Hard Start, Popping, and Black Spark Plug

I searched and search for the past day and I'm tired of reading. The bike is a 05 YZ450F.

Starting routine is choke, two twists of throttle and kick.

Bought it 3 months ago and could get it started in 3-5 kicks cold and 5-10 hot. I then checked the valve clearance and shimmed them back to spec. They were out pretty bad. After that, I tried to crank it and it took like 10 kicks cold. Ever since it has been the same, anywhere from 7+ kicks and sometimes I just get tired of kicking and give up. When I do get it cranked it pops/backfires like crazy revving it up. Same thing on decel. It also tends to do it while trying to crank it. It will backfire while I kick it. I know there have been all kinds of threads on this and I am tired of reading them as they aren't specific to my bike.

Engines need spark, fuel and air to run so...

I pulled the plug and grounded it against the engine and I am getting spark. The plug did appear to be black. It didn't have build up on it but it was just black which makes me think it is running rich.

Next, I checked the timing and it is spot on. The cam chain is tight, the dots on the cams line up, and the lobes point out at TDC. While here, I went ahead and checked the clearances and they were all in spec.

Next, I read up on carbs and jetting. I pulled the carb and blew out the jets with air. I didn't blow any air through the carb as I didn't was to mess anything up. I pulled the float cover off the bottom and it appears that the leak jet was not even installed. It was just loose in the float bowl. When I pulled off the cover the leak jet just fell out. I screwed it back in the hole where I think it went, the only one it would fit in on the float cover.


I put it all back together and tried to crank it again. 5 kicks and it fired up. Seems like it may start a little easier but the popping is still there. I mean it's horrible.

My jetting is as follows:

Altitude: Less than 100'

Start: 72

Leak: 40

Pilot: 45

Main: 170

I dont know where the needle clip is set because I couldn't find it/don't know where it is.

Thanks in advance.

If it's popping while holding the throttle steady or accelerating, and the plug is black and sooty, the problem could be an intermittent electrical open. Look for a loose or dirty ground connection, weak wires at connectors, etc. It could be a faulty stator, too, but this is difficult to verify except by swapping in a known good unit. Sometimes you can connect an analog VOM and tap or wiggle the coils. If the VOM jumps, you may have your culprit.

Ok so I'll look for loose connections. What you're saying it that it may be missing spark every now and then causing the fuel to not ignite and thus providing a black plug? Also, would I be correct in assuming that the un-burt fuel would then be pushed out of the cylinder on the way out through the exhaust only to be ignited the next time the spark plug catches a charge which is why I am hearing all of the popping?

Yes. Erratic ignition can do all of that.

this sounds exactly like the problem I'm having with my '06 I just bought, was there ever any resolution to this issue??

Not yet. If I figure it out I will post back.

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