Topic: I finally finished my first tune-up....sorta

[Nortstudio]

1976 CB 550k

I have been plugging away on my first tune-up on this beast/beauty, with the help of you all, and I have come to a point where I can now say, I think I've tried all the basic setup, to figure out whats happening with my hesitation problem from idle to 1/4 turn (aprox).

Still stumped.  I have done the cam chain adjustment, valve clearance, dynamic timing and finally, the carb clean.  It has fairly fresh plugs (replaced 2 weeks ago when I first started this whole fiasco), brand new plug caps and new fuel lines. 

The hesitation is always at 3000 RPM.  I know that I should be judging it by throttle turn, but just so you know, 3000 it is, every time, on the nose!  The throttle is almost always at about 1/4 turn.  It hesitates, and then if I flick through it, no problem.  If I accelerate from stop through the throttle throw quickly, not a problem.  But being that it's NYC, Im behind a line of traffic 96.3% of the time.  So I use low throttle often.  Another time it happens is if I have to creep in traffic...just a notch above riding the clutch, there is this bog and bucking.

The main thing that is not stock is the 4-1 exhaust.  Air box is stock with UNI filter.  I have tried spraying WD-40 on the intake to see if idle speed changes, and it doesn't.  Screws are 1.5 out.  It idles after warming at 1200-1400 pretty well.

Any thought?

Thanks in advance....I'm trying here.

[scunny]

does your spark advancer(behind the points) move freely and snap back into position ? 3000 rpm is about were the weights should be flinging out and advancing your ignition timing.

[Frostyboy]

When you cleaned the carbs, did you remove the emulsion tubes above the main jets? I was staggered by the amount of gunk stuck in mine when I pulled them apart.

[Nortstudio]

does your spark advancer(behind the points) move freely and snap back into position ? 3000 rpm is about were the weights should be flinging out and advancing your ignition timing.

I don't think I know exactly what the spark advancer is. I obviously have dealt with the points, but what part am I looking for behind that?  Is this something I need to take the plate the points attach to off to get to?

I cleaned the emulsifier tube quite well. Actually, all of the carbs were surprisingly clean compared to the rest of the bikes condition.

Thanks for the help.

[totty]

Mine has similar symptoms but at 4200 rpm.
At one point I was convinced that it was the ignition at fault so I replaced the full system including the advancer with a £160 Boyer kit that didn't affect the symptoms.
After lots of troubleshooting raising the needles by 1 notch is the only thing that made an improvement but didn't totally cure it. Mine is stock filter and Motad Exhaust.

[Nortstudio]

does your spark advancer(behind the points) move freely and snap back into position ? 3000 rpm is about were the weights should be flinging out and advancing your ignition timing.

Ok, did a little research and found out that I'vr never gotten back behind the points plate to the advancer. 

Is there a way to check this without removing the plate? (not in front of the bike right now).  That would throw off the timing - which I guess I'm getting decent at by now, so not worst scenario.

I'll check this out. Apparently supposed to be well oiled???

And suggestions for when I am in there will be much appreciated.  

[MoMo]

No way to check without removing the points plate. Since you already set timing, mark the plate so you can put it back in the same spot. You will need to remove the 10mm bolt that holds the large 23mm nut as well as the spark advance unit, and remove the three screws that hold the points plate.  I agree with totty though, in that raising the needles may cure your symptoms, as 3000 rpm is pretty much when the midrange needle jets kick in, Larry

[Nortstudio]

I'm a little nervous to get into the needle adjustment, but it seems that's where I'm headed.

Sounds like it might not be a bad idea to oil/lube the spark advancer - because everything I have found in my research says it should be done. Based on the condition this PO left this bike, I would bet it needs it.

Thanks for all the help folks. Hope you all had a great holiday.

[Frostyboy]

If you can get your hands on a strobe timing light, you can check the operation of the advance mechanism without disturbing your points plate. If max advance is observed around 2500 (I think) all is good with the advancer.

I've recently refitted the carb rack to my 550 & set the needles 2 grooves richer than when I dismantled them. I can't believe the difference it made. It's now an absolute pig at lower throttle openings. Runs great if I give it a fistful but.

I've put em back to where I started & fired it back up. The smooth idle has now disappeared. I'll have to re-sync with the vacuum gauges again, it seems I've really upset it by fiddling with the needles. They are quite sensitive to the clip position, only move one groove at a time I reckon.
Cheers.

[Nortstudio]

I have a timing light (strobe) that I can use - but what I may have failed to mention is that I have not vacuum sync'd the carbs. I do not have that tool, and plan on getting them (gauges) as my next purchase.

I have been trying to be methodical about the tune-up and all the changes I have been making. I know that normally the vacuum sync would be next (after cam chain, valve, timing and now carb clean) but the hesitation led me to believe I might have a jet issue.

I guess it's not a bad idea to try to lube the spark advancer if its something that goes wrong often. But ultimately, maybe I should get through a proper sync and then figure out if it's still happening. I'll check back after that.

[totty]

I've recently refitted the carb rack to my 550 & set the needles 2 grooves richer than when I dismantled them. I can't believe the difference it made. It's now an absolute pig at lower throttle openings. Runs great if I give it a fistful but.

If richening the needles improves roughly 1/2 + throttle but makes it worse below 1/2 then it sounds to me like you need to go up a main jet size.

[dave500]

if the carbs have been off the bike and /or apart theyll need to be synced,do this first,sometimes a leaner primary jet will cure this hesitation,as you wind the throttle up a transition from slow jet to main occurs with a slight over lap between the two,its a richness issue for a short burst and as you open further the engine will accept it,try winding the air screws out more,tune these when the bike is fully hot,if it cures it good,how it performs cold might be a bit worse but youll learn to live with that,older guys will remember the pre efi days with cars that had to have the exact amount of choke and pedal pumps,or itll never start,and how untill warmed up would run shakey and not idle with out the choke(which on most cars raises the idle stop)this might be the case once you sort it hot.

[Nortstudio]

Thanks so much. I will get to the sync as soon as I can get the gauges. And then I can take it from there.

Appreciate all the help.

Scott

[Kevin400F]

The idle air bleed screws can have a significant effect just above idle up to 1/4 throttle.  If checking and lubing the ignition advancer doesn't do the trick, try adjusting the air bleeds 1/4 turn to 1/2 turn at a time.  Clockwise richens the off-idle mixture, counterclockwise leans it out.

Kevin

[Nortstudio]

The idle air bleed screws can have a significant effect just above idle up to 1/4 throttle.  If checking and lubing the ignition advancer doesn't do the trick, try adjusting the air bleeds 1/4 turn to 1/2 turn at a time.  Clockwise richens the off-idle mixture, counterclockwise leans it out.

Kevin

Can you clarify if you are talking about the air mixture screws - one on each of the Four carbs???

I have them at stock 1.5 turns out.

Or is there another screw that I don't know about (totally possible!!!)?

Thanks so much for the suggestion.

[Kevin400F]

Yes, the idle air mixture screws, one per carb, oriented toward the outside on each carb body.  Dave500 mentions these as well above.

Kevin

[MoMo]

Scott,  if your ear is sensitive you adjust each air screw individually by turning it out until the idle falters and then back in a 1/4 to a 1/2 turn, which will usually be the highest idle for that particular carb. Make sure overall idle is reset to 1200 after adjusting each carb. Buy a Morgan Carbtune for the overall sync-it is the best unit I've use in 40 years.  Larry

[Nortstudio]

Scott,  if your ear is sensitive you adjust each air screw individually by turning it out until the idle falters and then back in a 1/4 to a 1/2 turn, which will usually be the highest idle for that particular carb. Make sure overall idle is reset to 1200 after adjusting each carb. Buy a Morgan Carbtune for the overall sync-it is the best unit I've use in 40 years.  Larry

Hopefully I can pull that off.  Im actually an audio engineer, so my ears better be up to the task!

I will give the air screws a shot tomw.  Believe it or not, I can not seem to find a local place that sells a vacuum tester.  I was hoping to spend less than the one you suggested, I've seen them for about $50 on eBay.

Have you had issues with the old school round gauge ones?  Or is the other one just much easier?

Thanks for the tips.

[MoMo]

The old round gauges I had fluctuated and the mercury type ceased working.  The Morgans are steady, reliable and well made.  For me, the 110 was well worth it as I use them frequently, Larry

[totty]

I took a gamble on one of these as I didn't want to spend much and didn't trust cheap gauges

http://cgi.ebay.co.uk/UNIVERSAL-MOTORCYCLE-CARB-BALANCER-VACUUM-GAUGE-TOOL-/330500895277?pt=UK_Motorcycle_Parts&hash=item4cf363722d#ht_1692wt_1139

I've used it twice now and it seems to work alright.

[Kevin400F]

Just so there's no confusion, the vacuum gages (mercury, Morgan or analog dials) are used to sychronize the throttle slide openings, which is a completely different adjustment than the idle air mixture screw settings.   You probably knew this already, i'm just sayin......

[Nortstudio]

Yep. I'm on it. I know I need the vacuum gauges for the final part of the tune-up and then will mess with the air screws.

Thanks for the tip totty with the alternative gauges. Are these a single gauge, which needs to be moved from carb to carb?  It seems that might be worth spending the money on - having 4 in a row to be able to bounce from carb to carb.

[totty]

It's not really a gauge, it's basically a length of hose with suitable fittings and restrictions and a ball in it. The imbalance moves the ball and you line it up with a second ball in another piece of hose. It's very simple but appears to work fine. You sync each carb to the one that doesn't have an adjuster. 

[dave500]

i set the idle screws by turning them in slowly and steady till it slightly falters or changes,then come out 1/2 or 1 full turn,,you end up with the screws not all being the same turns out from fully closed,this is what the engine needs as the vacuum in each cylinder is ever so slightly different even with well synced carbs.dont chase carby woes untill the ignition is absolutely spot on.

[Nortstudio]

Dave, do you start turning in from the stock 1.5 turns out from full in?  Also do you do this before the carb sync?  I don't have the gauges yet - so I wonder if i should wait for that???

I am definitely trying to adhere to the TT order/method of the tune-up, but man do I want to be movig on

Since it was my first time doing all this, I imagine (weather permitting) I will go back and do each of the procedures again, to make sure I nail it, and all in a shorter period of time.

[dave500]

i do it after its synced,and fully hot and ridden,from the base setting i turn them in till it falters,then out one turn,one at a time.

[Nortstudio]

Thanks Dave