Z400 Backfireing Through Carb Wont Start. - Suzuki Z400 Forum : Z400 Forums
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post #1 of 17 (permalink) Old 11-24-2008, 07:51 PM Thread Starter
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I have an 03 z400, a while back it jumped timing, I put a new timing chain and piston/rings.
It cranks over, but wont start. If I spray starting fluid through the carb it will spin over but back fire out the carb when it attemps to start.

I checked the valves, they all look straight, The timing marks are 2, 2 top dead center and 15 notches on the chain. What am I doing wrong here?
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post #2 of 17 (permalink) Old 11-24-2008, 09:47 PM
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when you set tdc which way did you spin the 17mm crank shaft nut. dont go clock wise. spin the crank counter clock wise or you will have some slack in the timing chain which could cause your timing to be off a bit.

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post #3 of 17 (permalink) Old 11-24-2008, 10:12 PM
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QUOTE (deviousdvx @ Nov 24 2008, 06:47 PM)
Quote:
when you set tdc which way did you spin the 17mm crank shaft nut. dont go clock wise. spin the crank counter clock wise or you will have some slack in the timing chain which could cause your timing to be off a bit.[/b]
sounds like it's 180 out to me like it was set on tdc on the intake stroke instead of the exhaust stroke.
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post #4 of 17 (permalink) Old 11-24-2008, 10:18 PM
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you mean it should be tdc on compression not exhaust

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post #5 of 17 (permalink) Old 11-24-2008, 11:40 PM Thread Starter
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QUOTE (deviousdvx @ Nov 24 2008, 07:18 PM)
Quote:
you mean it should be tdc on compression not exhaust[/b]

That I didnt know, so I need it to be tdc on compression stroke then put the intake one 3, exhaust on 2 with 15 links inbetween?

When I did it, I just did tdc 3,2.

Ok heres another ? How do I make sure its tdc on compression stroke.

Thanks for the help
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post #6 of 17 (permalink) Old 11-24-2008, 11:54 PM Thread Starter
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Okay, I just checked it.....

I spun it over counter clockwise with a rod down the spark plug hole, then 3 intake 2 exhaust is straight up, The cam lobes are pointed out and the piston is tdc.

If it was 180 out wouldnt the piston at this point be at the bottom?

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post #7 of 17 (permalink) Old 11-25-2008, 09:12 AM
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QUOTE (brandon1566 @ Nov 24 2008, 08:54 PM)
Quote:
Okay, I just checked it.....

I spun it over counter clockwise with a rod down the spark plug hole, then 3 intake 2 exhaust is straight up, The cam lobes are pointed out and the piston is tdc.

If it was 180 out wouldnt the piston at this point be at the bottom?[/b]
yes you are on tdc then
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post #8 of 17 (permalink) Old 11-25-2008, 09:32 AM
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Check your valve clearances...

I'm betting they are pretty tight....

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post #9 of 17 (permalink) Old 11-25-2008, 09:55 AM Thread Starter
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QUOTE (Blackkawi400 @ Nov 25 2008, 06:32 AM)
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Check your valve clearances...

I'm betting they are pretty tight....[/b]

If they are tight, what do I need to do replace the shims? Also does anyone know the tolerances? Thanks again
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post #10 of 17 (permalink) Old 11-25-2008, 10:04 AM
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stock cams?


Cold engine, set at TDC..
IN: 0.10~0.20mm (0.0039~0.0079 in)
EX: 0.20~0.30mm (0.0079~0.0118 in)

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post #11 of 17 (permalink) Old 11-25-2008, 10:43 AM Thread Starter
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QUOTE (Blackkawi400 @ Nov 25 2008, 07:04 AM)
Quote:
stock cams?


Cold engine, set at TDC..
IN: 0.10~0.20mm (0.0039~0.0079 in)
EX: 0.20~0.30mm (0.0079~0.0118 in)[/b]

Alright, I think we found the problem, now what to do about it, I bought some feeler guages and a compression tester,

on exhaust I was able to get a .010 under one side and .008 under the other.
on Intake side, I couldnt really get the .008 under it.

Assuming I did this correctly, you put the lobes up in the air, and measure under the backside correct?

Also spun the engine over, has no compression I mean it really didnt even budge the guage. It has a new 12.1 piston and rings
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post #12 of 17 (permalink) Old 11-25-2008, 04:03 PM Thread Starter
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Alright got her going, its slow, It was the valves being too tight...

mid way through the rpm it kinda falls on its face then picks up. Now that I have the 12.1 piston and full exhaust im assuming I need jetting. Thats another task. thanks all for the help
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post #13 of 17 (permalink) Old 11-26-2008, 11:22 PM
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yes if its midway then it would be the needle or main jet depending on exactly what you are considering the middle. good find on the valves. when it gets hard to start go to the valves....

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post #14 of 17 (permalink) Old 11-27-2008, 10:38 PM
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Look, if it jumped timing & it is now back firing through the carb you need to do a leakdown test to see if you bent any valves. If you DID it doesn't matter what else you do, it is NOT going to run correctly till you fix that. It's called "process of elimination" when trouble shooting. You don't even need the cams in the motor to do a leakdown & that's where I would start. Ray.

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post #15 of 17 (permalink) Old 11-27-2008, 10:58 PM
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QUOTE (suzukiray @ Nov 27 2008, 09:38 PM)
Quote:
Look, if it jumped timing & it is now back firing through the carb you need to do a leakdown test to see if you bent any valves. If you DID it doesn't matter what else you do, it is NOT going to run correctly till you fix that. It's called "process of elimination" when trouble shooting. You don't even need the cams in the motor to do a leakdown & that's where I would start. Ray.[/b]
yeah thats true i just figured that if it ran then the valves should be straight. i could be wrong considering they did not have any clearance when he checked.

Suspension & Appearance
GT Thunder front and rear shock with link, pro armor skid plates throughout, shredder rear tires 20x11 R9, IMS pegs with kick up, IMS nerf bars, IMS heel guards, IMS brake and clutch lever, +2 lone star a-arms, +1 houser Stem, pro taper fat bars, DRZoo2 dash, gusseted frame, RTC scoops, louvers & levers, RPM axle, yz start buton, precision stabilizer, quadtech seat cover and memory foam seat upgrade
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ESR intake with splash guard, yoshi full exhaust, megacycles cams, (ricky stator and new starter gears thanks to flywheel bolts), vortex 10x ignition, Athena 434 FCR 39mm carb, Kibblewhite black diamond valves & springs, DRZ base gasket,DID timing, engine ice, -16oz flywheel, pro design impeller, secret clutch package with hinson basket.

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