Idle weirdness. My '85 VF500

I just took out my bike for about a 50 mile trek, just gliding around empty parts of town practicing my braking, shifting, turning (Pressing, leaning, rolling), swerving, etc. and my High Idle RPM problem is back about 3/4ths the total trip (i had laid the bike down last week at about 15 MPH when it started happening but went away). Anyway, instead of idling at the service manual specified 1,300 +- 100 RPM, it hovers at about 2.5-3k with no choke applied sitting still in neutral or first and clutch. Sometimes, but seldom the idle RPMs will return to 1,300 at random when not moving.

The engine sounds and feels like it's running like a dream once I get going from a stop, it pulls steadily/predictably and very smooth (keep in mind though I haven't really ridden anything other than my bike and the ones at the MSF course, so my opinion of it may be off). The temperature gauge kicks up to about the middle zone when sitting still for a while, but very quickly returns to the 1/4th mark when at a steady but brisk pace.

So, any ideas?

 

I would guess that either a throttle cable is binding or the carburetor linkage is binding. When it idles high, is their any play in the throttle grip, or is it completely tight?

If I remember correctly, you dropped it on the left side, and had to adjust the handlebar back into position. Is that where the choke lever lives? If so, make sure that the choke cable is not binding somewhere.

When it returns to a "normal" idle, does it do it all at once, or slowly?

 

yeah, my choke control is on the left handle that I had to adjust back. The throttle has no play, it snaps to close as soon as you let go.

When it returns to idle, it does it pretty slow kind of in steps. It'll slightly bounce around 2.5-3k maybe drop down to 1,900 then for a second or two. Then 1,500 then finally stay at 1,300.

 

When the throttle is closed, is there any free play when you rotate it, or is there constant spring tension? There should always be a little bit of free play, and it should be checked with the handlerbars turned fully left, and fully right. Given that your idle speed is slowly coming down, it sounds like the throttle cable is too tight.

Your manual should have a section that shows the cable adjusters, and also the recommended free play. I would check the choke cable for free play, too, although the only place to adjust it is probably down by the carbs.

 

I think you might have it there. There's no wiggle room between when the throttle is at rest and any twist catches the cable and RPMs star rising (i don't recall there being any before the accident either though).

I'll go outside and check that right now, thanks!

 

I also have an 85 VF500F; I assume you have already tried adjusting the idle. I would agree that you should check cables and linkage and also adjust your throttle free play. If all is well then synchronize the carbs because when a bank of carburetors get out of adjustment you get varied idle rpms. Another sign that the carburetors are out of sync is a slow return to idle with the RPMS hanging up or very slowly declining. If the Idle is still not right, pull the carbs and check the diaphragms for small tears, examine the main and slow jets and clean them with solvent and compressed air. Blow out all the air passages etc.

 

LGN called it. I should have noticed I had to dig the choke lever out between the control housing and the left mirror. I remember now that after I laid it down, whenever I had turned the bars to the full left my horn was going off; laying it down rotated the control housing so that the furthest back my choke could go was against the mirror.

Also, I also noticed that my throttle cable was in fact extended out to the point where it was under constant tension from the carb springs. Screwed that in and secured with the nut, i adjusted the free play to a good 3mm of play.

It idles like a dream again! I'm guessing the intermittent return to normal idle was just the housing kind of rotating a bit (it was loose).

@ Jimtt. No, i hadn't tried to adjust the idle, she was idling just fine before I laid her down. Though, since you have a VF500F, how far back does your choke lever go when not applied? Since I reassembled the control housing and rotated it, it comes to about 10mm to the mirror at the closest distance. Sound about right?

Also, it still does kind of return to idle a bit slow (but it doesn't do it in levels as bad any more). I think I will have to do an inspection of the carbs though.

I'll go ride it around the block a couple times around. I'll take a video of the RPMs and you can tell me what you think of it.

 

Just one more thing; it is probably worth lubing all of your cables.That might take care of the slow return to idle. Probably worth lubing things like the rear brake pedal pivot points, shift linkage (if it has multiple parts), and probably clutch lever and front brake lever pivot points. Good job!

 

The choke lever is about 10mm from the mirror stalk when fully closed, also here is a better pic of my 500.

 

Use the idle speed adjustment screw on left side (black knob) to reset idle quickly and easily.

Some folks (me) use this screw as a cruise control out on the interstate, but it can be a little risky............

 

Very nice! Aside from the the seat, the black towards and your exhaust our bikes are twins!

But as for the video, I can't for the life of me find the data cable for my camera. I guess I'll have to hunt that down some time tomorrow so I can show you.

Thanks for the help both of you.

 

All right the problem's back. I took her out again and she started doing the 3k Idle with the sometimes back down to 1.3k today (but more often than last time). I tried doing the same adjustments as last time, they didn't do anything this time around. Turning the bar side to side doesn't affect the idle speed. Also (it only happened once though) I was at a stop light today and it was idling at 3k, it dropped back to 1.3, went to 900, then died (the people behind me weren't happy about having to wait another signal rotation). I had to use the choke on full blast to get it going again (even though I had been riding for a good 30 minutes). Temperature read normal.

I think I'm going to have to dish out the money for the carb sync tool (I read the process in my service manual, seems fairly straight forward), and I'll probably end up cleaning out the bowls and inspecting the diaphragms. When revved up to a 9k (not sustained, quick open/close throttle) white smoke billowed out my exhaust (though it may be the SeaFoam I added to last tank full).

I'm yanking the plugs when it's light out tomorrow to see what's going on.

:frusty:

 

I would sync the carbs first and see if that helps.

 

There's a lot of sync tools out on the market, which one/type would you recommend that would be easiest to use for the bike?

 

alright, I haven't really been riding since I'm waiting for the a new air filter before I sync the carbs. I decided to ride around for a half hour at freeway speeds to keep the battery up.

Anyway, the idle problem seems to be getting worse, which makes me think that carb syncing wouldn't fix it. It doesn't hold 3k idle any more, it varies between 3-4k now. I should have mentioned that it doesn't idle high when it's first started, it's normal then. Also, I used to be able to 'reset' the idle temporarily by letting go of the clutch with the brake applied, so the RPMs went down a bit and stayed there. That is no longer the case and the RPMs shoot right back up after the clutch is disengaged. Also, the temps are starting to perk up a lot faster than they used to (presumably because of the higher idle).

Doing a bit of research online, I think the culprit may be a really bad vacuum leak. I'm thinking that since each cyl has its own independent carb, the one with the vacuum leak should show lean operating conditions when reading the plug? What likely locations should I spray WD-40 to see if idle note changes?

Thanks again for all your help guys.

 

Spray around the intake boots. Do small sections at a time so you can tell what you sprayed......


Lane

 

Yanked the plugs, both plugs on the left side are running hot (insulators white). Right side is a little dirty, but nothing a short high speed ride wouldn't clean out.

After riding around to warm the engine up I got it to idle high again. I dismounted the bike with the kickstand and dabbing WD-40 around the boots. Oil on the front left boot caused a very slight change in note, so i waited for the oil to dissipate and the RPMs climbed again. Tightened the respective clamp, had the same effect as oil, but RPMs stabilized.

The left rear cyl is odd. Oil around all parts of the boot made no difference, but I know it's running hot because it had white insulators.

Then I noticed something as I was comparing my carbs to the ones in my Clymer manual. The plugs that need to be removed before pilot adjustments were not there, the pilot screws are exposed. I'm thinking the previous owner did some maladjustment of the left side pilots causing a lean condition.

I'm going to follow the adjustment procedure in the manual and see what effect that has. I'll keep you guys posted.

 

I'm going to follow this, cuz mine is doing the exact same thing but it's the front. And if I figure anything out I'll keep ya posted

 

Sounds like it's running waaay too lean. My money is on a vacuum leak.

 

A couple things come to mind that haven't been mentioned, although it's a stretch to think they would occur because of tipping the bike over. You mentioned the left rear cylinder spark plug looks hot and lean. If you check the intake manifold on that cylinder, you'll see there's a vacuum hose that runs from it to the fuel petcock under the tank. Make sure it's intact, not cracked. An easy way to determine this would be to pinch it off right at the manifold when it's doing its high idle thing and see if your idle drops (you can't do this indefinitely or your carbs will run out of fuel...your petcock needs vacuum to flow fuel). By the way, it's not unheard of for that vacuum petcock to fail, symptoms would be various shades of fuel starvation. You can easily test it by unplugging the line at the manifold, hooking up a hand operated vacuum pump, and pumping it up to around 6psi...it should hold that vacuum. If it doesn't, it or the hose is bad.
The other thing I've seen on occasion is tight valve clearance. When the bike is cold, they seal fine...but once the bike is hot and things expand, the clearance disappears and holds a valve a little bit open. You should be able to spot this by doing a cold compression test, get it hot and failing, and then check it again. If one or more cylinders is losing compression, a valve lash inspection is in order.