I am at my wits end here. I'm all out of ideas, brutally frustrated, and just don't know where to go from here.
First to clarify, I am not new to working on engines. I spend most of my time working on cars but I recently bought a motorcycle to save on gas (just graduated from high school and don't have a lot of coin) and just have a little more fun. This is my first post on these forums, but I have spent hours a day for the last 3 weeks reading these forums (especially the FAQ) - just searching for answers, so I am by no means new.
So, about 3 weeks ago I bought this 1975 CB550F from the son of the second owner. The bike has 6700 original miles on it, never been tipped, always garaged, has original paint and seat in remarkable condition. The wiring is untouched and original - near perfect. The man I bought it from claimed that he rode it about 3500 miles in the last 8 years. When I bought it, it looked pretty neglected (not abused), but it was straight, so I spent an entire day polishing every surface and the bike came out looking so gorgeous I can't even explain without a picture. I got it for $850.
So After I got it started, I took it for a ride and found that it ran ridiculously rich and had absolutely no power. I brought it home and started taking things apart and adjusting and what not.
First things first, I adjusted the valves (.003" in and .004" ex - based on the advice of the forums), and replaced the plugs with NGK D8EA's. I then cleaned and gapped the points and regreased the rubbing block and cam. I set the timing with a timing light. After that, I took it for a ride. No change in performance. The bike pulled hard up to about 3500rpm, then lost power by 5000rpm and would not accelerated past 5000rpm. In 5th gear at 5000rpm, the bike would not go past 60mph. It's just gutless... worse than my gz250. I decided that it might be an inconsistent distributor advance mechanism, so I pulled it, cleaned it, and regreased it. After taking it for a ride, still no improvement.
So I dug into the carbs. I pulled them off and discovered that they were stamped 627B - carbs off of a 71-73 CB500. I thought that was odd. Anyway, I completely disassembled the carbs one by one and found that all of the rebuild items were new. O-rings were fresh, gaskets like new, and jets shiny. I pulled every jet, float, needle, slide, and float pivot and cleaned and polished with 0000 superfine steel wool. The carb bowls were spotless. The carbs are in such good condition that they still shine and have that pearlescent pink-green color to them. All of carbs had 40 pilot jets, 100 main jets, and the needles set at the 4th notch down. I removed the needles and set them at the 2nd notch down (as a CB550F would, not a CB500). I soaked the carb bodies in Chemtool. I then completely assembled all the carbs, and bench synced with a 1/8th drill bit. I polished the float needles and lapped them against the seat for a good seal, then set the floats. I then installed the carbs on the bike, set the idle air screws at 2 turns out, hooked up the intake (I should mention that this bike has the stock airbox and filter), and fired it up. I then did a full vacuum synchronization of all four carbs. Feeling like I covered all of my bases, I took it for a ride. No improvement.
I pulled the plugs and they were heavily carbon fouled, with a bit of a white ash on the electrodes. There is no oil fouling, just soot. After reading about the higher heat range of the D7EA plugs, I replaced my D8's with a new set of D7's. This made a difference in the plug fouling and start-up, but no help in the upper RPM range (5000+). I should also mention that all of the plugs are firing; however, I couldn't really measure how consistently with my timing light.
So to recap, here are the symptoms of my bike.
Turn on the petcock and ignition, and the bike starts on one kick. It usually doesn't even need choke. A little coaxing with the throttle for about 10 seconds and the bike idles down to 1100RPM smoothly and stays there, ticking like a clock. I take it for a ride and it runs smoothly all the way up to 3000 rpm, with very little sputtering and no popping. When I try to accelerate smoothly (no sharp pulling - no accelerator pump), the bike will begin to blubber at 3500rpm, getting worse as I approach 5000rpm. After I reach 5000rpm in first gear, The bike sputters a ton; however, it does accelerate, albeit gutlessly, with no pull or power to speak of. I shift at 7000 and the bike pulls good from 4k to 5k, then nothing. All through 3rd to 5th gears, the bike can't pass 5000rpm. I can't even make it up a long hill in 5th gear. With the throttle pinned at 60mph in 5th gear, the bike loses speed, slowing to about 50-55mph. The bike also guzzles fuel like none other. I just can't figure this out and I am at my wits end... never have I felt so frustrated and baffled.
Now to recap what I have done to troubleshoot:
-Cleaned and gapped the points (like new), greased the cam, set the timing with timing light.
-Replaced the plugs with NGK D7EA.
-Cleaned and regreased the distributor advance.
-Adjusted valves.
-Cleaned and polished the carbs parts (light rebuild -it really didn't need it)
-Set needles at 2nd notch.
-Vacuum synced the carbs.
-Set idle air screws at 2 turns out.
-Set floats as high as I could without allowing the carbs to overflow (I don't know how to actually measure the float depth)
-I also realized that I didn't clean all the emulsion tubes. I cleaned two of them but they didn't need it so I left the other two. The carbs are literally spotless.
-The exhaust is a baffled 4into1 header off of another CB (650?) Its got some sizeable dents. PO put it on to replace rusted out original exhaust.
-The carbs are 627B's (changed by PO for some odd reason) I found that stock is 069A's for the '75 CB550F.
-The coils look like new from the outside, and the plug caps have no weathering or cracks. The brass contacts inside the boots shine.
-The spark plugs all put out a strong blue spark.
-The battery is good and the starter starts the bike in less than a second. All lights work, including signals, and that odd tone that comes from the flashers. I doubt the issue is electrical as the charging system works correctly- I drove it into town for about 30 mins and had no issues other than the inability to pass 5000rpm.
Can somebody help me with this stumbling and lack of power or ability to pass 5000rpm? Sorry for the novel, I am just trying to eliminate any possible holes in my diagnosis. I am at a loss to this entire phantom issue. Any help or tips that I haven't already covered are much appreciated. Thanks in advance,
Austin
