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Discussion Starter · #1 ·
Hey alls,

So a friend of mine brought his '03 Z400 by the shop to have me check it over. He was getting ready to call it a day and hit a fairly hard dip on the way back to the trailer when it died. Would crank and crank but nothing.

We found that the plug was cracked so we changed that... still no change. Pulled the valve cover and lined up the timing mark on the crank. The cams looked to both be a tooth off (assuming it jumped on the crank). We decided to go on and pull it apart for a new chain/tensioner and pulled the head to make sure it didn't eat a valve.

No damage to valves or piston. Filled the ports to check for valve leaks and all is good there. Timing chain was definitely stretched. Cleaned everything up and installed a new head gasket. New chain and tensioner... timing set to spec. Valve clearance is in spec and timing is spot on. Has a nice strong blue spark at the plug. Got it all back together and still no start.

Figured it may be a carb issue so hit it with some starting fluid... still nothing. Not even a sputter. No popping back through the intake or exhaust... nothing. Checked spark again and double checked cam timing and everything is good.

Now what to check? Seems to have good compression... is it possible that the ignition pickup is out of place causing ignition timing to be way off?

I'm really scratching my head on this one.

Thanks for any input.
 

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I would verify compression. No point guessing at this point. Also I would cover the carb with your hand and confirm suction while cranking.Then I would look at the magneto, see if anything is out of place.
 

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Discussion Starter · #3 ·
I would verify compression. No point guessing at this point. Also I would cover the carb with your hand and confirm suction while cranking.Then I would look at the magneto, see if anything is out of place.
That's what is weird.. it feels like I'm getting suction.. and a slight blow back which is why I pulled the head. It felt like it had an intake valve issue... but there are no signs of valve damage. There were no marks on the piston or valves at all and I filled the ports with the head off (using brake clean.. so pretty thin stuff) and no leaks. It also cranks over like it always has... and there is a big difference between cranking with the plug out and with it in.

I'll have to go rent a compression tester as the only one I've got is for diesels.

It's like the valve timing is slightly off on the intake side or there is some overlap like the intake valves are opening slightly early... but timing is dead on and the lobes are at 10 and 2 roughly.
 

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It's possible the natural overlap is doing that as well. Sounds like have have everything right, if the compression is there.
 

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Discussion Starter · #5 ·
It's possible the natural overlap is doing that as well. Sounds like have have everything right, if the compression is there.
A bit of an update on it....

I went out and started tinkering a bit more tonight... with my hand in the air box, was still getting a little suction.. then pressure from the intake. "Checked" compression with my diesel tester (sorta) and pressure was way low. Still thinking valve issue, I pulled the carb to see if I could see the valves but right when I took the carb off, I decided to spin the engine over and got a VERY strong suction on the intake.. but no push back.

Now very confused... I put the carb back on but left the airbox unhooked completely. Spun the engine over again and am getting good suction through the carb... no push back at all... but kept feeling air blowing on my hand as it was resting on top of the carb. Started looking around for a source and found the pressure was coming from the crank case breather (the one that connects to the intake).

This now is starting to make sense. The pop back I was feeling in the air box was pressure from the crank case... not the intake itself. I don't think it ever jumped time. I know the chain was stretched when I pulled it apart so I'm leaning towards that being the reason the timing marks weren't lining up. Also, when I drained the oil, there were 2 small chunks of metal stuck to the magnet on the drain plug. I was assuming it was from the chain "jumping time"... but now I'm leaning towards a bigger failure. The top of the piston looked fine when I had the head off but I didn't spin it over or pull the cylinder to check for scoring or anything of that nature.

I'm starting to think it died from sudden compression loss (not timing)... and it either broke the piston or a ring. I'm going to pull the head back off and pull the jug to inspect the piston and rings as well as the cylinder wall for scoring. I did find ash on top of the piston when I took the head off... likely from burning a bit of oil.

We'll see later tonight or tomorrow hopefully.
 
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