Topic: '76 CB550 runs like it's choked out

[2tall]

Hey all,

Brand new to this site, and to street bikes as well. I bought a 76 CB550 with 11k two weeks ago, and have been going through it setting everything to spec and just cleaning stuff up.

I just set the tappet gaps tonight and put all the stuff I had taken off for cleaning (top valve/cam cover, air box, carbs, and other random gak). BUT, now that I have it all back together, it just runs like crap. Almost exactly like it's being choked out. It is very reluctant to rev above 5k, and also reluctant to "rev down" after releasing the throttle. This all points me to the carbs, but I'm not sure.

If I had to describe its condition in another way, it could be described as having low compression in multiple cylinders, which would point me to the valves. I triple checked the gaps before I buttoned it all back down, and I am pretty sure they are set correctly (.002 on the in and .003 on the out). Is it possible to screw the gaps up??? Seemed like a simple operation to me.

Its very frustrating; Other than a little valve noise, it ran great. Now, the valve noise is gone but it runs worse than my dads old Alice Chalmers lawnmower.

Ok, enough for now. Any help would be appreciated. Let me know if I can get you any more info.

EDIT: I also futzed with the cam chain tensioner, but didn't get anywhere with it. I'm not sure I understand how its supposed to adjust, so I just set it back. Don't think that matters, but I thought I would mention it anyways.

Paul

[OldSchool_IsCool]

What did you spark plugs look like before you started cleaning things up?  What do they look like now?

Is your timing set correctly?  Did you static time the engine or did you use a timing light?

To set the tensioner, set your crank to TDC 1.4 in its compression stroke (T 1.4 lined up with the pointer, both intake and exhaust tappets wiggle).  Then, rotate the crant another 15 degrees clockwise until the advancer spring post is in the window.  Loosen the tensioner lock nut.  If the tensioner is working right, it will self-tension.  Lock the nut down again.

EDIT:  By the way, welcome to the forum!

[mikethejeepguy]

Hey man! welcome to the forum. There are some amazingly helpful people here, full of knowledge and experience. Welcome to the adiction.

I had similar problems with m 76 CB550F. Bike ran like crap. When I got on the throttle, it felt like a choked moped, stuttering, and chugging no matter how much I twisted the throttle. It ended up being my plugs for the most part.

+1 on check your plugs. Did you ride/run it with the choke on for some time? that will foul up plugs pretty quickly. Clean them thoroughly with a wire brush/sand paper/carb cleaner. My bike won't run with full choke for more than 20 seconds (not that that is right) and then I have to go to half choke for warm up.

Check your fuel delivery... are the carbs getting sufficient fuel? pinched fuel line?

Also, I had some difficulty with my cam chain. Here is a link to the responses to my post. Hope it helps. http://forums.sohc4.net/index.php?topic=51903.0

I thought I had to twist the stud, but that should not be necessary. Make sure you are adjusting at 15 degrees past TDC on #1. Am going to re-do my adjustment b/c I am not sure it got adjusted.

Good luck! I will try to remember what else caused my bike to run like crap. Did you check to make sure you didn't leave a rag over the air filter? (Don't ask me how I thought of this one) 

Mike

[Frankencake]

What did you do to the carbs?  You said you had them to clean?  Did you pull any jets?  Did you forget to put the jets back in?  Did the clips holding the jets in place go wonky when you put the bowls on?  Is their a wiener in the warpdrive?

Yes, yes.  Welcome aboard.  Keep your muck boots on as it sometimes gets deep around here.

[Johnny5]

After you adjusted the valves, you can hear them, right? Just making sure, since you said the valve noise is gone. They should make a little bit of chatter.

Is the timing good? Are your carbs clean? Sounds like the slow jet might be a bit clogged if the rpms are hanging on you. Or the throttle cable is a little sticky.

Welcome to the forum!

[TwoTired]

What procedure did you use to adjust the tappets?

Is the air filter clean as new?

You took off the cam cover?  Did you back off all the tappet adjusters when you put it back on?  There is a specific warning in the shop manual to be attentive about adjuster to valve stem alignment.  If you do it wrong, you get bent valves that won't run right again until replaced.

Are you aware that the choke lever up is choke on and lever down is choke off.

[TwoTired]

Here's the issue

[TwoTired]

I don't know if you're bike has this issue.  If it did when you reinstalled the cam cover then you bent one or more valves.  If this happened, the valves don't seat correctly on the seats and they bind in the valve guides.  It effects idle, as there is loss of compression, it effects achieving engine RPM as the valves float due to binding in the valve guides.

I am not sure your engine has this issue.  You have to determine that.  It HAS been an issue for other posters after reinstalling the cam cover without the proper care to the interference issue.
You are the one that put the cam cover back on.   If you are confident that the adjusters were all aligned correctly and no valves were bent, then no worries.  You were the one that said the bike ran well before you removed and reinstalled the cam cover, and doesn't now.  Is there a connection here?

If your carb overhaul doesn't fix your idling and RPM issues, then do a compression check to verify the valves are seating as required.  If not, then you have valves to replace.  If the compression is good then it is not an issue for your bike.

What I meant was, "this is an issue I am bringing to your attention".  Pardon me for not being wordy enough.

Feel free to disregard anything I post here.

Good luck!