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Discussion Starter #1 (Edited)
What happened: The main drive nut loosened up, causing the main/lower cam chain sprocket to come off of the crank key while the exhaust valves were open. They got whacked. Bike ran fine until this abrupt failure. Bike sat for five years in this state.

What we did: New valves, new guides, seats checked, inspected head/cylinder/piston/cams/buckets/springs - they were surprisingly all mint. Inspected main and all cam sprockets and key-no problems. Slid main cam sprocket back onto the key, torqued bolt, reinstalled cams, set timing and confirmed X 4. Cam lobes were at 10 o'clock (exhaust from left side) and 2 o'clock (intake) and timing line was in center of peep hole. 15 pins between the numbers on the cam sprockets and #1 arrow on exhaust sprocket was flush with head/valve cover interface. Cam clearances shimmed to perfection (.010 intake, .020 exhaust).

We cleaned out the gas tank and carb, checking and cleaning the pilot jet and main jet and all related ports. The screen on the valve seat was clogged to all hell so we replaced that and confirmed no other blockages (we're getting gas to the bowl anyway). Set pilot screw 1.5 turns out from lightly seated.

I did not replace the cam chain, but probably should have while in there. :-( I am going to. But it just stopped spinning...no violence on the chain except maybe some push back on the exhaust cam when the valve got whacked. And everything seems to be lining up fine just the same.

Confirmed intake plug is in and vacuum line connected from head to carb.

Symptoms - will not start, occasional puff back through carb, occasional violent backfire through exhaust.

Tests we ran:

1) timing/spark: Confirmed strong, blue spark with spark plug out and grounded to head. Using a regular automotive timing light, I tried to confirm the spark timing. Oddly enough, it would not strobe with spark plug in the hole, or with it out and grounded to head. But I was still getting a strong, blue spark with the spark plug grounded to the head. The timing light just wouldn't work any time the plug was grounded. When I took the plug off ground, the timing light appeared to be functional, showing ignition just before TDC (line was visible on right edge of peep hole). This seemed odd...wrong kind of timing light? Reliable reading this way?

2) ruled out fuel/air - took boot off of air box side of carb and saw fuel squirting a steady stream towards intake during start attempts. We also sprayed ether right into wide open carb and tried to start. Symptoms did not change.

3) Compression confirmed, kind of. Using a standard (not leak down) test, we confirmed 160 lbs. dry and got a whopping 260 with a cap of oil in the cylinder. Obviously higher than the range specified (120 to 150 I think), but there was no piston-to-wall-clearance related compression issue before the failure, so I'm writing this off to the test type perhaps not being ideal. I was also expecting low compression, because of the automatic decompression assembly. Given the readings, that assembly may not be working. But since some people just disable the auto decomp, I'm not worried about that. I don't think it would prevent it from running - just hard to crank and the electric starter does not seem to have any trouble turning her over at a good clip. Bottom line is that we have compression.

My thoughts-since we have spark, fuel and compression, and are not running and are getting occasional puff back from the intake/occasional backfiring out of the exhaust, either the mechnical timing is fine and the spark is occurring erratically/at the wrong time, or the timing of the spark is fine and the mechanical timing is off because of a stretched chain. I can't see how we would otherwise be getting exhaust backfire without an extreme lean condition (which we've ruled out)...one or the other of these two things has to be off.

I'm replacing the cam chain but am skeptical that it is stretched to the point that it would not start. Any troubleshooting tips? Stator pick-up? CDI? Coil? What kind of timing light do I need?

Thanks for any help!
 

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This sounds similar to the problem I was having. Try and get a hold of a DVA volt meter. It measures the split second peak voltage from the trigger, stator, CDI box. I was getting a good visual spark like you are but the machine was barely running and running very rich. Turns out I was only getting 1.7 volts to the primary of the ignition coil but still getting a visual spark. Specs call for 130 volts to the primary. We Ohmed out the ignition coil and it checked out, heated it up with a heat gun and still in spec. Bottom line= bad CDI box. I'll have a new Dynatek tomorrow and will know for sure. If you can borrow a box from somebody to try it will save a lot of hassle.
 

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Discussion Starter #4 (Edited)
Thanks JWT. Found this site on building a DVA: http://forums.iboats.com/johnson-evinrude-outboards/how-make-dva-adapter-multimeter-371144.html

I'll build one and try that test if the cam chain replacement is no help. From where did you take the voltage with the DVA? Location? Wire color? I can probably figure it out from the wiring diagram, but if you know off hand that'd be great.

PS-I got whacked by the voltage to the spark plug while holding it to the head and it was a damn good kick. Still think I'm getting low voltage to the plug?
 

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Make sure you have a clean ground @ the coil. With the primary connected to the coil, measure across the primary to ground with the sparkplug grounded to the head. I don't think you want an open circuit out of the box because if your box isn't bad, it will be. Crank it over a few sec. should get 130 volts. Also, ohm out the primary wire from the coil to the box to make sure it isn't shorted to ground. Even with low primary voltage, you'll still get a visable spark, which will bite, but not strong enough to fire properly under compression. I should have my new box Wed, I'll let you know the results.
 

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If it was running fine before the valves got wacked, and it is popping through the carb and exhaust I would lean towards it being a valve timing issue. Usually, if you replace the valve guides, the valve seats should be recut to center the valve on the seat. Usually if just the guides are replaced and reamed without recutting the seats the valves would leak. You said you have good compression so maybe it is just out of time.
 

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Well, put the new Dynatek in, hit the start button, it fired right up with no choke. Idled great............. for about 2 minutes. Then it started running rough,wouldn't idle without keeping my thumb in it.I let the damn thing sit for 5-10 minutes, fired right up again and ran fine for about 2 minutes. I followed the troubleshooting flow chart in the service manual. Low primary voltage-inspect ing. coil. Saw no cracks and it ohmed out to specs. Next would be shorted wiring harness which is OK, Then cdi box. It did start alot faster with the Dynatek and ran the way it should for a short time. I'm thinking something is going on with the coil. That is my next step. Stay tuned.
 

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Discussion Starter #9
Thanks JWT and 03 Z. J-You sure it is not a fuel delivery issue? Odd that it runs great for a spell. I suppose the heat, once the bike is heated up could cause a e-malfunction. Hmmm

03-yes, I had the guides machined and centered and the valve seating checked and I am getting compression. I'm just blown away that the timing mark and the numbers/arrows all line up, yet it is somehow firing with the exhaust valve open. I think I've ruled out that I can be 180 degrees off, because the plug fires on both strokes. But when I'm putting the chain on, I plan on turning it over with the valve cover off, so I can see that the exhaust valves are opening just after TDC. If the timing mark spins by twice per rotation, I'll also set it to the other one for the hell of it.

Do either of you think the timing chain could be stretched enough to make it not run? Any thoughts on why the standard auto timing light is not working?
 

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I replaced the petcock with one from a Yamaha that does not have the vacuum thing. I've had the carb apart 5 times checking float level, pilot jet, etc. When I bought this machine it hadn't run for 3 years. It ran, but barely, spewing gas out of the overflow and into the crankcase. Valves were shot along with the timing chain. All replaced, shimmed and timed to perfection. After the coil, I'm running out of ideas.
 

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Discussion Starter #11
Really sounds like fuel. You're not talking about that vacuum line from the carb to the intake, are you?
 

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Discussion Starter #12 (Edited)
You clean out that carb real good? Sticking float will starve it for fuel or cause slow/sporadic replenishment in the bowl. Also, the fuel valve seat (that the fuel valve goes in and out of when the float goes up and down) has a screen that gets gummed up. The one I am working on was clogged up solid...couldn't even blow through the gas line with the float valve out! Hate to send you back into the carb, but if you did not check that, you should. It's brass, has a hex shaped head and comes out by removing the phillipes screw. Mine was a beyatch to get out though, it was so gummed up. Really sounds like it is consuming fuel faster that it can get replenished. Take the boot off the air filter side. When it starts running crappy, look to see if you're getting a steady stream of fuel out of the jet. Also, spray some ether into the carb and see how she responds. If it improves, your electrical is fine.
 

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Carb was nasty when I got the machine. Took it all apart & soaked it, blew thru all passages,new needle & seat,screen, fuelscrew,o rings. Float height set by the book and works freely. Had it apart 4 more times just to check pilot jet and float action. The new petcock is just a valve. I plugged the small vacuum port on the carb that goes to the stock petcock. Coil will be in tomorrow, I'm in it this deep so what's another $57? LOL
 

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Discussion Starter #14
Huh. This is my first four stroke top end rebuild, so I'm learning as I go. But on mine, the vacuum line goes from the carb to a union on the intake port on the head, just below the petcock. It's part number 13685-29F00 (#29 on the parts diagram) for mine, and fairly critical according to some advice I've gotten. See OEM Parts But I don't understand it. Might be something about the lower pull off the carb that a four stroke has. But I'm sure you know what you're doing.
 

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Discussion Starter #15 (Edited)
Anyone have any tricks for torquing the clutch basket nut and the primary gear nut without the tools? I hit them pretty good with a heavy duty electric impact wrench (which also took it right off no problem), but it's not my bike and the top end already failed once from the primary nut loosening up. I can probably get the 50# I need on the CB nut with it in gear and the brake on, but getting 80# on the primary is a bugger. Couldn't get the cover off the starter gear, so I could remover the rotor cover and use a 26 mm wrench on the rotor either...stripped out he phillips head screws trying. Would love to find a way to just torque the f'er and see if she runs.
 

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I just hit it hard with the electric impact....maybe I've been lucky.
 

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lucky .........i would say yes ...............because i was not so lucky one time
 

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Discussion Starter #18 (Edited)
Thanks Spize. Cataway, what happened with yours? Strip it, or did it loosen up? I hit it hard with the impact, and it did not strip, but I was afraid to put it back together. That's what happened to this top end...primary loosened up and the main cam sprocket fell off the key and he whacked both exhaust valves into the letter S. So I'm hesitant to cut corners.

Either of you have any thoughts on whether I could be 180 degrees off on the timing? Someone else disassembled, so I just guessed on which stroke it was on when I set the timing the first time after rebuilding the valves. Some also told me it did not matter because you get a spark at TDC every time anyway, which made sense. But I got no start, occasional backfire through the exhaust, occasional puff back through the carb. So we decided to replace the cam chain like we sould have to start with. Put it back together this time 180 away, but have yet to try it because of the aforementioned torquing issue. But am anxious to see what more people think. If it did not matter, why is everyone saying to be sure on disassembly to visually check that you are TDC on the compression stroke by ensuring the cams are at 10 and 2, and then maintain that position through assembly?
 

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Are talking about the nut that's supposed to be torqued to 101 lbs? I used a torque stick that was for 100 lbs. with the impact wrench and worked great. As you may know, tire shops use torque sticks for alloy wheels. Harbour freight sells them as a kit with assorted torque values. They look like extensions but they twist at the torque value.
 

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Discussion Starter #20 (Edited)
Yes, although my manual (for a 2002 DR Z400-E) has it at 79.5 ft. lbs. Has to be the same nut...no other nut is big enough to carry more than 20. The clutch basket nut is 50.5 though, like yours. Thanks for the lead on the torque sticks...seems like a great solution. Although as I read about them, I'm horrified to learn how powerful that impact wrench is, and how easily I could have wrecked the crank or transaxle! They crank up to 400 lbs and this one was no light weight!
 
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