73 tx woes

[CHAZZ]

well the tx decided to give me another headache,
now it wont even run,it coughs through the carbs etc but not fire,ive even put the carbs on the wifes xs2 chop and it fired up first kick,so carbs are fine.
i did a compression test and was getting 124 right pot and a measly 90 in left.
now after trying to get it running, and another compression test i still get 124 on the right but the left doesnt even register on compression dial until you spin the motor at least 14 times and then i get a reading of between 25 and 45.
i even did the old thumb over plug hole trick and right has good compression but left is pathetic,it does eventually put some pressure against your thumb but you could go and make a coffee in the time it takes
all signs are looking at a rebore,what you reckon

 

[hard_y_rd]

I wouldn't say re-bore. My 73 registered 0 on the compression tester. Lol. Both Pistons were froze to the cylinder walls.
I would pull the jugs and inspect pistons. You might get away with honing and new rings.

 

[fredintoon]

Hi Chazz,
or it could be the valves. Put the dodgy side at TDC on compression stroke, check the valve clearance, pour some oil in the exhaust and intake ports as a Q&D valve seal test.

 

[gggGary]

put r up on tdc put air in the plug hole listen to where it's coming out, that'll tell you something.

here's some idears.

http://www.xs650.com/forum/showthread.php?t=11693

 

[angus67]

I tried that pressurizing the cylinder on a ol xl250 with almost zero comp. didnt hear a thing. Took the head off, upside downed it, water ran straight through the exhaust valve, had both valves relapped, runs like a... Well....a old xl250 with a 250# rider on it.

 

[CHAZZ]

cheers guys
i ended up taking barrels and head to a local engine guy,since i had them off anyway
seems the barrels are fine just need honing and new rings [as suggested by hard y rd ]
the guy thinks the head is suspect and is giving it a look over today,i could do it myself but dont have time and at least i will know its been done proper
once again cheers for the advice

 

[5twins]

The valves pretty much always need some attention. They develop pits on the seats just through normal use. After enough pitting develops, they start to lose their seal and leak. Eventually they get to leaking so bad, you start losing compression. The exhausts are usually worse than the intakes. They flow hot exhaust gases out. The intakes have an easier job, letting cooler air/fuel mix in.