Topic: '75 CB550F Engine Misfiring? (videos)

[TravisB]

My bike has been running great until this morning.  About 2 miles into my ride my I noticed an almost total loss of power (I was hitting over 6000 RPMS just to get moving in first). I also noticed the engine didn't sound as if it was firing properly and if left to idle the rpms die down quickly and the engine dies. I took it for a spin during lunch this afternoon and was experiencing the same symptoms, however I was able to get it to seemingly fire on all four cylinders a few times, but it would then go back to what sounded like misfiring.  I also heard some clicking noises coming from front left side of the engine, but couldn't pinpoint the exact location. Any ideas on where to start?

[Brandotheamazing]

had the same issue with my 550, turned out to be a failing coil. so it was intermittantly running on two cyl. Check your coils, and make sure the contacts for any wires are clean.
an easy way to check what cyl is misfiring is exhaust pipe temp right at the head, you can use your hand (if you're quick) or an infared thermometer.

[TravisB]

So we made it home, and I noticed a few other things.  The engine seemed to surge and drag and sputter and pop while accelerating.  My spark plug wires are covered in electrical tape from the PO, could faulty wires be causing this issue or should I start looking into a dyna?

[matt mattison]

Arcing wires could be an issue, especially if you see all that e-tape. Run the bike in the dark and see if it arcs.

[TravisB]

The bike is under a street light and I won't be able to get it to a dark place until the weekend.  I was planning on pulling the tank this weekend to run new throttle cables and clutch cable and right hand controls -- I might as well add new plug wires to the list.

[Brandotheamazing]

Unless it has aftermarket coils, the wires will be part of the coil, non replaceable... and you'll need to replace the coils. I bought a set of Dyna coils and swapped them in, never looked back, I'm still running stock points and plate, no problems in almost three years.

[TravisB]

I'm a little confused about the Dyna coils.  Do I only need these (http://www.z1enterprises.com/ItemDetails.aspx?itemDescription=Dyna+Dual+Output+5.0+Ohm+Coils+(pair)+DC8-1&item=DYDC8-1) and a new set of wires for a complete swap?

[mronegear]

and check the sparkplugs, maybe one ist quitting its job.

Also you can measure the resistance of your plugcaps with an
multimeter...
Only if 1+4 or 2+3 cylinders are failing at the same time
(check the temp to find out which one isnt firing) then it
might be the coils.
I would check plugs, caps, wires first.

[TravisB]

I checked the plugs and they look good.  I retaped one of the plug wires to the cylinder with the pipe I thought was coolest, but I'm still having the same symptoms.  It fires right up, but I have to keep on the throttle at or over 2k rpms.  I hear this kick/popping sound coming from somewhere between the airbox and under the tank...but only at low rpms. I'm going to try to get a video of it to see if I can pick up the noises.

[TravisB]

It sounds like its coming more from under the seat...

Kickstart
CB550F Kickstart

Clicking
CB550F clicking

[TravisB]

Could there be something in the air box?

[TwoTired]

When was it's last tune up check list completed?

What do the spark plugs look like?

When was the last carb vacuum sync?

[TravisB]

When was it's last tune up check list completed?
I purchased the bike about about two months ago and have changed the oil and oil filter. I'm not 100% sure what the PO had done to the bike, but claimed he tuned it up previous to selling. Also the engine has been running great since I bought it.  I've put about 500 miles on it so far including to jaunts of about 150 miles.  This problem started halfway on my commute to work (~8 miles) Monday morning.

What do the spark plugs look like?
The plugs have a slight carbon coating and are on the checklist to replace, but would this contribute to the clicking?

When was the last carb vacuum sync?
Not sure, but would the carbs come out of sync instantly?

[TwoTired]

If you don't know when the last tune up was completed, it is due now.  Normally, it's on a 3000 mile schedule, and it is the first thing to review when there are any run time issues.  A bad tuneup will make the engine run bad.  And there can be many symptoms.  You never want to adjust a bike to perform well with a bad tune up.

Fouled or bad spark plugs can contribute to misfiring.

When was the last carb vacuum sync?
Not sure, but would the carbs come out of sync instantly?

When you say instantly, to you mean 30 years of use?

I thought the sound on the vid was representative of a "spit back" through one carb.  Would you rather have the carbs out of sync or a bad intake valve  (could also be an intake valve that was too tight (from adjustment wander, loose adjustment, or bad adjustment).  Either way, the possibility would be eliminated by performing the tune up schedule and a routine carb sync check.

A proper tune up often cures a number of run time ills on this bike.  It is the foundation of a good running bike.

[Teatimetim]

Sounds out of time to me, and in the first video I saw a faint hint of a lil leak out of number 2 or 3 manafold.

[TravisB]

The noise is definitely a "spit back".

[seanbarney41]

Replace points and condenser, set point gap, set timing...should cost less than $50 depending on quality of components purchased.  My guess is one condenser went bad and burned up one set of points...time to replace that stuff.  Pay attention to tune up/service intervals in the future

[TwoTired]

The noise is definitely a "spit back".

spit back causes:
Carbs out of sync
Leaking intake valve (bad valve/seat or bad adjustment)
Very early spark timing

All except a bad valve are mended during a routine tune up.

Good luck!

[TravisB]

Okay I've printed out my 3000 mile tune up check list, I'll update once I get these tasks completed.

[TravisB]

So some new information has come to light.  The elbow in the image attached is more or less split all the way through and was leaking.  I wrapped it up as best I could with tape and it seemed to greatly reduce the back spit issue, and I'd say the engine was running better than it ever had when the bike was above 1500 rpms.  Can someone fill me in on the purpose of this line and if this could be causing the issues?   

[Strangexj86]

some more details on there this line goes, what is hookes into could help a lot. I (still a noob though) can't really tell where it is.

[TwoTired]

It looks like the air plenum drain.  When new, it went to a reduced diameter (about 3/16") had a bit of open cell foam stuffed in the end and routed to between engine case and swing arm.

If the carbs over flow, that drain stops it from pooling in the plenum and air filter box.

Yours looks like it routes forward.  True?  Where does the other end attach?

[TravisB]

It comes out of the plastic box between the carbs and air cleaner.  I dropped my bike off at my brothers this afternoon so I can work on it in his garage, but I'm pretty sure it was routed into the engine case.

[TwoTired]

It comes out of the plastic box between the carbs and air cleaner.  I dropped my bike off at my brothers this afternoon so I can work on it in his garage, but I'm pretty sure it was routed into the engine case.

At the top of the engine?  If so, that is wrong.  The top of the engine breather should go to the side of the air filter box.  What do you have at the bottom of the filter box?
Look at chapter 8 of the Honda Shop Manual.

[TravisB]

Yes at the top of the engine.  Before I make anymore guesses as to how things are routed I'll reply tomorrow when the bike is in view.  In the meantime I'll look through the manual.