Pilot jet question

Just cleaned and re-installed carbs on '85 VF750F. When i bought the bike pilot covers had already been drilled. What is the best procedure to adjust pilot jets? They are currently at 2 1/4 turns. The bike runs great and pulls well over 6000 RPM, but is rough on take-off, and lacks a little mid-range.

 

Welcome to the world of vfr...

Do you have to use the choke to start your bike or does it fire up without the choke when the engine is cold?

Those are actually the mixture screws to which you are referring--the pilot jets are screwed into the carb body from the bottom after removing the "bowls" i.e. the float chamber covers. You can click on my user name to go to my profile and pull up the latest started threads to find some pictures and info on the location of the carburetor circuits.

Do you have a service manual for your bike? Use the search feature to find the link to download it if not. It contains a detailed procedure for adjusting those mixture screws and the idle such that it will run good and not waste fuel running too rich. Use the search feature for "cleaning carbs" to find some excellent instructions and pictures of this task and check that you did it correctly.

 

It fires up with no choke, therefore too rich, correct? I will check the manual as you suggest. Thanks very much for the info.

 

Yes the mixture screws are too far open or your butterfly throttle valves are open. What is your idle speed at it warms up and settles in?

 

At 2 1/2 turns it would idle high for a few seconds then settle down to a regular idle. On take off, it would sputter and run rough for a few seconds. I re-adjusted the screws following the manual as you suggested, although I didn't have a proper tach. Now the screws are at 1 3/4 approximately, with great improvement, and smoother power up to 5000 rpm, The idle is now even and regular. What would be the symptoms if it is too lean? Should I re-do with a better tach? Thanks for the help.

 

Stalling, misfiring on acceleration, backfiring on deceleration.

If it is adjusted fairly well and close to ideal then you will need to use choke to start, the idle will be as low as possible yet steady when warmed up, and the throttle butterfly valves will be closed. The purpose of the idle adjustment screw is to keep the bike running while you make the mixture screw adjustments, not to "set" the idle speed. The mixture screws are the correct way to set the idle speed.

Ride it for a while to get a feel at this setting or tweak it down leaner to see how that feels also. Now that you know how it's done you can make adjustments and monitor the effects until you get it how you like it.

 

I'm facing an issue all of a sudden; when my 84 VF1000F is cold it runs great. After about 10 minutes cruisin' the power cuts about in half and the tachometer drops to zero and it won't idle. It gets really sluggish. Once it cools down again it's back to normal.

Anybody else experience somthing similar? I've tried putzing with the pilot screws in the carbs but it doesn't seem to help.

Thanks!

 

^^^ That's electrical, like an ignition coil or pulse generator or maybe CDI box screwing up.

Hey, there's a nice VFR just across the border in Madison, Wisconsin on CL !!

 

One more thing I discovered yesterday; if I rev high with the clutch in, everything comes back to normal. So confused!