low compression?

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cashonly

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greetings , ive got a 78 xs that has compression issues

2 weeks ago i
put a new dual output igition coil on
(mikes xs #17-6822) and the solid state regulator rectifier from tc bros
(followed the forum
advice and wired the points together and used one condenser)

after that it rained for a few days so i didnt fire it up but normally this is my only vehichle im dedicated to this bike i ride it every day and it gives me little if any problems

today the bike fires up no problem as usual , but now when its warm it dies unless the choke is on

then i noticed when i went to check the oil that theres enough air coming out of the oil filler hole to pump up a small air mattress

timing is spot on , carbs are clean, so i check compression

the compression readings i got in june when i bought the bike were low but within the right tolerance of eachother i think
123~ right cyl
125~left cycl

the reading i just got today was
130 right cyl
120 left cyl

im hoping that my compression tester is off or its user error i can accept that but im wondering if the fine folks in the forum have any idea why the readings may have changed in such a weird way possibly in light of my afformentioned recent repairs

im anticipating a top end rebuild considering the compression was already the lowest it could be in june

normal things that come with a rebuild checking valve clearance and replacing piston rings but maybe im not seeing something

i should add too , since the ambient air temp in atlanta has been colder ive had to let the bike warm up long and longer before riding , somtimes in excess of 20 mins just to keep it runnning smoothly without dying
 
cashonly said:
greetings , ive got a 78 xs that has compression issues

2 weeks ago i
put a new dual output igition coil on
(mikes xs #17-6822) and the solid state regulator rectifier from tc bros
(followed the forum
advice and wired the points together and used one condenser)

after that it rained for a few days so i didnt fire it up but normally this is my only vehichle im dedicated to this bike i ride it every day and it gives me little if any problems

today the bike fires up no problem as usual , but now when its warm it dies unless the choke is on

then i noticed when i went to check the oil that theres enough air coming out of the oil filler hole to pump up a small air mattress

timing is spot on , carbs are clean, so i check compression

the compression readings i got in june when i bought the bike were low but within the right tolerance of eachother i think
123~ right cyl
125~left cycl

the reading i just got today was
130 right cyl
120 left cyl

im hoping that my compression tester is off or its user error i can accept that but im wondering if the fine folks in the forum have any idea why the readings may have changed in such a weird way possibly in light of my afformentioned recent repairs

im anticipating a top end rebuild considering the compression was already the lowest it could be in june

normal things that come with a rebuild checking valve clearance and replacing piston rings but maybe im not seeing something

i should add too , since the ambient air temp in atlanta has been colder ive had to let the bike warm up long and longer before riding , somtimes in excess of 20 mins just to keep it runnning smoothly without dying
Click to expand...
also i should add it has always leaked a little bit of oil on the left side of the head it usually it drips off the cam chain tensioner acorn nut

anyways heres a picture of my 650
 

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I Like these type bikes .. Remembering when I was a lot Younger

So -- Compression wont make the bike stall as far as I know
The measurement of compression is not so straight forward ..it need to be done properly
Is there soft resistance on the kick starter
please read and look there

https://www.xs650.com/threads/81-su...valve-adjustment-on-compression-stroke.67540/

Is there smoke coming out
Any rattle

There is a crank case ventilation that can need inspection please search crankcase breather

There was a modification 2 weeks ago And if problems after that I would recheck there
 
the kick start may be soft but i have no refference because this is the only bike ive ever kick started and im a fairly strong person

also no smoke or rattle coming off the bike
 
Welcome Cash
That there's an interesting bike for sure.
You haul dynamite for a livin by any chance? :D
Just jokin, truly I like it.
Some have had problems idling on the side stand and prefer the center stand. :yikes:
Pressure in the block :umm:. Mud Daubers?
A 20 min warm up is abuse. My bike will idle within 3 min in dead of winter.
Sounds like tune up time.
Bad electric voltage and/or poor connections will make you chase your tail.
Hot coils and condensers will do the same.
Poke around in the Tech section, lots of info there.
 
JOHNDADDY said:
Welcome Cash
That there's an interesting bike for sure.
You haul dynamite for a livin by any chance? :D
Just jokin, truly I like it.
Some have had problems idling on the side stand and prefer the center stand. :yikes:
Pressure in the block :umm:. Mud Daubers?
A 20 min warm up is abuse. My bike will idle within 3 min in dead of winter.
Sounds like tune up time.
Bad electric voltage and/or poor connections will make you chase your tail.
Hot coils and condensers will do the same.
Poke around in the Tech section, lots of info there.
Click to expand...
i always felt like the 20 min warm up was a red flag ,
all the electronics are brand new and im very dilligent with my wiring

when i put the new dual coil on i kept the old condenser , just wired it to one side , should i have gotten a new condenser maybe ? i figured they got no moving parts why replace
 
JOHNDADDY said:
How long have you been running the bike?
Why the ign change?
How was it running before?
Jetting with open headers will give you grief to say the least.
I added 12" of straight pipe on my 75, Knocks down the backfire on decel.
Vent on gas cap? Make sure your crankcase breather isn't plugged up.
Click to expand...
ive ridden this bike every day since june 28th
it always ran good, kickstarted first try every time and never broke down on me for any thing besides ignition coil problems

the oem coils from tc bros or mikes xs kept giving me greif , and both websites recently raised the price of them thats why i switched to the dual output coil it was cheaper and i could fit that rad britsh tank over the single coil as opposed to the stock doubles where i couldnt

saving up for some new pipes right now
i know mine are not ideal but i havent had problems with them yet

gas cap is vented
and i havent checked the crankcase breather , where is it located ?
 
cashonly said:
ive ridden this bike every day since june 28th
it always ran good, kickstarted first try every time and never broke down on me for any thing besides ignition coil problems

the oem coils from tc bros or mikes xs kept giving me greif , and both websites recently raised the price of them thats why i switched to the dual output coil it was cheaper and i could fit that rad britsh tank over the single coil as opposed to the stock doubles where i couldnt

saving up for some new pipes right now
i know mine are not ideal but i havent had problems with them yet

gas cap is vented
and i havent checked the crankcase breather , where is it located ?
Click to expand...
currently its stock jets from the mikesxs mikuni vm34 kit except i removed the air jet from the intake side of the carb and the main hex jet i bumped up a little

just checked all that too and everything is clean
 
mine has a single fitting
i pulled the tupe off and saw no blockage
do some people route this tuble into a catch can or something like that ? mine was routed to the chain side
 
Auto chain oiler if you have the right cover.
I was doing that with my sporty but hated the mess so i made a catch can for it.
You have spark, you need either fuel or the proper mixture.
A tuned warm engine will stall if you hit the choke.
A hot coil will kill you if it's bad, plenty of "bad right out of the box" stories to go around.
Got a guesstamate of your idle speed? Could be too low, need 1,200-1,300 cold
 
the timing is correct so that should mean the coil is good no ?
idle is prob around there maybe a little higher
previously it did stall if you hit the choke once its warm
 
JOHNDADDY said:
A bad coil will give weak to no spark when it gets hot.
Click to expand...
i put my hand on the coil
to check it and make sure its not hot to the touch very often when trying to diagnose this issue
not sure if thats a good method of ruling out a bad coil though
 

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