XJ900 Diversion Misfire Problem

Mitch

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Mar 25, 2013, 5:38:04 PM3/25/13

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So it did the 700 mile slog to Malaga running really sweet but next day
would'nt fire up on one cylinder (no. 4) despite being in a dry garage all
night. The spark plug (new at start of journey) was wet with petrol so I
changed it and it ran OK for 30 ish miles then starts misfiring at low revs
but okay above 3000rpm. Took out the plug and it was black and fouled up as
if running rich. Same again a new plug and it was okay till about 20 miles.
WTF? No smoke from exhaust. Compression OK. I've since drained the carb (no
water), checked jets clear, diaphram, float valve, needle and HT leads for
arcing and nothing found. Good spark at (new) plug. I'm thinking coils/HT
leads/plug cap by ellimination and I've ordered a new coil but have this
nagging feeling its not that. Any suggestions? Bike is too good to move on
and I love that shaft drive. If it was bad petrol it'd affect other cyls and
ditto the CDI surely? Do XJ9's have a specific common fault like this?

Mind you thank F it did'nt happen at the Bilbao end!

M

c...@nospam.netunix.com

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Mar 25, 2013, 6:26:14 PM3/25/13

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Do a compression test. Does the bad cylinder have (even slightly) less
pressure ?. Is it using oil ?.
Sounds like it might be burning oil due to a broken ring. If so DO NOT
ride until it is fixed, a broken ring could rapidly ruin the bore.

--
05 Yamaha YP400 Majesty
75 Suzuki GT750 Kettle
81 Suzuki GT200 X5
++May contain nuts.++

Wicked Uncle Nigel

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Mar 25, 2013, 6:50:30 PM3/25/13

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Using the patented Mavis Beacon "Hunt&Peck" Technique, Mitch
<ma...@mitchelmores.plus.com> typed

> I'm thinking coils/HT
>leads/plug cap

Does it have individual coils? I thought most fours has two coils, in
which case two pots should be equally affected by a bad coil, no?

--
Wicked Uncle Nigel SBS#39 - "He's hopeless, but he's honest"

Contains moderate bullshit and simulated opinions.

rick

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Mar 25, 2013, 7:00:35 PM3/25/13

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Gotta be the HT lead or plug cap iwht - poor join at cap end maybe?

--
Rick Brown
Sprint RS, R100RT

Mitch

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Mar 26, 2013, 4:52:42 AM3/26/13

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> Does it have individual coils? I thought most fours has two coils, in
> which case two pots should be equally affected by a bad coil, no?

Yes two coils, so one for cyls 1 & 4 which would suggest I should lose two
cylinders but it could be the (quite long) HT lead tracking before it gets
to cyl 4? Annoyingy the HT leads are different lengths so I cant swap em
over to test.

Thanks

M

Mitch

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Mar 26, 2013, 4:54:54 AM3/26/13

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> Do a compression test. Does the bad cylinder have (even slightly) less
> pressure ?. Is it using oil ?.
> Sounds like it might be burning oil due to a broken ring. If so DO NOT
> ride until it is fixed, a broken ring could rapidly ruin the bore.

Its not smoking or noticeably using oil and I did a thumb compression test,
which it blew off convincingly. Maybe I'll put a gauge on it.

Thanks

M

Mark Olson

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Mar 26, 2013, 5:08:11 AM3/26/13

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You could try running it [optionally, with the tank off] in a dark place
and looking for arcing.