72 cb350 twin points problem (searched) - Ive tried it all

Not too sure how to diagnose it while running. I know that white smoke is an indicator.
I've heard that holding a stethoscope to the engine can help to hear what's going on but you'd have to know what to listen for.
 
did you adjust the valves ? if you have a stuck valve it wont really run at all(on that cylinder)
and the 350 has a very short adjustment range on valve clearance a stuck valve would make it impossible to get an adjustment set
there is a specific range of rotation on the eccentric adjuster shaft that must be maintained
adjust the cam chain tension while you are at it
set the valves and do a compression test correctly on it, warmed up
there is no valve seals on a 350
piston blowby doesnt create backfires :( ::)
onnce you get the valves and static timing set set the timing for full advance with a strobe timing light it is the last and most important setting
put mufflers back onit and put the airbox back on you cant run straight pipes on the street,they wont work well anyway unless very long
besides straight pipes are for fucking assholes dont be that guy
and it is just as stupid to run stacks with no filters unless you never ride and just want to park it and look at it :-\
you need to see if you can get it to run stock before you fuck it all up anyway
if you cant tune it stock don't even bother trying with it all fucked up
 
Haha xb33bsa, good advice. I adjust the valves once but it was my first time ever doing it so I'll go back and do it again. I'm having longer pipes made (if I could ever get the bike to the shop....) and I'll recheck all this with the filters on


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;D
getting the valves set correctly is very tricky one slight move on the eccentric and they are way out... and make sure the little pointer hashmark next to the screwdriver slot is pointed in the right direction
 
I heard that using a vacuum gauge on each cylinder can isolate a stuck valve.

xb33bsa great tips, glad you are on this thread, cheers. Wondering if you have any other general suggestions for valve jobs and diagnoses.
 
Hey xb33bsa, I rechecked the valve clearances at .002 intake and .004 exhaust, threw my old k&n pod filters on, reset the cam tensioner at 90 degrees past TDC. I don't have a compression tester but will get one later in the week to check that.

No white smoke or anything like that. But plenty of black puffs from back firing. Just a steady idle and it will pop here and there, any revving and I get some big back fires.




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good !
well it may be the carbs, i guess you did test for leaks with starting fluid and unfortunately i am not much help tuning CV carbs i can only suggest make it stock,make sure the parts are all in the right place diaphrams good float hite correct etc and and go from there
 
Hey xb33bsa, do you know any obvious indicators of blow by? A friend suspects that he's got it on his 550.
Very interested in this thread as I've got a 73 350G in the ranks waiting to get restored.

Black smoke is supposed to indicate over rich fuel mixture but could the stuck valves be what's causing the back fires?
 
blow by is going to be showing some evidence at the breather should be white smoke
usually if you have blowby it will be burning oil as well, white smoke out the exhaust pipe
sooty black smoke is generally understood as a fuel rich mixture
stuck valve will be showing way loose i figure when attempting adjustement
with a few simple tools you can also do a pressure leakdown test of individual cylinders
very handy test
 
xb33bsa said:
blow by is going to be showing some evidence at the breather should be white smoke
usually if you have blowby it will be burning oil as well, white smoke out the exhaust pipe
sooty black smoke is generally understood as a fuel rich mixture
stuck valve will be showing way loose i figure when attempting adjustement
with a few simple tools you can also do a pressure leakdown test of individual cylinders
very handy test
Click to expand...

What kind of evidence at the breather would show in blow by? Like some oil and gas mixture leaking?
 
Not stuck, just trying to find out what some of symptoms are.
As mentioned a friend thinks he's got blow by happening but no white smoke.
He said he found fuel or oil in the exhaust.
 
Hey everyone,

I pulled the carbs back off and tore each one down to check for anything that might stand out as odd or incorrect. I noticed both floats were a little bit off (even though these were one of the first things i checked when i started having issues.) I replaced the slow jet and needles and put everything back together.

The bike now idles much more smoothly and can be rev'd and driven with very little popping and no backfiring. The bike still likes to break up at higher RPMs and runs sluggishly overall. See as I am running 130/82 jets, should be gapping the plugs larger than .30~?

I also plan to get a strobe light on the bike and fine tune the timing later this week.
 
oily fuely exhaust pipes is classic over rich

fuel in the oil is not from blowby it is from overflowing float bowls on the carbs,gas got in on the pistons and sat there, drained into the crankcase and the fuel thinned oil could ruin the engine
change out the oil, fix the carbs
 
o2sensorheating said:
Hey everyone,

I pulled the carbs back off and tore each one down to check for anything that might stand out as odd or incorrect. I noticed both floats were a little bit off (even though these were one of the first things i checked when i started having issues.) I replaced the slow jet and needles and put everything back together.

The bike now idles much more smoothly and can be rev'd and driven with very little popping and no backfiring. The bike still likes to break up at higher RPMs and runs sluggishly overall. See as I am running 130/82 jets, should be gapping the plugs larger than .30~?

I also plan to get a strobe light on the bike and fine tune the timing later this week.
Click to expand...
plug gap is fine in that range you cant change carb tuning with larger plug gap
get a few sets of new ngk standard plugs to have on hand for tuning
 
xb33bsa, so it seems all that is left is carb adjustments and strobe timing to get this thing drivable seeing as all other variables have been addressed. Ill report back with an update. Anything else i should be taking a look at?
 
xb33bsa, thanks again, my buddy will be happy its not blow by, I didn't think that it was.

Once your carb floats are all good and you've got the right air/fuel mixture, I would get new plugs, gap them, then do your timing with strobe.
Carb sync should be the last step after everything else is taken care of.
 
o2sensorheating said:
xb33bsa, so it seems all that is left is carb adjustments and strobe timing to get this thing drivable seeing as all other variables have been addressed. Ill report back with an update. Anything else i should be taking a look at?
Click to expand...
make sure the advancer works smoothly just grab the points cam and twist it should snap back on its own
if it is real sloppy until you feel the spring pressure you should retension the springs and clean and lube the thing
have fun they are a jewel of a motor when running good :)

https://www.youtube.com/watch?v=w9DD5iLzD_g
 
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