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Discussion Starter · #1 ·
Sooo I bought myself a $500 dvx400 with all sorts of goodies on it, Athena big bore, dynatec cdi, all that fun stuff. The previous owner wrecked the starter clutch and shredded the stator wiring, then parked it for a year. I put a new stator and starter clutch, and a spark plug that I verified was sparking. The carbs off as it was spewing fuel everywhere, in the process of rebuilding that now. My problem is, it won't even fire on starting fluid, just an occasional backfire out the exhaust. So maybe it's a dumb question, but would getting into the flywheel and starter clutch mess with timing at all? Like, I have good spark, it should theoretically at least fire once on ether. I'm a little suspicious that the valves might just be nasty dirty from sitting for so long, but I figured I'd ask the experts first to see if I'm overlooking something stupid obvious
 

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It shouldn’t change the timing at all. If I were you I would take the head off and check the valve clearance and take the head all the way apart and clean it and put it back together to spec.
 

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Do a compression test.. See what you are working with.
 

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Check valve clearance, compression test, and verify timing marks line up. If all of those are good, it should fire.
 

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Discussion Starter · #5 ·
That's what I'll do then, first compression test just to be 100% positive then I'll get into the top end. I'm hoping the valves aren't cupped like people say happen a lot. The guy I bought it from said it ran up to the point the stator wires got ripped. My other concern is the possible damage from the starter clutch. He pop started it and kept riding, and I found springs from the starter clutch in the bottom end along with a good layer of ground metal. I don't really want to put a lot of money in the top end just for the motor to grenade the first time I go to ride it.
What all do I absolutely NEED to replace while I'm in there. Also, is there a way to identify my Athena big bore size? Obviously besides measuring the bore
 

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Discussion Starter · #8 ·
I'm new to the forum stuff, should I make a new discussion for other questions so they're not under "no start" or is it ok here? Like what my cams are, and is my yoshi a full system or a slip on, that type thing
 

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Its best to start a new post for those questions. You need to leave this one up until you solve it an post what your fix is. That way in the future if someone has the same symptoms it gives them a possible solution to their issue.
 

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Discussion Starter · #11 ·
So here's what I found so far, I'm definitely not thrilled with it.
Compression: 30 psi (engine cold obviously 🙃)
Exhaust valve clearance: 0.25 mm
intake valve clearance: Smaller then my smallest feeler gauge, which is 0.038 mm, so I'm gonna say its probably 0.000
 

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Discussion Starter · #12 ·
So assuming the intake valve is shot, could that be why it's only got 30 psi compression, or do I likely have more then one issue going on here?
 

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You can change shim va
So assuming the intake valve is shot, could that be why it's only got 30 psi compression, or do I likely have more then one issue going on here?
Definitely could be your source of low compression..
 

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Discussion Starter · #15 ·
I thought I read that if valve gap is 0.000 it's cupped, and shims aren't gonna fix it at that point. I could be wrong, I would definitely rather put a single shim in then replace the valves
 

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You can try shimming the intake valves to see if it will start. However once the valves start cupping there's no stopping them. You will need to eventually do a valve change.
 
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