Topic: 77 Honda CB550K

[aschreiber]

1977 cb550k with some weirdness going on. It currently has pod filters and stock exhaust, 5 OHM coils and some type of electronic ignition. The carbs are clean and the valves have been adjusted. New spark plugs. The intake manifolds seem loose despite having the clamps tightened, but they have no cracks. The bike has a surging idle that appears when hot. Seems like a vacuum leak, but the timing cannot be set correctly. There is no position of the ignition timing plate that will align the "F" mark. I'm wondering if this ignition is installed incorrectly or is this a possible symptom of slipping a tooth on the cam chain? Also are these the correct carbs for this year/model? Thanks.

[DaveBarbier]

The correct carbs for your bike if it's a '77 550k K3 are PD46A. It'll say that stamped on the right most carb by the bowl area. Looks like the right carbs.

I don't know what kind of ignition that is but if you're having issues setting timing then that seems like a problem. What about the advance setting? Did you put a strobe light on it and rev to about 3k rpm? That's about when the advance will kick in. Another member should be around shortly with help on that front.

It's possible that the rubber carb insulators are on backwards. That will make one side very tight and the other side loose. Which will be prone to leaks and cause running issues. Have you taken the carbs off? How do you know they've been cleaned? These have pressed in pilot jets that need to be pulled out (sometimes easy sometimes not so much) and cleaned thoroughly. Also there are tiny holes in the main jet holder (emulsion tube) that must be spotless for proper operation.

The fuel line routing especially with the in line filter could be an issue. There is already an in-tank filter, or at least there should be. Look in the tank and if it seems in good shape I'd toss the inline filter. Also, try to run the fuel line without a big loop in it. The in-tank filter can be removed and cleaned if you wish. Remove the petcock and twist in a bolt and pull.

Fresh fuel in the tank and is the tank spotless?

Have you synced the carbs?

What's your current jetting? And slide needle height? Jets have a K stamp on them to indicate they're genuine Keihin jets?

[calj737]

Surging idle is a telltale sign of too lean a fuel mixture, common to bikes with pods. If you have thoroughly investigated the manifolds for a vacuum leak, and your valves/timing are correct, its time to turn your attention to the carbs.

Start with a fuel level verification via the Clear Tube method.
Then proceed to an IDLE Plug chop with fresh plugs.
Then move to a Wide Open Throttle (WOT) plug chop with fresh plugs.
Then you get to go through a series of Throttle Position chops with more fresh plugs.

Sooner or later depending upon your perseverance, you might get your bike idling and running well.

[TwoTired]

Put the stock air filter box back on.

[Bankerdanny]

The '77 and '78 K bikes use the PD series carbs, which are different from the ones used on all other years and models of 550's. They came from the factory set up to run a bit leaner than prior years for emissions purposes. As TwoTired says, putting the stock airbox assembly back on (if you have it) might cure your issues.

If you don't have it you may have to change out your jets. Personally, I would recommend finding a stock setup on line as it is easier to go back to stock than to mess with jetting. Particularly on the 550 because the carbs have to come off to change the jetting, and extra particularly on the PD carb bikes because the slow jets press in an are harder to get out.

[TwoTired]

The inlet horn on top of the air filter box for 77-78 has a added restrictor fitted, which is not found on the F models using earlier carbs.

The effect of this is to make the carbs suck harder on the fuel jets to draw more fuel through their small orifices.  The result is nearly ideal mixtures delivered for the engine, and low emissions out the tailpipes.

Remove the inlet restrictions and the jets deliver less fuel making the engine run very lean and hotter, an artifact of pod installation.

On the other side of the cylinder is the high pressure stock exhaust, which works to hold a bit of the last power cycles unburnt exhaust, to be burned on the next cycle.  This slightly offsets the engine's fuel needs, allowing less fuel delivery requirements.  The stock carbs are tuned to expect this.
Replace the exhaust with less pipe pressure, and the carbs then deliver too lean mixtures, as the carbs have no way of knowing about exhaust (or intake duct changes).

You can band aid the inlet restriction by taping off a bit of the pod filters (about half) to deepen the pressure in the carb throats and make the carbs deliver more fuel from existing metering jets.

All this assumes the carb internals are clean and otherwise unmolested from its as-new delivery date.

The real danger with intake and exhaust mods for this model, is running the stock carbs with the resulting now way too lean stock settings.   This results in a very hot running engine, as the fuel does contribute to engine cooling and lean mixtures burn hotter (double whammy).  The hotter engine gets meaner to oil temps, and cheap oil then breaks down, and stops doing proper lube of the engine.  Usually the engine top end suffers early wear issues, and subsequent parts needs.

I have a 78 with worn exhaust valve guides, which is probably the very hottest part of the engine.  I do not know the oil quality used before I got the bike.  Suspect it wasn't top of the line with proper additives for MC use, though.  Still runs well, but a pretty good mosquito fogger.  On the plus side, the oil in the exhaust has preserved those well.

Cheers,

[aschreiber]

Thanks some really great info here.

Looks like the carbs are in fact correct.

Yes I tried using the strobe light to correct the ignition timing, but ignition plate refused to align. Wonder if the cam chain slipped a tooth or perhaps it wasnt installed correctly. Will need to explore further

Carbs have been pulled, cleaned, and synced. Currently mains are #120.   

Sounds like the easiest solution is to ditch the pods and reinstall the stock air filter. Will need to get my hands on replacement boots for the air filter box because one boot has a significant tear. Any suggestions on where to purchase?

Thanks,

[RAFster122s]

David silvers spares may stock them, if a Honda part and your local dealer can order you might get it cheaper through them...

The repro exhaust is available if you really wish to return to stock. ($1k)  Don't just accept that pods are a good idea, especially for stock motors.  Cheap pods are often merely for cosmetic looks.  Don't know how often you want to rebuild your motor, having ineffective filtration brings your motor to that state faster.
Pods are really good for a very narrow power band and really were a product from racing where the engine spent most of its time in a narrow high rpm window...it is the range a street bike sees which challenge them.  Riding the bike in heavy rain and they will suck water into the intake and they can drown out the motor and generally run like crap.  But, they can be tuned to work pretty well on a modified motor and some get them dialed in, others are constantly fighting with them to get them to perform better or well in normal riding.
Odds are you will not be running stock exhaust, so you are going to need to tune for that so you do not run too lean.  So, don't give up hope, just be prepared to spend time and money to get them dialed in.  Cal and several others are able to give you sound advice on getting them properly tuned ( they run pods on their bikes) but it will require you to be persistent with that journey.

Good luck in your journey and ownership, the 550 is a fun bike.

[calj737]

Carbs have been pulled, cleaned, and synced. Currently mains are #120.

120! Geez, thats huge for a 550! Stock is either 98 or 100. I'd suggest you do a thorough examination of the actual brass components (idle jets, mains, emulsion tubes and needles) and set them all to factory specs before you go too much further.

Pull the ignition plate, rotate the motor to #1 TDC and inspect the advancer. Does it align? If so, reinstall the ignition plate and move ahead. If not, pull the advancer, examine/clean it, and reinstall it, then the ignition plate. You can verify the cam with #1@TDC by checking the valves for clearance.

[Lostboy Steve]

Carbs have been pulled, cleaned, and synced. Currently mains are #120.

120! Geez, thats huge for a 550! Stock is either 98 or 100. I'd suggest you do a thorough examination of the actual brass components (idle jets, mains, emulsion tubes and needles) and set them all to factory specs before you go too much further.

Pull the ignition plate, rotate the motor to #1 TDC and inspect the advancer. Does it align? If so, reinstall the ignition plate and move ahead. If not, pull the advancer, examine/clean it, and reinstall it, then the ignition plate. You can verify the cam with #1@TDC by checking the valves for clearance.

Wasn't stock 90 for 1977?

I have a 550 with pods running 105 mains, stock needle position and it runs very well and idles nicely.


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[DaveBarbier]

Agreed, 120 is too big. I ran pods and velocity stacks on my 550 and used a 110 and needle raised one position. It ran great in the high rpm ranges as well as when I was just putting around town.

The cam slipping a tooth won't effect where the ignition fires. I would hold off on that diagnosis until you go through the ignition system.


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[Bankerdanny]

My current 550F has pods (it came that way when I bought it) and a Kerker 4-1 and the jets are stock size. That said they are also not Keihin, so it is possible they are actually somewhat larger than stock, can't be sure. But it starts right up, idles clean around 1k RPM's and has no flat spots.

[DaveBarbier]

My current 550F has pods (it came that way when I bought it) and a Kerker 4-1 and the jets are stock size. That said they are also not Keihin, so it is possible they are actually somewhat larger than stock, can't be sure. But it starts right up, idles clean around 1k RPM's and has no flat spots.

Could be drilled out

[Bankerdanny]

Yep. There are a lot of possibilities. The carbs from my '77 550F basket case have 115's in them. It came with headers and pods in the boxes. I am planning to swap in the stock jets from my '74 roller bike.