[Lou627]

Working on a 1974 cb360, rebuilt/cleaned carbs twice. Has good idle and runs smooth, but will not exceed 4000 rpms, and occasionally hangs at 4000 for a few seconds. Any ideas?

 

[66Sprint]

What are your compression readings?
Is it correctly timed?...does it advance properly to between the advance indexes?
Does the advance unit return to the "retarded" (idle) position when you let off the throttle?
Are the carbs synched?
Are the valves correctly adjusted?

Lots of possible causes...Need more input!

 

[Lou627]

hey, didn't answer right away cause i didn't have a compression tester and therefore no way of checking anything. i checked and i was wondering what the results mean. when checking comp when cranking the bike (kick start or electrical start) i got a comp of 150 on either side. when it's idling, it drops to somwhere around 100-125. when i rev it, it drops even lower (50 to 75). not sure what the specs are, but looking around at other posts, i pretty sure that's not a good thing. haven't checked anything else yet cause i don't know what the results mean on the comp test (it's my first bike, i'm learning as i go). my guess is new rings, but i figured i'd confirm before i got parts and started working.

as for the carbs and the valves, i'm gonna synch the carbs and check the valves this weekend with a friend of mine who knows what he's doing.

thanx in advance, this site has been plenty helpful already. just by going through old posts, i got a lot of questions answered.

 

[MNellis]

hey, didn't answer right away cause i didn't have a compression tester and therefore no way of checking anything. i checked and i was wondering what the results mean. when checking comp when cranking the bike (kick start or electrical start) i got a comp of 150 on either side. when it's idling, it drops to somwhere around 100-125. when i rev it, it drops even lower (50 to 75). not sure what the specs are, but looking around at other posts, i pretty sure that's not a good thing. haven't checked anything else yet cause i don't know what the results mean on the comp test (it's my first bike, i'm learning as i go). my guess is new rings, but i figured i'd confirm before i got parts and started working.

as for the carbs and the valves, i'm gonna synch the carbs and check the valves this weekend with a friend of mine who knows what he's doing.

thanx in advance, this site has been plenty helpful already. just by going through old posts, i got a lot of questions answered.

All right, I'll bite.....how do you check the compression with the bike idling and revving? You're not referring to vacuum readings are you?

 

[66Sprint]

Engine fully warmed up (HOT).....Both plugs out, Kill switch off, key on (if e-starting)....Compression gauge screwed into one spark-plug hole (to get a reading on that side).... Throttle wide open (fuel shut off at petcock or gas tank removed)...... Kick or electrically roll over the engine at least 6 to 8 times..... Take reading....repeat.... put gauge on other.... take two readings there....

 

[Lou627]

arite, i had someone tell me to run it on one cylinder and check it with the throttle and choke open and the bike running. thanx, i'll do it right this time.

 

[Lou627]

ok, made a lot more sense this time. compression was 145 and 150 on right, 150 both times on left. i'm gonna open her up tomorrow and check clearances and the cam chain, i'll keep you posted.

working on a two-bottle carb syncher, hopefully i'll have that worked out by the weekend too.

 

[Lou627]

so i checked compression, the valve clearances, reset the cam chain, checked the breaker points, checked the timing (statically, i don't have a timing light), and cleaned the carbs five or six times (and syched them). here's where i'm at.

with the choke open, it idles great and rev's up as high and as quickly as i want it to. with the choke closed it continues to bog between 4 and 5k rpm's. i tried it with the boxes on and off several times each and got the same result every time.

i'm at a loss, any ideas?

 

[Bird76Mojo]

With the choke closed it's gonna bog. Maybe we have a little misunderstanding here on "open" and "closed"?? Using terms like "choked" or "not choked" may be more easily understood.

Boxes?

GB :mrgreen:

 

[Lou627]

With the choke open (butterflies open) it revs straight to red line, but with the choke closed (butterflies closed) it bogs at 5000 and wont exceed. When the airboxes are on we don't have the screw that connects them to that shared passageway under the battery box. The openings in the airboxes are not connected to this. Could this be the cause of the bogging?

 

[66Sprint]

Here's the problem...Choke (closed) is just for cold weather start-ups....The bike runs with an open choke (butterfly NOT blocking passage).....

 

[Lou627]

jesus christ. So the butterflies on the choke are supposed to be wide open for riding? Just want to make sure cause weve been fing around with this thing for a good month thinking its the exact opposite. Thanks

 

[fasterspider]

With the choke open (butterflies open) it revs straight to red line, but with the choke closed (butterflies closed) it bogs at 5000 and wont exceed. When the airboxes are on we don't have the screw that connects them to that shared passageway under the battery box. The openings in the airboxes are not connected to this. Could this be the cause of the bogging?

With the butterflies {choke} open is how it is supposed to run once it has warmed up enough to keep it running without the choke.
Closing the choke is cutting off the air and therefore will not run over 5000 rpm.
Leave the choke open and ride the bike.

 

[gs1327]

Is this thread real?

 

[Lou627]

100%. Never had anything with a traditional choke, just an enrichment circuit. This was playing out in my mind as a bike that only runs with the enrichment open, but stalls when "choke" (enrichment) closes. So yes, we really did this for month.

 

[Lou627]

100%. Never had anything with a traditional choke, just an enrichment circuit. This was playing out in my mind as a bike that only runs with the enrichment open, but stalls when "choke" (enrichment) closes. So yes, we really did this for month.

in hindsight should have realised we would have to be restricting airflow to enrichen the mixture. f***!... thanks

 

[Bird76Mojo]

Just goes to show, you learn something new everyday. Or in this case, every month. :lol:

GB :mrgreen: