4th Gen Dying under throttle when engine is warm

Hello citizens of VFRD,

I'm a new member here, but that's not what this post is about...

Now that the weather is starting to get halfway decent, I figured it's time to diagnose the issue with my bike that presented itself at the end of last season... Engine was warm i didn't just start revving the snot out of it while cold. The fluctuation in rpm and the engine dying completely all happened with the throttle at about 3/4. It's a fuel or spark issue. I thought maybe a clogged tank vent but same symptoms persist when running with open gas cap. When I go to restart the bike, won't run unless I twist throttle pretty good which results in large fireball out of muffler (neat but still an issue) then it idles normally. Give any kind of throttle and it's a repeat of the video. Bike is a 96 VFR750.

I'm leaning towards petcock and or fuel filter, may also also be plugs/coils. I hope it isn't carb related because those are absolute voodoo witchcraft to me. Any help or suggestions would be greatly appreciated.

This is the only video I have of the issue at the moment.  

I would start with the fuel filter then checking the pump. Hard to say from there.

take the top cover off the fuel pump and see if it does this:

http://vid113.photobucket.com/albums/n206/Dutchy_748/VIDEO0064_zpscda3d494.mp4

the "points" on top should be "clicking", for that is how the pump operates, by having the inside come up and by "shorting", lest it slide back.

IOn the vid you see the brand spanking new points.

Thanks for the reply Dutchy. Just saw this. Haven't had access to internet. I'll check that next time I get home.

Finally back state side, I have all the fairings off. How do I take the cover off the fuel pump?

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Fuel pump also appears to have a Mitsubishi logo on the top? [image: 450e0b22d6f43c4cae7efa7dad0603bd.jpg]

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I assume you've got a vacuum petcock on the 4G; if that is giving grief (e.g. not opening fully due to debris or age/perishing) then I suspect you'd have a similar problem. So check the vacuum line is intact with no cracks or splits, then try applying vacuum (a  good mouth suck would do) and see if you get a good gravity fuel flow through the petcock. They are not difficult to rebuild, and are a known failure point on many bikes (my VTR1000 and ST1100 for example) with age. 

Mouse nest in snorkel. This may actually be the cause of my problems. Air starvation... [image: dcab6627a0c2a3ce042c0df0d9d6c01f.jpg]

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3 hours ago, bdutton

Mouse nest in snorkel. This may actually be the cause of my problems. Air starvation... [image: dcab6627a0c2a3ce042c0df0d9d6c01f.jpg]

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I've sung that song a couple of times. Made for rough running every time. 

So I'd recommend everyone check for this when buying any used Honda. Esp. with bikes stored in pole barns.

Those damned rodents again !!  You might need a proper carb cleaning.

squirrelman Those damned rodents again !!  You might need a proper carb cleaning.

Started to put the bike back together just for kicks before even touching the carbs. Some combination of replacing the fuel filter, fuel pump, spark plugs and air filter including removing the mouse nest, has caused my annoying misfire to go away. Now it goes to redline without hesitation. The throttle is on the sticky side now however. Gonna pick up some dry graphite lube tomorrow and hopefully that alleviates the symptom.

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