Topic: 1975 cb550 poor acceleration, backfiring and spluttering

[loulou]

hey guys and gals

So I have a 1976 cb550, its all stock. A little while ago I decided to put some k&n cone filters on it. For about a week it worked great but then one day it started backfiring loads and acceleration was terrible. I decided to put the original filters back on the babe and wait till the summer to rejet the carbs for the new cone filters.
When I put the the original airbox back on the bike it didn't seem to make any difference. I still had the same problem. I have taken the carbs off, they are pretty much brand new but I still went over them with some compressed air. All of the rubber is in good condition, I have no holes anywhere.
I have used the bike a couple of times since putting the airbox back on and this is what normally happens. When I start the bike I have to turn the idle screw up quite high to get the bike to run. Then over the next 25minutes or so the revs and the idle will increase, so I slowly turn the idle screw down and the bike will run slightly better, but not great. About a week ago I was going to take the bike to a garage when on the way to it the bike just kicked back into its normal beast self. It was running great, just like it use to. I drove around for about 2 or 3 hours and I had no problems what so ever, at both low speeds and high speeds. The next day I went out on it again and the bike was back to its poor acceleration and backfiring.

Any ideas what my problem might be?

Where can I buy jets in the uk?

Anyone live in London who would like to exchange some knowledge of these bikes for beer?


Cheers

[PeWe]

Fuel lines OK?
Hose might have a kink blocking the fuel. That happened on my bike despite new lowest quality China fuel hose, soon replaced by Gates hoses made in USA.
Enough gasoline in tank, blocked petcock or dirty carbs.....

[loulou]

I just had a look and the fuel lines seem fine. Also the petcock is fine, the carbs are clean and there is loads of fuel sitting in the tank.

[Stev-o]

When was the last full tune up?

[loulou]

When was the last full tune up?

Its definitely time for a little tune up. I'm more confused why it went bad so quickly and didn't go back to normal even when I went back to the original air filter. Also why I also had this moment of greatness when for one day only it all worked fine.

[DH]

Is the problem more noticeable when it is humid/damp? Any loose or dirty electrical connections in the ignition system?
A flaky condenser?  Age of plug caps and tune up components? Heat related?....Intermittants can be a pain.  suspect
ignition/or something related to that flaking out?

[Stev-o]

When was the last full tune up?

Its definitely time for a little tune up.

Dont do a "little tune up". Do the full 3000 mile tune up recommended by Honda.
This will eliminate a lot of guess work and get you back up and running sooner.
Of course, if your carbs are dirty or have bad aftermarket parts in them, this will not help much.

[CapeCafe]

If you are still running points, I'd replace your condensors.  It's a cheap repair.  It's best to spend a couple extra $ for quality condensors when you do the replacement.  I've had them go bad where you lose two cylinders and the result is sputtering, funky idle, loss of power, backfiring.

[Duanob]

All it takes is one bad spark plug. Or a mis-connection with the spark plug boot. I put in a new set of Densos that lasted about a month before they started going bad. So new NGKs. Unscrew all the spark plug boots clip 1/8" off the end of the wire and screw them back on. BUT yes do a 3000 mile tune up if it hasn't been done by you.

BTW just keep the stock airbox, PODs on these bikes are a joke and only for posers anyway.

One more thing, pull the fuel lines from the tap with a bowl underneath and turn it on. You should have a good steady flow out of both nipples. If not your tap might be clogged or the in-tank filter has been gunked up.

[loulou]

It turns out my point were off. Massively off. One of the gaps was about 3 or 4mm.

I was driving to work a few months ago and someone pulled up next to me and complemented my bike. When I told him I was still using points (they asked) he told me about a British company who make a good ignition upgrade. I can't remember the name and I haven't found anything through google. Anyone have any idea what I'm on about or can recommend a good electronic ignition.

thanks guys

[Rgconner]

Putting EI on the CB550 can bring a world of hurt if your electrical system is not up to snuff.

Better is the Hondaman (he is an active forum member) ignition system that keeps the points but takes the load off them. The points require almost no maintenance with that ignition on, just check the timing once in a while.

Cost is very reasonable, $77 US dollars. 

[wjustinleigh]

Did you check for a banana in the tailpipe?  Sometimes that happens, especially if you're staking out Axel Foley.

Did the points solve your problem?  I have dyna in one bike and pamco on another, they both seem fine to me.  The dyna took slightly less effort to install as the wires were set-up to plug to the originals.  This one seems cool but I couldn't justify the cost: http://www.c5ignitions.com/.