Topic: First ride...observations and questions

[Scott S]

'71 CB500

 Other than 15 miles around the neighborhood, today was the first ride on the CB500. After sitting in a barn for over 28 years, I put 90 miles on her today. She did pretty darn good!
 The engine sounds like a sewing machine. She shifts smoothly. The MAC 4-1 sounds like "an angry bee in a Maxwell House can", according to my girlfriend.
 She's 99% leak free. I found one small drop coming off the shift shaft again. I recently replaced the seal, but there may be another small leak under that left side cover somewhere. At this point, it's very minor and not worth pursuing any further. Maybe this Winter I'll pull the cover and see what I can find.
  I'm used to driving big twins (Yamaha XS650) and the power band on these SOHC's is completely different. She seemed to really like to stay between 4-5K rpm. any lower and she wasn't happy. PLENTY of get-up-and-go over 5K!
 Observations:

 1) I had some issues with idle when coming to a stop. The idle wanted to drop and stumble. I made a few adjustments, but by the end of the ride she was idling too high at a stop. A 1000rpm idle just seems a tad low for this bike. I'm wondering if the tach is accurate? It sounds better at ~1150-1200 rpm, to me.
 
 2) There's also a slight hesitation at part throttle response. If I back off the throttle slightly, say for a curve or approaching traffic, and then roll back on, there's a slight pause or hesitation. No snapping, popping or coughing, just a slight pause.

 3) By the end of the ride, it was a little hard to leave from a stop without either a) a hesitation or, b) really giving it some RPM. Anything below 3K and it would stumble and shudder, but it's a little boy-racer to leave a stop light at 3k+, right? Or is this just something I need to get used to with a small bore 4-cylinder?

 4) At an indicated 55mph, she was turning ~4300-4400 rpm. At 65mph it showed 5200 rpm. Stock gears, stock sprockets and stock tire sizes (in a modern tire...close as I can get). Sound about right?

 5) Carbs have been cleaned/rebuilt. Floats set, new needle/seats, synched, etc.  Idle mixture screws at 1.5 turns out....more than the manual says, but it's rich at idle and I was trying to lean it out a bit.
  The guy that cleaned them for me has some drill bits he uses to check jet sizes. He says the mains look to be a 108 or 110. I think that's one step up from stock. The P.O. had some Jardine style, turn out exhaust pipes on it, so he MAY haved jetted up one size. Think this might have something to do with the idle and part throttle response?

 Overall, I'd call it a success. I know there are some timing issues (1/4 points at full advance, 2/3 points have some slop on the shaft). I plan on installing an electronic ignition/points replacement soon. After that, I'll really concentrate on the carb tuning.
 My GF has a cool "on the road" pic on her cell phone if we can figure out how to download it.

[Scott S]

 More observations:


 A) The only drip I see after a few hours of sitting is off the center stand bolt (). I'm guessing maybe there's  a slight leak under the left cover, oil is getting on the chain and dripping onto that bolt? Or maybe blowing back from the valve cover breather tube and dripping down to the centerstand area?

 B) On our last stop, the electric starter didn't want to work...dragged like the battery was dead or dying. Kick started OK and all electrics work. Checked the voltage at home and again just now...12.8-12.9V at the battery. Too much heat on the starter motor maybe?

 C) Didn't do an actual plug chop, but killed the bike at ~3500 rpm as I pulled onto my street. Pulled a plug and it looks OK to me. Porcelain is clean and the tip is a nice tan. If I HAD to choose, I'd say it's a touch rich rather than lean, but I think it looks fine.

 Thinking about going back closer to the factory settings on the mixture screws to see if that helps the hesitation, but I swear it acts like it's too rich. I.E., loading up at a stop light. Black smoke when I rev it after firing it up cold, but only at idle, etc. The plugs don't show it, though.
 I have a few things in mind to check...voltage to the coils, voltage at 3k, 4K, etc.
 Maybe even re-synching. I synched the carbs using vacuum gauges, but that was with pods. I now have a stock air box and Uni-Filter. May need to re-synch?

 Still looking for your thoughts and suggestions.....
 

[Frankenkit]

your starter thing-
under that left side cover is a cable that goes from the starter solenoid to the starter motor.  Check that cable and see if it's crimped etc.  Pull it off and see what the resistance is like when it's cold.  Maybe throw it in the oven and see what it's like when it's hot.  Either way, that cable caused me a lot of grief when it only cost $30 to replace and vastly improved hot and cold starting.

I also leave from a stop around 3k, but maybe I am a little bit boy-racer.   I don't know that there's anything wrong with it, but I'm adding my $.02 so I can see what others' answers are, and let you know it's not 'just you'. 

Idle is a touchy thing for my bike.  It *can* idle down to 1100 when it's nice and warm, but it always sounds best at 1200-1300.  If I were obsessively picky I would maybe try to clean my idle jets again, check for air leaks, etc etc, but I'm happy with my 1200-1300 idle. Oh, and I'm lazy. yeah that covers it.

[Stev-o]

My 550F likes a higher idle too, and I see no reason to keep it so low [1000].

Can you email the photo to yourself? Then download it on your computer, that is the easiest way.

Good Luck.

[Scott S]

 Anyone else? I'd really love to hear some more thoughts and opinions.

[IndyFour]

I agree with Meriggi....1000 rpm is a bit low from my experience with my 550.  I usually let it idle around 1500ish or a little less.  It just runs much smoother up there.  Idling just a tad higher may also help your hesitation issue a bit as well, although, I think there may be something else going on there.

Are you running a stock air filter in the stock box?  If so, is the filter clean?  A dirty filter could cause hesitation and a rich running condition.

5200 rpm at 65 mph sounds about right for stock gearing on a 500.

[Scott S]

 Finally got the pic off the camera and onto my computer.

[Scott S]

I agree with Meriggi....1000 rpm is a bit low from my experience with my 550.  I usually let it idle around 1500ish or a little less.  It just runs much smoother up there.  Idling just a tad higher may also help your hesitation issue a bit as well, although, I think there may be something else going on there.

Are you running a stock air filter in the stock box?  If so, is the filter clean?  A dirty filter could cause hesitation and a rich running condition.

 New Uni filter in the stock airbox. I plan on idling it up a bit, checking the synch and tweaking the carbs just a tad...see where that gets me.

[TwoTired]

These carbs have no accelerator pump with mechanical slides.  When the slides are opened, the vacuum is lost and the jets stop feeding or have very reduced feed.  Which is all wrong for the inrush of air.  So, the idle is purposely set over rich to improve off idle engine pick up.

The air screw, of course adjusts the pilot circuit.  This circuit does provide some fuel over the entire throttle range.  So, there is some leaning or enrichening for the  1/4-wot throttle settings, too.

So, leaning the pilot circuit is at cross purposes with enlarging the main.  And, probably accounts for the throttle stumble.  I wouldn't be surprised if the Uni is raising the vacuum a bit, making the pilot circuit leaner, as well.  Its membrane is less of a barrier than the stock paper type.

The pilot circuit (air bleed screw) is correctly set when: (assuming bike at operating temperature)

In any gear, at idle RPM, you can twist the throttle 1/2 total travel, and the engine will pick up smoothly.  In top gear it won't be too quick, but it will pick up without stumble and be predictable.

From what you describe, it would seem that correcting the air screw, making idle richer, and going back to a 100 main will give you a more streetable bike.

Do you recall what position the slide needle is in?

I don't have any issue with upping the idle to 1100-1150 ish.  Particularly, when each cylinder isn't perfect and breathing exactly like each of the other 3.  And you are right, the tach may not be accurate, anyway.

Please elaborate on your "loading up at the stop light" comment.
Does the idle speed change?  When you open the throttle is there immediate hesitation and then pickup like it remembered what it is supposed to do?  Or, does it burble back to life from the stumble?

Cheers,

[Scott S]

Do you recall what position the slide needle is in?

Please elaborate on your "loading up at the stop light" comment.
Does the idle speed change?  When you open the throttle is there immediate hesitation and then pickup like it remembered what it is supposed to do?  Or, does it burble back to life from the stumble?

Cheers,

 No, I do not recall what position the slide needle is in but I assume it's stock. I'm also well aware of what assuming can do for you 

 
 Yes, at the start if the ride, when coming to a stop the idle speed would drop off. The bike would want to stumble and/or stall. I tweaked the idle adjustment screw a bit a couple of times. If I tried to use the throttle to keep the revs up, it would burble a bit...and sometimes pick back up like it's supposed to, but at an idle that seemed too low (gonna raise the idle before the next ride). My co-riders told me the ONLY time they saw any black smoke was when the bike idled down too low like that and I revved it up and cleared it out. That's why I think it's rich at idle. I've seen the same thing in the garage with the bike on the centerstand.

 By the end of the ride, it was hard to leave from a stop. I had the idle up enough to keep it from stalling (a touch too high, actually), but I had to slip the clutch OR revit up to ~3K to take off. Lots of shuddering. Hard to leave the line smoothly.
 Runs great when I give it some throttle, though.

 The only other minor thing I noticed: Say I'm cruising along in 4th gear, about 4500-5000 RPM. I come up on some traffic, a curve, what have you....ease off the throttle abit but don't downshift; still above 3500 rpm. Roll back on the throttle smoothly and there's a slight pause. No snapping, popping, coughing, backfiring, etc....just a hesitation for a split second before it reacts and then smooths out again.

 Keep talking, I'm listening and absorbing all this stuff...

[TwoTired]

Being mechanical slide carbs, the throttle position is, in my analysis, more important than engine RPM.

No, I do not recall what position the slide needle is in but I assume it's stock. I'm also well aware of what assuming can do for you 

Whoops.
 

Yes, at the start if the ride, when coming to a stop the idle speed would drop off.

If the carbs are properly sync'd, that does sound like too rich for idle mixture.
You sure the pilot jets weren't drilled out?

If I tried to use the throttle to keep the revs up, it would burble a bit...

To me, burbling is the engine trying to clear out the over rich mixture.

My co-riders told me the ONLY time they saw any black smoke was when the bike idled down too low like that and I revved it up and cleared it out. That's why I think it's rich at idle.

You are probably right.  I'd double check those pilot jets, to see if the orifice still matches the number stamp.

By the end of the ride, it was hard to leave from a stop. I had the idle up enough to keep it from stalling (a touch too high, actually), but I had to slip the clutch OR revit up to ~3K to take off. Lots of shuddering. Hard to leave the line smoothly.
 Runs great when I give it some throttle, though.

A hot engine works better with a leaner mixture than one that is over rich.  You certain there wasn't some plug fouling going on?  What plug number are you using?

The only other minor thing I noticed: Say I'm cruising along in 4th gear, about 4500-5000 RPM. I come up on some traffic, a curve, what have you....ease off the throttle abit but don't downshift; still above 3500 rpm. Roll back on the throttle smoothly and there's a slight pause. No snapping, popping, coughing, backfiring, etc....just a hesitation for a split second before it reacts and then smooths out again.

Seems like a lean midrange with that description.  I'd try moving the jet needle out of the jet orifice a notch.

You know you may play the whack-a-mole game for a while as you fix one operating range problem and another pops up.
Sure would be nice to know what, exactly the carb internals are and their settings.

Um, any observations on the emulsion tubes and the jet needle orifice you'd like to share?

Cheers,

[Scott S]

 I sent an email to the guy who helped me with the carbs to see if he remembers what the slide needle position was. I'm pretty sure it's stock.

 The pilot jets are from a rebuild kit, as are the needle/seats, mixture screws, o-rings and gaskets. The mains that came in the kit fit loosely; one actually fell out on the first start up attempt.
 I went back and he measured the jets he took out, said they appeared to be around a 108-110. They looked OK, so we cleaned and inspected them and reused them.
 This bike had a Jardine 4-2 exhaust on it when I got it, so they could have been changed or drilled to the larger size.
 The mixture screws are aftermarket as well, so who knows how close they are to what's "supposed" to be in there?
 Add to that the Uni filter and MAC 4-1 exhaust and my "stock" set up is a mish-mash of parts.

 Plugs are NOT fouled and look great, actually. They are new NGK D7EA plugs. The tip is a nice tan color and the porcelain is clean.

 I think I'm really close and will fiddle with it some more this weekend. Stay tuned!

[TwoTired]

The pilot jets are from a rebuild kit, as are the needle/seats, mixture screws, o-rings and gaskets. The mains that came in the kit fit loosely; one actually fell out on the first start up attempt.

This sounds rather strange.  The mains have an oring to seal between the jet and body.  AND they are held in with a leaf spring pressed against the bottom of the float bowl.  There is no way they should be able to "fall out".

[Scott S]

 I guess the spring on that bowl wasn't installed correctly when he reassembled it. I saw it myself though that the jets were loose in the fitting. He has an assortment of O-rings and we decided to re-use the ones I had.
 Forgot to add: We also saw that the holes on the holder (emulsion tube?) in the rebuild kit were different. Smaller, less of them and oddly placed, so we re-used what was in the bike as well.

[TwoTired]

Were the main jets loose in the fitting due to corrosive metal loss of the jet mount?

We are talking about 627b carbs, right?

[Scott S]

 No, not loose b/c of corrosion. I was attributing it to aftermarket parts.

 These are stock carbs for a CB500, whatever that is.

[TwoTired]

No, not loose b/c of corrosion. I was attributing it to aftermarket parts.

If aftermarket were so different from stock, I wouldn't trust them. IMO 

These are stock carbs for a CB500, whatever that is.

Each carb mount flange has a number stamped on it, top right side.
The outsides of the carbs look the same through the 76 550 models. But, the internals are different among them.

How do you know they are original carbs?

Cheers,

[fullofdays]

Hey Scott,

I've got a 71 CB500F that exact same color AND I'm in Rock Hill!!  haha  Small world, I guess...  I laughed out loud when I saw your location on your post...

What is the float level setting you're using?
Is the spark advancer free and easy to advance by hand? The old grease in them often makes them sluggish to advance.

I cleaned the carbs out on my bike and it has the same issues in regards to the idle but my bike's idle will start running high to 2K or dipping below 1K and stumbling.  I also experience a hesitation off neutral throttle in the low end...  These bikes love to 4-6K. The dead start clutch issues are common too.   

Generally, these idle situations are caused by the O-rings at the head, where those castings bolt on. They are brittle now, and leak quite a bit of air when the slides are closed. This makes it real hard to try to adjust things.

[Scott S]

Today I checked THOROUGHLY for vacuum leaks and found nothing. Hooked up the vacuum gauges and checked synch again. Dead perfect. Reset the mixture screws to 1 turn out. Maybe ran a tad better but was noticeably rich at idle (could smell it...no smoke, though). It was STILL hanging up.
 We traced it to the #3 carb and I think I found the problem. I'm unsure of the proper name for it, but the arm on the carb body that has bushings; the one that moves the slide, seems to be bent on #3 carb. Not the part that attaches it to the linkage and not the part that you use to adjust synch. The part on the carb body that all that attaches to is bent.
 It drags on the holder at part throttle and actually hits the holder approaching WOT. Obviously, that carb goes out of synch at some point during throttle operation.

 In this pic, you can see the bottom arm is bent and not at 90 degree angles like the top arm.


 In this pic, you can see that the arm is actually touching the holder. It drags on the side of the holder at some point past 1/2 throttle and eventually touches the bottom of the holder.

[Scott S]

 Obviously, this would cause it to go out of synch during the rev range and probably is causing the hanging up/not returning to idle.
 Can this be repaired? I don't see that part listed separately in the parts diagram.

 Fullofdays, check your PM's.

[TwoTired]

At the end of that arm is a ball link inside the adjuster mechanism.  Being bent probably screws up the geometry.

It would seem that it could be bent back so the ball centered properly in the adjuster.  Might have to de-rack the carbs to do it right though.  I'd give it a try.

I notice your air bleed screws sunken into the carb bodies.  Most of mine are nearly flush with top of the bore.  Are these aftermarket air screws?  How are you counting the turns out?  Full turn, Half turn?

Cheers,

[Scott S]

 Those are the aftermarket screws. I seat them gently, then turned them out 1 turn.

 It's hard to see in the pics, but the end with the ball on it actually starts rubbing on the adjuster just past ~1/2 throttle. It touches the bottom of the adjuster at a different point as the throttle gets closer to WOT. Am I making sense?
 

[TwoTired]

Did the aftermarket air bleeds  have hollow tips and cross drilled hole?

I agree your linkage needs attention.  But, I don't think it is causing mixture issues.  Is it preventing the slide from moving?

Cheers,

[Scott S]

I believe that it's causing the hanging throttle. And, yes, at some point during the operating cycle it causes that slide to move differently and go out of synch.
 At idle it's OK. As I start to open the throttle, the bent piece starts rubbing on the adjuster arm in an arc, slowing down that slide. As I approach and reach WOT, it contacts the adjuster at a different point, actually touching the bottom of the adjuster as seen in the pic and preventing WOT on #3 cylinder.
 That cylinder goes out of synch before WOT though because of the contact.