Compression Test

[taylor88]

Hi all, I did a compression test on my standard Z1B after taking it for a nice run at the weekend. Even after the run the plugs were really sooty, its always run rich so I am hoping that the new electronic ignition followed by the carb overhaul may sort it out. That said the compression test was as follows:

Cylinder 1 = 90 PSI
Cylinder 2 = 90 PSI
Cylinder 3 = 78 PSI
Cylinder 4 = 100 PSI

I have only ever used my own (Gunson gauge) but I am a bit concerned with cylinder 3 being on the low side. I did squirt 2ml of 3in1 into cylinder 3 but it didn't make any difference which is probably good news to discount the rings, although not sure if 2ml was enough?

What's you views please?

cheers

[Compo1955]

All lowish.....Was this test done with the throttle wide open ?, if not repeat on full throttle

[markz9]

with the type of gauge your using only really good as a comparison with other cylinders the 78psi is a bit off try again with a bit more oil it should jump the reading up a bit if it doesnt probabaly your valve is not seating and needs re cutting are all the plugs sooty ? might need new valve stem seals as oil getting into combustion that
best check is a leak down test
mark

[ZedHead]

As already said hot engine, wide open throttle and fully charged battery. I would also use engine oil rather than wd40 to give a better seal around the rings. If number 3 is still low then it is time for the head off sorry to say.

[taylor88]

Thanks all

Yes all plugs are sooty
Yes I had throttle wide open
I used kickstart rather than electric start to do the tests

I even took a picture they are in sequential order....!



I have since fitted new plugs but they are now sooty after just a couple of miles

[PAULJAC47]

100 PSI is the service limit though i have seen bikes run ok with lower.Before you take anything to bits do a leak down test,this will give a good indication what is amiss,would give a better indication on comp test with electric start...

[zpower]

100 psi as mentioned is just about ok but these engines are bullet proof and will still continue to run.

As a rough smoking check guide...

Smoke at start up usually means valve guide oil seals.
Smoke when accelerating hard could be worn bores or broken rings or gummed up oil scraper rings.
Smoke on over-run could be either of the above but normally valve guides or valve guide oil seals.

So go out for a ride and watch your mirrors.

I agree with PAULJAC47 a leak down test is the best place to start here.

[Mowjoe]

My cylinder pressures are all in the 80's but the engine runs sweet so no need to strip it. To get rid of the a rough running motor and sooty plugs I did the following, coil feed via relay ensuring full battery voltage, removed blockages from the pilot air orifaces in two carbs and fitted new pilot jets to all, adjusted float heights and fitted Dyna electronic ignition. Also I keep clear of regular unleaded and fill with the more expensive version to avoid ethanol where possible. I have set and balanced the carbs and now have a smooth tick over and pull away. Plug tangs are coffee coloured and base of thread black but not sooty. I have achieved a very sweet engine all with info from this forum

[Jay1969]

Just checked the plugs on my Z900 engine: 1 and 4 perfect, 2 and 3 running rich. I know my carbs are in need of service, but now Mowjoe has raised a
point I was wondering about; the contact breaker points. I have plans to upgrade to Dyna S 3ohm coils and electronic ignition, but in the meantime,
could the contact breaker points have some relativity to fuel starvation and engine fade,
happens when I ride for a few miles / when the engine is warmed up to normal temperature. Other than that ticks over nicely without any misfiring on any cylinders.

[wilsonsjw11]

I run a restored Z1B and Z1 both bikes have had extensive work on the engines ete etc.The ZIB has Dyna coils and Dyna S and the improved performance is noticeable.I have bought both items for the 73 Z1 just need to fit both in the coming autumn.
Regards
Steve

[PAULJAC47]

Just checked the plugs on my Z900 engine: 1 and 4 perfect, 2 and 3 running rich. I know my carbs are in need of service, but now Mowjoe has raised a
point I was wondering about; the contact breaker points. I have plans to upgrade to Dyna S 3ohm coils and electronic ignition, but in the meantime,
could the contact breaker points have some relativity to fuel starvation and engine fade,
happens when I ride for a few miles / when the engine is warmed up to normal temperature. Other than that ticks over nicely without any misfiring on any cylinders.

Swap coil from 1 and 4 plus condensor and see if prob transfers,coils and codensors(capicitors) sometimes fail as they get hot...

[taylor88]

Thanks all for your help and suggestions it is really appreciated. I fitted the dyna-s electronic ignition and 3 ohm coils at the weekend, just waiting for the correct rotor to be sent! I will give it a good run then and recheck the plugs. It doesn't seem to smoke at all but my mate followed me down the M11 on Sunday and though he could smell petrol. I also only got about 90 miles from a full tank before going to reserve. Next action is to get the carbs a complete overhaul as they have probably never been done in 40 years

[z1bman]

My cylinder pressures are all in the 80's but the engine runs sweet so no need to strip it. To get rid of the a rough running motor and sooty plugs I did the following, coil feed via relay ensuring full battery voltage, removed blockages from the pilot air orifaces in two carbs and fitted new pilot jets to all, adjusted float heights and fitted Dyna electronic ignition. Also I keep clear of regular unleaded and fill with the more expensive version to avoid ethanol where possible. I have set and balanced the carbs and now have a smooth tick over and pull away. Plug tangs are coffee coloured and base of thread black but not sooty. I have achieved a very sweet engine all with info from this forum

yes what you have done will improve the running but ultimately the performance will be drastically reduced

[Mowjoe]

My cylinder pressures are all in the 80's but the engine runs sweet so no need to strip it. To get rid of the a rough running motor and sooty plugs I did the following, coil feed via relay ensuring full battery voltage, removed blockages from the pilot air orifaces in two carbs and fitted new pilot jets to all, adjusted float heights and fitted Dyna electronic ignition. Also I keep clear of regular unleaded and fill with the more expensive version to avoid ethanol where possible. I have set and balanced the carbs and now have a smooth tick over and pull away. Plug tangs are coffee coloured and base of thread black but not sooty. I have achieved a very sweet engine all with info from this forum

yes what you have done will improve the running but ultimately the performance will be drastically reduced

True enough but the motor is running sweet for a 38 year old and for what I use it for. My point is that by reading through threads here I discovered that I could improve a rough running engine by addressing all potential faults and not just concentrating on one or two things.

[PAULJAC47]

Sometimes ist the best way to go.if the bike is running ok leave well alone!