low compression z650

[z76]

i bought the bike about 6 months ago, got it running briefly and started working on the bike (not engine). it hasn't had a good run for a while as the last owner bought it as a restoration project and never got around to it. it may have been sitting idle for a good year or more. after i got it the compression was around 120, 90, 115, 120. it hasn't been run for about 4 months since i initially started it.

i gave it to a guy to tune it and said now it's only got 70, 90 in cylinders 1 and 2. the slacker didn't check 3 and 4. i thought, "this doesn't sound right".

could this idle time cause low compression?

i was told to try running upper cylinder lube in fuel to loosen valves. i've been letting the engine run for about 15min intervals to get the cylinder lube into the engine. i can't ride the thing coz it isn't registered yet so just letting engine idle.

will this help?

i also noticed a light sheen of oil appearing around the outside of the head gasket in a couple of spots. i don't think this is how it should look. then i started to think - low compression=buggered head gasket?? or...???

please advise

[OKC_Kent]

Do you know how many miles on the engine?

Check the compression again, it seems you know how to do it and the "slacker " doesn't. Hold the throttle WFO when you do, right?
Then I would do a leak down test. It could be the gasket, or the valves not adjusted to spec, or the rings are worn. A leak down test will tell you. I would even try some Yamaha Ring Free and maybe the rings will loosen and seal better. Check the valve clearance and adjust them, if that hasn't been done yet.

Good luck and write back.

[z76]

the last owner stated there was less than 30000km on it since it was rebuilt. but that is far from reliable information. it was fully rebuilt in '93 and had a new starter clutch put in in '04. that's all i know about previous servicing.

i'll check compression again most definitely. is a leak down test done by pumping up the cylinder using compressed air and listening for leaks??

i haven't head of 'ring free' in Australia. will have a look for it, is there another trade name for it/similar products??

if valves are tight i've heard this can cause leakage - true or false? if the other bozo checked i might have eliminated a possible cause. anyway, onwards and upwards!

thanks so much for your advice, much appreciated!

oh yeah, i definitely can feel in my bones somthing is suspicious with the head gasket and the 'glistening' spots around it when the engine gets up to operating temp.

[OKC_Kent]

i'll check compression again most definitely. is a leak down test done by pumping up the cylinder using compressed air and listening for leaks??

Yes basically. Leaks heard in the exhaust pipe or intake/carbs indicates valves are not sealing. A leak heard in the crankcase (listen from the oil fill hole) indicate rings are poor.

i haven't head of 'ring free' in Australia. will have a look for it, is there another trade name for it/similar products??

Try a penetrating oil

if valves are tight I've heard this can cause leakage - true or false? if the other bozo checked i might have eliminated a possible cause. anyway, onwards and upwards!

True

oh yeah, i definitely can feel in my bones something is suspicious with the head gasket and the 'glistening' spots around it when the engine gets up to operating temp.

A leak down test may help pinpoint this area too.

[z76]

i shall do a leak down test asap and then i'll know where she's leaking. (hopefully nowhere).

will a product such as CRC, RP7 or valvoline spray lube do the same thing as ring free?

[OKC_Kent]

Not sure about those products. I've never used anything but light penetrating oil . Some other products that bust up stuck items are PB Blaster, Kroil, WD-40 and I have heard of people using ATF fluid.
And then there is the fix-all to end all fix-alls, Seafoam.

Anything that frees up stuck items is worth a try. Remember to change your oil after using this stuff, it will get into the crankcase.

[z76]

i bought a compression tester and got vastly better results than the idiot i gave my bike to to check.

from cylinders 1-4 we have 125-130, 120, 120, 120.
i held the throttle wide open and kicked it over about 10-12 times until the needle stopped moving round the dial.
i did a wet test and they all pumped up to 180+psi so from that i assume the valves are not losing compression. the clearances will be checked never the less.

now i have noticed it's running rich (spark plugs are black), how can i make it leaner? i overhauled the carbs and the pilot screw is at the standard setting of 3/4 turn out from stop.
also, is mechanically synchronising the carbs as accurate as a vacuum gauge?

jamie

[StarGate]

You can lean it out with the mixture screws or change jets. No, mechanical sync is not as accurate as with gauges.

You might do a plug check too see if it's running rich at highway rpm's. Of course that means you'll have to take it out on the highway and then pull the plugs on the shoulder of the road.

[z76]

how much would i turn the mixture screws before rechecking? should it be done with as the engine is running?

[StarGate]

Well at 3/4 turn out and it's still running rich I would start to suspect the problem lies else where. Do you know if you have the same model carbs the bike came with. Do you know it the jets are factory size? Have you checked to make sure theres no obstructions in the intake area? What year model is the bike?

[elr658]

Without RIDING THE BIKE you're only chasing your tail. STOP until you have a plate.

[z76]

it's a B1, it has original carbs. i broke them down completely and cleaned them inside and out with carb cleaner. i rebuilt them with carb kits from z1enterprises and put in everyth that came with the kit. there were 4 main jet sizes and i put in 102. the other sizes in kit are 92, 97.5, 102.5. when i pulled the carbs apart they had 105 mains. the manual says main is 100. i have airbox and 4-1 vance/hines pipe fitted.


i might remove them and double check there aren't any obstructions in the internals.

[StarGate]

Check the pilot jets and what size they are if you go back in to them.

[z76]

is that the same as the pilot screw that goes in the bottom on the intake side of the carb?

[StarGate]

Originally Posted by StarGate

What year model is the bike?

No.

[z76]

pilot jet/starter jet size is 15. the jet that screws into the body above the starter jet is 50. main is 102.
i've also noticed there aren't any limiters around or on the pilot mixture screw.

another thing i discoverd was a black inky appearance to a little fuel that i saw around the drain plugs. i suspect the o-rings on the fuel pipes linking the carbs were not fuel tolerant and were slowly disolving. this will be remedied as soon as i can get hold of some suitable o-rings, any suggections where i can get them?