Another Carb Question Thread VF500...

Interesting technique for dialing the pilot screws.

Thanks for the tech tip.

 

Like IC says, mixture screws are mostly used to control A/Fmixture at idle and a bit above, and don't have much influence above 3000 rpm.

your diaphrams are correctly seated if the slides vibrate and move up with throttle.

It's important to try to isolate the problems to one cylinder if you can, and that should be apparent from plug inspection.

Just throwing this out for consideration: since engine runs with mixture screws closed, it's getting fuel from somewhere else other than the idle circuit. Most likely source of fuel would be dribbles coming from the main jet holder tubes, and that would be caused by improper float setting, leaky float valve needles, or possibly fuel getting into carb past worn needle valve O-rings. Each brass needle seat has an O-ring around it, and can leak if deteriorated, so pull them out and inspect, possibly replace O-rings if you can find the right size.

It's rare, but it can happen that even if floats are set right and needles are OK that excess fuel can get in around the needle seat no matter that the needles are shutting off fuel flow.

 

Well noted.

 

Well, I have been riding the bike since the last post. It will not idle, pilot screws are turned out to 2.75 turns, it will idle when cold with the choke on.

The bike runs smooth, except for a very weak zone between about 5K-6.5K, after that it is ready to go, although I have yet to get it above 8000 RPM's with the engine only having 275 miles on the engine rebuild.

I took the plugs out yesterday, and had a few questions on what i'm seeing. The pictures are, as if you are sitting on the bike, they plugs go in order, front left is left, back left is 2nd from left right back is 3rd ect...





So what do you get from those, the plugs have around 250 miles on them, and between 50 and 100 of those are since the carbs were last off. So what direction would you suggest I head next?

As always, thanks for the help!

 

They look pretty close. I would be more concerned about this dead spot that you have. The VF500 acceleration should be smooth and linear and there should be no flat spots like that.

 

Apologies for resurrecting an old thread. I do it only because despite so much discussion on how to adjust the pilot screw people still struggle with it in many a thread here and on other forums. This technique does sound promising and different to all the other ones I've read about.

However, I failed in my attempts at following your advice: as I turn the screw in the RPMs simply decline with no audible change to engine smoothness and the bike dies due to low RPM at around 600. Thinking that my baseline idle is set too high (~1700) - letting airflow pull too much fuel - to work with this procedure I tried playing with it but got more or less the same results.

Am I doing something wrong or does this only work on some bikes?