GZ 125 Possible exhaust leak/I gone done goofed.

[alex965]

I'll keep this short but I'm afraid the stupid levels will be through the roof here.

Basically, I took my exhaust off to strip rust of it, that was partially successful. After ordering a brand new exhaust gasket and brand new exhaust bolts (The other ones were rusted through and borderline rounded off), I whipped the old gasket out, gave the head a quick wipe around to get any remaining gasket out and then fitted the exhaust. Well for some reason I decided not to tighten the bolts enough and 1 mile down the road I pull over to check everything is ok, there was a massive leak between the head and the exhaust. I went back home and tightened the exhaust up far more this time round. There is no longer any exhaust gas (that I can see) leaking, but the bike doesn't sound right, it's now extremely vibey at anything over 45mph and last night while accelerating hard in 4th and then releasing the throttle it backfired.

Also, I decided it would be a good idea to start the engine and let it idle for a couple of seconds with no exhaust on at all. Why did I do this? A mixture of stupidity and wondering what it would sound like. I am hoping this hasn't done any damage and isn't responsible for the problems.

I'm really not sure to do. Do I need to order a new gasket and start again? Any advice appreciated to rectify my stupidity as I have to do a 300 mile journey in a couple of days on the old girl.
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Passed A2 licence 19th Dec '14.

[Nexus Icon]

What sort of gasket is the GZ one? Is it a fibre gasket?

Running it loose might have burned the surface and it could well now be leaking gas past. That would certainly explain backfires and misfires, etc.
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Greetings from Shitsville!

[Teflon-Mike]

What you did was ACTUALLY not far from 'best' practice.Reaso so many shear exhast studs is over tightening the the first place.
So, first a little praise for wot you dun good. 1, preventative maintenance, 2. new exhaust studs, 3, new exhaust gasket, 4, not over tightening.
Hanging the exhaust on loose studs from the head, aligning and leaving loose at the hangers then working back and putting just a 'nip' on the gasket , before runig up, lettng flange 'settle' checking for leaks, and nipping up 'just' until they go, then givig the motor a run, to get it hot ad pup some gas shake any loose into it, then re-checking and re-tightening IS just about the 'ideal' way about the job. So well done.
Onto the 'stupid'. Runnig the motor up, 'off-load' without reving the fuck out of it without exhaust is not SO bad. And is oft done to test a 'take out' or such. As log as it wasn't run for ages or revved the heck out of it, ought do no major harm on simple motor like the GZ, so don't sweat that one.
The 'doesn't sound right' and is a bit 'vibey' is rather vague symptoms... the back-fire... err possibly not so good.
So, backig up... you took the 'zorst off cos it was rusty. Possible that in taking it off, and cleaning off surface rust you have exposed a pin-hole rust had been plugging or you have shaken a rusty baffle loose inside the pipe; & unfortunately pipe were essentially shot before you begun, and your work and disturbance has simply brought fault to the fore..
Run it up, on the stand and see if you can see any obvious leak actually on the pipe... if its there it will probably be on the bottom where condensation settles inside the pipe, and likely to be on thinest section where straight tube has been stretched into a bend, so the outside curve at the bottom.
Roll-off poppig is quite common on an open(or fucked) pipe. I was getting a little embarrassed last week... I went to Wales, which is a BIT hilly. My bike has a fairly err... 'unrestricted' stainless 4 into 1 on it, and if I shut-off farly sharpish after hard load, does pop and crackle, and 'back-fire'... briefly... but last week I was in Llandudno, if you know it, trying to find and meet up with my mother and youngest son at the Ancient copper mines... at the top of the Gt Orme and due to varouse 'things' had to ride up and down that chuffng hill about half a dozen times.... and it's a bit fucking steep! Coming down on engine breaking gravity was driving the motor hard enough it was coughing and farting and spluttering and back-firing like some-one chucked a bag of pop-corn up the pipe!
However, pot is, to some degree, its tolerable, and on a modded bike can be a 'feautre' not a fault, but does poit to suggestion you have lost a baffle or found a pin hole, and exposed a fault, rather than made one... so just go back and start with fresh eyes, dont assume its something you have done 'wrong'... NEVER make presumptions in fault finding, and dont chase 'chaff' trying to find clues in prior knowledge; always work 'cold' on the symptoms you can see here and now.
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[alex965]

Thanks for the advice, I'm going to go and have a proper look over the exhaust system and see what I can find.

And with running it with no exhaust system on, it was literally in neutral for about 4 seconds, no heavy revving or anything like that.

Thanks.
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Passed A2 licence 19th Dec '14.