Hi All! I’m to the board and new to my bike. I just bought an ’81 cb650 custom. This is my first street bike, but I have been riding and wrenching 4 stroke dirt bikes for a while. In addition my Brother in law has about every tool known to man and has been working on all sorts of engines for many years. This is what the PO told me. He cleaned the carbs this spring (but put them back together with the original parts). New battery this spring. Recently new coils and new wires. Tank has been sealed (this spring) and new gas lines installed with filter. He also gave me a Clymer manual.
When I first test rode the bike it started right up and tool about 3 min before it would run without choke. When I first started out it missed a little but smoothed out very quickly. The only thing I questioned was it seemed to have a lack of power. It is not burning oil and starts on the first touch of the button.
What I did to it. When I got home I drained the oil, changed the oil filter and air filter. I set the timing (static- I don’t have a timing light yet.) We also checked the valve clearance and adjusted the timing chain. When I put it back together, I put in new plugs.
When riding the bike seems to do fine and is very smooth until you get above 5000 RPM. But as it gets warm, the power seems to be much less. If I’m riding at 40-50 mph (about 4000-4500) and try to pass the engine feels like one cylinder is cutting in and out. It has a hard time pulling above 6000 and has a great deal more vibration.
My brother in law suggested a compression test. With engine still warm, we got #1-90lbs, #2-91lbs, #3 84lbs, #4 90lbs. His comment was that he was surprised the thing even ran with that poor of compression. He squirted some oil in each cylinder and the compression went up to 185 except # 3 which was 168. He indicated the bike really needs rings but seems the valves are good. (could not believe it wasn’t burning oil)
Of course we are going to do rings as soon as we get all the parts we need. My question is do you think that the poor “HOT” performance and the missing/ dropping a cylinder is because of the low compression, or should I get the parts to take apart the carbs while I’m at it? BTW the plugs for #2 and #4 cylinder look perfect, #1 is a bit dark, and #3 is black and wet. I have not done a plug chop because the bike simply won’t run well enough at WOT. It does, however idle fine at 1100 rpm. Also the PO told me that the auto gas off has been removed.
BTW is there anywgere that tells what month a bike was built in? I was born in april '81 just wondering if the bike is older then me <G>
