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yzhaulin

426 backfire wont start. Cam Timing?

6 posts in this topic

Hello all.

I was looking at the other post for a no start and had a quastion on the Cam timing.

I recently picked up a 2000 426 that needed work. It has a new Wiseco 13.5:1 piston new valves and timing chain and new Hot cams with auto decompression.. When trying to start it after around a dozen or so kicks it will backfire from the exhaust one time then nothing. If I let it sit for 5-10 minutes it will backfire again after 4 or 5 kicks.I thought it was an ignition problem so I started swaping parts with my 2001 that runs perfect. Swapped 1 part at a time to the 2001 and it starts and runs with everything electrical, Coil with wire and boot, CDI, Magneto and flywheel, harness. Disconnected the blue wire to the neutral switch(Blue wire Mod) Also swapped the carb and the 2001 still starts and runs. The 2000 has the same symptom after all parts swapped. I rechecked the cam timing and it looks good. Compared the timing marks with the 2001 that has the hot cams also. They look a bit different but the 2001 has been together for a while so figured the chain could have some stretch to it.

I rebuilt the 2001 when i got it a few years ago with no problems and put the 2000 together the same way.

Ill post some pics of the cam timing so anyone can see if it looks good.

The pic with blue dots on the intake is the 2000 that will not start and backfires.

The pic with the shiney marks on the intake cam is the 2001 that runs fine.

Thats how the cams were marked when I got them.

Thanks for any help.

1444105202834.jpg

1444105210007.jpg

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Assuming you are at TDC and the flywheel key is good, the timing looks fine.  Your problem is more likely a blocked pilot jet. 

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Thanks for the reply.

Piston was at TDC, Key is good as Magneto and flywheel swapped. Timing mark alingment checked with screwdrive in plug hole.

I'll recheck the carb, but it ran fine on the 01.

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Find a nice hill, run and hop on the bike, bounce up and down and shift into second, as you pre-load the bike let the clutch go and give her gas. I recently did everything you just did (Piston, cams, valves) and that's all my bike really needed was just to run one time and for the rings to be seated.

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Just wanted to give an update on the 426 no start.

After swapping everything over from a good running bike with no luck. Cleaned carb with no help. Bump starting the bike would backfire one time and lock up the rear tire.

I went through the timing procedure and looked closely at the valve events while turning the engine over. What i found was that the decompression pin on the new exhaust cam was too long and held the exhaust valve open to just at top dead center of the piston not allowing it build any cylinder pressure and causing the no start. Swapping the exhaust cam from the other bike and it fired up in three kicks. I called Hot Cams and they replaced the cam with another one with correct pin length. Bike starts no problem with the new cam.

The bad cam pin was .095 over the base of the lobe. The good cam pin is .064 over the base of the lobe.

Photo of bad cam.

1455839246991.jpg

Photo of good cam.

1455839231025.jpg

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