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Why are 4-Strokes Hard to Start??

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First of all, I'm a newbie and I'd like to say Hi to everyone on the board. I've been reading this board for a long time now and figured it's finally time to register. Being an original 2-stroke guy, I'm not that educated on the 4-stroke technology, but my next bike WILL be a 4-stroke, and I want to learn about them before I make my purchase.

Anyway, on to the question.. Why are the 4-stroke engines so hard to start? And why are they even harder to start when they're hot? I understand they have very high compression, but figured that would only cause trouble in kicking them over, not how they actually start.

I haven't read all the posts here so maybe you have gotten the real answer already and maybe not, but here it is.

On a two stroke, every time the piston is travelling downward, it is on the power stroke. On a four stroke, it is only every other time. So if a typical kick rotates the engine ten times, a two stroke has the spark plug fire ten times to attempt to get the engine running but a four stroke only half that.

Greg

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Interesting point you have there too. I guess all these factors together make for a difficult start.. If you don't know the technique.

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Please name one modern four-stroke motocross bike that doesn't have some kind of hot-start.

My 2001 KTM520SX.

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i have a question regarding the starting of a HOT 450???...with my 500 i just hold the throttle open & kick it several times to "clear"it...how do i do this on a hot or flooded 2003crf 450???...i just bought 1 & am new to 450s...i have no trouble with my 500 but 450 makes me feel very silly some times:banghead:...(the valves r supposedely fresh also)

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i hope this is the correct way to ask this question rather than starting a new thread...if not plz tell me... thx

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the major reason for these thumpers hasnt been hit on yet. first off, 450cc is a pretty big bore, and its got alot of squeeze in it at tdc(high comp.). you are going to have to move that big piston through that cycle and it fires one time a four cycle. The other reason is because of the cam and its overlap. To run these high rpm's these cams have overlap-when the exhaust and intake are both open at the same time- while very minimally it does happen. that is another reason these things idle at 1700 rpm+,-. people are just not used to the fact that these things are super pumped up race engines and race engines are not always known as easy to start.

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i have never had a four stroke that was hard to start hot or cold.. i have a 06yz250f now and it will start on one kick if your not being lazy. the key is a strong kick, not a million sissy kicks like the pingers get going with

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KTM EXC 520 2002,

I just push the magic button (E-start). Not sure why there is a kick starter on bikes any more. For E-starting bikes (Husaberg, BMW...) the starts are even easier with electronic fuel injection (EFI).

On the lighter side, I agree, that hot valves grow/extended which changes the engine running configuration (valve seating). Having valves adjusted and a magician tune your carburetor will eliminate kick starting issues.

Having EFI and E-start will eliminate these types of threads.

Enjoy the long weekend,

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i have a question regarding the starting of a HOT 450???...with my 500 i just hold the throttle open & kick it several times to "clear"it...how do i do this on a hot or flooded 2003crf 450???...i just bought 1 & am new to 450s...i have no trouble with my 500 but 450 makes me feel very silly some times:banghead:...(the valves r supposedely fresh also)

I think it would of been better to ask this question in the Honda 450f forum rather than digging up this thread. Since most do not read the entire thread and just read the title your question will most likely not get answered and people will not realize this is a five year old thread.

I know with my friends 250r if it gets flooded I turn off the gas and crank it until it fires back up. Plus use the hot starter.

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jd jetting kit made my 4 stroke a breeze to start

+1 even with proper technique my klx450r was a bear to start, jetted it with the Jd jetting kit, now it'll start 1-3 kicks no matter what.:bonk:

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strange but mine starts more easily when I pull the hot start and open the throttle just slightly, if I dont it takes a couple more kicks

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