QuestionHello Mark,
I have a 1988 Kawasaki Ninja 600R that will not maintain Idle once the engine is warmed up.
History:
This started after the bike had sat last winter (2003-04). Last summer the bike was taken to a mechanic who fixed the wiring on the regulator rectifier and replaced the regulator rectifier and spark box. He also did a complete clean on the carbs as they were plugged with rust from the gas tank. The tank has been relined and the carbs are clean.
Current observations:
The bike will start and run when cold. Once the bike is warm enough to close the choke, the throttle is very sluggish. If it is turned to fast, the bike will stall. If turned slowly, the RPMs will go up, but then hold the high RPM for a few seconds and slowly go back down even when the throttle is back in resting position. Eventually when the bike is hot, the bike will stall out unless kept over 2500 RPM. I've had the bike also suddenly lose power at 5000+ RPM on the highway (like if the throttle is dropped)and stall out. If the bike stalls out when hot, it will not restart for 10-15 min until the bike cools down.
Any information you might be able to provide would be greatly appreciated as I spent most of last summer with the bike in the shop, or taking 5, 10 min breaks for what should have been a 45 minute ride.
Thank you
Stefan Tripp
AnswerHi Stefan,
Sorry for the wait...busy working OT lately.
Very good description. Thanks!
I suspect the carburetors have some form of obstruction. Likely fuel varnishing or fine rust particles obstructing pilot circuit jets and passageways. Check the float bowls for evidence of the above.
It should be known that even after sealing the tank and cleaning the carbs, rust particles can form or exist within the tank and re-contaminate clean carbs as soon as the fuel fills the float bowls. Fine rust particles can pass through paper element fuel filters and accumulate in float bolws. Rust will appear as a fine sediment when bowls are drained and examined, though will remain suspended in fuel when in use. Varnishing simply is a chemical change of liquid fuel to a gel-like solid, and advanced stages change to crystal powder form.
Always check cylinder compression as the fisrt step in diagnosing non-electrical engine problems.
I return tech information files via email. There was no email with question as requested. See sample file below...
Respectfully,
Mark Shively
Cylinder Compression & Leak-down Testing 101
You need 3 things to make a gasoline engine work, compression, fuel, and ignition. Without enough compression the engine will not function. Low compression causes you to crank the engine longer when trying to start it. As you crank the engine it slowly builds pressure inside and will eventually fire up. I cannot think of other problems it will lead to because once you have lost compression; you will not have a working engine, so nothing else can break.
What does it indicate as weak points in the engine and how is the leak down test are related? There are various possibilities for low compression and the leak down test pinpoints them fairly well. Your engine is an air pump and the leak down test measures the engine's ability to hold air. The combustion chamber has a theoretical limit of holding 100% of the air/fuel mixture that is drawn into it and compressed prior to being ignited by the spark plug.
The leak down test measures with a flow meter the actual amount of air the combustion chamber will hold. Weak points will be noted by the sound of rushing air. So, if the rings on the pistons are weak, listening at the oil filler cap while doing the leak down test will allow you to hear the sound of escaping air. A bad exhaust valve will allow air to rush out the tail pipe so you stick your ear to the tail pipe and you hear the noise of air passing by a bad exhaust valve.
The compression test uses a gauge to measure the build up of pressure inside each cylinder as you crank the engine. The cylinder leakage test uses compressed air that is forced into the combustion chamber. Both testers are screwed into the sparkplug hole.
To check the condition of the rings, you need a leak down test. This test measures the ability of the cylinders to maintain compression, thus testing the integrity of the rings and valves. The cylinders with low compression MAY have poor rings, but check the valves first. I had the valves done on mine, hoping that would cure the problem, but it was terminal; 3 of the cylinders had more than 50% leakage cold and about 70% hot - bad rings! I had a complete overhaul done. Now it runs like it just came from the factory (better, says my mechanic). If it isn't using oil, the rings are probably good for many more miles.
A compression test tells you the compression provided by the piston on the compression stroke. It is a relatively instantaneous measurement, but if you keep the meter on the port you can see how the compression decreases over time. If it decreases too quickly, something's not right; either leaky valves or rings. The leak down test quantifies the compression fall-off as a percentage over time and (usually) at cold and hot engine temperatures. It is a better indication of engine condition and is sometimes used to predict remaining engine "life." If your rings are bad, you'll usually see two things:
- low compression
- high (or higher than usual) oil consumption
You may also see white smoke from the exhaust in extreme cases. If there is no smoke and the compression tests are good, then the engine should be fine. If you still have doubts, check the valve guides and valves (if you see a puff of white smoke when you leave a stop light - after decelerating) it could be valve guides or seals. A valve job is easier and MUCH cheaper than a ring job. A skilled mechanic can usually determine if it's the valves or rings.
You should not get any more than 10% variance between cylinders. I'd start by keeping things simple. First, check all valve clearances; you can lose compression through the valves. Once this is done, check the compression again, and do it a few times to be sure it's not your compression tester that is out of calibration. There is a procedure for testing valve problems, which is also a possibility here. Pour some oil down the spark plug holes just before you take the reading. If the reading changes, then you've sealed the problem with the oil (i.e. your rings are gone), but if it doesn't then it's more likely to be your valves - which means a rebuilt head (much cheaper than the alternative).
As the cylinders wear they get a taper -bigger at the top and smaller at the bottom. You can go up to about .015'' of wear overall or .007 per side. The rings have to expand and contract every time the piston moves. So, they tend to break at high RPM but can handle 3,500 for years. Engine wear is about .001'' per 10,000 miles on average - some better and some worse. If you have a vehicle with lower compression and over 100,000 miles it's a safe bet that you have cylinder wear, the same wear that will break rings at high RPM.
You can sleeve them with no problems. If its standard bore you can go up several sizes over. This will clean out even the worst cylinder wear in most cases, but not deep gouges in the wall. Excessively deep gouges will need a new sleeve.
Re-torquing the head bolts after head re-assembly should be done after a few hours of running on a warm engine. Undo each bolt one at a time only. Start in the middle just like a regular sequence and undo a bit and then tighten up to the final amount which is usually a bit more than the initial setting. You should get another 1/8 turn out of some of them. Also use a bit of oil on the threads and washers so they screw down evenly.
