Major Problem

My bike was running on Friday, now it is not. I had the bike running and was attempting to synch the carbs and I decided to give up for the day. It was running at a decently high rpm for a while, but I had done that previously. Now my bike wont start at all. I didnt change anything that would impact the bike not starting. Yesterday I took the battery in to make sure it was ok, and it was. I have changed the plugs, as the old ones were fouled from running rich. Yesterday I was able to get the bike to start up with the throttle open but it would quickly die. now I cannot get it to run at all.

After changing the plugs I decided, on a wave of frustration, check the compression. I dont know if my gauge broke, but it read 60psi on every cylinder (cold). Either my gauge is broken or something happened to my motor that ruined compression. If anyone has any ideas, I would love to hear em. Thanks.

Was the engine allowed to seriously over-heat during the attempted carb syncing?

Can perform a leak down test to determine where the compression is being lost.

A leak-down test injects air pressure through the spark plug hole to pressurize the combustion chamber.

Can perform a poor-man's leak-down test by introducing compressed air into a spark plug hole and listening to where it escapes from the combustion clamber. This may be done at TDC or any other cam positions where both valves are fully closed. Top dead center (TDC) is when the piston is at its highest position. An easy way to tell TDC is by alignment of the T mark with the case mark when viewed through the timing window.

May introduce a spurt of compressed air by using a rubber cone-tip blow gun (rubber air nozzle) held into the spark plug hole. And of course keep holding it in position to keep air from coming back out the spark plug hole while listening for escaping air at other places. The air compressor should not be running while listening because the noise will likely drown out any sound of escaping air. Or just use a portable compressed air tank.

Air heard escaping from exhaust port indicates exhaust valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from carb intake indicates intake valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from crankcase breather indicates loss of compression past rings into crankcase (perhaps worn piston rings or cylinders).

Air heard escaping from head gasket area indicates loss of compression past head gasket (perhaps due to a blown head gasket).

A leaking valve may sometimes be resolved by adjusting the clearance to within specs.

A leaking head gasket may sometimes be resolved by torquing the head fasteners when the engine is stone cold (such as after sitting overnight).

Good Fortune!

To start a cold KZ650 -

First - make sure you have sufficient gas in tank, that the oil level is between the lines, and that the battery is charged.

I recommend you start it using the kickstarter since the battery may not be 100%; Here's how:
If you have the stock vacuum actuated petcock put it to PRI (prime)
Choke ON
Key ON
Do NOT pull in clutch lever when kickstarting.
DO NOT touch the throttle!
Give it a few hard kicks on the kickstarter; it should start pretty quickly.
Ed

Patton, I do not know if the bike was seriously overheated. I can only assume that something happened during that last time it was operational. If it turns out my compression gauge is working correctly (which I would assume it is), then whatever happened is happening to all the cylinders simultaneously as all of the cylinders are registering 60psi. If I had to guess I would say I either blew a head gasket or cracked the block. Unfortunately, I do not know what happened. I will try the leakdown test tomorrow and hope for the best. Thanks for the advice.

The compression test normally should be done with the engine at operating temperature, but since the engine won't start expect the readings to be a bit lower than normal. When doing the compression test did you have all 4 spark plugs out; the throttle wide open; and a fully charged battery? If not, the test results won't be accurate.

I seriously doubt that you blew a head gasket or cracked the block. To my knowledge that doesn't happen to KZ650 engines.

Try kickstarting it as I outlined above to see if it will start. Keep in mind that any problem with the starter or battery that prevents the electric started from spinning at full speed or draw too much current can cause the engine not to start and also possibly the low compression readings. Ed

You can put a tea spoon of oil in each cylinder and see if it changes. If it goes up, rings.
Steve

If you put a teaspoon of oil in each cylinder the compression will definitely go up because it reduces the volume of air in the combustion chamber when the piston is at TDC, so it isn't a really good test of the condition of the rings. Here's a generic example of what I mean. Ed

Perhaps the compression tester is faulty.

Will the compression blow past a finger held tightly against the spark plug hole?

If not already done, would also double-check routing of the plug wires from the coils.





Good Fortune!

So far it all points to bent valves, 60psi, full throttle to start, is there a part of the story we're missing like missed a gear at high revs?. Personally I hope I'm wrong. Good luck

Bozo, I can understand where you are coming from, but I am not sure how I would have bent the valves given I didnt change anything as far as cams or timing chain and the like.

Have you checked to be sure you are still getting fuel? How about checking to see what the spark looks like?

Patton, I have checked the plug wires. This is an enigma to me. It was running, I didnt change anything and no longer starts. What if it did overheat. What would be possible problems?

Racer, I just changed the plugs, charged the battery and went so far as to install the WG coil mod. To be honest though, I have no idea what the spark is actually supposed to look like. I pulled the plug out and rested it against the block. it looks to me as there there were several small arcs across the gap. I know the common thing is a fat blue spark, but is this one arc that is fat blue or several smaller ones. the arcs across my plugs (this is during the daylight) do not appear to be all that fat or blue. I checked after the WG mod. Also, I know I am getting fuel to the carbs because today I pulled the carbs and checked the float levels and cleared the jets to be sure.