Hey all, I recently put a 750cc 9:1 compression ratio big bore kit in my 1975. I haven't gotten the bike started yet but the problem is I'm having massive issues when turning the bike over via the kickstarter, when the spark plugs are in it's an absolute bear to get the kickstarter to move at all, even with all my weight on the kickstarter it doesn't move. With spark plugs out it rotates very easily via kickstarter. I did a compression test without the carbs on the bike and valves adjusted, in neutral with a little oil in the cylinders and got a reading of 230PSI on each cylinder. Is this too much compression?
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Big Bore Rebuild Really Hard to Kickstart??
- Thread starter xs4life
- Start date
AUTOMAN
XS650 Addict
230 sounds like cam is too far advanced(dynamic compression)
Static compression sounds like 11/1 or so.
Do you have build sheet with swept volume/head volume/cam timing?
cliff
Static compression sounds like 11/1 or so.
Do you have build sheet with swept volume/head volume/cam timing?
cliff
oil in the cylinders could make a big difference in a high compression motor.
Madness (high compression 750) was 190 PSI about 20,000 miles ago, wasn't much fun to kick over.
Madness (high compression 750) was 190 PSI about 20,000 miles ago, wasn't much fun to kick over.
Agree with automan.
1 tooth advanced means about 10° more compression time. Intake should close about 68° ABDC.
One tooth puts at at about 58° ABDC.
That's a whole heap of a lot more compression ADDED to an already high compression piston.
1 tooth advanced means about 10° more compression time. Intake should close about 68° ABDC.
One tooth puts at at about 58° ABDC.
That's a whole heap of a lot more compression ADDED to an already high compression piston.
Quick and easy camshaft timing check I did a couple of weeks ago. Well worth doing before anything more invasive.
(I'm assuming this motor uses the stock camshaft with the 750 conversion. If not, the timing may be different). Link -
https://www.xs650.com/threads/camsh...ed-one-crankshaft-tooth-out.66347/post-839155
(I'm assuming this motor uses the stock camshaft with the 750 conversion. If not, the timing may be different). Link -
https://www.xs650.com/threads/camsh...ed-one-crankshaft-tooth-out.66347/post-839155
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I put a little oil in my cylinders thinking it would help protect the sleeves
while waking up a sleeping motor. Locked right up after a quarter kick.
Tried it 20 min later and got it to kick through. Gotta be two months later
and she still kicks hard. That's with a stock 650 with a lot of miles.
A brand new 750.
could be.
while waking up a sleeping motor. Locked right up after a quarter kick.
Tried it 20 min later and got it to kick through. Gotta be two months later
and she still kicks hard. That's with a stock 650 with a lot of miles.
A brand new 750.
could be.AUTOMAN
XS650 Addict
yes old or over oiled bores will seal up quite well for a few rotations.
Assembly "honey" oil will make it worse.
A case where more oil is worse maybe?
cliff
Assembly "honey" oil will make it worse.
A case where more oil is worse maybe?
cliff
