I need your help here guys, this one has me a little stumped. My bike has been running great since my 20k service (which I did myself) and I changed bars, throttle/idle cables and replaced my plugs. Today however, not so good.

I rode to work on Monday, Tuesday, Wednesday, all with no problems. Thursday I worked from home, but today I went in. I needed to get gas, so I filled up at my normal station (Chevron, Premium 93 Octane) and went on about my business. The bike ran great going to work, no problems.

Now, when I came out to leave work and come home at about 1PM, she took a while to start and idled real rough. I racked the throttle a few times, and there was hesitation, but it was manageable. Once I got going the bike rode ok, but not great and twisting the throttle would result in some hesitation. Whenever I hit a light the idle was rough and almost to the point where I thought she would stall a few times. Taking off from idle there is some serious hesitation until you get the RPM up.

Now, to me there are a few of possibilities (bike is mostly stock, only XIED's and new throttle/idle cables):
1) Bad Gas - but if it was bad gas why didn't I have a problem on my 41 mile commute to work? Why only after it sat for a few hours? Contaminants needed time to settle maybe?
2) Vapor Lock - I don't know about EFI bikes, but I know on gravity fed carb bikes, on a hot day like we have regularly here in Central Florida, if the tank doesn't vent properly it can vapor lock and prevent enough gas from getting to the carb until vacuum demand (RPM/Engine Speed/Manifold Pressure) is sufficient to overcome the vapor lock and suck the gas out of the tank.
3) Air leak - I would think this one would have been evident from the point of my 20k service, but I'm open to the argument
4) Problem with XIED's - I am running XIED's and since they affect closed loop operation, this is a possibility to consider.

What do you guys think I should tackle first? Given the above scenarios, what do you think is most likely? Oh, it should be noted that after I got home I pulled the air cleaner cover and restarted the bike. It ran smoother, but still a little rough and hesitated coming off idle, but less than before.

 

You know if you did the 20k and bars like yesterday, I could see a connection to the throtle cable, or the plugs, etc. But if it's been running good for a week and now this just happened while parked and nothing else going on, I'd have to really guess it may be bad gas.

I have also not heard of vapor lock on the EFI models, but I am at 8k feet in the mountains, so what do I know about hot?

 

I did the 20k service several weeks ago, actually, Father's Day weekend to be precise. That's why I don't think it is related to the service, but I wanted to put it out there for full disclosure.

I am leaning toward bad gas too, it's just weird that it took so long to become evident. Normally with bad gas you know right away.

 

Bad gas can do some weird things to the way the bike runs. try running mid grade gas with an octane booster that is approved for the o2 sensors etc. I have had to do that sometimes here in the mountains. the premium gas here sits for months in the ground tanks. Also if you get gas right after the fuel truck has been there it can stir up all kinds of crap in the ground tank that will get into your gasoline when you fill er up.

 

Have you checked your battery cables? A 41 mile ride should have had driveability issues especially coming off highway speeds to surface street stop/go. If you suspect the gas dump the tank (siphon off) and try a different brand for a tankful.

 

Senior, it's not cutting out, just hesitating but checking the cables won't hurt. I'll do that in the morning. I'll probably just dump this tank and see where it goes from there. Unfortunately I don't have a lot of time to troubleshoot tonight.

 

Check plug leads and plugs as well , someone may have played with them , one of mates used to do things to my bike , its not funny after a nights work at 2 am in the morning , he thought he was clever , so i put a little piece of rubber inside one of his plug leads , it was small enough to get wedged in the without being seen, his bike ran like **** for weeks , i told him it was probably bad petrol , he drained his tank , messed about with the carbs and all sorts ....lol . then i said id look at it for him , after a day or to i told him id found the problem , it was the LMBA valve , he needs to get a new one , another day or 2 passes and he calls me , and asks what it stands for , because none of the Yamaha dealers have heard of it , so i told him , its a leave my bike alone valve , he got the message ,
its a long winded reply , but work mates can be arseholes ,

 

You can probably rule out the XIED's but it's easy enough to pull them and see if there is any change. Low fuel pressure can be a cause, either from a clogged filter or hole in the line.

 

You're not going to believe this, but it turned out to be the plugs. I tried out those E3 plugs this time and I guess I had them less than perfectly gapped. After all my other troubleshooting, I pulled them and checked the gaps, made a few adjustments and now it runs like a top again.