Backfire when throttle closed

[flainn]

This weekend my GZ started backfiring when I let off the throttle. Pop-pop-pop. Never done that before.

Also, it does not seem to want to idle. I had to turn the idle screw way up just to get it to idle properly.

The only thing that I've done to it recently was, I bumped the muffler when I was backing it up. The problems seemed to develop afterward, but it could just be a coincidence.

Any ideas? I'm thinking it's a good time to give 'er a tuneup anyhow.

[Dupo]

How hard did you bump the muffler?

[flainn]

Not hard enough to cause any visible damage, but hard enough for me to be pissed at myself for being such a klutz.

[Easy Rider]

This weekend my GZ started backfiring when I let off the throttle. Pop-pop-pop. Never done that before.
Also, it does not seem to want to idle. I had to turn the idle screw way up just to get it to idle properly.


Something has suddenly caused it to run even leaner than normal. The pipe bump may have broken or cracked something in the exhaust system; check for exhaust leaks between the cylinder head and front of the muffler. Also check the back plate of the muffler; might be busted loose.

THEN consider that the muffler bump might be just a coincidence (Murphu WILL get you!!).
A more common cause of what you describe is a leak in the intake side, either the boot between carb and engine or something loose with the air box allowing a leak past the filter.

Last but not least, your idle jet might be plugged. The bump might have jarred a little piece of "crud" loose in the carb.

[dan_]

What about a backfire upon starting.. like every time it starts? I had a slight drop on my bike.. okay I completely dropped it onto the muffler side. It was raining and I was putting it in a trailer, slipped, dropped, ouch. Runs fine but whenever i start it "POP!" Should I be worried? Or just tell the dude when i finally take it in for service?

[flainn]

Something has suddenly caused it to run even leaner than normal...

I've been meaning to give it a good going-over since I first got it running. Sounds like this'll give me the kick in the rear I need. Thanks for your advice.

[Easy Rider]

Runs fine but whenever i start it "POP!" Should I be worried? Or just tell the dude when i finally take it in for service?

Now that's a new one......on me, at least. :??:
I'd guess small exhaust leak.

Does it do that when restarted hot/warm too ??
Are you using any choke ?? When ridden fairly frequently (every other day or so) in the summer time, mine takes about 1/2 choke and usually fires on about the second revolution.

If that's the only strange thing it's doing, I'd say wait and SHOW the service dude instead of just telling him.

[dan_]

Just when started cold. When cold if I don't give it full choke it wont start. Also if i don't let it run a minute or two before I take it off of full choke it'll stall out.

[Easy Rider]

Also if i don't let it run a minute or two before I take it off of full choke it'll stall out.

That part is perfectly normal and is worse if your idle speed is set too low.

If the pop and requirement for full choke only happens when it is "winter" cold, then my guess is that is normal too.

Had mine running for the first time in winter weather last week, just to ride it inside off the trailer from the service shop and it sounded more like 50cc.......and appeared that it would take a good long 5 minutes before it would be running smoothly.

[dan_]

How do I know where my idle should be set? I prolly have it set to low because It kinda has that low thump thump.. but not really ya know?

[Easy Rider]

How do I know where my idle should be set? I prolly have it set to low because It kinda has that low thump thump.. but not really ya know?

Tough call when you don't have a lot of experience. Best I can tell you is turn it up a little at a time until it just starts to smooth out a bit and the individual thumps are hard to distinguish.

This is a case of not knowing what is enough until you find the point where it is TOO much.
If you get the feeling that the engine is racing a bit, then it is probably too high.

May God forgive me.......think about a gasoline lawn mower. Most of them idle nice and smooth when set right. For some strange reason, your GZ should sound about the same when it is set at the right speed. :whistle:

[flainn]

You've just got to love that lawnmower sound! Sure beats a sewing machine though.

[dan_]

Is it bad to have the idle set to low? I mean the guys already say it sounds like a lawn mower.. but none of them have bikes so its prolly all jealousy..

[alanmcorcoran]

Mine stalls... a lot. but it didn't do this for the first 2500 miles or so. I'm not sure if the idle is too low, or the carburetor is effed up or there is crap in my gas tank. I'm going to try the seafoam for a few tanks and see if there is any improvement.

It actually is hard to re-start once it stalls. I've had to take the choke off becaase it get's flooded. I now have to kind of keep the throttle on a little as I'm slowing down for lights and stops. I've also become an expert at push starts. Unless I'm going up hill, I use the push start to conserve the battery. And I'm doing it in second gear now.

And this is after a near $300 3K "service." Nice to know motorcycle dealers are just as inept at servicing carbureators ascar dealers are. Glad the Strat has fuel injection. At least until those get effed up, too.

[Easy Rider]

Is it bad to have the idle set to low? .

Bad as in hard on the bike....no.

Shifting is usually smoother if it is set right and getting off the line is easier 'cause you don't need as much throttle.

[Easy Rider]

I now have to kind of keep the throttle on a little as I'm slowing down for lights and stops.

THAT is exactly what the idle speed adjustment DOES.

You are probably keeping the choke on longer than you need to just to bring the idle speed up.

I was amazed at how low the shop had set mine; I think I cranked the knob about TWO FULL TURNS......but the engine was still cold so I'll probably have to back it off a bit next spring.

Seafoam won't hurt but, please, tweek up your idle speed. You will be much happier.

[BusyWeb]

I now have to kind of keep the throttle on a little as I'm slowing down for lights and stops.

THAT is exactly what the idle speed adjustment DOES.

You are probably keeping the choke on longer than you need to just to bring the idle speed up.

I was amazed at how low the shop had set mine; I think I cranked the knob about TWO FULL TURNS......but the engine was still cold so I'll probably have to back it off a bit next spring.

Seafoam won't hurt but, please, tweek up your idle speed. You will be much happier.

Here is my experiences about engine idle speed.
With my DIY(ha ha ha...) RPM meter, I could measure pretty accurate gz engine speed.
(TIP: you can measure RPM with digital multimeter which equipped with frequency measurment
HZ >> 1 HZ = 60 RPM >> point to the ignitor negative cable)
Service manual says about 1300 is for the GZ. (measuer when engine is warm/hot)
Surprisingly, around 1300 is far low for my GZ, sounds really slow engine running.
However GZ runs well enough without stalling, if I do give more care on the throttling at stop.
Which means that gz seems not very happy with it at the lower speed.
I tried to put rpm to 1800 -2000 idle speed, gz sounds little hurry but not much.
And lower speed jerking problem is gone, and more smoother gear shifting for me.
One thing though, engine temperature goes little higher when I riding in city environment...
Frequent stop and start at lower speed...
That's all for my experience/opinion, as Mr. Easy had to do for the idle speed.

[Water Warrior 2]

I would wonder about proper oil pressure and oil circulation with a low idle.

[alanmcorcoran]

With my ... RPM meter, I could measure pretty accurate gz engine speed.
Service manual says about 1300 is for the GZ. (measuer when engine is warm/hot)
Surprisingly, around 1300 is far low for my GZ, sounds really slow engine running.
However GZ runs well enough without stalling, if I do give more care on the throttling at stop.
Which means that gz seems not very happy with it at the lower speed.
I tried to put rpm to 1800 -2000 idle speed, gz sounds little hurry but not much.
And lower speed jerking problem is gone, and more smoother gear shifting for me.
One thing though, engine temperature goes little higher when I riding in city environment...
Frequent stop and start at lower speed...

Hey, Mr. Web. This is probably the most scientific analysis of this issue I have seen. Thanks. Here is my theory about the idle speed: When the bike is brand new or the carburetor, piston and spark plug are in 100% perfect working condition, the bike will idle fine at 1300. If there is any gunk in the carb, on the plug, in the cylinder, or grit/sand in the fuel line, or crap in the gas tank, the conditions are going to be less than ideal and the bike is going to stall until it is heated up but good.

I don't like a high idle because the bike tends to "drive itself", runs hotter like Busy said, and uses more gas. But I also get very annoyed with the stalls - it's very distracting, is hell on the battery and is dangerous, because about half my attention now is dedicated to effing with the controls at stops so it doesn't stall.

When I drove taxi's we had a few old Chryslers in the fleet (this was pre-FI) and they had this irritating tendency to stall when you accelerated from a stop. They'd hesitate, cough, then, down she'd go. No matter how many times we had them serviced, they basically sucked. The typical solution was to crank the idle up so you could do about 20 mph without ever touching the gas - at a stop light, you had to "hold your horses." This of course, wasted gas and used up brakes faster. Not to mention irritated the piss out of you. But the mechanics we had could not fix it.

I find that a really good mechanic that actually knows what he is doing and works for a trustworthy outfit is a rare commodity these days. The problem is that like a lot of American business models, the people that do the actual service get paid the least. The guys that write up the order, the "manager", the owners and the landlord all get paid the lion share of the service fee so the service person with half a brain tends to migrate into something more lucrative. I often feel the guys that are working on my bike are the ones that are too dumb to migrate. They are also not skilled or experienced enough to expertly service the bike. They are probably also under pressure to close tickets in an unrealistic amount of time and do the bare minimum on a routine "service."

If I felt I could take the bike somewhere with a master mechanic and he could truly "service" the carburation system I think I'd be happy with the 1300 idle, but, in all likelihood, I'll probably just crank mine up and learn to live with it.

[Easy Rider]

[Here is my experiences about engine idle speed.
With my DIY(ha ha ha...) RPM meter, I could measure pretty accurate gz engine speed.
(TIP: you can measure RPM with digital multimeter which equipped with frequency measurment
HZ >> 1 HZ = 60 RPM >> point to the ignitor negative cable)


This is just wild speculation (at this point) mind you but I have a theory about that.

It seems to me that the proper "real" tach to get for the GZ is a "double fire" model, the same as is used for V-twins that fire the plug TWICE on each revolution. If that is true, your DIY solution might be reading twice the real RPM and you might actually be setting yours about 1,000 RPM, which is about where I think it should be set. In all my riding, I have never set an idle speed as high as the "book" recommends.

If true, that illustrates the problem perfectly. Setting the idle where it should be just sounds and feels way to fast for most people. Then there are those who seem to prefer to keep re-starting and push starting when it only take about 3 seconds to adjust it........mmmmm...A.C. ???

I know there are (or were) a couple of folks on here with tach's. Wonder where they have their idle set ?? (Off to do a couple of searches).

Edit: Sarris.....5th_bike.......help me out here, please ??

[Sarris]

My idle varies w/ weather conditions, but I keep it at about 1200 rpm on my tach. My GeeZee idles lumpy at 1000, and seems to be happiest at 1200 rpm. Also, as a side note, my mc guru says that a low idle in hot weather may result in bearing failure (or excessive wear) with less than recommended oil pressure at a lower than spec idle. No prob if moving, but get stuck, and you could overheat. Mr. Suzuki says 1200 ~ 1300, and Father knows best. (PS; I use the $50 tach recommended on site)

Oh yeah, those pop-pop-pops after a drop is usually a minor leak from disturbing the header to cylinder head seal. It may or may not heal it self after a few miles with normal running carbon build up. If not, replace whatever gasket/donut is used at the joint, and don't drop the MF anymore.

:2tup:

[alanmcorcoran]

I cranked up my idle a bit before heading off to work today, also let the bike warm up in neutral for a few minutes before I climbed on. I think I ended up cranking it too high - it was way up when it warmed up and I took the choke off. So I ratcheted it back down a bit when I got to the office. I may look into that $50 tach. Is it hard to install?

I have Yet Another Theory on my stalling problems. I think maybe my throttle cable assembly is a little sticky. Does anyone know if the cable is "relaxed" more, (stretches, say) then the idle will drop down? I think they adjusted the idle when the cable was not fully relaxed, and then, when the bike heats up, things loosen up and stretch, and the idle drops below sustainability. I do find it's all over the map for the first ten, fifteen minutes or so. Once the bike is thoroughly warmed up, it settles into a stable rhythm.

[Water Warrior 2]

The idle should be set on a fully warmed up engine. Maybe try a different brand of gas for a while, might make a bit of difference.

[Easy Rider]

I cranked up my idle a bit before heading off to work today, also let the bike warm up in neutral for a few minutes before I climbed on. I think I ended up cranking it too high - it was way up when it warmed up and I took the choke off. So I ratcheted it back down a bit when I got to the office.

Sigh!

When you told us you weren't too mechanically inclined, I thought you were probably exagerating your inept-ness; appears that is not the case. :cry: :biggrin:

One should NOT set the idle while the engine is cold and ESPECIALLY not while the choke is active. Geeezzzz !! :roll:

I thought about getting a tach a few times.......but it really doesn't accomplish much. I plan to visit my dealer and ask them to connect their induction tach just long enough to set the idle. Once you KNOW what the right speed sounds like, you don't need a tach anymore.

Thanks for setting us straight, Sarris !! :tup:

An idle at 1K sounds a LOT different with a thumper than it does with a V-8.......or even a V-twin !!

Yes, it is possible that too much slack and/or sticky cables COULD contribute to an erratic idle.......but it is not too likely. In addition to the spring at the carb, one of the cables actually PULLS the throttle closed when you roll it in that direction. The cables would have to be VERY loose or VERY sticky, unless you slow down by just releasing the handle grip......or you have a limp wrist !! :shocked: :whistle:

[alanmcorcoran]

Yeah, I'm not gonna put my mechanical skills up against anyone on here. Personally, just like a good doctor, I think to be a good mechanic you have to have a deep, holistic understanding of the entire machine. In some cases, symptoms and fixes are isolated to one adjustment or part, but, in most cases, they are a combination of things that need attention, and, more often than not, are also behavior related. (Like using bad gas, or under/overshifting, or riding the brakes, etc.)

But, does anyone else have an erratic idle? Like, you are sitting at a light and it suddenly drops from a steady whine to... nada. Or it starts to climb up, but you let the clutch out a little and it slaps it back down until it behaves itself. Mine is all over the map until the engine is hot. Since I have no problems with the idle when it is hot, it doesn't really accomplish much to adjust the idle when it is hot. It doesn't stall when it is hot. It only stalls when it is cold, warm, warmer and, almost hot. That's why I effed with it before it got hot.

I'll keep screwing with it. Eventually I might learn something.

[Easy Rider]

It doesn't stall when it is hot. It only stalls when it is cold, warm, warmer and, almost hot. That's why I effed with it before it got hot.


Well CRAP! My memory might not be as good as it used to be but.........I distinctly remember you NOT mentioning that little detail before. :skull: (Possible I missed it, I guess).

Anyhow, now we have a new ball game. Have you done the Seafoam thing yet?

Are you releasing the choke a little TINY bit at a time or are you going all the way from full to nothing?

You should not need full choke if the temp. is above 50 or so; 1/2 or 3/4 shoud be plenty and then 30 seconds or so after it starts, you should adjust the choke a TINY bit to maintain an idle speed that is just slightly higher than normal. You should leave the choke set there (or adjust it only in tiny increments) to maintain that slightly faster than normal idle until it gets thoroughly warm. This might be anywhere from a couple of minutes (miles) to 10 or so. And yes, it is perfectly OK to leave the choke partially operated..........forever really, as it has almost no effect except at idle.

Yes, mine is a little erratic when COLD but responds like you describe ONLY when I release the choke too soon. Did you mention this when it went in for service?

Are we getting close to something that sounds like it might be a factor here ??
This really isn't rocket science, after all !! :poke2: :biggrin:

[mrlmd1]

My bike is a '99 and runs like a fine watch from the day I got it over a year ago, before that it sat idle for a few years. It starts instantly with some choke when cold, warms up quickly, runs smooth, never stalls unless I unintentionally made it do that on starting out from a stop (like being it too gentle on the throttle and too quick on the clutch release as any bike will stall if you don't do it right). I think most of the bikes on here run perfectly without adjusting things on the carb, idle, etc, every day, to try and get it right.
AC, you should bring the bike back to the dealer and have them fix it so it doesn't stall, set the idle to specs, stop theorizing and adjusting things you don't understand or you will continuously get it so out of kilter that it won't run or be reliable at all. As they say, a little bit of knowledge is a dangerous thing - let someone with the expertise and the tools get it running right, or go take a small engine maintenance mechanics course or read the shop manuals to gain the knowledge to do it yourself. This was a new bike 6 months ago and was probably running fine right out of the crate before someone screwed it up or abused it, or filled the tank or carb with dirt, or whatever happened to it. Once it's running right, it should be like "set it and forget it", it should keep on going. It seems like 5% of the members on here have 90% of the problems, and most of these shouldn't happen to a new bike with relatively few miles on it. :??: :poke2: :cry: O_o

[BusyWeb]

It seems to me that the proper "real" tach to get for the GZ is a "double fire" model, the same as is used for V-twins that fire the plug TWICE on each revolution.
Hi, there.
This is good information that I had suspected about it.
When I measuer on the spark plug it gives read exactly double values compare to the ignitor cable.
On the ignitor cable, it reads what I WANTED values... ha ha ha.
Some strange read I can get is when the engine speed is over 3000 (exactly 3000), it reads DOUBLE value, very strange.... :??: :??: :??:
So, I tride to fix with my calculation as possible as I could, but still double read after 3000 on ignitor cable.
Therefore, I put away my diy rpm meter from my GZ :blush:
I think that there is something going on this little GZ inside ingnition system.
But less than 3000, it seems correct if I ear-measuring with engine speed.
Anyway, it's always fun with GZ....
I also want to borrow the Tachometer from a body shop to see what the exact value GZ runs.

[alanmcorcoran]

Anyhow, now we have a new ball game. Have you done the Seafoam thing yet?

Yes, but, since I am only using the GZ for my work commute I'm only about 25 miles into the first tank.

Are you releasing the choke a little TINY bit at a time or are you going all the way from full to nothing?

Well, yes and no. I find that moving the choke a tiny bit at a time has no effect. However, you get to a certain magical point, and BAM, it drops to almost stall or actually does stall. So, I don't go from full to nothing, but I don't move it in tiny increments either.

You should not need full choke if the temp. is above 50 or so; 1/2 or 3/4 shoud be plenty and then 30 seconds or so after it starts, you should adjust the choke a TINY bit to maintain an idle speed that is just slightly higher than normal. You should leave the choke set there (or adjust it only in tiny increments) to maintain that slightly faster than normal idle until it gets thoroughly warm. This might be anywhere from a couple of minutes (miles) to 10 or so. And yes, it is perfectly OK to leave the choke partially operated..........forever really, as it has almost no effect except at idle.

This is pretty much exactly how mine worked when it was new. Now, that was in June. And it's consistently warm here in June. So... maybe I just have my expectations too high. But it definitely is more stall-y now than it was before.

Yes, mine is a little erratic when COLD but responds like you describe ONLY when I release the choke too soon. Did you mention this when it went in for service?

I did. And it stalled right the eff out when I stopped before I left the parking lot. I thought about taking it back, but, to be honest, I just wasn't up for the usual service department bullshit. For starters, they would need to carefully test it when it is COLD. My experience is, this requirement alone is enough to disqualify you from making any progress. Plus, they already had it for FOUR EFFING DAYS! To change the oil, allegedly clean the carb, and perhaps put air in the tires. Sorry, but my conclusion is they are not able to fix anything complicated.

Here's some other stuff:

1) If the idle suddenly drops real low (for some mysterious reason) and I twist the throttle, it will re-settle higher. Thus my sticky cable theory.
2) Conversely, if it suddenly gets crazy fast, and is racing like a MF at a light, if I let the clutch out a tad, to the friction zone, and then pull it back in, it will resettle lower.

These two phenomena make me very suspicious of the stability of the idle. This behavior occurs even when the engine is hot.

On the ride home tonight, I had fewer problems, but I warmed the engine up for five minutes before I left the office. I did not stall at all, but the idle was still too high once the engine got hot.

[Easy Rider]

Well, yes and no. I find that moving the choke a tiny bit at a time has no effect. However, you get to a certain magical point, and BAM, it drops to almost stall or actually does stall. So, I don't go from full to nothing, but I don't move it in tiny increments either.


OK, this is rapidly becoming pointless. Really wish I was there to SEE the bike. Not much can be done by remote control. Any chance you can get an "old hat" to stop over sometime for a test ride when cold?? I'm beginning to think that's the only way your going to get a good analysis of the situation.

One last thought: Your description of adjusting the choke reminds me of my wife adjusting the thermostat for the furnace. She thinks that they higher you set it, the faster it will get warm. She KNOWS how a thermostat works but it just doesn't sink in somehow.

Apparently something has changed since new but until you get that figured out, I think you need to leave the choke set above that threshold spot for a little longer.

If there IS a problem with something sticking, it's beginning to sound more like the choke cable instead of throttle. Just don't lube the choke lever on the bar; it is supposed to "stick".

Oh, and one more thing: You aren't using "premium" gas, are you ??

P.S. I hope you adjusted the hot idle back down where it should be.

[alanmcorcoran]

Sorry for the endless chatter Easy, but, what is it, like zero there? Not like you are going to do any riding today.

Not using premium gas in the GZ (it IS recommended for the Strat, and I have been using it there.) I dropped the idle back down a tad but it's going to take a number of days of experimentation to find the magic point (if there is one) where the idle is fast enough when it's cold so that it doesn't stall and not crazy fast whe it's hot.

If I didn't have the other bike, I'd probably suck it up and go on a quest for a good bike shop. Since I'm likely to be disappointed, and this is supposed to be (mostly) about having fun, I'm putting that futile exercise off for now. If the seafoam doesn't work, and he idle adjustment doesn't work and the stalling gets more irritating (and it will) eventually I will take it in again.

[Easy Rider]

I dropped the idle back down a tad but it's going to take a number of days of experimentation to find the magic point (if there is one) where the idle is fast enough when it's cold so that it doesn't stall and not crazy fast whe it's hot.


Guess I need to be a little more specific: The idle speed adjustment knob is for HOT idle ONLY. When the choke is in use, it OVERRIDES the idle adjustment stop.
SO.......
Set the idle speed adjustment when the engine is HOT. Do NOT TOUCH IT when the engine is cold. Along with enriching the mixture a bit, the choke lever also makes the idle speed higher, using a mechanism that is seperate from the idle speed adjustment knob.

If the engine is not warmed up yet and it stalls, then you didn't have enough "choke" dialed in.
So, there it is. Been trying to get there for about what, 6 weeks now ??? :)

And as for the tiny adjustments of the choke lever not making any difference, after thinking it over, I think that is probably normal too.

Start, warm up for a minute with choke on.
Ride a mile or so.....to first stop. Adjust the choke a tiny bit. May not make any noticable difference.
Ride to the next stop. Adjust again.
After 4 or 5 stops and 5-10 minutes of riding, you should find that the choke is now OFF and the idle speed is still OK....AND.....you never did hit that threshold point where the idle drops too much and it stalls.

If, after the gas with Seafoam is gone, you can't do that, then something is FOOBAR and you will need service.

And, no, there is no riding here. Was out on the tractor shoveling SNOW !! :skull:

Thinking about going to the Int. MC Show in Chicago on Saturday but probably won't 'cause it might make me cry !! :cry:

[alanmcorcoran]

Thanks. I'll see if I can make some more progress today.