I just finished doing the valve clearances, put everything back together and tried to start the bike. With full choke, the engine turned over and sounded like it might start a couple of times, but did not. I tried to give it a little throttle and then heard a huge bang. I let go of the throttle. I tried starting with choke and without throttle (too scared to touch it) a couple more times, but the engine sounded like it was struggling to turn over and then stopped. Pretty sure I ended up draining the battery. Any ideas what the problem is here? Did I do some irreparable damage to the bike (like a cracked piston rod) with the bang?
Some more info:
- Battery voltage reads 11.9V with the bike off.
- It used to start but would struggle initially and sometimes die, even with full choke.
- The valve clearances on the exhaust valves were <.04mm when I measured. I put new shims in to bring the clearances up to .10mm-.13mm on both. One of the intake valves was also tight, so I replaced it and the new clearance measured .08-.10mm (a little out of spec, I know). Could the intake valve be the problem?
- At some point my friend tried adjusting the idle knob, but it didn't seem to do anything.
Any help would be greatly appreciated. This is my first bike, so I really hope I didn't destroy it.
Battery voltage reads 11.9V with the bike off.
Your battery is f.ucked.
Even a top condition battery will drop to about 10.5 to 11V at the moment it starts to turn the engine over. So if you have a charger and charge it back up to full power keep an eye on what it drops to under starting load. If it goes down to say 9.5 even if it has a full charge it's a walking dead man.
I figured. I'll try to jump it once I have a car.
But it was turning over initially and not starting. Made a couple noises like it was about to start. Then bang. Then it turned over some more and then slowly stopped.
The bike did sit for about 2 weeks while I worked on the valve clearances. Could it be an issue with the carbs?
Quote from: nit on May 16, 2018, 09:05:26 PM
- Battery voltage reads 11.9V with the bike off.
- At some point my friend tried adjusting the idle knob, but it didn't seem to do anything.
These two things may be prime candidates.
Standing voltage should be high 12s, almost 13v. As
user said, it may dip to the 11s when under load but any lower than that and it's presumably toasted. Especially if you've been cranking it so much that it rotated slower and slower before dying, the battery is at least drained and potentially damaged.
If your friend adjusted the idle knob with the bike off there's no telling where it's at right now, it could be too closed off to allow the bike to idle. I'd maybe give it a healthy turn or two "open" just to be safe and you can reset the idle at a later time.
2-weeks is really too short a time for any carb issues, unless the carbs were already in poor shape and overflowed into the engine. Smell your oil. If there's gas in the oil you should change it immediately, and also change your needle&seat in the carbs. If not, I don't think it's a carb issue.
When you say there was a loud bang, was it like a gunshot type bang or like a metallic bang? Gunshot bang is just a backfire and probably a condition of dumping several cylinder's full of unburnt fuel vapor into the headers and getting an ignition that caught it all at once. Nothing to worry about. Metallic bang is another story.
If you're in doubt turn the engine by hand (socket on the ignition rotor) and listen carefully.
I hate to think compression if you just did valves, but is it possible you did the valves wrong? Might want to go back in with the feeler gauge and verify the clearances are correct.
If all else fails:
Double check you're getting spark.
Make sure no rats made a home out of your airbox.
See if it'll fire on starting fluid.
I wouldn't even consider the carbs until you have a known good battery. Sitting for a couple of weeks wouldn't hurt it. Is it a sealed battery or does it need to be topped up with distilled water? If the latter, have you let it get below the plates once or twice. This can kill the battery even though it will take a charge and show 12.6V which is the minimum for a wet cell battery.
This happened to me, it took a charge fine was out on a ride turned the bike off for a sandwich and it never turned on again. Fortunately a battery shop was nearby, had it been the day before which was a public holiday this could have turned out to be a very expensive error on my part.
If it's a sealed battery it should get to at least 12.8V maybe more when new, that's after you have removed the static charge. After the battery is charged, you need to turn the lights on for a minute to get the static charge of the battery, to get the real charge.
But even with a good charge you need to be able to hold a decent voltage during cranking.
EDIT: I see there's been a post while writing. I shot a video of the voltage while cranking...
In response to Watcher:
My friend rode the bike home for me after buying it. That's when he adjusted the idle knob. The bike was running at the time, but the knob did not look like it did anything to the idle speed, which i thought was weird. In order to remove the valve cover, I removed the throttle cable and readjusted it when I put it back. Could it be that the idle screw was/is set too low, but previously a poorly adjusted throttle cable was not closing enough, allowing the bike to idle? I'll try opening the idle screw and restarting (once I can get a jump). Just to confirm, opening the idle screw is the same thing as screwing it in (clockwise)?
I don't think there's any gasoline in the oil (although my sense of smell is kind of poor). I pulled the spark plugs and one of them smelled faintly like gasoline. I don't think the carbs were in great condition before, but the bike was running.
The bang sounded like a gunshot. Turning the engine over by hand does not seem to make any noise.
It seems like compression maybe low on the right cylinder when putting a finger over the sparkplug hole, but this was also the case before I did the valve clearances. The way to test this would be to put some oil in there and see if compression improves right? I'll double check that the spark plugs are sparking once I can get a jump.
In response to user11235813:
Thanks for the video. The battery is sealed. If I get a jumpstart from a car, I should still be able to diagnose the starting issues even with the existing battery, right?
Thanks for all the help.
+1 for battery when it is weak the engine can push back against compression and the starter clutch makes a nasty clonk.
Was it a bang (gas exploding) or a clonk (metal knock)?
Just to be sure you did not do anything wrong with the clearances (shim popped out?), id remove the plugs (to make engine easy to turn over), put the bike in gear and turn the engine by rotating the back wheel (on centre stand obviously) to listen for any funny noises. If all ok button up and try with good battery. should be around 12.6V at rest.
Don't worry about idle knob, just give it some throttle when starting that will override this. you can adjust it later once its started. You really need to ride for about 20 minutes before adjusting this knob otherwise engine is not fully warm and will not idle properly when started cold etc. not sure if your friend did this.
Loose valves shouldn't cause the problem, but if you didn't turn the fuel petcock back on in the tank that could be.
Cool.
Buddha.
Quote from: nit on May 17, 2018, 12:08:32 AM
I don't think there's any gasoline in the oil (although my sense of smell is kind of poor). I pulled the spark plugs and one of them smelled faintly like gasoline. I don't think the carbs were in great condition before, but the bike was running.
The bang sounded like a gunshot.
Another way to test the oil is to put a drop on the back of your hand. If it "fills in the cracks" and you see the oil moving along your small wrinkles it's been thinned by gasoline. If it remains in a bead and/or coats your skin it's still oil.
Gunshot sounding bang is a backfire and not particularly a concern, not when there's trouble starting like this.
Thanks for all the help guys. I hooked the bike up to a car today and managed to get the bike started! Took a while of playing with the choke, cranking, and giving throttle but I finally found the magic combination that worked.
Now I have a new problem: hanging idle. Basically, with half choke the bike runs and the rpms increase for a while. Then turning the choke off, the bike idles fine. But whenever I apply some throttle the revs go up and then very slowly come back down. Here's a video: https://streamable.com/jxt39
- I tried backing out the idle screw to the point where it no longer seemed like it was doing anything.
- The throttle snaps back no problem, so I assume it is not a stuck throttle cable.
- The bike doesn't want to start with full choke, only half-choke. Not sure if this is relevant.
- I just did the valve clearances and I'm fairly confident I did them correctly.
- The video is me opening the throttle and then letting it go completely. (Sound didn't come out because my phone is a piece of crap.)
Thanks!
Not even going to bother watching the video.
"Hanging Idle" is a symptom of a vacuum leak. The whole "half choke" thing may be another story but before you diagnose ANY fuel issues the vacuum leak needs to be found and fixed.
It's easy to deal with. Fill a spray bottle with clean water and set it to as "misty" as you can. With the engine running mist around the carbs. The vacuum leak will draw in the water and the idle will drop. Use the method to locate the source of the leak, fix the leak. 9/10 times it's a dried out and cracked vacuum line. In your case it may be a carb boot wasn't seated completely.
Makes sense. I'll start looking for the leak tomorrow. I'll start with the vacuum lines and the intake boots. My bike also has the California emissions stuff. Is there any vacuum in that system? Should I just remove it?
Since the bike is from 1999, I might as well just replace all the vacuum hoses while I'm in there. Does anybody know the right size of hose to order?
Thanks.
I've seen 99 or earlier bikes with perfect hoses and the thing crumbling on an 07. The miracle of Chinese made garbage.
They have better hoses nowadays, but the material doesn't like sunlight. Make sure you cover it with a bit of wrap where its exposed to sunlight.
Cool.
Buddha.
Not to argue with Watcher, but while hanging idle can be related to a vacuum leak, and you probably have a vacuum leak (everyone does!), hanging idle is almost guaranteed to be caused primarily by the "idle speed" being set too high. Literally you can get the bike fully warmed (20 min riding on road) and then turn down the idle speed knob until the hanging idle goes away completely. Then if you have idling issues when the bike is cold then you solve that with pilot jet and pilot mixture adjustment.
And you probably also have a vacuum leak and possibly a starter or battery going bad.
Quote from: mr72 on May 18, 2018, 07:01:21 AM
hanging idle is almost guaranteed to be caused primarily by the "idle speed" being set too high.
That doesn't really make much sense to me.
I mean, the idle speed screw basically just opens the throttle a little bit, so an idle set too high would simulate not rolling off the throttle completely. That would result in a high idle, but not really a hanging idle.
If I roll on my throttle 3/4 and get the RPMs really high, then roll off to 1/4 throttle, I won't get back to idle speed but the engine will drop quickly down to a much lower RPM. If I chop off the throttle and the idle wants to be lazy I wouldn't suspect it's just from the butterflies being open a little too far, the drop in RPM should be rapid unless there was something else wrong.
At least as far as I understand it.
Quote from: Watcher on May 18, 2018, 09:41:17 AM
Quote from: mr72 on May 18, 2018, 07:01:21 AM
hanging idle is almost guaranteed to be caused primarily by the "idle speed" being set too high.
That doesn't really make much sense to me.
Yeah, however the other explanations make less sense.
But anyway, I can explain it (and BTW it's in my blog post about tuning these carbs):
First you have to understand that the position of the slide, and therefore the needle in the main (or mid) jet, is caused by vacuum and nothing else. The position of the throttle plate has no direct effect. When you open the throttle it has the effect of increasing vacuum which pulls the slide up and allows fuel to come out of the main jet.
At idle, during the pilot circuit operation, there is another air passageway that supplies air across the pilot jet,
not the main throat of the carburetor. The bike should idle correctly with the throttle plate
completely closed. The reason is that when you open the throttle plate at all, you are adding AIR but not FUEL because the slide is still down and the main jet is closed.
THIS IS WHY PEOPLE THINK IT'S A LEAN IDLE. It's because the bike is truly running "lean" at "idle" but that's because you have the throttle plate stuck partly open allowing too much air in without the requisite amount of additional fuel.
Anyway, so why would this cause hanging idle? It's because with the throttle plate nearly closed but not completely closed, there is not enough vacuum to keep the slides up, to overcome the return spring, etc. But there may be ALMOST enough to try to keep the slide up, so as it attempts to return to idle, it stops near whatever rpm the engine would run if the throttle were able to be held at that position, and stays there until the vacuum goes down enough to allow the slide to drop completely. Closing the throttle plate more will reduce vacuum under "idle" conditions and therefore tend to prevent this slow return to idle.
The fact is the bike is intended to idle with the throttle plate closed completely. You may have to open the throttle plate a little bit ("increase the idle speed screw") at idle as the carb may get gunk clogging the very small air passageway that feeds the pilot jet, in this case you wind up with too little air at idle. If you do this then you will still have a lean idle but then you might be able to adjust it with the pilot needle screw to compensate up to a point. But the real solution is to clean the pilot air passage and fit the correct pilot jet, then close the throttle plate completely at idle.
Bike should run and work just fine with that throttle stop screw removed completely. But in reality it will wear and over time you will have to probably crack the throttle plate a tiny bit AND adjust the pilot needle richer to compensate for partial clogging of the pilot air passage until such time as you break it down and clean it.
BTW if you attempt to hold the idle at like 2K rpms on a GS500, even if doing so by adjusting the throttle cable etc, it will eventually return to idle after like 30 seconds. That's also the same symptom of "hanging idle". It'll just return to a very lean idle, but once the slide settles down and the main jet gets closed then the pilot jet only will supply enough fuel to sustain a 1.1K or so idle rpm.
:cheers: