Topic: 550k tuning...which demon do I chase?

[kerryb]

I got this "frankenbike" with a '77 CB550k motor and frame. PD 46A carbs, 42/90 jets.  point gap .016, dwell 42 degrees.  Carbs cleaned only once so far, bench synched, vacuum synched, valves adjusted (two were tight),  timed...idles very well from 700 to 1000rpm, revs up smooth BUT!!!... I can't get it to run steady between 1000 and 1300 rpm.  It zooms up to 2000 rpm and has a little trouble settling back down.
Also, having trouble with the idle mixture screws.  They don't seem to have much effect.
From my readings here, it seems I still have carb issues , although I was surprised at how close they were bench synched, the vacuum synch went very easy  (WooHoo!)

Do I hafta clean the carbs again first or is there something else I'm missing.  How do I know if the needles are worn?
All suggestions appreciated, I couldn't have gotten this far with this forum, thanks everyone.

just for fun...kerry

[HondaMan]

If it were here, I'd go after it like this, presuming you have the idle air screws set at the stock setting and the hose clamps on the carbs are good and tight:
1. Remove the carb castings at the head and install new O-rings in them. It is the same size O-ring as is found in the valve caps (#91302-001-020).
2. Remove and clean/relube the spark advancer. The grease gets old in them and can make them sticky, which can simulate what you are seeing.
3. Replace the condensors, if it has points, If they are more than 5 years old they are leaking, which makes for weak spark below 3000 RPM.

Only THEN would I go after the carbs again.

[kerryb]

Thank you Hondaman (I love your book!) 
Yes ,the idle air screws are set at 1 1/2 turns out, carb boots are tight front and back, wd-40 sprayed on them didn't affect idle.  Stock airbox & filter is in place. 
New o-rings and condensers should be easy, I'm excited to get back to it...just one more newb question...What grease do I ask for at the auto parts store? My favorite local honda shop (which I love,
 Lock City Honda ) didn't have a tube to sell me last week.
Will any brand condenser be as good, or is there a "best" brand.  I have the Tec points plate on this engine.

just for fun...kerry

[TwoTired]

The PD46 carbs have Idle Mixture Screws rather than the earlier style Air Bleed regulator screws.

The stock exhaust on this model had higher back pressure than earlier models as well as aftermarket exhaust systems.  The back pressure allowed the carbs to provide less fuel, and thus run leaner after an exhaust change.
 All ranges of carb operation are affected.  So, stock book settings are unlikely to be correct any more.
The idle mixture screws do have limited effect.  But, to ensure the pilot circuit is functioning turn each screw all the way inward to lightly seated while idling the motor between 1000-1300 RPM.  Closing a single screw should kill the cylinder and the exhaust will go cold.  If the cylinder continues to run, then the screw isn't shutting off the fuel for idle operation, or the pilot circuit isn't working at all.
If you can kill the cylinder with the IMS closure, I speculate that a 2 turns out setting would be more appropriate for an exhaust with less back pressure than the stock one, and it should improve throttle response from low RPMs under load.

Also with a more open exhaust, I would expect the carb to need slightly bigger mains.  (suggest #95)
After checking the spark plug deposits, I'd also consider raising the slide needles a notch.

Cheers,

[crazypj]

Check advancer springs, they are probably loose and advance is coming in 'early'

[Kong]

Let me ask you this, have you put any miles on the bike and if so have you taken a look at the plugs.  Also, can you tell at all if its one or two cylinders that aren't working right or is it the engine overall?  I ask that because something like advance springs, as crazypj mentions, will effect the whole engine whereas something like a sticking slide or two might give the same symptoms but only effect their respective cylinders.  A check of the plugs might help you tell the difference.

[HondaMan]

Thank you Hondaman (I love your book!) 
Yes ,the idle air screws are set at 1 1/2 turns out, carb boots are tight front and back, wd-40 sprayed on them didn't affect idle.  Stock airbox & filter is in place. 
New o-rings and condensers should be easy, I'm excited to get back to it...just one more newb question...What grease do I ask for at the auto parts store? My favorite local honda shop (which I love,
 Lock City Honda ) didn't have a tube to sell me last week.
Will any brand condenser be as good, or is there a "best" brand.  I have the Tec points plate on this engine.

just for fun...kerry

Just about any grease will do, so long as it is not fibrous like many wheel bearing greases are. You might be able to get some "points cam lube" in little bitty squeeze packages for a few cents if you're just looking for a tiny amount. It also comes in small tubes (3 ounces or so), which is about a 200-year supply for even a dozen bikes.

The condensors: there seems to be 2 types around these days. The type with the rubber top where the wire comes out seems to be the cheaper one and less well sealed, while the ones with the epoxy-sealed top will last longer since moisture can't creep in over time. They both work OK. I usually nab a couple from PartsNmore or Vintage CB750 when ordering something else, just to have a few on hand. I seem to get both kinds from them, at random.

[kerryb]

Ok...I got grease, waiting to get to shop for o-rings and condensers, so that leaves the advancer as the first demon.  I disassembled, cleaned, reassembled, tested, Doh!, disassembled, reversed, reassembled the advancer.  Did you know that the spark is in the wrong place if the parts are reversed? duh!  So the idle is now beautiful from 650 - 1000 rpm, then zooms to 2000 and wont come back down until the idle screw is backed off.  So it seems my scientific method has shown that the advancer is not the culprit even though I didn't test the spring strength (I'll have to look that up)
I did find the #2 idle mixture screw was all the way in, and backing it out makes little to no difference.  Even though the idle is very smooth, the exhaust from #2 seems cold and there is a faint popping from that side once in a while.  #2 pipe is hot (from revving?)  This seems to point to #2 idle circuit.  I'll put in the orings and make sure the idle circuit passages are clear.

Also...the pipes are 4-4 with only small holes in them.  Backpressure should be near stock but I plan to go with a 4-1 in the future.

[TwoTired]

It is important to know at what throttle position the head pipes are cooler.  At throttle positions higher than 1/4 the the throttle valve begins adding fuel.  Lower positions rely on the pilot circuit.  There is a transition point where both supply the determining mixture.

The "zooming" could be where a cylinder is getting just enough from the throttle valve to begin contributing to crank rotation power.

At idle position, is there a head pipe cooler than others?  If so, you've got a pilot circuit issue on that associated carb.

Otherwise, recheck your vacuum sync, as you have a cylinder dropping out for some reason.

The exhaust holes are significant with these pipes.  If you are satisfied that the pilot circuits are working, you might try temporary patches on cold cylinder muffler.  It should require less fuel at idle with more back pressure.

Cheers,

[kerryb]

SUCCESS!!!!!  The only things I did were to replace the o-rings on the carb (manifolds/ spigots?) and to lightly blow through the idle jet (removed) to be sure it wasn't plugged.  Then spray carb cleaner through the idle air circuit passages and check the mixture screw.  Turned all 4 mixture screws to 1 3/4 turns out and reassemble.  No other changes or adjustments.
Fired it up cold...if fired right away, stumbled a little with choke till it was warm, and then acted like a BRAND NEW ENGINE!
revs great, settles right down, idles perfect.  Then I looked at the clock and thought "Oh God, I better get some sleep, I have to be at work early for kids club"
Soon I'll go back and play with the mixture screws, vacuum tune, and just what rpm the advancer is coming on.

THANK YOU HONDAMAN, THANKYOU TWOTIRED, THANK YOU ALL!!!

we're having BIG fun now.