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crazycanuck

Bomb Start

15 posts in this topic

I just bought a 2000 yz426. Ive had to bomb start it a couple time because i couldn't get it to fire. Haven't mastered the four stroke starting technique yet. :crazy: Any ways i heard you guys say that it was very bad to stall your engine using the decomp lever. Is it also bad to use the decomp lever when bomb starting it. It seems to be the only way i could get it to fire. Any feed back would be appreciated.

_______________________________

When in doubt, pin it out.

2000 YZ426

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I'm not sure what a bomb start is, is it a bump start? The reason you shouldn't pull on the decomp lever while the engine is running is because it can bend the valve.

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When I tried to start my friends old 426 I had to pull in 20 different levers kick it down half way let it up slow kick it down 3/4 of a way let it up fast and then kick it as hard as I can. :crazy: I hated that bike.

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Bomb start is a dead bike that you coast down a hill and pop the clutch to get it running. Sorry about the slang.

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Bomb start is a dead bike that you coast down a hill and pop the clutch to get it running. Sorry about the slang.

Yep, no worries, we call it a bump start.

If you're bike is really hard to kick start and the jetting is correct, you might need the valves adjusted. I'd get the valve gaps checked, especially seeing it's an older bike that you've only just bought, and the previous owner may have never had 'em adjusted. It will also run a lot better if the valves are adjusted properly.

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mine starts every time. assuming your jetting is cool bring the kick starter to were you feel the most resistence. then bring it all the way up and use the decomp to bump the piston just past tdc. you should feel the kick starter move about an inch. bring it all the way back up and kick it hard. should fire. do not use the throttle.

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These bikes are bullet-proof. Run through some standard check-ups and you should be on your way: Is your fuel fresh? Old fuel can make for some tough starting. Is your carb clean, and adjusted properly? (when you do finally get it running, is it smooth at idle, and through the rpm range? If not think of performing a clean and or rebuild.) Do you have good compression? You should easily be able to find TDC, the point where you motion the kick until is stops, If you cannot find this point, you are losing compression, you may need a valve adjustment, or rings etc. Are you getting spark, and is your plug new, or not fouled? Have you checked oil level? That's all I got off the top of my head. Check these things, get the starting process down, use your choke, and you should be good to go.

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When I tried to start my friends old 426 I had to pull in 20 different levers kick it down half way let it up slow kick it down 3/4 of a way let it up fast and then kick it as hard as I can. :crazy: I hated that bike.

oh....come on they're not that hard to start once you learn the procedure :ride:

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Can I just point out that I think 'bomb start' is funny. :crazy: I like the sound of it. I think I'm going to start using it. Is that a Canadian thing? I have a friend that lived in BC for a few months BTW. He says it's a sweet place.

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All right - this is interesting because I have the exact opposite problem:

My 2000 YZ426 with a Wiseco high comp piston and 12 oz + flywheel starts on the first kick when cold. It starts on the first kick when warm.

However, it refuses to be bump started. No combination of traction and speed that you can reasonably expect from a push or a coast will light it up. It is purely kick start only. I have not tried feathering the decomp lever during a bump start, primarily because I didn't think of it, but also because I'm not sure I have the manual dexterity to do it while engaging the clutch.

I know it doesn't sound like much of a problem - just kick it, right? But this manifests itself in other ways: When racing a TT last weekend, I was squeezing the rear brake into a tight corner, and I inadvertently locked the rear wheel with the clutch engaged, killing the motor. I was still carrying some speed - a more friendly bike would have lit right back up when I eased off the rear brake. Not mine... even after releasing the rear brake, I slid, slid, slid, stopped, and dropped. So then I had to pick up and kick a flooded bike to rejoin the race several positions down.

How do I get my bike to allow a bump start/bomb start/push start? Do I have to go back to a stock piston? Do I need to put a later exhaust cam in with a centrifugal decompression?

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How do I get my bike to allow a bump start/bomb start/push start? Do I have to go back to a stock piston? Do I need to put a later exhaust cam in with a centrifugal decompression?

You can do it using the decomp lever, but if you don't feel that you have the 'dexterity' to do it, then you can swap out the cam for an autodecomp cam and remove the decomp lever all together. :crazy:

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Yes fellas, i guess "Bomb Start" must be a BC slang. :ride: I think it comes from when we used to push dead cars down the hills to get them started. they would backfire when you poped the clutch, sounding like a bomb. Great fun untill you hit a corner and the car wasnt fired yet. And yes BC ROCKS. :crazy:

Pull in clutch and decomp, get up a half decent speed, pop clutch and then decomp right after, fired both times for me. Thanx for all the suggestions folks.Going to check the valves ASAP.

_________________________________

When in doubt, pin it out.

2000 YZ426

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For a bit, I thought you might have adapted a Coffman starter to your bike. :crazy:

Bump starting using the compression release is OK, and is really about the only way it can be done. Pull the clutch and CR, roll the bike, let the clutch out and get the engine to turn over at least once, then ease off of the release with no throttle, opening it slowly and pulling the clutch in as the engine fires.

Engaging the compression release at any speed higher than cranking should be avoided, as it runs the risk of breaking the decomp shaft and/or valve lifter, and possibly damaging the head itself.

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