Topic: 78 550k - New cleaned carbs installed...need some tuning help. VIDEO!

[VigCS]

Hi all.

Bike is a '78 CB550K with PD46C carbs.

I managed to do something stupid and use a BFH on my old set of carbs to get the rubber boots on the intake pipes.  Needless to say I bent the barrels of the outer two carbs out of round.  So, I ordered a new (used) set of carbs off of ebay, cleaned them out real good, and transferred all the lower bowl parts from the damaged carbs to the new ones (floats, jets, needle valves).

My mission today was to get her fired up, and I was successful with that.  I've never tuned carbs before so I feel way over my head with getting it running right.  A video is included below to show how it's running right now and possibly get opinions on any symptoms it may be doing what it's doing.

CB550 After carburetor rebuild
Sorry for the semi-crappy quality.  It's a cell phone video.

Is the way my bike is running indicative of any specific symptom, or just needing a general tuning? Keep in mind all I did stick the carbs on and fire it up.  No fussing with any screw settings.  It seems to rev up real high and drop down low and act like it's going to die, then I'll bump the idle up to compensate, and the revs will shoot up.  It happens in the video around 0:48.

Here's a list of facts about the new carbs and setup:
-Pod filters (I know, I know...they're going away.  I just got ahold of an airbox)
-105 main jets and 42 pilot jets
-The damaged carbs had screw in 42 pilot jets, so I had to dig and get a set of 42 push-in jets for the new rack.  One was plugged and I got them all freed up.
-I installed new vacuum lines between the carbs.
-Gas in the tank is from last fall (I added stabilizer for the winter)
-The air mixture screws are set 1.75 turns out (that's exactly how they were on the old carbs, so I figured I'd try to match them).
-The air mixture screws DO NOT have the o-ring and washer at the end...they're on the way.  Damaged carbs didn't have them either and it ran fine with those.
-New carbs were bench synced but not vacuum synced yet.
-There seems to be some popping and cracking on the overrun.  You can kind of hear it on the video.

Any input is greatly appreciated.  Thank you!

[Bankerdanny]

Without the o-ring and washer, I'm not sure that the number of turns out is that important. They are tapered, so in or out will have some impact, just not as much. The manual says 1.5 turns.

That jet size is large, I have a '77, which uses the same carb as your's. The factory manual says the main jet is a 90, and that is what I recall seeing when I cleaned my carbs. I had to watch the video via my phone (no YouTube at the office) but it appears (and sounds) like you are running a 4-1 with minimal (or no) baffling. So the increase in the jet size is likely warranted.

The idle speed is supposed to be about 1,050rpm, but my bike seems happier (and more stable) around 1,200.

I wouldn't do anything until the stock airbox is in and the o-rings and washers are in place.

[VigCS]

Without the o-ring and washer, I'm not sure that the number of turns out is that important. They are tapered, so in or out will have some impact, just not as much. The manual says 1.5 turns.

That jet size is large, I have a '77, which uses the same carb as your's. The factory manual says the main jet is a 90, and that is what I recall seeing when I cleaned my carbs. I had to watch the video via my phone (no YouTube at the office) but it appears (and sounds) like you are running a 4-1 with minimal (or no) baffling. So the increase in the jet size is likely warranted.

The idle speed is supposed to be about 1,050rpm, but my bike seems happier (and more stable) around 1,200.

I wouldn't do anything until the stock airbox is in and the o-rings and washers are in place.

Thanks for the input.  It has 105 jets because of the pods and the exhaust.  I'm honestly not sure what type of exhaust it has, but it's a pretty loud 4-2 system.  I'm just confused why the revs come down so slow and it'll randomly shoot the RPMs up at idle (like at 0:48).

I have all the plastic pieces for the airbox, now it's a matter of finding the rubber boots and the rubber seal between the two plastic pieces.

[VigCS]

It sounds like a POS, check all the pipes for heat with your hand cause maybe its running on 2 or 3 cylinders.

RT

It's running on all four.  That was one of the first things I checked.  It sounds like a POS cause it's running like a POS right now, lol.  Something isn't right.  I have to wait until next weekend before I can start playing around with it again.  Here's a video of it running before I messed the carbs up (last fall).  Ignore the carb farts, it had a slight exhaust leak.  It sounds a ton better, haha:

1978 Honda CB550

[VigCS]

Well I managed to find an all-new seal kit at cycle 2 cycle, with air screw o-rings and washers.  Hopefully that'll help something.

I think I'm going to pull the slow jets back out again and make sure they're clear again (even though I was meticulous about it before and I could blow air through them all equally). 

I'm on a mission now, haha. 

[WarwickE36]

I spy PODS...

Mission 1 original airbox with a new filter

[TwoTired]

OK here goes...
Stop trying to do the "quick fix", buckle down and do all the basics first.  You've got a nice bike there, but it needs serious attention to details.
Clean or renew the spark plugs, verify gap. Ensure each of the spark plug caps screws tightly on to the wire.
Check/adjust all the tappet clearances (cold).
Reset cam chain tension.
Gap points, set timing.  Must be the same for both sets.

NOW, you are ready to deal with the carbs.

If you want it to idle consistently, you MUST vacuum balance the carbs.  Bench sync gets it running.  Vacuum sync gets all the carbs trying for the same crankshaft RPM, instead of them trading off for dominance.

Your video shows it will run on all four with the throttle open, but it isn't running on all four at idle.  Could be due to bad carb sync, or pilot circuit issues.

FYI: PD 46 Carbs don't have "air screws".  They have Idle Mixture Screws.  There is a difference, and they are adjusted in opposite directions to change mixture.  If you are still experimenting with pods, you will likely have to turn those outwards to 2-3 turns.  Book settings do not apply to engines with modified induction and exhaust.

When cleaning carbs with air, note it is invisible.  Blowing at it and seeing it actually flow are different conditions.  We've had several threads where flow was assumed (soaked and blown with air) but not proven.  That's why I prefer aerosol carb cleaner to "prove" each and every passage for both fuel AND air, showing it is capable of flowing.

You are almost there. A bit more patience and diligence, and you'll have it.

Cheers,

[VigCS]

OK here goes...
Stop trying to do the "quick fix", buckle down and do all the basics first.  You've got a nice bike there, but it needs serious attention to details.
Clean or renew the spark plugs, verify gap. Ensure each of the spark plug caps screws tightly on to the wire.
Check/adjust all the tappet clearances (cold).
Reset cam chain tension.
Gap points, set timing.  Must be the same for both sets.

NOW, you are ready to deal with the carbs.

If you want it to idle consistently, you MUST vacuum balance the carbs.  Bench sync gets it running.  Vacuum sync gets all the carbs trying for the same crankshaft RPM, instead of them trading off for dominance.

Your video shows it will run on all four with the throttle open, but it isn't running on all four at idle.  Could be due to bad carb sync, or pilot circuit issues.

FYI: PD 46 Carbs don't have "air screws".  They have Idle Mixture Screws.  There is a difference, and they are adjusted in opposite directions to change mixture.  If you are still experimenting with pods, you will likely have to turn those outwards to 2-3 turns.  Book settings do not apply to engines with modified induction and exhaust.

When cleaning carbs with air, note it is invisible.  Blowing at it and seeing it actually flow are different conditions.  We've had several threads where flow was assumed (soaked and blown with air) but not proven.  That's why I prefer aerosol carb cleaner to "prove" each and every passage for both fuel AND air, showing it is capable of flowing.

You are almost there. A bit more patience and diligence, and you'll have it.

Cheers,

Thanks for the advice TT.  I'll give the engine a tune-up this weekend (it's been needing some attention anyhow).  I'm 99% sure the pilot circuits are clear.  When I was finished cleaning out the carbs I got on ebay I sprayed carb cleaner through all of the jet passages, and all were perfectly clear (came shooting out the jet outlets before the choke). 

Once I give the engine a tune up I'll vacuum-sync the carbs (and put new o-rings in the mixture screw).  Hopefully that'll fix the idle problems...if not...off come the carbs again!

[TwoTired]

No surprise if it doesn't idle well with only a bench sync.  You'll need a vacuum sync to sort that out.

[VigCS]

Can the lack of a vacuum sync cause a cylinder to cut out at low revs, though?  It doesn't make sense that a cylinder would completely cut without a vacuum sync.  Either way, going to vacuum sync this weekend.

Also, backing the mixture screw out richens it up, correct?  I'd rather run a little rich while doing these things than risk blowing a hole in a piston.

[TwoTired]

Can the lack of a vacuum sync cause a cylinder to cut out at low revs, though? 

Of course.  You have 4 individual air/fuel supply sources all vying for for dominance of each piston driving the crankshaft.
If three want it to turn at 1500 and one wants to run at 1000, then either the one won't contribute at all, or if it does it will add to crank speed when it does fire.

It doesn't make sense that a cylinder would completely cut without a vacuum sync.  Either way, going to vacuum sync this weekend.

There are other things that can make a cylinder cut out, for sure.  But, poor vacuum sync can certainly be one of the causes.  My 78 gave me fits alternately racing and dying at idle position.  Carb sync fixed that.  But, of course that was the only thing wrong with it at that point, too.

Also, backing the mixture screw out richens it up, correct?  I'd rather run a little rich while doing these things than risk blowing a hole in a piston.

Yes, backing the mixture screw enriches the mixture.  But, its contribution is very marginal above 1/8 throttle slide position.
Further, idle is the coolest temperature running speed.  It is very unlikely you'll burn a hole in the piston, at idle setting.  It is quite a different scenario withe the engine making max power (slides open).  And the Idle Mixture Screw setting won't save the engine in that regime.

Having said that, it is an air cooled engine.  If you are going to run it at idle (or ant RPM) for long durations while stationary, have a window fan blowing air over it.  You won't burn holes in pistons, but it can heat up to swell and seize pistons in the bores, and cook the oil to out of safe limits, destroying the oil.  Running the engine with the oil destroyed, will ruin the entire engine.

Cheers,

[heel_touge]

So i would like to verify the four idle air screws in front of the carb bowls are used to sync?

[TwoTired]

So i would like to verify the four idle air screws in front of the carb bowls are used to sync?

The 77 and 78 CB550K were stock with PD type carbs.
The screws in front of the carb bowls are for adjusting idle/pilot mixture.  They aren't air screws, they are idle mixture screws and behave differently than earlier carbs on the CB550.
The screws for adjusting carb vacuum sync are under the top covers on PD carbs.

If you want to successfully work on a bike, it is a pretty good idea to have the appropriate shop manual.
They have pictures and pointers as to what is what on the machine.

[cmonSTART]

So i would like to verify the four idle air screws in front of the carb bowls are used to sync?

The 77 and 78 CB550K were stock with PD type carbs.
The screws in front of the carb bowls are for adjusting idle/pilot mixture.  They aren't air screws, they are idle mixture screws and behave differently than earlier carbs on the CB550.
The screws for adjusting carb vacuum sync are under the top covers on PD carbs.

If you want to successfully work on a bike, it is a pretty good idea to have the appropriate shop manual.
They have pictures and pointers as to what is what on the machine.

Yes, if you don't have a manual, do get one.  This will show you exactly where all the adjustments are and what they do.

Also, I too spy pods.  Pods can be problematic and require a lot of effort and time to tune for.  I'm not sure what jetting changes your carbs may have had in the past, but a used airbox and filter from fleaBay may help you a lot. 

Nice bike!

[Accolay]

The only thing I can add is that before my carbs were synched, the bike sounded like a lawn mower/ old propeller plane idling- kinda like yours.

[Bandit18]

Well I managed to find an all-new seal kit at cycle 2 cycle, with air screw o-rings and washers.  Hopefully that'll help something.

I think I'm going to pull the slow jets back out again and make sure they're clear again (even though I was meticulous about it before and I could blow air through them all equally). 

I'm on a mission now, haha. 

Hey guys, I did a search and I could not find cycle 2 cycle.I'm also looking for carb orings and washers.

[TwoTired]

Hard to help when we don't know what bike is being referenced.  Same as op?

[heel_touge]

Thank you all for that information! I have a manual for my bike but this was a last minute surprise and my friend who owns the bike doesn't have a manual.