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Very perplexing-Weird, won't start-problem

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I've read all of the "won't start" posts I could find, and I'm perplexed! Please help! I understand you need fuel, air, spark, and compression to get the engine to fire/start, and run. I have a basically stock 2002 DRZ400S that has run quite well for the last 9000 mi.-until recently. I just replaced the OEM stator, which failed on its charging circuit, with a Moose Racing stator purchased through TT. With the new stator the engine started fine, ran fine, and the charging circuit was providing 14.5V. Out for a ride, and after only 12 miles of running just fine, the engine let out a loud backfire, sputtered briefly, and then would no longer run nor start. Now no spark at the spark plug even after trying several different plugs. Towed home, again. Later testing showed the pick-up coil had failed (only 5.9 ohms resistance instead of the recommended 390-600 ohms). I received a replacement Moose Racing stator from TT (Bryan Bosch was very helpful), installed it, and now the engine has excellent spark, but the engine won't start, won't even pop. Following the advice of many of the posts, I have: put in new fuel, checked for any water in the fuel, installed clean air filter, new spark plug, removed and cleaned the carburetor (it was clean), checked valves-all within normal tolerance, cam timing looks correct with all the correct marks aligning, with the piston at TDC on compression stroke, cam chain snug (has MCCT). As I don't have an appropriate compression guage I can only guess at the compression. With the rear wheel off the ground, and the spark plug removed (in fifth gear), there is moderate resistance when I turn the rear wheel by hand. When I then put in the spark plug there is much more resistance to turning the wheel. At least it has some compression. I don't know how the decompression system affects it. The really unusual thing is even when I put starting fluid into the intake I get no popping or firing. When I remove the plug to check, it still has great spark, and is wet. I'm frustrated. Any ideas would be greatly appreciated.

Thanks, Ben

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I have read it is posible to install the pick-coil up-side down. Take a look at that. Try jumpering on a car battery so it cranks faster, but don't overheat the stater with excessive cranking.

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Is it possible the pick-up coil is wired backwards? Do you have anything to compare it to?

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Noble, I checked the pick-up coil and it is installed properly.

William1, It is possible that the key anchoring the flywheel to the crank has sheared (this happened to me once on an old YZ465). The flywheel seems tight on the crank, at least when trying to move it by hand. I think I need a flywheel puller to remove the flywheel to actually check it though. (I don't have one). In the absence of that could I hook up a timing light to the spark plug, and while engaging the electric start, see if the T mark on the flywheel shows up in the access hole when I press the start button? I think that should let me know if the spark is at the right time, or if the flywheel has moved. What do you think?

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That does get me wondering How is the spark timed? maybe the CDI went south.You've done a good job of checking everything, keep at it you'll get it

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Checkint timing is a good idea. I was going to suggest it. You will have to add some marks to the flywheel. The only mark is at TDC. I think the timing for starting is 7 deg advance. If the cam marks all line up with TDC, then the key is OK.

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Checkint timing is a good idea. I was going to suggest it. You will have to add some marks to the flywheel. The only mark is at TDC. I think the timing for starting is 7 deg advance. If the cam marks all line up with TDC, then the key is OK.

He could use a light with an adjustable advance. Set it at 7deg and see if it hits TDC, could he not:excuseme:

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Not a bad idea to confirm if the spark is correct or at least in the appropriate vicinity. Very possible (as apparently you have experienced this first hand in the past) when the previous stator died and you got that nasty backfire, the sudden off-timed explosion may of sheared the key. That's where my money is.

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I'm planning to determine the piston position when the spark plug fires by using the timing light, but I won't have access to a timing light until this weekend. If timing is correct, then I'm thinking that only leaves inadequate compression as the problem. Is it possible that the automatic decompression device can malfunction and hold the valve open constantly? Can I inactivate the automatic decompression so I can do an accurate compression test? Basically what is the best or easiest way to check for adequate compression without having to visually inspect the top end for a problem? Thanks for all the help so far. Ben

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Almost anything is possible, a failed decomp is not likely. You problem started with a failed stator and a replacement problem. Stay with the electricity until it is eliminated. You do not have to use a adjustable timing light. A 7 btdc flash should still show the mark, albeit to the leading edge of the view port.

Also, Noble makes a good point that if you pop off the cam cover, align the cams to TDC, the TDC mark on the flywheel should be right there. This will also confim flywheel key integrity. While you are at it, you can confirm valve clearances.

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So here are the latest updates on the problem. Using the timing light was not a good idea. Even when the engine doesn't start, just cranking it over with the electric start blows a geyser blast of oil out the inspection hole, and no way to see the timing marks. What a mess! So I removed the valve cover to check everything again. Cam timing is right on, so flywheel hasn't rotated on crank. However, this time on checking the valves, exhaust valves were fine at .011, but both intakes were showing .009 whereas last weekend check (and hasn't run since) showed .006. Strange. Next I checked the compression. Service manual states it should be 135 psi (with automatic decompression actuated). First test of ~15 cranks showed only 20 psi max! I repeated it three more times over the next 5 min. and it would pump itself up to only 60 psi. Now I rechecked the valve clearance again. Ex. .011, but both intakes were now .006 (back in spec!). Strange. Checked the compression again several times over the next few minutes. It pumped itself up to 70, then 80, then to a max of 90 psi. It's sounding like rings beginning to seal after enough oil gets up around them. So I thought maybe 90 psi is enough to run. I put in the spark plug, sprayed starting fluid into the intake, and after a few cranks it fired right up, (Yes!), still a bit sluggish when cold, but as it warmed up it ran normally. I even shut it off a couple times and it restarted without a problem. Once warmed up ~5 min I rechecked the compression, but could only get a max. of 95 psi. Sounds like rings to me. I don't know what the story is with the intake valves. What do you think? Thanks, Ben

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I take it you never tried my "jump from a car battery" suggestion. That most likely would have started it much sooner. (faster crank= more compression) I know this sounds crazy to some but 4 stroke singles just occasionally refuse to start. My theory is loss of compression due to a carbon flake under a valve. (you remember how it backfired when the ignition went out) You never see this on multis because 1 cylinder will fire and that is all you need to start. Run it for a hundred miles and I'll bet it runs perfect. I can't tell you about the compression test with the comp release, never tried it. If you are concerned about valves and ring seal, do a leak down test.

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A leakdown test is done using a leakdown tester. It is an adapter that screws into the plug hole. It is connected to a compressed air source usually a compressor. With the cylinder at TDC it measures the amount of air that is lost into the engine either through the valves, past the rings, or through a bad head gasket.

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Is a leak down tester something you purchase, or can you improvise using something like the compression tester hose and fitting, and then inject a measured psi of air into the cylinder and measure how long it takes to dissipate. How long should it take? How can you determine whether it is lost past the rings, valves, or gasket?

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I think you may have a valve issue, doubtful it is the rings. Esp. since the intake seems to be getting wider. As Noble mentions, it may be a tiny bit of jit stuck to a valve, holding it open and it may well crumble and go away but then again, it could damage the valve or valve seat, thereby never sealing 100%. Worth looking into.

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For a 1 time test I would take the bike to a shop that can do the leak down test. Valves have a hard life but survive most things. Valves routinely crush up carbon and rust and anythng else that goes thur an engine. If the bike ran well before the ignition failure, there is no reason to suspect it will not run just as well now. Ride the crap out of it for 100 miles then see if it needs further evaluation. I can tell you that every 4 stroke single I have ever owned has at some time refused to start. After swearing, kicking, pushing (or pushing the button) long enough it eventually starts and runs perfect.

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a quick poor-man's leak down test, is to test the compression, then put a small amount of oil down the plug hole, turn the engine over a bit to get the oil spread around the combustion chamber, and then recheck the compression. If it comes up significantly, its rings. If it doesn't move, its valves

Be careful about the amount of oil you add. Too much will reduce the combustion chamber volume and give you a falsely high reading because you are in essense increase compression ratio

just a tablespoon or two is all you need

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