Topic: cb650 81

[revchuck]

i picked up an 81 cb650  custom  even though i was warned away from the cv carbs.   it had been sitting definitely year that i know of last registered in 08  so most likely 5 in all.  at any rate  im not completely new to these engines i had a few 750's  before, but never with the vacuum carbs. 

so i yanked the carbs off scrubbed them reinstalled, destroyed the tank screen on the petcock so an inline filter was installed.  got it back together and fired it right up.  good ol honda's  i temped the exhaust and got 4 different readings inside 2 HOT  outside 2 warm #4 cold in comparison to all.  changed the plugs.   

question 1
am i right to assume the readings should be similiar across the board? i would imagine the inside 2 would be hotter since they have all the heat basically. 

once running i noticed a nice  cascading waterfall of oil  from the #1 side of the bike,  out came the compression tester i had 130 120 110 and 130  from 1-4.  i have read these oil leaks  are fairly common but i think its time to fix this one. 

question 2   
can i buy just the head gasket or head gasket kit?   

so i think the bikes running good i plate it and do some riding, park it  and the bike starts running screwy idle is everywhere bike seemed possessed.  so i decide  to see if running it would clear it up  i got 3 houses down and blah litterally  blah.  while pushing the bike back i noticed a nice trail of gasoline.  then i discovered the air box was full. 

what all can cause that issue and how can i fix it? 

i suspect 2 with the accelerator pump is sticking the float but unsure.   i tore it back apart and recleaned it today  no word on if this issue still exist's. 


thats all i have for now am still fighting carb issue's  as number 1 seems to have a random misfire at idle even though the bike seems to have plenty of power  all plugs seem to have a rich condition

sorry if i asked alot of the same old questions. 

[revchuck]

cool.  should i look elsewhere help?   

[my79650]

Yes you can just order the head gasket; but you also need new o rings for the oil channels under the head at each end. These are know for leaking.  Clean up any carbon on the head and pistons while your at it. Even CV carburetors need a good cleaning. The idle jet is a press fit in those 80 and 81 year carburetors. The 82 model year 650 had a screw in idle(slow)jet. Is is smoking when you had it running?  Your compression numbers from Cyl. #2 and 3 could be down due to a burnt valve or just carbon buildup. Or bad rings. Turn the motor over by hand when you have the head off and check the cylinders for scratches and scoring. Sometimes just a good cleanup and run it daily for a week or 2 then check compression again. A ring may be stuck on a piston and might loosen up from setting for 5 years. Do you have a shop manual for your machine? 79, 80 model years used mechanical carbs. 81 on used CV carbs and different head spacing making it so you had to swap heads when going from mechanical carbs to cv and vice versa.

[revchuck]

thanks for the reply,  all i come up with on the head gasket is the engine kit.   120 bucks,  i called my local honda dealer and he informed me the  gaskets  were back order/ discontinued. 

it was smoking a little today  and ive been through the carbs 3 times it keeps having random issue's today the choke cable is stiff and inoperable.   im pretty sure its firing on all 4 now though but #1 temps alot cooler with the stand down im assuming its rich on that side  while  leaning. ? . 



i appreciate the help trust me i dont mean to seem impatient  but my heads rattling over a few of these.  im a bit of a high strung guy

[revchuck]

so i guess  im gonna have to kick the bike out of the garage until i figure this gas problem out.   

petcock isnt shutting the fuel off at all anymore so now that carb can over fill all it wants 

[my79650]

If your gas line has some slack in it; cut it and use a screw or small bolt to plug the line, at least you won't lose all your gas. Athena does complete gasket kits for these engines. I got a full set 2 years ago. Order aftermarket or check ebay. Plus get an inline fuel filter.

[trueblue]

First, if it is pouring fuel out I would either say your float heights are out or your float valves are crook.  Next, if that doesn't fix it make sure your idle jets are clear.  Don't worry too much about the compression numbers as long as they are relatively even.  If you are using a car type compression tester it can cause a low reading due to the extra volume of the hose .  Your compressions aren't low enough to be a burnt valve, don't worry about that.  Sort out your carb issue, then worry about the rest, but it does sound like you're up for a head gasket as well.

[revchuck]

i bought a lawn mower shut off today while i await for a petcock i bought from ebay, i needed one for one of the mowers anyway  so no loss if the other petcock fixes it        


i notice the bowl gaskets  arent seating anymore they are intact  and dont leak when the bikes running but sitting the drip.   any tips maybe a little oil on the seal    i plan to buy new seats and gaskets  but it has to wait 2 weeks. 

good news is bike finally seems to be running even across the cylinders.