1986 VFR750F fast idle. Can anyone help?

Hi all.

Recently bought a co-worker's 1986 VFR750F. It's in really good shape (2600 KMs) and hasn't been run in over 14 years.

After cleaning everything I've pulled the carbs and cleaned out the junk, made sure they move freely and all 4 chokes are operational. At first when I started it up it wouldn't run without the choke fully on and the throttle pushed far closed. After a lot of perseverance and a volt meter I found that some jackass disconnected the tach cable. Yay me!

Now I got her up and running reliably. But she idles at about 2000K. That's pretty high. Not only that but even after shoving the throttle forward it will spring back to about 1900 to 2200 depending on how warm she is. I've got the manual and I set the idle screw so the stop doesn't even touch it. I've adjusted the throttle cables so it's as loose as it can go. She still rears up to about 2000K RPM.

If anyone has a moment to please fire ideas my way. I'm all ears.

Please and thank you.

 

Did you clean the air port passages on thie intake side of carbs sound like they might be clogged?
I had a 85 vf700 and mine did same thing I cleaned ports and all went back to norm.
Hope this helps.

 

As jafo said, make sure your pilot jets and circuits are clear and pilot screws are 2 1/2 to 3 turns out. Also, you should check/adjust valves. After all this, the carbs must be synchronized. Good luck.

 

Hold on, cowboy; that ain't right !!

In order to actually control idle speed the adjustment screw MUST come to rest touching the stop.

 

Well, exactly!

I have to push the throttle all the way forward (clockwise) to make it behave.

I rode it around yesterday. She runs and sounds beautifully but still creeps up over 2000 RPM at a stop, or in neutral (sometimes up to 3000).

These forums are a gold mine. I've got a full checklist now:
-Check for kinks and re-lube the cables.
-Check carb boots for air leaks
-Pull the carbs again and clean all the jets

I've got gauges to do a dynamic sync but I've never actually performed one before. Wish me luck.

 

You read my mind.

 

my 83 VF750F is doing the same thing, gotta dig into it soon...thnx for the tips

 

BEER !!



Did it again !

 

Curious. I'm in the middle of cleaning and all the jets (mains and pilots) are pretty firmly seated when I removed them (screwed all the way in). You mentioned installing the pilots 2.5 to 3 turns out. What does that accomplish?

As well, I've done a bench sync to make sure the butterfly valves are opening the same amount but carb #1 does not close all the way. I think this may partially explain the high idle and my ability to slow it down by pushing the throttle forward. If I manually push the throttle body a little I can get the #1 butterfly valve to close all the way. Is there an adjustment for this?

Gentlemen I thank you for the advice. Should we ever meet, beer's on me. FER SURE.

 

Maybe I read you wrong - JUST TO CONFIRM.... do you mean the pilot JET or the pilot SCREW? Sorry for sounding like a newb but I don't wanna mess this up.

 

Idle jets must be screwed in tight, but idle mixture screws should be about 2 1/2 turns open from closed (fully clockwise).

If all throttle plates don't close equally, synch is impossible, and would account for the fast idle problem. From the master carb (#1) with idle adjustment screw, the other carbs are set using the synchronizing screws.

If the alloy airbox base was removed from the carb set, some springs might have been lost.

 

OK. I'll clean and reseat all the jets fully. I'll check how the pilot screws are set, or go through the "idle drop" procedure in the book.

Assuming that all the throttle plates are SUPPOSED to close 100%, the #1 carb remains open a teeny bit. I can adjust the other 3 closed 100%. That's how I first noticed the problem, by trying a bench sync.

If there is no adjustment for this, what are my options?

I know it sounds silly, but could I try to bend the plate a tad? The base was never removed and the carbs were never separated. I honestly can't explain the situation with this throttle plate......

Thanks again.

 

Follow up:

I moved the spring aside on the very last adjustment screw's plate. I bent the plate up a bit so the first throttle plate would close fully. Then manually synched them all with some tiny feeler gauges. The throttle will ACTUALLY come to rest on the idle screw now.

Two of the pilot jets were gummed. One had crap in it. Goes to show - even though a bike RUNS, it may not be running a well as it COULD. :crazy:

I think the pilot screws need a tad bit more adjustment once I get her out for a quick burn but she's running strong now.

All I can say is, this was a bit of a chore, but it was TOTALLY worth it. The bike sounds amazing now and the throttle response is sa-weet!

Cheers!

 

I LOVE A HAPPY ENDING.