I have a 1990 VR that has been sitting for eight years. After putting a new battery in, it started right up, but didn't idle. I drained the gas tank (the fuel in it was amber) and refilled with BP Premium spiked with 4 oz. Sea Foam.
I've cleaned the carbs and checked the slides and diaphragms, and adjusted and cleaned til I'm blue in the face. The bike will idle and has decent throttle response until it gets hot. When it gets into mid temperature gauge territory, the idle begins to climb until it is at 4.5K and I can't stand it any more, where upon I shut it down. This scenario happens whether sitting in the garage on the center stand or while riding. Sooner or late the idle will climb to the 3-4.5K range and make stop lights rather embarrassing and shifting very ugly.
I've been running Sea Foam through and have adjusted the pilot screws to 2.5-3 turns out (notably, turning the pilot screws in all the way or out all the way has NO effect with idle). I have synchronized the carbs (using mercury sticks) and they are very nearly perfect and never seem to change synchronization. I have tested the pressure sensor (vacuum sensor, boost sensor) and find voltages well within spec (2.18 when at atmosphere, .65 volts at .90kpa on a mityvac vacuum pump). Pulling vacuum on the pressure sensor causes an increase in rpm...sometimes. Idle must be over 1000 rpm for pressure sensor vacuum to effect it, apparently. I removed the pressure sensor and it's harness and connectors and cleaned them. I removed the TCI connectors and cleaned them. Some of the spade connectors were corroded, but not bad. Still, though an increase in vacuum always caused a voltage drop, this voltage drop did not always/usually result in an rpm climb ON A COLD TO WARM engine.
I checked for vacuum leaks at all the usual suspects; the pressure sensor vacuum hose and restricter = AOK, the sync plugs = AOK, the carb to head boots = not AOK. Number 3 and 4 seemed to be leaking at the carb bases. I checked for leaks with carb cleaner spray. Regarding the leaks at #3 and #4 carb boots: I removed the clamps and ground off the tabs that seemingly prevent the clamps from tightening too tight (?), and reinstalled the clamps on the boots and re-tightened. Spraying with carb cleaner around the newly tightened boots did not result in idle change, IE, no leaks. Curiously (and significantly ?), pulling the sync plugs off the idling bike, one at a time, has little effect on the idle, EXCEPT for #2. Opening the sync port on that cylinder, slows the idle significantly.
I have checked the float bowl fuel level and found all to be at 19mm below the reference line. I have monitored the fuel level on the running bike and it has remained very stable at this level. (I have rigged four fuel level gauging tubes attached to the carbs for testing). I realize that the fuel level is lower than spec, but that also indicates that an overfull fuel chamber is not causing the hot high idle, doesn't it? Or, could it be that the hot engine is running leaner and leaner and perhaps the lean condition is causing the high idle?
I changed the spark plugs (NGK DPR8EA-9). The old plugs (NGK DPR8EA-9) looked new, including the rather white porcelain. Perhaps running a bit lean? (However, during the course of testing and fixing, I ran through a tank full of premium and got just 25 mpg. Granted there was a lot of stationary running, testing, full throttle "testing", etc.
The mechanical parts of the throttle system are up to snuff: cables free and lubed, idle stop screw allowing for fully slow idle, carb butterflies all equally closed, and though I had a slide hanging initially, all slides/diaphragms are AOK.
As the bike sat there idling nicely away at about 1000 rpm, I was beginning to feel like I had fixed this vexing problem of high hot idle, but NO!, soon the rpm began to climb; first quickly to 3000, but then soon was at 4500 and I couldn't take it anymore. About 10-15 minutes has elapsed. I pulled the pressure sensor vacuum line from #2 and immediately the rpm dropped to about 1500 rpm. I reattached the vacuum hose and it zoomed to 4500 again.
I shut the bike down and had a beer.
I have been chasing this for days and am discouraged. I am seeking some new insight from someone out there. I have reviewed all pertinent threads, especially the one from warthogcrewchief this year, where he had a similar problem, but his solution doesn't seem to fit my problem.