richie
XS650 Member
Hi all, I have a newly acquired 1977 with some cafe style mods. Mileage unknown.
Issue is the compression check: RH cylinder reads 142 and LH 122 measured with carbs removed and again with carbs on throttle full open. plugs: RH dark black, LH nice tan color. Looking for suggestions on things to check before a tear down.
Other relevant info: There is a whistling sound that I don't recall hearing before I rebuilt the carbs. I think it is from the vent tubes which are both plugged with a rubber stopper that has an 1/8th inch dia hole in them on the center axis. Definitely has air moving through these holes. I didn't feel any air leaking at the head gaskets. (BTW, what is the typical breather tube arraignment when the stock air box is not used? is this venting the crank case at the top of the engine?)
When I cranked the engine with the starter during compression check (the second time) I though I heard what might be a light tapping of a hammer on steel. My impression was it was from the LH head. Is this a poorly adjusted cam clearance or (ouch) bent valve hitting the piston? could the bike run with a bent valve? - I'd expect no compression
Other background: My impression of the PO is he is not a mech. On the phone he said he rebuilt the engine, and in person said his buddy looked a the timing chain and valves and it all looked good (apparently they took it apart but didn't rebuild it - although the base gasket looks new) It ran but had fuel related hesitation during a spin around the block. I drove it the next morning with the same results and after it warmed up the idle stayed high (2K ish). bought some stuff from Mike's, Took carbs apart cleaned and replaced 132 with 135 main jets (bad move) kept the 27.5 pilot jets. It has those crappy K&N knockoff POD air filters. After cleaning, it runs better, can spin it around for a few miles - runs pretty good but cuts out at idle. Needs a through carb tune (sync, return jets to smaller etc) but mean while I'd like to know more about the compression issue. Thanks! I have three of these machines now- none are running - ah-haa!!
Issue is the compression check: RH cylinder reads 142 and LH 122 measured with carbs removed and again with carbs on throttle full open. plugs: RH dark black, LH nice tan color. Looking for suggestions on things to check before a tear down.
Other relevant info: There is a whistling sound that I don't recall hearing before I rebuilt the carbs. I think it is from the vent tubes which are both plugged with a rubber stopper that has an 1/8th inch dia hole in them on the center axis. Definitely has air moving through these holes. I didn't feel any air leaking at the head gaskets. (BTW, what is the typical breather tube arraignment when the stock air box is not used? is this venting the crank case at the top of the engine?)
When I cranked the engine with the starter during compression check (the second time) I though I heard what might be a light tapping of a hammer on steel. My impression was it was from the LH head. Is this a poorly adjusted cam clearance or (ouch) bent valve hitting the piston? could the bike run with a bent valve? - I'd expect no compression
Other background: My impression of the PO is he is not a mech. On the phone he said he rebuilt the engine, and in person said his buddy looked a the timing chain and valves and it all looked good (apparently they took it apart but didn't rebuild it - although the base gasket looks new) It ran but had fuel related hesitation during a spin around the block. I drove it the next morning with the same results and after it warmed up the idle stayed high (2K ish). bought some stuff from Mike's, Took carbs apart cleaned and replaced 132 with 135 main jets (bad move) kept the 27.5 pilot jets. It has those crappy K&N knockoff POD air filters. After cleaning, it runs better, can spin it around for a few miles - runs pretty good but cuts out at idle. Needs a through carb tune (sync, return jets to smaller etc) but mean while I'd like to know more about the compression issue. Thanks! I have three of these machines now- none are running - ah-haa!!
