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YZF750 poor tickover when warm and hard to restart.

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Nobby the Bastard
Harley Gaydar



Joined: 16 Aug 2013
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PostPosted: 16:30 - 08 Nov 2019    Post subject: Reply with quote

Sounds like an air leak, but I'd blame the mussies just to be on the safe side.
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Easy-X
World Chat Champion



Joined: 08 Mar 2019
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PostPosted: 17:17 - 08 Nov 2019    Post subject: Reply with quote

Nobby the Bastard wrote:
Sounds like an air leak, but I'd blame the mussies just to be on the safe side.


Not kewl, man!

(checks name of poster)

Oh, that's okay then... as you were Laughing

All cylinders firing okay? Might the backfire be some unburnt fuel from a cold cylinder?
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Tankie
Crazy Courier



Joined: 24 Feb 2017
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PostPosted: 17:55 - 08 Nov 2019    Post subject: Reply with quote

Balance the carbs with vacuum gauges
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Fizzer Thou
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Joined: 06 Aug 2011
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PostPosted: 22:50 - 08 Nov 2019    Post subject: Reply with quote

Do a compression check when the engine is cold then once the engine is hot and the niggles start to appear.If the valve clearances are tight because of the seats becoming contaminated then it may well be that the centre two cylinders have reduced compression compared to when cold.

When you had the carbs off did you check the inlet gaskets between the cylinder head and the inlet manifolds?

Part 11 on the fiche https://www.cmsnl.com/yamaha-yzf750r-1996-4hd7-england-264hd-300e1_model38768/partslist/0011.html#.XcXiHriaLTQ

On my Exup1000 they are oval shaped 'O' rings and two out of the four on my engine had shrunk and stopped sealing correctly with the heat from the engine.No amount of carb balancing would compensate for leaking gaskets.I would expect to see fluctuating readings with gaskets that were compromised.
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Shaft
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Joined: 27 Dec 2010
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PostPosted: 17:20 - 09 Nov 2019    Post subject: Reply with quote

Nobby the Bastard wrote:
Sounds like an air leak


I had almost identical symptoms on my last XJ900.

I was aware it hadn't been in regular use for a while before I bought it, so I did all that stuff too, plugs, injector cleaner etc.

Made it better for a while, but not totally sorted, then started to get worse again; didn't like to hot start, would drop a cylinder from time to time (although not properly, just seemed like it would miss every few cycles) sluggish revving, poor idle, the odd pop and bang.

I only spotted the problem when I was trying to start it in almost total darkness - hit the starter and noticed what I thought was a flash under the tank.

Bent down to have a look and there was an air pipe running from between carbs 2 and 3, which had obviously hardened over time and then split, the flash being a tiny flame that appeared through the hole in the pipe.

Replaced the pipe with some generic fuel line, problem solved.
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