Question about 1976 kawasaki Z 750

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82 gpz 750 r1. Could a compression reading of 110 in cylinder 2 cause mild fluttery sounding rev above idle, lack of torque and a dry, near white looking plug? Could these symtoms be caused by the fact the mac header has no gaskets?

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Yes it is low compression and can cause problems,may be a valve problem, judging by the sound, check the clearances,
really tight , burnt valve
really loose, stuck valve
No gaskets can cause that, but would generally take quite a few kilometeres.

Posted on May 05, 2010

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Can to tell me what compression does a 3y motor should be thank you.

Toyota mota ?

Any compression figure above about 130 psi is OK. A dead new engine might reach higher than that. Any reading below 100 psi indicates that cylinder has a problem with either rings or valve sealing.

However of far more importance is the variation between cylinders. Ideally you want no more than 10% variation (max 15%) between lowest and highest reading, for smooth running and idling. So one reading of 110 psi and the next at 150 psi still needs some further investigation, at least a repeat run.

Oct 10, 2016 | Cars & Trucks

2 Answers

Have a spark plug not firing.

Are you sure it's actually a plug?
Are you getting oil on the plug?
The plug may be firing but you may be losing compression which gives the symptoms of a misfire. As you've changed the plug, lead and coil this points to to a problem elsewhere.

Your first course of action should be to get a mobile mechanic carry out a diagnostic check for you.

To put your mind at rest, do a 2nd compression test using a light oil squirted into the bores:

Doing a Compression Test
Warm the engine. Remove all the spark plugs.
Get a pencil and piece of paper to note down the readings.
Put the compression tester into the No1 cylinder and crank the engine for 10 seconds.
Note down the compression reading.
Repeat process for all cylinders.

Here's an illustration of what you may expect on a 4 cylinder engine:
Cylinder 1 2 3 4
psi 125 122 120 124

125 is the uppermost figure for that engine. Here, this engine is fine. There's a slight variation in psi figures, but that's perfectly normal.

Here's the same engine:
Cylinder 1 2 3 4
psi 110 112 114 112

The psi reading is down. However, as all the figures are pretty much equal it doesn't indicate head /gasket problems. It may point towards worn pistons or burnt valves.

Now consider these psi readings:
Cylinder 1 2 3 4
psi 125 84 86 124

There's more than a 10% drop - a difference - between cylinder 1 and 2, and cylinders 3 and 4.
The compression readings for cylinders 2 and 3 is down; low. There's something clearly wrong.

It suggests that there is a defective head gasket between cylinders 2 and 3 or a crack in the cylinder head. The rising piston compresses the gases which escape into the adjoining cylinder via the defective gasket or cracked head.

However, it could also mean that there is a problem with the valves (burnt/not seating properly) or perhaps piston / ring problems.

A burnt valve - it's usually the exhaust valve as they bear the brunt of the combustion - can cause a reduction in engine power simply because the combustion process isn't occurring properly. Compressed air/fuel gets squeezed out of that cylinder because of the damaged valve . There even may be a misfire - a surge as the car runs.

Worn or broken piston rings allow compressed gases to leak past into the crankcase. A compressed crankcase can force oil out of the dipstick tube. The pressure in the crankcase will leak to atmosphere anywhere it can find an outlet.

The 2nd Compression Test
The second compression test is known as a 'wet test'. The first compression test was the dry test because no oil was added to the bores. The second 'wet' test can give an indication of whether it is the rings or valves at fault (though bear in mind rings and valves do not cause overheating or water in the coolant symptoms).

Spray a liberal amount of light penetrating oil into each cylinder - aim for the cylinder walls, not the centre of the piston. You want the oil to run down the cylinder wall and around the piston to form a seal.

Place a rag over each spark plug hole and spin the engine to eject the surplus oil.

Then carry out a full compression test noting down the results.

Here's the previous results with the 2nd compression readings added:
Cylinder 1 2 3 4
psi 125 84 86 124
Wet 128 112 110 126

The readings have increased. This because the oil sprayed into the bores has formed a temporary seal around the piston, thereby enabling the compression to be raised. It also indicates that the bores/rings are worn on cylinder 2 and 3 - the 'oil seal' has increased the readings but is still low in comparison with cylinders 1 and 2.

This could also indicate that in addition to worn rings there is also burnt valves. Oil cannot form a seal around a valve. A worn or split valve will cause a low compression reading and misfiring symptoms.
Compressions readings should be taken in conjunction with other symptoms. It will help you identify the problem:

Low compression readings between two adjoining cylinders point towards a head gasket/head fault if your vehicle has shown signs of coolant loss, coolant in the oil system - mayonnaise, overheating, rough running and lack of power.

If those symptoms are not present it points towards burnt valves/piston rings. A worn engine may be difficult to start and pressurise the crankcase, but it doesn't cause overheating problems.

Feb 09, 2016 | Cars & Trucks

2 Answers

My 1998 Yamaha R1 rev counter is jumping up to 7.500rpm then dropping down to 0, then going back to normal, also it sounds a bit louder than usual. It sounds as if an exhaust gasket may have gone. Any...

Typically Yamaha used the firing cycles off one coil for input to the tach. The noise you hear may be misfiring on one or more cylinders. When tach drops to zero cylinder coil isn't firng, when it jumps up its firing again.
The erratic tach usually means an igniter (ignition black box) problem.
Get a manual and start with testing the pickup coils, they signal the igniter when to fire the ignition coils.
Then test the ignition coils for primary and secondary resistance, check igniter connectors for clean tight connections, full battery voltage supply to igniter etc..
Occasionally getting the igniter wet can cause erratic behavior till it dries out.

Mar 05, 2011 | 1999 Yamaha YZF-R1

1 Answer

My GSXR 750 J runs extreemly rough between 7000 and 9000 rpm. Its a mildly tuned engine with after market cams, a dynojet kit and I recently installed some inline fuel filters. The bike runs perfectly...

I would check and adjust the static ignition timing as if too far retarded it will tend to misfire at mid range revs. and suffer from lack of power at the top end.

Mar 01, 2011 | 1988 Suzuki GSX-R 750 J

2 Answers

82 GPZ 750 R1 w/ mac 4/1 exhaust Will the lack of exhaust gaskets affect compression?


But it will affect how well it idles and reduce your torque due to a lack of back pressure.

May 05, 2010 | 1976 kawasaki Z 750

1 Answer

My 82 GPZ/kz750 4 doesn't sound right - # 2 cylinder plug white

yes it could be a valve problem.
Check the valve clearances
Do a cylnder compression test
Check for air leaks in the intake boots

Apr 30, 2010 | 1981 kawasaki KZ 1300 A3

1 Answer

Had a problem with one cylinder flooding and

jets sound like they are worn blocked or similar. you might have to clean it all again or try fuch's pro fst to clean them up. have you vacuum balanced them?

Jan 31, 2010 | 1987 kawasaki GPZ 500 S - GPX 500 R

1 Answer

The bike starts up but will not rev up when

Has it been sitting for a long time (a year or more)? If so, then the carburetors are plugged with fuel varnish and need to be disassembled and cleaned out. If it runs better with the choke on, this is a sure sign that the carbs are plugged.
If it hasn't been is storage, then try draining the fuel from the float bowls. Sometimes an accumulation of water in them will get to the point that fuel will no longer be drawn through the jets. Also make sure that the valve tappet clearances are set correctly and make sure there are no air leaks between the carburetors and the engine (with the engine idling, spray WD-40 around the intake manifolds, any change in idle speed indicates an air leak).
Finally, if all of the above fails to remedy the problem, perform a compression check on the engine. With the throttle wide open, you should see at least 140 psi of compression in each cylinder. Less than that means the engine needs serious mechanical attention.

Nov 10, 2009 | 1989 kawasaki GPZ 500 S - GPX 500 R

1 Answer

Cylinder 4 misfire: lacks compression

the things that would cause lack of compression are:
  • bad headgasket
  • damaged piston rings
  • valves not sealing- could be exessive carbon build up, bad valve spring, bent valve

Oct 15, 2008 | 1998 Nissan Altima

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