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MarkGoy |
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MarkGoy Borekit Bruiser
Joined: 26 Jan 2017 Karma :
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Posted: 17:33 - 20 Mar 2017 Post subject: Gz125 (again) power issue related to revs |
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Hello,
1st, thank you to this forum, i came here a while back with the same issue and was told to fix my carb leaking first before anything else.
Well thanks to your help its fixed, no more leaks, so thank you, sincerely.
//
Right, to business, GZ125 K3 made 2003.
I plonk it in first and pull the accelerator, it gets to X revs and just cant pull anymore, making a weird judder noise from the engine.
Its exactly the same in all gears, but not with the clutch in or neutral, I can rev to my hearts content like that.
I sellotaped my mobile to my satnav to try and get a good video of the noise / speedo.
link follows.
https://www.youtube.com/watch?v=4FJ4TsGl7d0&feature=youtu.be
I hope this gives a good amount of detail?
thanks in advance. |
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jaffa90 |
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jaffa90 World Chat Champion
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MarkGoy |
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MarkGoy Borekit Bruiser
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jaffa90 |
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jaffa90 World Chat Champion
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MarkGoy |
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MarkGoy Borekit Bruiser
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jaffa90 |
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jaffa90 World Chat Champion
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MarkGoy |
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MarkGoy Borekit Bruiser
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Robby |
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Robby Dirty Old Man
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MarkGoy |
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MarkGoy Borekit Bruiser
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MarkGoy |
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MarkGoy Borekit Bruiser
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MarkGoy |
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MarkGoy Borekit Bruiser
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jaffa90 |
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jaffa90 World Chat Champion
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MarkGoy |
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MarkGoy Borekit Bruiser
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jaffa90 |
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jaffa90 World Chat Champion
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MarkGoy |
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MarkGoy Borekit Bruiser
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Posted: 14:53 - 24 Mar 2017 Post subject: |
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pic 1 spark plug hasn't done many miles if that makes a difference?
Aaaah, so if the carb slide doesn't lift high enough, enough air cant pass over the jets, pulling sufficient fuel into the engine, I hadn't thought of that. I assume that's effectively hitting the top of my rev range.
I've done a quick test, by you saying "watch it slowly going back to rest." I think its not right.
maybe i haven't fit the diaphragm properly, I got a new diaphragm last year, no holes or anything like that in it.
https://www.youtube.com/watch?v=kGimQLpl7fQ |
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talkToTheHat |
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talkToTheHat World Chat Champion
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Robby |
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Robby Dirty Old Man
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Posted: 15:51 - 24 Mar 2017 Post subject: |
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The spark plug looks like you've had a lean mix, and you've been cocking around with the carb, so let's consider that area.
3 areas to consider:
1. Fuel supply/flow to the carb. This is easy. Assuming a normal gravity feed with a fuel tap, does fuel freely piss out of the end of the fuel hose when you pull it off the carb. Direct it into a bottle, pour it back in the tank afterwards. Let it flow half a litre or so - if you only do a few cc of fuel then its just the bit in the pipe and filter if fitted.
2. Air leak on the carb rubber. Does the carb sit into the carb rubber in a secure way, assuming there is a big jubilee clip holding it in place, is this clip tight? It is possible that the lip of the rubber got folded under the carb during fitting, causing a big air leak. Also look for splits in the rubber. Easiest to see with the engine running, because the rubber will pulse and flex a bit.
3. The carb itself. Take it off the bike, drain out the fuel into a clean container to look for contaminants, then get the carb on a clear, well lit work bench to go through it piece by piece and rebuild it to factory spec. In particular you should be checking:
a. The condition of anything rubber.
b. jet sizes, condition, cleanliness
c. Needle height and straightness.
d. Mixture screw setting.
e. Float height.
Clean any passageways you can find with a can of carb cleaner, using the straw nozzle to get in there. Wear eye protection, carb cleaner will get in your eyes and it stings. |
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jaffa90 |
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jaffa90 World Chat Champion
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MarkGoy |
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MarkGoy Borekit Bruiser
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Posted: 01:32 - 25 Mar 2017 Post subject: |
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talkToTheHat :
Thanks, I understand your point, but I disagree, I believe the GZ to have a bit more power to give, and i can prove that with the spark plug test.
I'll add CDI unit to "things to check", thank you.
Robby :
1) One of the first things I checked, it is gravity fed and it does work fine.
2) Carb sits secure, yes clips on both ends, both tight, not possible for rubber seal to be folded I always check before attaching clips, I haven't checked for splits while the engine runs I will add that to the list.
3) No contaminants, Ive had the carb off and stripped many times each time I've checked, already been rebuilt to factory specs with suzuki parts.
a) all good, or replaced if otherwise.
b) factory settings jets for this carb, placed during rebuild
c) by needle do you mean jet needle? I assume so again factory set, definitely straight.
d+e ) set to book settings but the book doesn't match the carb, can't work out why. I have also tuned the mix screw just in case. Its my understanding that mix screw only affects low rev range.
I have already cleaned the carb with carb cleaner and pressurized air, and Ive had it cleaned professionally.
jaffa90 :
I understand the basics of how carburetors work, I'm not sure on the exact differences with constant velocity other than on this model I control a butterfly valve rather than the slide bit where the jet needle is...
I'll do more research on the subject.
Thank you, ill be back when I either get stuck or solve the issue (but the bike still runs bad).
//
thanks to all. |
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talkToTheHat |
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talkToTheHat World Chat Champion
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talkToTheHat |
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talkToTheHat World Chat Champion
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MarkGoy |
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MarkGoy Borekit Bruiser
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MarkGoy |
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MarkGoy Borekit Bruiser
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Posted: 01:33 - 26 Mar 2017 Post subject: |
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"The fundamental frequency of the strongest signal peaks at 125Hz. "
Do I have this right? at the strongest signal, or clearest? part of the audio the lowest (presumably consistent) frequency you could find was 125hz.
So the rpm its doing at that present time, would be worked out by ..... I think that 125hz comes from 125 explosions per second which can be heard, which would make 7500 explosions per minute.
But as you say, the fuel mix explodes in the engine once every two cycles (explodes, exhaust, intake fuel air mix, compression).
Meaning that 7500 explosions, multiplied by two revolutions per explosion = 15'000 rpm.
Ok, I think i've got what your saying now..
//
One explosion per cycle sounds bad, very bad...
The only thing I can think of is fuel air mix is entering engine when it shouldn't be..
is that a timing issue? but if it was a timing issue, wouldn't the bike not run at all?
I'm a little scared right now..
//
Edit : had a quick think... I don't think it could be timing because the engine runs fine out of gear.
So what's the difference between being in gear and not, I'm thinking resistance to the action of the piston...
The difference in gear ratios would create different resistances to the action of the piston, which would by my top speed in 2nd is roughly 25mph and my top speed in 5th is 48ish...
Unless gear ratios don't work like that...
The normal resistances that come with a gear box would be overcome by the fly wheel...
What if the up stroke of the compression never fully gets there, the spark ignites, there's a very weak explosion... if the piston never gets to t.d.c what happens to timing....
If it just tried that step again, the exhaust gasses would never leave.
But you said one explosion per cycle, which would mean the exhaust is vented and it switches straight back to the fuel air mix step, if possible.
But it must be possible, assuming you are correct in saying the explosion happens once per cycle, the piston becomes stuck between those two steps.
So the fuel air mix it pulls in is being mixed with part of the exhaust gasses, showing it as not enough fuel air mix?
Would that not leave a different residue on the spark plug? Or does exhaust gas cause nothing on the plug..
Currently I'm now thinking, what if... on the down stroke of this 2 stroke action the piston pulls in air fuel, the spark happens part way through, the piston then on the up stroke it vents the exhaust gas? Rinse repeat?
Sorry about the very very long message, my brain is exploding with thoughts and ideas, I've just written down all my thoughts over time.
But if that motion is right, the air/fuel intake valve would be open during the explosion and some of the gasses would travel backwards into the carb, slowing down the flow of air into the engine or at least causing eddies/ mixing with fresh air/fuel. Subsequently causing a pressure drop in the venturi of the carb, dropping the slide... if this is true.... the engine receives less flow of air/fuel and revs slower? Putting itself under that problem rev range? Then as the revs increase the issue would start again... |
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talkToTheHat |
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talkToTheHat World Chat Champion
Joined: 21 Feb 2012 Karma :
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Posted: 14:05 - 26 Mar 2017 Post subject: |
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MarkGoy wrote: | "The fundamental frequency of the strongest signal peaks at 125Hz. "
Do I have this right? at the strongest signal, or clearest? part of the audio the lowest (presumably consistent) frequency you could find was 125hz. |
Fundamental frequency is the lowest frequency present. You are almost always going to have related (harmonic) frequencies, usually loads, so you look at the lowest frequency signal.
Quote: |
So the rpm its doing at that present time, would be worked out by ..... I think that 125hz comes from 125 explosions per second which can be heard, which would make 7500 explosions per minute.
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It's not necessarcarily explosions, just a noise or vibration and the sensor is fixed to the bike in a manner that transmits engine vibrations. This is why I asked what the phone was fixed to. I think we're just seeing the once per revolution motion of the pistion in the same signal.
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One explosion per cycle sounds bad, very bad...
....I'm a little scared right now.. |
Don't panic that much, we're just seeing mechanical noise being indistinguishable from engine noise. Mechanical noise could be excessive, but the GZ engine is fairly noisy
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Edit : had a quick think... I don't think it could be timing because the engine runs fine out of gear. |
If your timing chain is out there is a strong chance the valves will hit the piston and many bad things will happen, menchanical failure is rare and usually more catastrophic. You'll hear that. More likely is your CDI is recieving bad data. Do you have a throttle position sensor on the carb? Small black cyinder with slotted dog-ear mounts on each side, mounted on the throttle butterfly shaft on the opposite side to the pulley. This could be sending bad data and as throttle position is used to determine spark timing. They're a pain to align if you need to replace one as you need to know the idle and WOT resistances. You will need a service manual or half an hour of garage time. Solve running lean first.
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So what's the difference between being in gear and not, I'm thinking resistance to the action of the piston... |
In neutral, very little drag on the engine
In gear and clutch pulled in, some drag from the clutch
in gear, clutch out and rolling, lots of mechanical and aero drag
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there's a very weak explosion...
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Yes if your mixtures are out. if the spark timing is out then this is like pushing a friend on the swings, too early and you waste energy pushing against the rising piston/friend, too late and piston/freind gets away from you before full energy transfer. Spark time is a little more nuanced as one has to account for the burn speed of the fuel, which is fast but not instantaneous, and is influenced by mixture, temperature, fuel composition, pressure, turbulance, combustion chamber shape and a handful of other things I CBA to remember. It's been a long time since I studied this.
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Would that not leave a different residue on the spark plug? Or does exhaust gas cause nothing on the plug..
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Your plug is showing you combustion products and temperature artifacts. It's suggesting you are running lean.
I think the engine is so lean that you're not making enough power to reach peak rpm, and likely leaner at high rpm. This is consistent with the problem robby is talking you the fixing of.
The mixture screw on the GZ is for the idle mix. It will have a small effect on WOT running but only minimally. Your needle assembly does the midrange operation and there is maybe an additional jet that works at wot, but I think the gz carb does it all on the needle.
Check for air leaks, diaphram damage and carb blockage. If you have a cheap 3rd party diaphram that is a bit stiff might be your problem.
You should be reaching 9000rpm under load and you're not. ____________________ Bandit. does. everything. |
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jaffa90 |
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jaffa90 World Chat Champion
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Old Thread Alert!
The last post was made 7 years, 30 days ago. Instead of replying here, would creating a new thread be more useful? |
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