I still plan to de-pair over the winter but for now, I wanna ride.