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900A4 Carburation question

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NickH
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900A4 Carburation question

#1 PostAuthor: NickH » Tue Dec 04, 2018 1:32 pm

Chaps
I'm 95% there with my A4 project; she's been running 10 times better since a good friend re-did the ignition, and I've loved riding it around and feeling that joy! Carburation seemed absolutely fine, no fluffing, clean-revving throughout the range, etc, however, one issue is still the mixture; she's a KZ recently imported and had a reproduction full 4-4 system fitted, post-import and the plugs tell me she's running rich. Very sooty plugs on all 4 pots.

My logic went along the lines of "Well, it's probably had a 4-1 on it at some point in it's life, so has probably been upjetted to suit. Maybe she's running rich because it's got too bigger jets in, so I'll go back to standard".

Hoiking the carbs off for what seems the 5th time in as many months, yes, there are 120 jets in there, whereas Z-Power say they should be 115's. I am for the moment assuming she has Mikuni 26's on there as I can't work out how to identify them properly. I should also say, she has a Z1A/B Airbox too, making things more difficult to diagnose.

So - I fitted the 115's last night, thinking she'd fire up and run sweetly - however, as sod's law so accurately states, quite the opposite happened. She's running as rough as an old dog, will only run on choke (full choke gives around 3,500 RPM, half-choke gives 2,000, and no choke, it won't run.) On any of these choke settings, even gently moving the throttle causes it to bog down and die. She's suddenly smoking like hell - something she's never done before!

So dear knowledgable friends - what on earth have I done wrong? I suppose I cold have checked the needle clip settings, but I only want to change one thing at a time.

Thanks all :-)

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Re: 900A4 Carburation question

#2 PostAuthor: Ultim8pc » Tue Dec 04, 2018 2:53 pm

Nick

Using the earlier z1 airbox with the later z900 carbs has proven to be problematic for others. However, other than the richness you describe, it does seem it was running OK prior to the main jet swap.

Replacing 120 main jets with 115 shouldn't make the difference you describe. Starting, idling on very low throttle openings don't use the main jets.
What you describe sounds like blocked pilot jets or overfull float bowls. Is there any way crap could have got into the float bowls when you changed main jets? Or any chance you somehow changed the float heights. (For example by inadvertently swapping floats or needle vales or both)?
But you could of course just go back to the original 120s and see if it goes back to being OK...

Measuring the diameter of the carb mouth (cylinder head side) is the best way to determine what size carbs you have.

I'll PM you my number, please feel free to give me a call if you get stuck and need some help/advice.
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Re: 900A4 Carburation question

#3 PostAuthor: weaver » Tue Dec 04, 2018 5:00 pm

this does sound like something is not right after reinstallation,throttle cable all ok?choke?

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Re: 900A4 Carburation question

#4 PostAuthor: engz1b » Tue Dec 04, 2018 6:23 pm

i would take the carbs back off and clean all the jets and everything again, what are the inlet rubbers like, ? you have had the carbs off a few times, and if they are old, they may have cracked when you took the carbs off last time, causing them now to leak

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Re: 900A4 Carburation question

#5 PostAuthor: Pigford » Tue Dec 04, 2018 8:06 pm

The new-reproduction pipes are very restrictive..... Also even tho' ignition is better, check there's a good 12v at coils when running!!!
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Re: 900A4 Carburation question

#6 PostAuthor: NickH » Wed Dec 05, 2018 3:43 pm

Thanks all - I'll be able to get those carbs off pretty swiftly, and re-check everything.

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Re: 900A4 Carburation question

#7 PostAuthor: NickH » Wed Dec 12, 2018 11:15 am

So - erm....I finally got to the bottom of this one - I'd managed to top the tank up with bloody DIESEL (maybe 3-4 litres). First time in 50 years I've done it. Carbs off, everything cleaned again, flush tank, re-assemble, and Ping! Running like a beauty. What an utter nob I've been..

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Re: 900A4 Carburation question

#8 PostAuthor: Ultim8pc » Wed Dec 12, 2018 11:59 am

HaHa!
Glad you got it sorted though.
http://www.airevalleyclassics.co.uk
10% discount code Z1OCTEN
Keyster rebuild kits & carburettor spares - airscrews, jets, needles, starter plungers & gaskets.
Also petrol/ethanol proof float bowl gaskets. IMD pistons preferred seller.

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Re: 900A4 Carburation question

#9 PostAuthor: gpjes » Wed Dec 12, 2018 12:08 pm

I see it all the time up at garage where I fill van up, daft Asian women do all the time, pick up wrong pump start and stop then pick up right one :lol: I run 3 bikes, a 635d coupe, petrol rav-4, and Toyota hiace swb dturbo, odd one out is coupe it fills up on wrong side :hah!
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Re: 900A4 Carburation question

#10 PostAuthor: 8 Valve Mark » Wed Dec 12, 2018 12:17 pm

NickH wrote:So - erm....I finally got to the bottom of this one - I'd managed to top the tank up with bloody DIESEL (maybe 3-4 litres). First time in 50 years I've done it. Carbs off, everything cleaned again, flush tank, re-assemble, and Ping! Running like a beauty. What an utter nob I've been..

done it myself once, filled my petrol van with diesel and ground to a halt on the m4@ Heathrow!! you'll be ok for degreaser for a while eh?

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Re: 900A4 Carburation question

#11 PostAuthor: ADRIAN H » Wed Dec 12, 2018 4:49 pm

Glad you have managed to sorted it out.
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Re: 900A4 Carburation question

#12 PostAuthor: Philippe » Thu Dec 13, 2018 7:31 am

Hi Nick
seems to me you have a one of a kind A4, with a diesel engine! JC, the newest technology! Where will it end?

Only joking! I hope you don't mind...
Glad you found out what it was.
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Re: 900A4 Carburation question

#13 PostAuthor: NickH » Thu Dec 13, 2018 10:01 am

Honestly, I don't think I've ever been that dopey in my life. Obviously I gave myself quite a stern talking to.

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Re: 900A4 Carburation question

#14 PostAuthor: rickm » Thu Dec 13, 2018 10:13 am

NickH wrote:Honestly, I don't think I've ever been that dopey in my life. Obviously I gave myself quite a stern talking to.


I admire your honesty.
I'm sure a lot of folk would have come back saying they "found x or y (not diesel) after stripping the carbs, and now I've sorted it" ! :blush
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Re: 900A4 Carburation question

#15 PostAuthor: Taffus » Thu Dec 13, 2018 1:02 pm

It could be more embarrassing....
You could be on a ride out with the club and have about 20 bikes waiting for you to lose the diesel you just filled up with and replace it with petrol!
It wasn't me but one of mackems but not big green bus..........


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