Weird idling issue

One by one I'm picking these problems off, but now I have an issue with the idle. Here's the background: Carbs R & R multiple times now for cleaning, re-checking float levels, more cleaning, fixing a leak, more cleaning... you know how it goes. Now that the carbs are back on and the bike is running, it will idle fine for a minute or two, then slowly die. BTW, I"ve gotta give a "thank you!" to whoever is was that mentioned the helpful hint about positioning the rear carb boots to aid in getting the carbs re-installed on these bikes. Just wish I had been aware of that 15 years ago! Anyway, throttle response is less than desirable. If I turn the idle speed adjustment up just a tad, the RPM's want to hang up between 2 - 3K on the way back down. I've checked for vacuum leaks around the new boots and all around the carbs. Idle mixture screws were initially set to 2.5 turns out, but throttle response is better and idle doesn't hang as bad with them set to 2.75 - 3 turns out. It just seems to bog immediately off of idle, then it revs up quickly. The idle speed adjustment screw seems to be very touchy. Just about 1/8 turn is enough to make the difference between hanging up really bad or hanging up just enough to be a nuisance on the way back to idle. I've checked and re-checked the diaphrams on the slides, idle mixture screw o-rings are present but not the best. Nonetheless, no rise in RPM even when I shoot carb cleaner directly onto the idle mixture screw, so I believe they are doing the job. Anyone have any suggestions? Thanks

 

You've done a lot of work on the carbs, so I doubt that it's a problem with them being dirty, although 3 turns out is way too rich for the V4 to have to have in order to stay idling. The idle adjuster screw being that touchy, I have to wonder if you have synchronized the carbs after replacing them?

The VFR's are very touchy and if they are more than 1.6" Hg apart from each other then you can expect problems. According to Honda, the carbs are to be sync'd as part of regular maintenance every 8k miles... but I think that's kind of overkill if it's your daily commuter.

 

i think a vacuum leak may be afoot, spray small amounts of carb cleaner near the top, middle and bottom of each barb while the bike is running, if you have a big increase in revs, you found your leak

 

That reminds me, I should sync mine again before I go messing with my mid-range "flatness" issue. I've had them off since the last time I synced them. I've also fixed mechanical issues since, so I'm sure I should prioritizes a sync right up there with resealing the valve covers, and rechceking the valves.

My idle issues have gotten better the more I ride the bike, although tonight it was idling higher than normal, around 2k, compared to 1200-1500. My idle screw seems to not be very touchy, and the idle doesn't hang as bad.

 

Well, I removed the carbs again and sprayed carb cleaner and compressed air through every passage, watching closely to ensure that all passages were clear. They weren't. Two of the carbs had at least one clogged passage (one of the three small holes by the bottom of the butterfly valve). Put the carbs back on, and idle is much better, and the idle speed screw is not nearly as touchy. Still need to do a better job synchronizing them though. My carb sticks had too much moisture and not enough mercury in them to get a reliable reading. Any suggestions as to a better sync tool? My old mercury sticks have seen better days.

 

The new Motionpro sticks don't use mercury, they're around $100. There's another out there that people here say is better, but I can't remember the name.

 

The Morgan 'Carbtune Pro' is a great product, if you are looking for a new addition to your tool box:

http://www.carbtune.com/

 

Thanks for the info on the Carbtune. I'm assuming you have one? The ad says that there is no mercury, or any liquid. How does it work? It sure looks like mercury, or some type of liquid. Also, has anyone used the 90 degree carb adjusting tool available from Carbtune? I have one of the Honda tools for this job, but it is still very difficult to make these adjustments with the oil and water lines so tight.

 

Nevermind on the how it works part. I hadn't read the rest of the carbtune site. Duh.
Still, any recommendations on an a sync adjusting tool that works good are welcome.

 

Is this the carb adj tool that you use?

 

mine looks just like that except without the 2nd bend at the end. Mine just has a single bend, making it difficult to get into position.

 

The image above is for the Factory recommended tool - it's all about the bends, as you have noted.

I purchased this tool through David Silver Spares, though you may want to try your local dealer first.

 

A cheap bastard alternative. See my pics at the end:

http://vfrworld.com/forums/1st-2nd-generation-1983-1989/30292-homemade-carb-sync-tool.html