'64 CB77 w/ 15k miles hadn't run since 1981. Since the PO had drained the carbs (in '81), I thought I might give it a try without rebuilding them. Cleaned the tank and rebuilt the petcock, cleaned and reset the points, changed the oil.
While it was impressive that the bike started and idled, it didn't have any mid-range on the road. I decided to do a budget rebuild just to see if I could find the smoking gun. The #42 low speed jet was a little clogged up so I soaked all the jets in carb cleaner while I cleaned the carb bodies. I used Purple Power and hot water and blew all the passages with compressed air. Set the floats to lm's top-O-jet-holder. It started right up but the idle was high and it didn't want to settle down to the stops. I finally got the idle down and on the road the mid-range was back. The first blast sounded great and the power was smooth BUT just like before, It started losing power and it was all I could do get it back up the driveway. It would run and had kind of a lazy throttle response but as soon as you loaded the engine by letting the clutch out, the power would just drop out and you would have to pull the clutch back in to keep it running. I ran beside it to get it up the hill.
It started looking like when it got hot, that's when the problems would start. I checked the compression and got 85 psi on the left and 115 on the right. The left side would make a metallic kind of chain rattle sound as you were getting on the gas. I don't like the compression numbers and I'm a little worried about the rattle.
What about the valves getting tight when it gets hot? Does that happen?
Seems fuel related though. What makes the slides hang up and not return to idle? (they're not backward)
Lots of popping like it's lean.
Good spark.
Plugs look lean.
Thanks for any comments, C.
My barn find is running but I have some issues...Chrispy1
On the tight slides. If the carb flange is overtiightened you can distort the body and this will cause the slides to stick. Check the carb flanges for flatness against a steel rule. The slide bores can be relieved a little with fine abrasive paper, and the flanges can be trued by rubbing on a sheet of plate glass with a sheet of abrasive paper between. Check out my 1961 CB72 restoration for trueing them in a lathe. Sounds like you have something going on with the left side cylinder. I would be tempted to lift the head just to see what's going on..... G '60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160 '66 Matchless 350 '67 CL77 '67 S90 '77 CB400F Chrispy1
On the tight slides. If the carb flange is overtiightened you can distort the body and this will cause the slides to stick. Check the carb flanges for flatness against a steel rule. The slide bores can be relieved a little with fine abrasive paper, and the flanges can be trued by rubbing on a sheet of plate glass with a sheet of abrasive paper between. Check out my 1961 CB72 restoration for trueing them in a lathe. Sounds like you have something going on with the left side cylinder. I would be tempted to lift the head just to see what's going on..... G '60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160 '66 Matchless 350 '67 CL77 '67 S90 '77 CB400F Thanks G, I had read about not overtightening the flanges so I don't think I did. I put a light film of motor oil on the slides before reassembly but noticed the throttle is still a little sluggish going back to idle. It doesn't snap back like my other bikes but this is my first twin.
The sound in the left reminded me of pinging at first. I think it was happening just as I was rolling off the throttle. Not as it was revving up and not coasting but right at the transition. I'm still not convinced after reading 50 posts about float height, that I might not be a little lean with the float. That first blast was really promising; good sound, pulled through the range but 20 seconds later, nothing past idle. Thanks again, C. I will be checking the flange faces and spacers. I checked the valve clearance last night and they were spot on. Kind of hoped they would be tight :/
Could I have stuck rings and when the bores grow after warm up, it looses power? It has been 30 years! When I got the 85/115 compression readings, it was hot. I guess I could try cold. Even with that compression, it ran great for 2 minutes! Sure does seem like it's running out of fuel. The bowls don't seem full enough when I pull them.... I posted on the engine board that I had not done my compression test properly. With the throttle open, I had a solid 150 psi for both sides. That was a nice surprise.
Now I'm on to why it won't run hot and am focusing on the stuck slides. The throttle is very lazy to return to idle if it returns at all. Seems worse when hot. I'm going to check and surface the spacers and the carb flanges. Not sure how I'm going to do it but I have various ground tables on machines, a surface grinder at work, the proverbial sheet of glass and I have a milling machine. What about a big flat file... being very careful. C Edit: Used 400 Wet or Dry with WD-40 on my ground table saw table. Did the carbs and spacers. Worked great. After seeing how much the 400 takes, I would be hesitant to use a file. C.
Last edited by Crispy1 on Wed Sep 17, 2014 9:23 pm, edited 1 time in total.
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