06 yz450-f ignition \ starting problems


10 replies to this topic
  • clevernickname

Posted June 19, 2010 - 01:35 PM

#1

I have an 06yz450 that i just rebuilt, it was running great, needed the fuel screw to be adjusted. After i washed it i could not get it to start easily, im talking 100 plus kick here, Or run for long when i get it started. Its getting spark but after testing the coil, the part the plugs directly onto the spark plug, i got a low ohm reading. Its supposed to read between .8 and 1.0 and im getting reading between .2 and .5 at most. Could this cause the bike to not start easily or run well? Ive check the rest of the electrical and everything seems to be working fine.
Ive check the valves, its getting compression, and its getting fuel /air. The carb needs adjusting but it should start ok even with adjustments needed.
Ive tried new plugs and it seems to start a little eaiser but it will not stay running.
So what do you guys think? do i need a new ignition coil?

  • grayracer513

Posted June 19, 2010 - 03:24 PM

#2

The carb needs adjusting but it should start ok even with adjustments needed.

Not so fast, there...

One of the keys to getting the YZF to start well is having the pilot circuit properly adjusted. It's nowhere near as insignificant as you seem to think.

That said, the problem started after you washed it, so why not look for the obvious; water in the carb?

  • clevernickname

Posted June 19, 2010 - 04:16 PM

#3

I know its important. Im running a 42 pilot and a 155 main and the fuel screw about 1 3/4 out. Btw im in denver so that should be a good setup. At least enough to get it started, thats what worked before. As far as water in the carb i did completely disassemble the carb and clean it out when it first happened. Right now its just giving me a bunch of backfire and semi starts. Ive been working on it all day and havnt been able to get it to go. I checked the valves and they are all in spec... The bike has new rings in it, new head and base gasket.
The only thing out of the ordinary that i noticed is at the bottom of the cylinder next the the dipstick the gasket has a little bit of oil around that seal. I wiped it off and after kicking it for a while it came back. Its hitting pretty hard on the compression but when i slowly push the starter i can hear a bubbly air sound coming from around the chain guide hole.

  • clevernickname

Posted June 20, 2010 - 05:42 PM

#4

I think the bike is out of time a little bit. All the timing marks are lining up, really they are perfect. and its with a new weisco chain, one thing that concerns me is that it fell into the hole and when i pulled it out it was kinked a bit. And it also kinked when i had it off today.

When i ground a spark plug to the engine, while leaving another one in, i can see it sparking just as the exhaust starts letting out. Maybe this is normal for this bike? But i would think it would either spark just before the decomp or on the way back down after the valves close.

I really need some help on this one guys.
cdi? ignition coil?
I cleaned the stator and made sure the flywheel key was ok, it was, tested all the electrical system and still the only thing off is the ignition coil. But maybe my power meter dosnt go low enough to check the ohms on it correctly.
Anyone?

  • grayracer513

Posted June 20, 2010 - 05:57 PM

#5

When i ground a spark plug to the engine, while leaving another one in, i can see it sparking just as the exhaust starts letting out. Maybe this is normal for this bike? But i would think it would either spark just before the decomp or on the way back down after the valves close.

The spark occurs just prior to TDC on every revolution, so you will see a spark at the end of the exhaust stroke as well as when both valves are closed at the top of compression.

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  • clevernickname

Posted June 20, 2010 - 08:24 PM

#6

So if its supposed to occur prior to TDC and its actually occuring while the exhaust valves are opening on the compression stroke that would mean that the timing is after tdc just a bit. Which makes sense why im shooting flames out of my exhaust every once in a while.

After inspecting the exhaust cam it seems to be a little bit high. Opposed to the intake cam. Its a new stage 1 hotcam, maybe it the gear moved a little bit. I found another post of this happening to someone. My decomp is not on top of the valve at tdc but it is just barely passed over it. Looking at the picture that gray posted my exhaust cam looks like its been rolled back a little bit, maybe a cm or 2, and could maybe be a bit higher than it should be.

http://www.thumperta...ghlight=bad cdi

Whats some other things that could cause the spark to happen late?
And its not the woodriff key, i already check that...

  • grayracer513

Posted June 21, 2010 - 07:33 AM

#7

So if its supposed to occur prior to TDC and its actually occuring while the exhaust valves are opening on the compression stroke that would mean that the timing is after tdc just a bit. Which makes sense why im shooting flames out of my exhaust every once in a while.

The exhaust valves do not open on the compression stroke. The engine needs two complete revolutions to complete an operating cycle, which means the piston will travel up or down the bore 4 times. Thus, 4 "strokes" of the bore, and the name of the engine design.

The cycle begins at top dead center (TDC) with the intake valves already opening. The piston travels down, creating a void filled by atmospheric pressure, the incoming air bringing fuel with it from the carburetor at bottom dead center (BDC), the intakes have begun to close, and the compression stroke starts. The air and fuel is compressed to 8-13 times it's natural density against the closed valves in the combustion chamber. At between 5-45 degrees before TDC, depending on speed and load, the ignition spark occurs, igniting the fuel. As the pressure from combustion builds, the engine passes over TDC, and combustion pressure drives the piston down for the power stroke. As it nears BDC, the exhaust valves open, the piston swings up through the exhaust stroke, pumping the spent fuel charge out of the chamber. As it nears TDC, the intake valves open again as teh exhausts are closing, and the cycle repeats.

It is at this point that the second, "wasted" spark occurs. The reason you get an occasional pop off of fuel in the exhaust is that the unburned fuel introduced during the failed starting attempts has built up in the exhaust, and the waste spark ignited chamber vapors with the exhaust valve open. One of the reasons this happens is because it is much more difficult for a spark to jump the plug gap under compression pressures than at normal pressures. A plug can show a normal spark on the exhaust stroke, but short out under the pressures of compression due to partial fouling or weak spark and fail to fire the engine.

  • clevernickname

Posted June 21, 2010 - 08:07 AM

#8

right... so now my bike is running perfect... Starts first kick every time, its funny because it wouldn't start until about midnight of last night, started normal this morning too. The only thing i did was test the continuity of the wiring harness. I tested all the wires plugged it all back in and PRESTO it started. I keep shaking / pulling on wires to see if it was something with the harness but it just keeps running. I know the problem didn't fix itself and i really hate to say this but i wish it would stop running for me so i can fix the damn thing.

  • grayracer513

Posted June 21, 2010 - 08:37 AM

#9

Probably already did fix it. The cause was likely a poor connection at some point related to the wash job.

  • clevernickname

Posted June 21, 2010 - 10:02 PM

#10

Well got to ride for about an hour or so today... It was running great! Wreaked and started right up. Then about 5 minutes after i stopped and let it cool off. It wouldnt start back up, i coasted downhill for a while, in gear most the time didnt start, then stopped when i came to an uphill. Thought to myself " i really dont want to push up this F(*&ing hill" so i tried starting it and after about 20 kicks it started. Got up the hill stopped to put my helmet on and it wouldnt start again, coasted to my jeep and messed around with it for a while and it wouldn't start, just backfire occasionally. Got it home, about 20 miles by highway so it had plenty of time to cool, and still wouldn't start, waited a few hours went out and tested the harness again, this time tearing it down to inspect the wires, everything tested \ looks ok so i put it back on, just the stator and cdi, pumped the gas put the choke on and it started after 3 kicks. while warming it up it died and it started again, 2 kicks this time. It died and started back up 3 or 4 times on the last time i popped the choke off and it died. Now it wont start back up no matter what i do, its giving me semi starts and backfires again.

I REALLY NEED SOME HELP HERE GUYS, I WOULD TAKE IT TO THE SHOP BUT WHENEVER I DO THEY TELL ME I NEED MAJOR ENGINE WORK, IVE REBUILT HALF THE ENGINE! ITS CLEARLY ELECTRICAL AT THIS POINT! WHAT COULD IT BE?

I played with the cdi with an ohm meter last night, touching every combination of prongs together just to see what would happen. Could it be that the CDI is making the bike go out of time or not putting out enough spark?

  • clevernickname

Posted June 25, 2010 - 06:48 PM

#11

Yep put a new coil, cdi and wiring harness on it today. Started first kick, Going out tomorrow to see how she rides!





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