New member with a 1967 CL77 and questions about losing power

[coydogsf]

Depending on how the carbs are set up, a vacuum in the tank could affect one side before the other.

If you're not happy touching the hot pipes you could get hold of a thermomenter.

Okay, so I got out for another test ride and the issue came up around the same time. I was able to open the gas cap while underway with no effect on the condition. I also managed to pull the left side plug (!) which killed the half-powered engine right away, leading me to believe the problem is on the right. Hard to tell which pipe was hotter to the touch, but the left was "Oh my effin' ouch!" hot and the right was just "Holy crap" hot which confirmed that assumption.

Finally, once I got it home, I did notice a fast idle. Spraying carb cleaner at where the boot from the air filter connects to the carb on the right side slowed the idle back down to normal, from what I have read, a pretty conclusive sign of a vacuum leak. I tried using some ring clamps from my CB750 to tighten the seal, but the rubber on the boots is pretty rock hard. I have a set of new boots on order and hopefully they'll arrive in time for one more test ride!

Dave

[LOUD MOUSE]

DO you think a leak between the carb intake and the intake boot is your problem?. ................lm

Depending on how the carbs are set up, a vacuum in the tank could affect one side before the other.

If you're not happy touching the hot pipes you could get hold of a thermomenter.

Okay, so I got out for another test ride and the issue came up around the same time. I was able to open the gas cap while underway with no effect on the condition. I also managed to pull the left side plug (!) which killed the half-powered engine right away, leading me to believe the problem is on the right. Hard to tell which pipe was hotter to the touch, but the left was "Oh my effin' ouch!" hot and the right was just "Holy crap" hot which confirmed that assumption.

Finally, once I got it home, I did notice a fast idle. Spraying carb cleaner at where the boot from the air filter connects to the carb on the right side slowed the idle back down to normal, from what I have read, a pretty conclusive sign of a vacuum leak. I tried using some ring clamps from my CB750 to tighten the seal, but the rubber on the boots is pretty rock hard. I have a set of new boots on order and hopefully they'll arrive in time for one more test ride!

Dave

[coydogsf]

I do. Seems consistent with the problem only occurring with a warm engine and the idle changing when carb cleaner is sprayed. Red herring or am I on the right track?

Thanks again!
Dave

[G-Man]

A leak between carb and air filter should not have as much effect as a leak between carb and head like bikes with 'inlet' rubbers like the Honda fours. You should be able to run with the air filter rubbers removed without too much trouble.

It would be interesting to see if the 'dead' cylinder is sparking when it dies.

G

[bamacl]

Sounds like it's starving for fuel. Have you checked float levels and free movement of them?

[coydogsf]

Well, I'm not sure if I have a conclusive resolution this issue, but wanted to update the thread. After installing the new, supple air boots and spring clamps, the bike would barely run the next day. Hmmm.

Frustrated and with only one more day before the vintage rally on the weekend, I tried everything. Petcock, fuel lines and filters, fresh gas, new plugs, oil change and filter cleaning, clean jets and bowls, float levels, timing and point gaps! Ed Moore's Special Tuning Recipe (http://www.honda305.com/cb77_700/cb77-716.htm) and tons of posts from all of you (Loud Mouse of course, deserves particular thanks for always on-target posts) were particularly helpful.

And in the end, she ran perfectly! In fact, I left the next day for an almost 800 mile rally from San Francisco and Red Bluff (108 degrees F!) and the following day on high speed twisties out to bumpy remote roads along the Lost Coast of CA, including the rough Usal Rd connecting back to Highway 1.





Unfortunately, only 9 miles from Ft. Bragg, I looked down to find my rear wheel coated in oil and the dipstick showing an empty tank. From what I can gather, it appears I blew a clutch pushrod seal. Not a bad place to break down though and not a huge problem given the frequent chase trucks as part of the rally. If I'd gone down on the 40 miles of rutted dirt on the Usal Rd., I might still be out there now!





In the coming weeks, I'll pull the kicker cover and see what the seal looks like and check the centrifugal oil filter for any signs of a disintegrating cam chain roller which I've been told could have caused the blow out by clogging oil passages with broken bits. Any other thoughts from the CL77 brain trust?

Thanks again to all for helping a ambitious CL noob.

Dave

[LOUD MOUSE]

Bad deal with the oil leak.
Lets see which seal may be the source then go from there.
As I know the engine and how oil is offered to the pump (through a screen) and the pump compresses it inside the pump I sort of wonder how it can have anything that isn't like powder close the oil system and that still doesn't make sense to me.
A ring may go and cause case pressure and do what you have and often is the problem.
I await you taking parts off. .......................lm

Well, I'm not sure if I have a conclusive resolution this issue, but wanted to update the thread. After installing the new, supple air boots and spring clamps, the bike would barely run the next day. Hmmm.

Frustrated and with only one more day before the vintage rally on the weekend, I tried everything. Petcock, fuel lines and filters, fresh gas, new plugs, oil change and filter cleaning, clean jets and bowls, float levels, timing and point gaps! Ed Moore's Special Tuning Recipe (http://www.honda305.com/cb77_700/cb77-716.htm) and tons of posts from all of you (Loud Mouse of course, deserves particular thanks for always on-target posts) were particularly helpful.

And in the end, she ran perfectly! In fact, I left the next day for an almost 800 mile rally from San Francisco and Red Bluff (108 degrees F!) and the following day on high speed twisties out to bumpy remote roads along the Lost Coast of CA, including the rough Usal Rd connecting back to Highway 1.





Unfortunately, only 9 miles from Ft. Bragg, I looked down to find my rear wheel coated in oil and the dipstick showing an empty tank. From what I can gather, it appears I blew a clutch pushrod seal. Not a bad place to break down though and not a huge problem given the frequent chase trucks as part of the rally. If I'd gone down on the 40 miles of rutted dirt on the Usal Rd., I might still be out there now!





In the coming weeks, I'll pull the kicker cover and see what the seal looks like and check the centrifugal oil filter for any signs of a disintegrating cam chain roller which I've been told could have caused the blow out by clogging oil passages with broken bits. Any other thoughts from the CL77 brain trust?

Thanks again to all for helping a ambitious CL noob.

Dave