Topic: runs better with choke, where to start?

[jvandyke]

'75 550, complete carb rebuild, tear down full clean, all jets o-rings, everything new.  All stock settings.  Stock jets, needle on 2nd notch (stock depending on where you look). 4 into 2 exhaust, stock air box, stock filter.....(not new yet though, waiting on that).  Valve gaps set. Points, gap, static and dynamic timing all done. Fuel clean and fresh. So it had NO power on first test runs, re-did timing, it was off a tad, now much better but still stumbles on acceleration. With choke partially on it runs much much better.  I messed with A/F screws, was at the standard 1.5 out, under assumption that, since adding choke helps, it was lean (choke limiting air thus enriching, yes?) So I went all the way in to 1/2 turn out, no noticeable difference.  Just for fun went to 3.5 out (which I believe would be leaning it even more) still can't really tell a difference.  Again, adding some choke makes her happy.  I will double check for air leaks but unless it's as simple as a dirty air filter (blew out old with compressor and "looks" fine, but a new one will be here tomorrow).  Am I looking at jetting up?  I spent a lot of time on float height trying to nail it but could be off.  I did sync with vacuum gauges as well.  I will triple check timing and check for air leaks.  All advice welcome.

[RAFster122s]

Carb intake boots and orings between the intake manifold and head can have air leaks that contribute to lean running conditions. If spray with carb cleaner on these areas changes the running when the bike is running you are getting air leaks at those areas. Buy Honda rubber intake boots, not aftermarket.

[Gary in NJ]

When you say that the carbs got a "full clean", did that include spraying carb cleaner (I prefer brake cleaner) into each passage and confirming the it exited the correct location? Did you then blow out each passage with compressed air?

If not, then it was a partial cleaning and you may have clogged passage, which is no different than a clogged jet.

[sbutler]

It appears that the air/fuel is running lean. 

One way to troubleshoot your bike is to reread/review some of the info in The SOHC/4 Technical Documentation Library (such as Carburetor Troubleshooting Table, Basic Principles of Carburetor Operation, and Float System) while you keep in the back of your mind when the bike appears to be running tool lean.  For me, I am always surprise how the subconscious can figure out a problem when I start at first principles.

Good luck and let us know what you find!

[Shtonecb500]

if my bike runs better with choke I jet up.

[jvandyke]

By full clean I mean complete tear down and multiple baths ending in a sonic dip. Yes, compressed air was involved and certain stages. I did spray around with carb cleaner and I found the idle would dip when I hit one of the intake seams, I can even stall the bike by spraying heavily right on it.  Based on that I have some 0-rings on order and am getting ready to pull the carbs. I imagined I would see an increase in rpm and not a dip and stall but it's totally repeatable.

[TwoTired]

Did you replace carb internal brass with Keihin components or aftermarket?

[jvandyke]

Used these kits: https://www.common-motor.com/Honda-CB500-CB550F-CB550K-Carburetor-Rebuild-Kit

[RAFster122s]

If you replaced stock Keihin brass with anything other than genuine Keihin brass or brass from Jets R Us you are going to have running and tuning problems...

[TwoTired]

Used these kits: https://www.common-motor.com/Honda-CB500-CB550F-CB550K-Carburetor-Rebuild-Kit

I hope you saved all the old brass which you can clean and avoid a dyno retune of the carbs with the unknown dimensioned parts in your kits.  Unless you have installed the stock 4 into 1 header and higher pressure muffler as well as the stock filter arrangement to match the #98 mains stated in the kit contents, you’ll need at least #100 for the main.  I also have no idea what taper angle and main diameter a #26 jet needle has.  So, at the very least you’ll need to experiment it’s notch positions on a dyno or learn to read spark plug deposits from test track runs. Also For throttle positions of W.O.T. And 1/4 through 3/4 while the engine is under load.

[Scott S]

 Dumb question, but are you sure you're operating the choke correctly? The lever on the 500/550's is a little counterintuitive if you haven't had one before.

[jvandyke]

Used these kits: https://www.common-motor.com/Honda-CB500-CB550F-CB550K-Carburetor-Rebuild-Kit

I hope you saved all the old brass which you can clean and avoid a dyno retune of the carbs with the unknown dimensioned parts in your kits.  Unless you have installed the stock 4 into 1 header and higher pressure muffler as well as the stock filter arrangement to match the #98 mains stated in the kit contents, you’ll need at least #100 for the main.  I also have no idea what taper angle and main diameter a #26 jet needle has.  So, at the very least you’ll need to experiment it’s notch positions on a dyno or learn to read spark plug deposits from test track runs. Also For throttle positions of W.O.T. And 1/4 through 3/4 while the engine is under load.

I do still have the old brass.  Will pull carbs to do intake o rings and check mains, possibly reuse old. I don’t recall what size they were, assumed it was all stock, one owner bike. Wondering should I use old pilots too? Sorry, my ignorance is showing. I’m learning.

[jvandyke]

Dumb question, but are you sure you're operating the choke correctly? The lever on the 500/550's is a little counterintuitive if you haven't had one before.

There are no dumb questions when dealing with noobs like me. Lever up is choke plates open, lever says “open” with arrow pointing up. It runs better with choke lever down 1/4
Nope, I'm an idiot, you were right.  It still runs better on partial choke.

[Deltarider]

With the lever horizontal the chokeflaps are closed for a cold start, with the lever down the chokeflaps are open and is it time to start riding. It's in every owner's manual.

[TwoTired]

Lever up is choke on, plates closed to incoming air.  Lever down is choke open run position after start up.  In between is feather position for partial enrichment.  The lever is stamped with a label for operation.

I would reuse all internal brass that isn’t obviously corroded but cleaned of stale gas deposits.  Your carbs should have a stamping that says 022a, which signifies standard tuning/ set up for a 74 CB550 with 4 into 4 pipes, and stock air filter.  My 74 had 4 into twos installed on it for years, and ran well with stock set up 022a carbs.  Later, I also put a foam reusable filter in the air box, because Honda upped the price of the stock one to 50-60 bucks each back in the 90s.  I saw no effect on carb tune with the UNI foam filter.  But, my wallet shrunk a lot less.  But I sure did notice moisture collapsed paper filters fouling plugs during rainy winters, even with frequent draining and cleaning the filter case bottom foam water separator, usually with coincident chocolate milk on the oil dipstick base.  The later cleared up with an extra long run and the motor making good power and heat.  In winter, the Vetter with lowers made just above freezing rides rather comfortable.

[jvandyke]

With the lever horizontal the chokeflaps are closed for a cold start, with the lever down the chokeflaps are open and is it time to start riding. It's in every owner's manual.

Wait, what?  That's pretty funny.  I will look into this.  BTW it's a friend's '75 (I had said 74 earlier) I have a '72 500, you'd think I'd know by now.  Getting old I guess.
Yep, you're right of course, brain farting over here, still the fact is it runs better with partial choke.  With bike nice and warm and choke full off (lever down, duh) It won't get out of it's own way, can hardly pull away from a stop.  Once the revs are up it's okay.  Adding some choke helps.  I did just now revisit ignition timing for the 10th time which does seem to improve things.  It's dead on the F mark at low idle (both 1/4, 2/3) and does seem advance well (as per timing light).  I did have to adjust the points gap slightly out of spec to get 2/3 on the money.  You know what they say, 90% of all carb problems are ignition related, and 90% of alll ignition problems are carb related.
I am still planning on doing the intake o-rings since dosing the seam with carb cleaner and/or starting fluid makes it stumble and even stall.  No sense spending too much time until that is sorted.
BTW the main jets I pulled out where 100s so I'll clean those up and put them back in.

[Scott S]

 Forget where it is at idle and set it to the 30 degree mark (between the two hash marks) at around 2500 RPM. Re-adjust idle speed afterward if needed.

[jvandyke]

Okay will do.  BTW the mains in the kit were 100s already so they can stay I guess.  I pulled the intake and the o-rings were pretty tired, especially #2 which was so brittle it exploded into pieces on removal.  That was the one that would make the bike stumble and stall when hit hard with spray.  Thanks again fro the input, much appreciated.

[jvandyke]

While waiting on intake 0-rings (which are the same as the tappet cover 0-rings I believe) I decided to do another bench synch.  I found some play in #4 slider, wasn't giving me a consistent return to spec.  I was doing the drill bit method.  I found the bolt that holds the slider cam to the shaft was loose, oops.  This could explain some weirdness too I think, no?

[Scott S]

 Absolutely. Those both look like they're missing the little lock tab.

[jvandyke]

Absolutely. Those both look like they're missing the little lock tab.

Yep, no locking tabs on any of them.  Must have been left off by the other guy many years ago.  I wonder if those can be had separately?

[jvandyke]

There were little split ring lock washers underneath them all. I added a drop of blue Loctite and snugged them up good for now. O-rings came in, installed fired up, reset timing as per above, runs awesome in the garage. Hope for road test tomorrow. Thanks again guys.

[Stev-o]

So...how was the road test?