Topic: CB550 Tune-Up

[GregAmy]

Yesterday was full tune-up day on my '76 CB550, with the goal of improving drivability and economy (I'm currently at 40mpg). I did the plugs, points, condensors, valve adjustment, cam chain adjustment. Unfortunately, I don't have a vac gauge to sync the carbs...

Anyway, the shop manual specifies an idle speed of ~1000 RPM. However, my engine just will not run smoothly at that speed. Anything below 1200 and it just sounds like it wants to die. The idle "sounds" best at around 1200-1300. Could this be an effect of out-of-sync carbs? Any suggestions for a value-priced vac gauge?

Also, when I was setting the ignition timing, I set it initially to the test-light method, then followed up with a timing light. The 1-4 timing was very stable (including total advance), but the 2-3 timing was fluctuating all over the place (the reason I decided to replace the timing plate whole). I chose to clean all electrical contacts to the coils and back down the harness, and using dielectric grease on everything. It seemed to improve the strobo action, but I still get a random fluctuation. Any other suggestions?

Finally, the old spark plugs had some gas, maybe oil, on them, looks like it's running rich. I cleaned out the carbs and replaced the main jets 5 years ago when I bought the bike (they were all varnished up from sitting for a couple years) but I've done nothing else since. Is there something else I should do to them besides sync'ing?

Thanks in advance.

[KB02]

I would say start with a good carb cleaning. If it's been five years, they're probably due.

As for the timing issue (and maybe some of the mroe experienced guys can jump in on this one if I am WAY off base), you may have to adjust the individual points on the timeing plate. when I was timing my 750 I had to resort to fine adjustments of the 2-3 points set to get it to fire on the timing marks (1-4 was right on, but 2-3 was still off a bit).

And, as for idle speed, I have the same issue. My suggestion is go with what sounds right. My engine sounds like it is going break itself in half if I try to idle it arounf 1000, but about 1500 sounds perfect...  granted... I also think the tach gearing is off, like the drive and the receiver came off of different models.

[bistromath]

Get a real tach to set the idle speed. My 550F didn't want to idle at 1000 either, until I finally rebuilt and re-sync'ed the carbs. Now 1000 is quiet and smooth as a Swiss watch. My advice is to sync it at 1200 and then back it down to 1000, repeat the process. It won't hurt anything to idle at 1200 but it'll heat up more in traffic.

[TwoTired]

I find that carb sync can have a dramatic effect on idle smoothness and speed.  But, it is only one factor.  Compression check? Cylinder pressures (equal compression across all cylinders) and precise timing also play a part.  Worn carburetors won't idle as well as new, tight fitting ones either.  The slides wear with time and vibration.

Check your points cam for smoothness.  Ideally it would be as flat and smooth as a mirror, and certainly well greased.  I had one that got grooves in it from lack of lube.   The points would open eraticly depending on whether it followed the grooves or the ridges.  I was able to buy a new replacement from Honda that solved the problem.

 The emulsion tubes downstream from both the main and slow jets have cross drilled holes in them.  These add air to the fuel before it is delivered to the carb throats.  These holes are quite small and easily plugged up with varnish.  Are you certain these were cleaned when you cleaned out the carbs?

Other things to check would be the spark plug cap resistance and equal plug gap settings.  I would like to know what spark plugs you are using if they are not NGK D7EA.  Did all your spark plugs appear to have the same color and quantity of deposits?
Did you compare them to the pics at:
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

It would also be helpfull to know which model bike you have and if it still has the stock exhaust and air filter.
Also, you didn't mention cleaning the air filter or replacing it recently.  A dirty, restrictive air filter will increase fuel consumption and make plug deposits sooty.

Let us know your progress.

Cheers,

[stevej]

Dont forget to check your bikes plug caps they dont last forever.   

[GregAmy]

Thanks, guys, I appreciate the responses.

KB02, you're probably right, it's probably time for an overhaul again, especially given the bike's only gone 1000 miles or so. I remember it was a beast getting them in and out; maybe with 5 additional years of amturity it'll be easier... As for the timing, I did properlt time each separately. My problem was that the 1-4 was a steady strobe, but the 2-3 was fluctuating and not keeping the timing mark steady, indicating a possible electrical problem.

Bistromath , thanks for the suggestion. I'll snag a timing light from a buddy that's got the tach built in. That way I can compare it.

TwoTired, I didn't do any compression checks, but I will. the head is leaking a bit of oil, and it's probably the original engine no rebuild, s so I'm guessing it's getting tired, too. As to spark plugs, I put new D7EA's in this weekend too, and checked the gap before install. Didn't seem to matter. The old plugs had gasoline on them, looking pro bably between numbers 1 and 2, with some carbon, too. All plugs were equal in quality and deposits (I'm guessing it's running rich.) I'm n to sure what you mean by plug cap resistance, but the wires appear new, although they're at least 5 years old (I've never replaced them).

It's got a new stock paper air filter, stock 4-pipe exhaust.

Sounds like a card overhaul is in order. Suggestions for source for rebuild kits? Thanks again! - GA

[TwoTired]

An oil leak at the head of this engine does neccessarily mean the head gasket is leaking.  There is an oil gallery in the engine that runs up to the cam and rockers. It is sealed by orings separate from the headgasket that get brittle from age and the heat of the engine.  They can weep for years and not have any effect on engine run characteristics.

If you have plugs that are wet with gas and or oil, that is a significant observation, as it may mean those cylinders aren't firing.  It's important to distiguish between gas and oil, too.  Oily plugs indicate a mechanical integrity issue the cylinder itself.  Look at:
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html
Compare yor plug deposits with those pictures.
If your plugs are wet with gas, check the head pipes for temperature to see if they are warming.  Also, check to see if the float valves for those cylinders are closing properly or the float height is set correctly.

The boots that fit onto the spark plugs have resistors in them.  They unscrew from the wires.  So, you can check with an ohmmeter their current value.  They are 5K when new, and shouldn't be more than 10K and still be used.  The contacts (both ends) should be clean and shiny.

[bistromath]

Also if it idles sooty try backing out your pilot air screws to lean out your idle. Mine was idling rich until I followed the procedure to set idle mixture: set all pilot screws to 1-1/2 turns out, idle it warm, and slowly back out each screw to maximize idle speed and smoothness. Do it with a digital tach to make it easy.