CB77 Popping

Slotsky · Post by **Slotsky** » Thu May 10, 2012 9:22 pm

Hi All,
I've been lurking for a while but am posting for the first time. I finally finished my 66 CB77 project bike but am having an issue with the engine. The engine is original (11K miles) and wasn't touched. Pryor to my resto it hadn't been run in 4 years. The problem is this - when backing off the throttle either between shifts while running or sitting on the stand and blipping the throttle the right cylinder will pop and "cough" or let off a slight backfire. It seems to run fine when accelerating and idles fairly well but when I put my hand over the left muffler outlet I can feel a strong pulse but the right cylinder seem a bit weak and and a bit uneven. Sometimes I can feel a few drops of water coming out (I'm pretty sure it's water - smelled it) Now for the list of things I've done/replaced with all new parts. Probe electronic ignition, timing is dead on, new coils, new plugs, plug caps, new wires. Plenty of spark on the right cylinder. Carbs taken apart and cleaned (more than once) all passage ways are clear, floats checked and set - the right carb has gas. New main and pilot jets, new o-rings on the mixture screws. However when adjusting the right mixture screw it doesn't seem to have any effect on the idle. When pulling the right plug wire the bike will run on the left cylinder but will die and not run on the right cylinder. When I took the plugs out they both were the chocolate brown color we look for - not wet or any signs of oil. The motor does not smoke and both cylinders have 135 psi compression. Valves adjusted more than once and at specs (.004) I've done everything I can think of to cover all the bases but am stumped on what could be the problem. Should have mentioned the needles and needle jets were not replaced. Another issue is that when backing off the throttle it takes a while for it to back down to idle. I'm thinking the advancer springs need replaced. Any ideas What could be the issue with the right cylinder ? Thanks in advance,

davomoto · Post by **davomoto** » Fri May 11, 2012 7:17 am

Have you synced the slides? You'll need to remove the air cleaner conncting tubes, and either watch, or feel to be sure the slides rise at the exact same time. you can adjust them at the top of the carb. Make sure idle screws are backed all the way out.

Davo

Slotsky · Post by **Slotsky** » Fri May 11, 2012 9:19 am

Davo,
Yes, the slides are synced and free.

LOUD MOUSE · Post by **LOUD MOUSE** » Fri May 11, 2012 9:26 am

Start it.
Turn in the right slide screw and the left out as the engine idle increases. ............lm

Slotsky wrote:Davo,
Yes, the slides are synced and free.

Slotsky · Post by **Slotsky** » Fri May 11, 2012 7:34 pm

LM,
Did what you suggested. Still idles fairly consistantly but no change in the way the right cylinder feels. I should probably clarify that the bike idles well and runs well on accelleration but I can notice that slight difference between the cylinders. Maybe I'm being somewhat anal about this. What's your thought on where the needle clip should be ?

G-Man · Post by **G-Man** » Sat May 12, 2012 1:53 am

Have you looked at the carb flanges to see how flat they are? Sometimes they get distorted and allow air in to the inlet.

Also have a look at your exhaust pipe joints. Sometimes air getting into the hot exhaust will cause popping.

G

LOUD MOUSE · Post by **LOUD MOUSE** » Sat May 12, 2012 2:19 am

Clip second from bottom.
If ya have no change with the air screw ya shouldn't find it is doing it's job on that side.
Often the other carb is causing the engine to idle and the bad carb comes on when the slide is lifted.
Ya may want ta replace the slow speed jet with another and while it is out remove the air screw and blow compressed air into the screw hole. ...........lm

Slotsky wrote:LM,
Did what you suggested. Still idles fairly consistantly but no change in the way the right cylinder feels. I should probably clarify that the bike idles well and runs well on accelleration but I can notice that slight difference between the cylinders. Maybe I'm being somewhat anal about this. What's your thought on where the needle clip should be ?