Topic: 1981 CB650C high RPM prob

[radman]

Well I guess I'm a newbie to this new to me interface. I used to read and post on SOHC4 when it was .net. Used to have my buke in the 650 gallery but this has all changed. Been away from the forum because my bike has been sitting in my garage. I lived in PA and moved to Arkansas for my job in 2002. Right before I moved I crashed my 81 cb650c. I went off the road in a hairpin turn luckily in a dirt and weed clearing. I even rode the bike home afterwards. Cracked my small headlight fairing, bent the bars all to hell, crushed a headlight fork ear and a turn signal. Other than that it was just a lot of dirt and weeds platered all over. Minor injuries to me, rotator cuff probs for a while and cut my knee up bad. Helmet saved me in this I'm sure.

I just started getting the motivation and time (three young kids and night school), to start gettin the bike back up to snuff. I got it running, new bars and linkers and headlight fork ears, got the front forks rebuilt while I was at it. When I ot it running it idles great, was very responsive when revving it from idle in nuetral, but when I rode it, if I eased it through the gears I could barely get over 60 mph but when I got high in the rpms in any gear it would sputter and start to deaccelerate like it stalled. A couple of times it did. It acted like it was flooded because I could smell the gas when I stopped and would not start for several minutes. I got it home and it died.

I let it sit for a couple of months because of school, and work, and kids, and wife, before I started messing with it again. I couldn't get power at all. I was fed up with trying to figure the manual out and work through this myself as the wife would always peek into the garage and ask how long I would be. So I took it to a repair shop. This guy does great work.

Here is where we are right now. I read through past posts and started getting freaked out that I was suffering the symptoms of bad electrical problems I was reading about. I don't want to dump huge amounts into this bike. I bought it for 350 bucks and it ran like a champ until now. I rode it for three years in PA all over the place. He has checked everythin I can think of. Cleaned and synced carbs, checked the charging system, swapped egulators from his cb650 and no difference. blocked air filter and removed air filter and rode it that way. This bike has a MAC 4 into 1 with original carbs, no rejetting, but like I said it ran like a top before. he removed the pipes and ran it, He id a couple other electrical checks that are greek to me, I don't know much about the electrics on this bike. I rode it just an hour ago to see what it felt like so I could post here with some knowledge on how it was acting. It starts right up and idles like a dream. It revs to about 9000 rpm and stutters, if you let off just a little and rev back up and it gets a little smother. On the ride it accelerated decent when you shifted sooner than you really should and eased her through to 5th and about 65. It probably would have gone up to about 70 but I didnt want to get too far from the shop. When I started heading back to the shop I got on it and it stuttered in high rpms in every gear. but definately ran better probably from the carb clean and sync. He is stumped at this point because he can't find anything wrong woth the charging system. the battery is holding a charge and getting a charge, it idles and starts so easily. He said my engine is very quiet compared to his earlier cb650 so he was going to check the valve clearances. He says that can affect top end and rpms a little.

He thinks its fuel delivery or electrical. It acts like its not getting enough gas or getting too much at high rpm or its electrical somewhere.

What should I do. What should he do. He's been checking with his buddies and he has tried just about all he knows how to do.

Thanks Conrad Hamp

[rob]

Hi Conrad,

Good to meet someone else with a 81 cb650c.  Glad to hear that both you and the bike survived your crash.  Do you happen to have any pictures of your bike to post?

As for the performance trouble a couple of ideas: Have you checked the fuel filter and petcock?  Perhaps while it sat for a while some rust formed in the tank, subsequently clogged the fuel filter or petcock and is now restricting the fuel flow.    Have you taken off the carb float bowls and taken a look?  See if while the bike sat the carbs got gunked up, or if there is some rust flecks in the bottom of the float bowls?  Has there been a change in elevation between PA and Arkansas?  This could affect the air-fuel mixture and change how the bike performs?  Have you taken a look at the spark plugs to get an idea of if the bike is running rich or lean?

I have never gotten my bike to 9k rpms.. I try to avoid going that high even though the tach says it redlines at 9.5k

Rob

[cb650]

Try removing the air filter cover.   Seems to be problem with age for some reason.   How is the air filter.  I never had it but by now all my 650s have pods.



          Terry

[radman]

Rob and Terry,

[radman]

Rob and Terry,

     Thanks for such quick responses. I think we are set on the carbs and the fuel air mixture. Air filter is new and my mechanic guy said he tried all the trouble shooting tricks with the airbox, running it open and closing it off and such. I am going to call him first thing in the morning and tell him not check the valve clearances as this would be a waste of time. It ran great before the wipe out so I don't think the valves are going to mysteriously change just sitting there. The tank was a piece of crap on the inside. It looked as though someone had tried to creme the tank and didnt do it right. It had rust and particles of the creme junk floating around in it. I cleaned the tank when I first got the bike but never had the inside reconditioned or cremed the right way. So I think now that this may have been the culprit all along. I am going to pick the bike up tommorrow and clean the tank, petcock, get new fule line and filter, and possibly check and replace all the other little hoses in that area. Am I safe to asume these are vacuum lines? I don't even have my manual to refer to right now, I let the guy at the shop use it if he needed it.

I do have some real good pre crash pictures that I have to scan in. Pre digital camera. I will take a pic tommorrow when I pick it up with the digital also to show post crash condition. Doesn't look bad but it needs some care cosmetically.

Oh yeah the mechanic sais he replaced the plugs but I don't remember if he checked the old ones and said they were balckened. Or if the new ones displayed this. I never replaced the two inner plugs. I never got the right socket tool to reach inthere. I removed the two outer and cleaned and regapped, but I checked these and they always looked good acording to the little spark chart in the clymer manual.

[rob]

Terry,

Thats a good point.  My 650 runs much better with the air filter cover off.  Because the air filter is underneath the side cover, I don't think that having no air filter cover is a big deal.  I think I saw a 20/30 km/hr increase in my top speed and the bike definately pulls much better.

Rob

[Vatch]

This brings up a point with these 650's.  I had heard the bikes were air restricted, and a number of people say they run better with the air covers off.  This suggests the bike is running a little rich, yes?  With this in mind I put in the K&N OEM replacement filter.  The bike was running lean for a while, and then some adjustments due to the choke cable breaking were made.  The bike is now running a little rich, but top end power is better.  No problems at 9000 rpms, speed is at about 100 mph and no hesitation in the engine.  So with the stock set up are these bikes air restricted?

Sorry to hijack the thread.   

[Chris Schneiter]

Timing. My CB750 was great, then started bogging at the high end, fouling plugs, making me crazy. I had the carbs cleaned, traced every wire on the bike...all kinds of superstition...then this spring, did a static timing....not anywhere near enough advancement...now it runs like a normal bike. Have your mechanic check your timing...check your timing....check your timing....And change all of your plugs to give you a fresh start..

[cb650]

Mostly they where lean for emissions.  But they where set for sea leaval and how many of us are at S/L.    Timing shouldn't be a prob with the cdi electronic igy.



          Terry