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poot performance on compression test, what next?

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pork6156
Renault 5 Driver



Joined: 11 Mar 2011
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PostPosted: 14:52 - 15 Jan 2015    Post subject: poot performance on compression test, what next? Reply with quote
Hi.
My 97 zzr600 wont start, changed many parts.
This morning I did a compression test.

Cyclinder 1 - 60 psi (not good)
2,3,4, all around 90 psi, not great.

This test was done from cold as the bike turns over, but wont start.

What do I do next?
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temeluchus
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Joined: 01 Oct 2008
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PostPosted: 14:59 - 15 Jan 2015    Post subject: Reply with quote
Did you hold the throttle fully open?
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pork6156
Renault 5 Driver



Joined: 11 Mar 2011
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PostPosted: 15:02 - 15 Jan 2015    Post subject: Reply with quote
Erm..... No. Guess I should have?
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mentalboy
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Joined: 05 May 2012
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PostPosted: 15:07 - 15 Jan 2015    Post subject: Reply with quote
pork6156 wrote:
Erm..... No. Guess I should have?


I too am curious...it shouldn't make any difference. Low piston PSI will still be proportionately lower than the other 3, regardless of throttle position

Edit: have you tried the teaspoon of oil down the spark plug hole and then rechecked (all chambers, not just the low one)?
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pork6156
Renault 5 Driver



Joined: 11 Mar 2011
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PostPosted: 15:29 - 15 Jan 2015    Post subject: Reply with quote
I have now done the same test with throttle open. All cyclinders are then between 130 and 140 psi.

So still I am none the wiser as to why it wont start.
It has had new plugs, a new coil pack, new cdi ignition starter.
New fuel and oil.
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Aff
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Joined: 05 May 2011
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PostPosted: 15:33 - 15 Jan 2015    Post subject: Reply with quote
pork6156 wrote:
I have now done the same test with throttle open. All cyclinders are then between 130 and 140 psi.

So still I am none the wiser as to why it wont start.
It has had new plugs, a new coil pack, new cdi ignition starter.
New fuel and oil.


Is fuel getting to the cylinders? Do the plugs come out wet after trying to start it?

Does it have a spark?

Randomly replacing components is an expensive way to diagnose a problem.
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pork6156
Renault 5 Driver



Joined: 11 Mar 2011
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PostPosted: 15:42 - 15 Jan 2015    Post subject: Reply with quote
The plugs are sparking. They don't come out wet.
However it stinks of petrol after trying to start it. And there is fuel in the oil.
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mentalboy
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PostPosted: 15:54 - 15 Jan 2015    Post subject: Reply with quote
Is this the same bike that was giving you grief back in September? If so did you ever sort out the problem/attend to carb O-rings?
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pork6156
Renault 5 Driver



Joined: 11 Mar 2011
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PostPosted: 15:55 - 15 Jan 2015    Post subject: Reply with quote
There is spark on all plugs. They are not wet after trying to start. It often stinks of petrol and there is fuel in the oil.
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pork6156
Renault 5 Driver



Joined: 11 Mar 2011
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PostPosted: 15:57 - 15 Jan 2015    Post subject: Reply with quote
mentalboy wrote:
Is this the same bike that was giving you grief back in September? If so did you ever sort out the problem/attend to carb O-rings?


Yes it is the same bike. I was not convinced with the rings being the problem.
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mentalboy
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PostPosted: 16:08 - 15 Jan 2015    Post subject: Reply with quote
pork6156 wrote:
mentalboy wrote:
Is this the same bike that was giving you grief back in September? If so did you ever sort out the problem/attend to carb O-rings?


Yes it is the same bike. I was not convinced with the rings being the problem.


Rings? Do you mean the piston rings being stuck, which is what your original thought was, or O-rings in the carbs?
If it's been stood three months then you'll be needing fresh fuel. Oil and filter change to remove the fuel from the lube system (ie there isn't supposed to be fuel in the oil!! Definitely not to the extent that you can spot it).

Carbs will at least need draining off, so it'd make sense to get in there, check float movements, inlet needle seating, jets (and funnily enough those O-rings that were previously recommended!)
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pork6156
Renault 5 Driver



Joined: 11 Mar 2011
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PostPosted: 16:14 - 15 Jan 2015    Post subject: Reply with quote
Yes I originally thought the piston rings were getting stuck. Now starting to think the carbs will need looking at.
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temeluchus
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PostPosted: 16:37 - 15 Jan 2015    Post subject: Reply with quote
mentalboy wrote:

I too am curious...it shouldn't make any difference. Low piston PSI will still be proportionately lower than the other 3, regardless of throttle position


So trying to fill the cylinders with air, to get a good pressure reading is best done through the tiny gap on closed throttle and the idle circuit passages?
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mentalboy
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PostPosted: 18:05 - 15 Jan 2015    Post subject: Reply with quote
temeluchus wrote:
mentalboy wrote:

I too am curious...it shouldn't make any difference. Low piston PSI will still be proportionately lower than the other 3, regardless of throttle position


So trying to fill the cylinders with air, to get a good pressure reading is best done through the tiny gap on closed throttle and the idle circuit passages?


Not disputing that you should use WOT with a warmed up engine but I was quite surprised that the low psi cylinder registered within an acceptable 10psi difference with WOT. After all, the 4 cylinders are all restricted by a closed throttle, not just the one. Live and learn!!! Thumbs Up
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