Any help would be greatly appreciated :-D

[RickTaff]

Have a ZXr 750 J1 1991, H reg. 26k miles on the clock.

Took it out of the garden today for its MOT, bought the bike privately and fixed it up ready to MOT.

Started it up normal and let it idle on choke while i sat on the bike; anyway after about 4-5 mins it suddenly started making an underlying kind of knocking noise. It'll still start and idle, but that 'knocking' is still present. fresh oil in the bike, too

Balanced carbs about 2months or so back and had bike running a good 30mins without a hitch, and haven't started it since then with fuel in it so this is a sudden issue. Only thing i can say is i had a mate grab me £15 worth of fuel [tank was totally empty, may have been small amount of old fuel still in carbs though] so i could start the bike this morning as i have no alt. transport, and when i rung him this morning to ask what fuel he had me, he informed he had bought me E10 fuel. Soon as he told me I knew my bike could not have this fuel due to age. I have heard it perishes rubber and O-rings over time... but it also affects detonation apparently, so im wondering if this is perhaps my issue? and i need to drain it all out?

Thanks. Rick

[MarJay]

Here's my prediction, and you're not going to like it.

Sat for months, dried out O rings and carb needles etc. Fill with E10 Fuel. Fuel drains down past the float seals and enters the sump diluting the oil.

Start 'er up. Oil is diluted with petrol... knocking is big end bearing.

My suggestion would be drain the oil and see if it's full of fuel.

{also, bit late now maybe but generally it's traditional to put the make and model of bike and a brief description of the issue in the thread title rather than just "Help!" }
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[RickTaff]

[WD Forte]

Unless the big ends were already iffy I'm not sure
slightly thinned oil would knock them out at tickover
unless you revved it like buggery for extended periods
or you caned the arse off it up and down the road with questionable
lubriciousness

There's hardly any load on a ticking over engine so unless it was run dry I cant see much damage being done
even if the oil has been contaminated with fuel.

Who knows though?
We can only make guesses based on what we're told or can see,
maybe it is the ends or an exhaust header or cam shaft knocking
such little info to go on..................
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bikers smell of wee

[MCN]

Unless the big ends are really fukid, you probably wouldn't notice at idle.
Usually the knock is only discernable on the over run. Rev it a little which tightens everything up. Then let the rpm slow down to idle. Everthing thats slack/worn will then rattle/knock.

The fuel in the oil coukd still be a thing.

When an Engine craters usually the debris is caught in the oil filter.
And also when you drain the oil any debris may be visible in the drained oil.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[RickTaff]

[RickTaff]

[WD Forte]

vid with audio
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bikers smell of wee

[RickTaff]

[stinkwheel]

Is it firing on all 4 at idle? A missing pot with a blocked slow runnign jet can make a godawful knocking noise.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[RickTaff]

[MarJay]

[A100man]

Agree with Marjay - it's nothing to do with the fuel.

Agree with Stinkers - running on less than four pots sounds baaad..

Agree with WD - contaminated oil not usually an instant death knoll (knell?)
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Now: A100, GT250A, XJ598, FZ750

Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600

[RickTaff]

[RickTaff]

[stinkwheel]

I put car oil in my bikes all the time.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[ThatDippyTwat]

[to v or not to v]

i used to lust after the blue version of the h1 when they came out, thought those tubes going into the tank were so cool.
sorry this post is no help, just wanted to say what a lovely looking bike it is.
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current bike Yamaha Thunderace.
Moto Guzzi V7.

[WD Forte]

31 years old and 26 thousand miles eh?
Thats's just 838 miles a year or 16 miles a week.

If its such a good bike how come no one wanted to ride it much?
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bikers smell of wee

[RickTaff]

[RickTaff]

[to v or not to v]

i remember bike mags at the time saying the seat was like sitting on a plank due to the rear shock and that a replacement was definitely needed.
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current bike Yamaha Thunderace.
Moto Guzzi V7.

[MarJay]

[RickTaff]

[yen_powell]

I had a Kawasaki start knocking once. Turned out all that had happened was that one of the rubber boots that blocks off the carb balance ports had fallen off. I was at traffic lights at the time and there was a VW Beetle in front. I thought it was clattering like they do until it pulled away and the rattle stayed with me.

I note you recently balanced the carbs, maybe one wasn't put back properly and it's come off.
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Blackmail is a nasty word........but not as nasty as phlegm!
XT1200Z and a DR350 in bits