High idle help...

Hey guys,

New to the forum...

I picked up a 23K mile 1996 VFR last fall. Rode it a few times, then out it in storage for the winter. Took it out last weekend. Fired right up and held idle, but one of the carbs was dripping gas.

So this weekend I took the carb structure off, cleaned everything a piece at a time - found the likely cause was a machine csrew missing from the bottom of one of the float bowls...

So this AM i put it all back together, start it up. Starts right up - DRY which was nice, but the idle JUMPED right away to 4500... One a stone cold bike... No choke, no issues with choke...

HELP!!

Thanks in advance,

Paul

 

The first question would be where is the idle screw adjuster set? And are the throttle cables installed without enough slack?

 

idle screw backed all the way off the stop

throttle cables re-installed exactly as they were. Just removed the 2 machine screws holding the throttle in place on the assembly, then reattached. No issue there...

just re-started with the airbox off... if i physically cover all the stacks one at a time, no change on any except #1... if I cover #1 stack, the idle drop to around 2500... (???)

 

also sprayed wd40 at the boot of #1... no change...

Totally perplexed...

 

On the bright side, at least your bike runs!

Where are the throttle butterflies sitting with the twist grip closed? Are they all nearly 100% shut?

Did you change the fuel screws at all?

What about the float height?

 

LOL ain't that the truth... Thanks for the perspective.

Yeah, the butterflies are even across the set, and essentially closed. Took off the assembly and took some pics. Should be attached...

Didn't TOUCH any of the fuel screws, jets or anything. Just pulled the jets to clean, then reinstall.

Float height is OK I think. I weighed them all at ~6 grams each when I had the carbs apart. No anomalies there. Float valves / springs all seemed operable.

The bike idled just fine prior to this... fix the damn leak and then this? Hoping it isn't a totally unrelated thing with impeccable timing.

 

Are you really sure the throttles are closed? That 4th image looks like the butterfly is more open than I would expect for idle.

AFAIK the only reason for a high idle is more air entering the engine than it should, so either a major air leak or the butterflies are open.

 

You're more eagle-eyed than I am! I am used to old-school Mikuni round-slides, which are very easy to measure for idle height...

No matter, your logic is of course rock-solid. It definitely makes sense its one of those two. I've left the shop for the night, but will affirm in the AM.If you're referencing the body in the left of image 4, that is the one that responds to choking out the velocity stack, soooo... you may be onto something!

 

Air leaking between the carbs and the intake will also increase the idle. How do the intake boots look? Are they hard or still pliable? Any cracks means replacement is necessary.

Hopefully it is only an unadjusted butterfly.

 

Hey. Yeah, they're not bad, really. Plus I sprayed looking for leaks at the boots, and found none...

 

I took another look at that photo, and it looks like the screw from the carb boot band is making contact with the closing spring? Might pay to reposiotion these so there can be no interference.

 

I just thought I would provide an update. You nailed it, Terry.

I took the assembly off and rearranged every single butterfly valve, backing them all the way closed and then opening them similar screw rotations.

I set the idle screw intentionally hi just to get it running, and within seconds I had a bike that runs smoother than it did the day I bought it last fall.

Greatly appreciate the additional input and extra set of eyes. You guys really came through.

 

That is great news. Glad that we found your problem together, and learned a little in the process.

 

Yeah I think rather than fix it correctly before, he set the idle of #1 high to compensate for another issue. I'm finding I'm cleaning up a fair bit of hacky work.

 

our Terry scores another touchdown, goal, basket, hole-in-one !! good work, matey !! :loyal: