Been browsing this forum for more than a year now trying to figure out the mystery of my CB650C 1980. First, Ill start with I literally have no previous history from the owner on how it ran but it only has 14k miles on it. I was told he wanted to downsize since he literally had 10 + bikes in his garage and it appears to have been garaged the whole time. The bike runs rough and fouls plugs. When cruising around in 3rd it seems the bike surges and feels like each cylinder is fighting each other even though ive sync the carbs 3 or 4 times now. If I shift up at a lower rpm to 4th it goes away. The highest speed ive gone is 55mph and its usually around 5k rpm which leaves the very tip of the white part clean and below it carbon fouled It spends most of its time riving it around 30 to 50mph. Ive literally been through 52 plugs now and counting ranging from D8EA to the current D8RES-L in it now.
About the bike
CB650C 1980 All stock
original airbox but no cover
4 into 4 original pipes
K&N air filter that came with it held by fender washers
Pilot screws at 2 1/8 but now at 1.5 turns out with after market
original paint
Now Ill try best to describe the symptoms but keep in mind this is my first bike and it was a project when I got it so I literally have no idea how a motorcycle should run or feel but I am however mechanically inclined. First thing I did when was get a new battery and change the plugs(cant remember what it looked like since that was 2 years ago). The bike started but choking it had no effect and I had to play with the throttle to start it. To it for a small ride but it was noisy and weak from the overly loose chain and squeaking at the wheels so I brought it back. Changed the oil and filter (which I destroyed with a pipe wrench)with lucas 10w-40 as the previous oil looked blackish and filter was black.
Then I removed the tank and flushed it with metal rescue which worked great in getting all the rust out and immediately filled with fresh 91 gas with 10% ethanol as California allows no fresh raw gas. After that I tackled the oil leaks by replacing the seals on the shifter shaft,cam cover, and the pucks inside the engine that were making a mess on the floor. Removed the carbies which are PD50 put all new float bowl seals, aircutoff valves, and rubber needles and adjusted the float heights to 12.5mm. Here I discovered someone elses work where the choke lever was broken so there was nowhere to mount the choke cable and jerry rigged a paper clip to operate both sides of the choke. I dissambled all carbs and soaked them and sprayed carb cleaner with compressed air several times since I've had the bike. All passages including idle air emulsifiers are clear as I have ripped them off to confirm. The pilot jets are the original Keihin 35 not drilled out and I replaced the stock 90 main jet to a 95 and put the carbs back along with a fuel filter that has good flow. I also eventuall changed the air vent tubes since they were hard and dried thinking with was effecting performance but not much change.
Next I tightened up the cam chain which was noisy unless it was the carbies. After that I opened up the top and adjusted the valve clearance to .003 intake and .005 exhaust which was the HondaMan specs I think but am not to sure anymore where I got the .003 from. Compression test with a crappy HF tester gave me from left to right 115,110,110,115 but I know they read low and the hose it like 3+ feet long. Adding 3 drops of oil from a syringe did nothing to raise compression which is a good thing? At this point a year into the bike Ive been running it reguarly with 10w40 and with all new igntion components like new EMGO 2.5 ohm coils, new silicone copper leads, and new NGK 5K boots with helped to increase the spark strength along with the now properly adjusted air gap at the pulse generator. The original coils were cracked and the bike would run like crap when it got hot.
I also switched to the DR8ES-L spark plugs to for 10k resistance to stretch the spark and I must say it feels alot better instead of like an angry lawn mower. Also did an oil change recently to lucas 20w-50 synthetic since the oil smelled like gas the second time. Floats are not sticking open as I have tested so it must be with the engine running getting into the oil from not properly burning as plugs are rich and dry soot. All these adjustments helped make it a little leaner but still fouling plugs. Recently every plug I put into the #1 cylinder came out lean with some goldish color around the base ring but its fouling and the number #4 is now the leaner cylinder so whats going on? Maybe the valve clearance idk anymore. I discovered as well the the rubber collar from the airbox to the carbs had slipped out which was letting or the air out but now I fixed it so the choke works and revs the bike to around 3k and can be taken off really quick. A month ago dropped my bike like an idiot and poked a hole in the #1 rusted exhaust at the megaphone joint
but at least it sounds cool haha.(this was after the lean condition on the cylinder). At this point I even cleaned all electrical contacts and made sure everythings nice and clean, rotor and stator check out ok, battery is still good as Im on my second one now. What should I do? Ill post pics if needed, what ever you ask for. Those 2 spark plug pics are in different lighting and the latest I had on was for 40 miles at different loads with the pilot screws at 1.5 turns. The ignitors also melted and I refilled them with epoxy if that helps. Pardon my rushed grammer.
