trouble getting steady idle under 2000

 

I finished going through the carbs meticulously, and carried out every check and adjustment that I have the tools to carry out. I cleaned every orifice carefully. I have new diaphragms. I set the the fast idling as best as I can with the faulty service manual, triple checked and triple adjusted the fuel service levels, set the pilot screws to factory specs, etc. I have previously double or triple checked the valve clearances and static timing. I have not put the timing light on it, but I'm not sure if I should or should not do that when I can't get the idle steady.

When I put the carbs back on it this AM it started up with no choke (its 75 degrees) and idled well at about 1200 rpm. I rode it 16 miles. It ran perfect. When I came to the first stop sign, it died, but started back up so I went home and shut it off. I went back to it 20 minutes later to check the pilot screw settings and it idled very high, about 3000 rpm. I checked for air leaks with starting fluid and found none. But I can't find a steady idle under 2000 rpm now. If I back the idle screw off verrrry slowly it will creep down toward 2000 but if I keep backing it off it will just keep going down until it dies and I can only save it with throttle. I try to get the idle back up to where it will stay running, but even tiny adjustments send it back into high idle again. Rinse, lather repeat. I just can't get it to idle and stay running below 1500, at least when its warm.

Not sure what to try first, and don't want to make matters worse by guessing.

Have you try to adjust the throttle cable slack?

No, good idea but I did just now. It seems to be at spec, 2-3 mm slack now. Being too tight could cause these symptoms, but if anything it was way too loose. I tightened it to spec but no change. It will almost die, hit throttle to save it, then it goes up to 2500 and sits there until it decides to start dropping slowly down to zero, or I have to back off the screw and it drops down to zero. Rinse, lather, repeat. 

I may have found the answer on the KZ305 Facebook page (which I just discovered), where someone was experiencing the exact same symptoms recently.
Its a thought that has been running around the back of my head for years.
 
Fellow sufferer says "Turn the air screw too much, it barely keeps the idle up, turn it too much the other way and the RPMs are at 5k when it's in first gear and I'm not even on the throttle. It's up and down and no sweet spot can be found. "

One answer:

"It's the carbs. Stock carbs are junk. Worst carbs I've ever worked with in my life. I have 11 bikes all carb bikes... this 82 kz 305 I have is the worst one.


 
 

Have you vacuum synced the carbs?  

Nessism wrote:

Have you vacuum synced the carbs?  
 

No, that's the thing I don't have the tools for. I planned to use the alternative method described in the manual, but if I do things in the order described, that would come after the idle adjustment. It doesn't say you HAVE to do it in that order though.

You can do a static sync with a feeler gauge.
I use a 0,15 mm blade to adjust the throttle flaps equal.
 

I did make sure they close synchronously as best as I could, and I did use a feeler gauge to make sure they were closed, but I wasn't smart enough to actually use it to measure a gap on both...dohhh! That probably would have been better.

They have another method in the FSM using your ears and your hands on the exhaust as "feeler" gauges. I do think it needs adjustment, the right side feels stronger. But I need to get more hose to run it with the tank off so it may be a day or two. Well... maybe I can use some of the vinyl tubing I bought for a different project as a temporary line...may try that, if it fits.

82KZ305Belt wrote:

Nessism wrote:

Have you vacuum synced the carbs?  

 

No, that's the thing I don't have the tools for. I planned to use the alternative method described in the manual, but if I do things in the order described, that would come after the idle adjustment. It doesn't say you HAVE to do it in that order though.
 

Actually it does say to do the idle first, which is pretty much impossible if it won't, ya know, idle.  I tried to do both tonight, the best i could under the circumstances. i think the carbs are better synched now but it still idles all over the place. Pretty much ready to drive it off a cliff.

I decided to prioritize fun over frustration. I haven't really been able to ride since the head gasket and piston problems 4 years ago, and I've put endless hours into this. So now I am going ride the bike and have FUN at least one hour for every hour of trying to fix whatever is still wrong. I've taken it on three 15 mile rides now, and each time it runs great except for the idle issue. After my most recent synch and cable adjustment it is running as well or better than ever, as long as its moving. It is peppy and very fun. I have several more fun rides ahead of me before I try to find the problem again. Currently it is still:

hard to start, and won't start with choke at 70-75 degrees FIt will usually start quickly but baaaaaaarely, and then dies in a second. I have to start it multiple to many times, each time it will run a fraction of a second longer before it dies, until eventually it stays running. Once it is running I have to give it some choke for a minute to keep the idle up.

Once it warms up it rides great, and will often idle stable at 2500 rpm at stops, which is obviously too high, but its better than dying. But sometimes it will just die if I don't stay on the throttle at stops. I've tested for air leaks over and over and find none. I've read that tight valves can cause some of these symptoms. I know they are set to spec, but whether they are worn or something I do not know. Should I check them hot? I considered buying vacuum tester for a better synch but I think I'd have to drill something out to even hook them up so I'm not rushing to do that.

Not sure what to do next, but further suggestions appreciated. I'm just gonna ride and have fun. If it blows up it blows up, at least I will have had my fun.  

There is no need to drill anything to vacuum synchronize the carburetors. Just remove the vacuum plug from each one and screw in the adaptors. Most decent synchronizers come with an assortment of such adaptors.

I am still putting my money on clogged pilot circuits or pilot mixture screws that have broken tips. Maybe badly worn throttle shaft bushings. Something is causing the idle mixture to be wildly off, and the only way to keep the engine running is to open the throttle plates just enough to engage the main jet system, which flows too much fuel for a nice 1100 rpm idle.

Yeah the drilling idea was something i read that some other clown did with a 305, but I had no intention of doing it. This bike has no vacuum caps though, but it does have vacuum plugs that just screw in.

I have considered getting a kit and replacing all jets and such but maybe I'll just try replacing the pilot screws. i did look at them under a microscope during the last cleaning and didn't see any notable damage, but I'm no expert.

yesterday the bike started better so I'm still in "ride it and enjoy it" mode...

Old fashion sync method for twins involves setting the idle up some (maybe not needed for this bike?) and then pull off one of the spark plug caps.  The idle will drop.  Set the sync so the idle is the same speed for both the RH and LH cylinder.  When done, set the base idle down to normal with both cylinders running.

If that doesn't work, your bike most likely has vacuum leaks.  Spraying junk on the carbs often doesn't find leaks, unless they are really large ones.