Topic: '75 CB550K rough idle

[db22]

After a bit of spring tuning-up, my old CB 550 runs great at highway speeds, but the idle is rough and tends to surge, and the engine stalls when left at idle any length of time after warming up.  Here's what I've done so far:

Removed Emgo pods and reinstalled factory airbox assembly
Set valve clearance to manual spec
Reset cam chain tensioner per manual prcedure
Checked jets for obstructions
Installed new properly-gapped NGK D7EA plugs (PO was using D8EAs)
Checked carb synch with the cheapo blue gauge set per instructions

Bike has around 12,000 miles, and is equipped with some aftermarket 4-into-2 exhaust system.  Jets are unmarked; I am assuming they are stock.  And the carbs are PD type, not correct for a 1975 CB550K, according to what I have been told here.  So far, I have not been able to read any of the stampings on the carbs.  Air screws are turned out 1.75 turns. 

I have little experience with a wrench, and am doing these things exactly as described in the Clymer and Haynes manuals, to the best of my understanding and ability.  What should I try next, to smooth out the idle and improve performance below 3000 RPM?  Thanks!!

[Nortstudio]

I've been having some issues that are not as severe as yours on my '76 550k. 

Couple questions: 

how do you get it up to highway speed?  Do you keep it goosed until you can get going above 3000?  Does it stall at stop lights?

What throttle positions does it have this issue in?  Is it in every gear, but onlynat certain throttle opening position?

Did you look at the needle positions when you cleaned the carbs?

What are the differences between running the pods and the air box?  Has there been improvement/decline in performance?

What do the plugs look like?

[bender01]

http://www.z1enterprises.com/
 My bike is suffering these symptoms now!
 I have #2 with a broken spark plug boot.
  Try running your bike in the dark to see if you have any sparks visible to you.

[dave500]

is it idling a little low?causing the stall?try the mixture screws one more full turn out,it sounds like a lean out condition,adjust the speed to suit,start it a bit high then wind it down once fully hot,you havent mentioned the float height,make sure its correct as well as the ignition which wasnt mentioned either,,,get the ignition spot on before you chase carb ghosts which might not exist.

[db22]

The bike accelerates just fine through the gears, once it gets past the initial stumble as the throttle is opened.  The trouble occurs at the point where RPMs are raised as the clutch is engaged, in first and second.  The engine starts just fine (better when cold than hot), but must be set at around 1200 RPM to remain running (as shown on the bike's tach -- I do not have a shop tach).  The most worrisome aspect of this is the surging, which climbs near 3000 RPM before settling down, slowly.  Air screws were set at 1.5 turns after the work I did yesterday.  Until I opened the air screws an additional .25 turn, RPMs settled very slowly after gunning the throttle.

Dave 500: The points looked fine when I had the cover off yesterday.  Plugs are sooty -- dry soot, no sign of oil or gas.  They were tan when the pods were still in place, which is a sign of lean mixture and overheating, as I understand it. 

Nortstudio: The bike only occasionally stalls at stops.  BTW, when should I send payment for tour patches?  Is Paypal acceptable?  Looking forward to them!

Bender01: I'll double-check the plug wires.

Thank you all for your Help!!

[Nortstudio]

Tour patches should be arriving sometime this week. I will be sending out a PM to everyone who ordered them as soon as I have them in my hands.

[db22]

Dave500: I opened the air screws another quarter-turn, and that seems to have helped somewhat with stumbling while accelerating in first and second.  When I have time to attend to the bike again, I'll try another quarter-turn. 

I set float height to 22mm per the manual, though I have seen 14.5mm listed as the correct height for PD carbs.  I don't have the time this week to pull the carbs again.  And, when I got the bike last year, the PO (or someone) had set the floats way too high, causing fuel leakage from the intakes.  This stoppped immediately after setting them to 22mm.

Thanks to all for the advice!!

[dave500]

ok cool,the points look fine but if you have a timing light make sure they are correct.

[TwoTired]

If you have PD carbs, the max float setting is 14.5mm.  22mm setting is way too high and probably feeding raw gas into the engine from overflow.  It would explain the sooty plugs.

Are you using the Honda manual?  The later chapters discuss the PD carbs.  The Clymer is ignorant about the PD carbs and their carb info will just mislead the neophyte.

Do you have a choke cable fitted?

The PD carbs don't have air screws.  They have Idle Mixture Screws in front of the carb bowls.  Out for richer, inward for leaner.

Where are you looking for the stampings on the carbs?

[db22]

TT: There is a faint stamping on a flat right under the letters "PD", on the side of the carb body.  It is too faint for my aging eyes to read -- will try with a stronger light and magnifier.  I'll look around for the Honda shop manual to download -- all I have are Clymer and Haynes.  Will reset floats to 14.5mm.  Chole cable is fitted and functional.  Engine starts on the first kick (I'm a bit paranoid about discharging the battery -- saving it for emergency electric starts when I stall in traffic.  And I just like the feel of starting the bike with the kick lever).

Dave500: Don't have a timing light... sounds like another trip to Sears' auto tool department is in order.

Rode to work yesterday for the first time.  Other than the falterng at low RPMs and rough idle, things went fairly well.  32-mile round trip, temps in the 40s F.  One of these days soon it's gotta warm up around here!  Thanks for your help!!

[Nortstudio]

I'm pretty sure you will be able to find a manual linked right here on the site - at the top of the main SOHC forum page (the one this thread is in).  It's priceless.

And while you are at it, grab a parts fiche (blow up diagram).  I have found that it has gone a long way toward helping me understand the layout and also the order in which to dismantle and reassemble.  They are available online at several sites, but having it on the computer has been much easier to sift through than waiting for the page to load when you are in full panic mode

[Tretnine]

Sounds like you should find out what's actually in your carbs. I'm having issues with mine, and that's the angle I'm taking. http://www.motorcycleproject.com/motorcycle/text/specs.html  That's a link to each carb and what should be inside. Your problems sound similar to mine, and I think it's caused by richness in the idle circuit. Take off your carbs or take off one bowl while it's in the bike and peek at the number on your idle jet. (You may not be able to see the numbers while in the machine.) While your carbs are off check which needles you have in your bike, they should probably be 2349f, and which clip position they're in.

You probably need to do carburetor vacuum sync and set your timing, if you haven't. Those will help.

Pull em off, look at what's inside and check it against the chart.

[db22]

Tretnine, thanks for the link.  The 1978 PD46C float height is shown as 12.5mm.

TT: flashlight and magnfier revealed "46A" stamped below the letters "PD".  The chart Tretnine linked to shows an X46A carb on '77 CB550ks, but the letters "PD" are plainly cast into the carb body on my bike.  The PO assembled the bike from parts, so it seems...

[db22]

Another issue: the jets seem to be stuck to the emulsifier tubes.  The guy at Jets R Us says they should separate.  Would soaking in oil do the trick?  Vinegar might dissolve mineral deposits that are sticking them together, but would also attack the brass.

Looks like another week or so of garage work to get this sorted out.  It just started to snow again here (!!!!), so I suppose this is a good time to pull the carbs again and try to make some progress.  Looking forward to your thoughts -- thanks!

[Fritz]

If you have PD carbs, the max float setting is 14.5mm.  22mm setting is way too high and probably feeding raw gas into the engine from overflow.  It would explain the sooty plugs.

Sorry LLoyd, but would 22mm float setting on a PD carb mean that hardly any fuel would get into the bowl? My understanding is that float hight is measured between the carb flange and the lower edge of the float. So a higher distance means that the floats close the valve earlier allowing less fuel into the bowl.

[TwoTired]

If you have PD carbs, the max float setting is 14.5mm.  22mm setting is way too high and probably feeding raw gas into the engine from overflow.  It would explain the sooty plugs.

Sorry LLoyd, but would 22mm float setting on a PD carb mean that hardly any fuel would get into the bowl? My understanding is that float hight is measured between the carb flange and the lower edge of the float. So a higher distance means that the floats close the valve earlier allowing less fuel into the bowl.

You are right, Fritz.  I claim mental inversion on my part.  (I wonder if that's part of my increasing dyslexia w/age?)    
Sorry for that error.
Still, 22mm is just way wrong for the PD carbs and needs to be corrected.

Could be that whoever put the pods on also meddled with the jetting.  The carbs will have to be checked for orifice size marks and/or drilling (so the numbers won't match the actual hole size of the jet).
Could also be that non-Honda parts were used in a prior rebuild.  Check the numbers on the slide needles.

Oh, and look where the slide needle enters the body of the carb.  There are supposed to be calibrated orifices for the needle to enter.  If those were left out or drilled too big, way too much fuel would get sucked in.

Another issue: the jets seem to be stuck to the emulsifier tubes.  The guy at Jets R Us says they should separate.  Would soaking in oil do the trick?  Vinegar might dissolve mineral deposits that are sticking them together, but would also attack the brass.

Try a 50% mix of acetone and Automatic Transmission fluid.  This won't dissolve brass, and is superior to most penetrating fluids.

The X46a the chart referred to, is from the Honda shop manual.  But, I don't think the X was ever stamped on the carbs.  I think that the Honda tech writer used advanced engineering info, and publication schedules didn't allow for corrections or final proofreading, before delivery of both machine and documentation to customers.

Cheers,

[Tretnine]

Those jets should pop apart, are you pulling them at the right spot? The jet itself is not very big, put the correct mm wrench on the emulsifier and the proper sized screwdriver in the slot and it should pop right out. It's brass on brass, hopefully it wasn't hamfisted together. Otherwise, go with Lloyd's rec. of penetrating lube or atf/acetone. I don't know that you'll actually need it. The other option is carb parts cleaner, that should get the stuff on the outside and possibly dissolve what's sticking, and THEN a round of some penetrating compound.

[dave500]

you have to look at every small part,i took apart a filthy carb set once to find 2x98 mains,2x100mains,,2x38 slow and 2x40 slow,the rack was three 627b and one o69a,thats a real frankenstein set up.