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Shawbridge Husky

Kick through compression stroke

18 posts in this topic

Any one able to kick through the compression stroke with-out using their de-compressor lever?

And if so can this really impede performance? Mine has a recent rebuild but the head was just cleaned and left alone. ( valves untouched )I can push down through the compression stroke when cold with effort over a few seconds but much less when hot. My ring end gap may be on the large size and I do have a half thou of ovality in the cylinder ( .0005" ) But the bike still rips!!

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My bike is a 00' I still can't kick through TDC. Have you tested the compression?

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Ive seen a dude start his bike by releasing the compression release while kicking. That is the closest thing I have seen of kicking through the compression stroke.

Isn't that why BBR makes billet kickstarters, because people try to kick thru the compression stroke and snap kickstarters?

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I took a nasty spill on my 00 once and busted the decomp lever. I was able to kick through the compression stroke, but it wasn't easy! I would say your fine Hugh, that sounds about like my 00 was when I had to do it.

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Some thoughts:

If your idle is turned way down you have less air being compressed, so it will be easier to kick through.

If your cylinder is dry you won't have a good seal, so pressure can leak by more easily.

Under these conditions I can slowly push my fresh '00 and my 100 hour '01 beyond TDC with no help from the release.

Hope this helps.

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Another thought, have you changed the layout of the bars. I moved the decomp lever to point down more and forgot about it. Later at a track, if I idled and turned the bars to the right, it died. It wouldn't start with bars to the right. After an hour or so, I put it together, pulled some slack in the decomp cable from under the regulator and it was fine.

Something to check,

mwc

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Just a thought...if you have checked everything that everyone else said on the prior replys you may want to check your valve clearance. I recently had to replace my crank and after a couple of rides with the new crank I lost compression in the kickstarter..(I could kick all the way through without much resistance and starting was more difficult when cold) I checked my valve clearance and all 3 intake valves were too tight. I adjusted them and my compression came back and it now starts 1st kick when cold.

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It may be worth using a leak-down tester to verify the ring & valve seals. Best figure I've seen on my big-bore YZF was 4%.

(For comparison, a stuck compression ring pushed the reading up to 20% and lost me around 3hp on the dyno..)

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if i stand on the kickstarter and push hard, and i mean hard, it will pass tdc.

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If I keep firm pressure on the starter for a while it will turn over very slowly. I don't think I'll be trying to start it that way though... :)

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It sounds to me as though you have normal compression when the engine is cold, Hugh. Since it loses some compression once up to temperature, I would think that there is a an issue with valve(s) lash. As you know, valve lash is measured and adjusted with a cold engine. As metal expands when it is heated, all it takes is one valve to be slightly tight and some compression will be lost when the engine heats up. Also, don't forget to put oil in it.

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Thank-you very much for the excellent advice guys! Nice to see some of the original members still out there. The de-comp cable is in place and in not creating a problem. I think the valve issue may be spot on and will take some mesurements over the weekend. I recall them being on the lower side last time I verified. As for there being more resistance on the kick start when hot and primed with oil is a very vaild point to keep in mind. Also I agree with Boit that topped up oil in the engine will help in many regards. :)

[ May 10, 2002: Message edited by: Hugh LePage ]

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I had the same prob on my '01 250f, no comp when cold but when warmed up the comp came back. I changed to YZ timing on the weekend and checked the valve clearances while it was apart, one of the intakes was very tight, no clearance at all, changed the clearance tonight and the compression was back when cold, I stand on the kickstarter with all my weight and it now takes about 5 sec to push through the compression stroke.

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I snapped my decompression cable, and was able to ease it past TDC. I ordered one through Terry Cable, and Im still waiting for it. If it is not here by Sunday, I will ride without it. Once you get it past TDC its no problem.

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Originally posted by Hugh LePage:

Any one able to kick through the compression stroke with-out using their de-compressor lever?

And if so can this really impede performance? Mine has a recent rebuild but the head was just cleaned and left alone. ( valves untouched )I can push down through the compression stroke when cold with effort over a few seconds but much less when hot. My ring end gap may be on the large size and I do have a half thou of ovality in the cylinder ( .0005" ) But the bike still rips!!

[ May 15, 2002: Message edited by: groundhog ]

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Originally posted by Hugh LePage:

Any one able to kick through the compression stroke with-out using their de-compressor lever?

And if so can this really impede performance? Mine has a recent rebuild but the head was just cleaned and left alone. ( valves untouched )I can push down through the compression stroke when cold with effort over a few seconds but much less when hot. My ring end gap may be on the large size and I do have a half thou of ovality in the cylinder ( .0005" ) But the bike still rips!!

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I have been tinkering with my bike for the last few days. Yesterday while trying to start it cold it would easily go through the compression stroke several revoultions, just like you had the lever pulled in. Then it would be back to normal, then go through a couple of easy compression strokes - always after using the compression lever & getting a good single kick. This happened 4 or 5 times and has never happened before. I have started the bike 7 or 8 times in the last few days to change oil etc., but never rode it or made any changes. I am thinking the cable or something is sticking, however the bike is almost new - nothing should be worn. I will probably get a chance to work on it today & let you know what I find.

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