Topic: '78 CB550K Running on Two Cylinders

[TedH]

If I only had two cyl's, I'd be ok, but it's an in-line 4. 

Just brought it home on Thurs.  It sometimes runs on 4 and then sometimes on 2.  I suspect the floats are sticking.  I am going to also check/set/replace the points as PO says the points haven't been changed since he owned it and he bought it in 2007.  It doesn't backfire or 'miss'.  It just isn't firing on two cyl's. 

Fresh gas.  The tank was nearly empty when I brought it home. 

If not floats or points... plug wires?  I would think that if it were plug wires, it would not be intermittent. 

Please advise.

This is my 2nd CB550.  But, it is my 4th SOHC.  Prior ownership:

'76 CB550F
'75 CB750K
'77 CB750F

The bike has 14.5K miles.

PO says he replaced the main jets but has not rebuilt the carbs when he replaced the OEM air box with 4 K&N cotton pod filters.  It also has an aftermarket MAC 4-into-1 exhaust.  Sounds great when it is on a 4 cyl's. 

Buddy 'Peterbylt' from Tampa, FL, has a '75 CB550F.  His has exhibited this behavior but it often smoothed out once he had it out on the road. 

I plan to also drain the carb  bowls (once it is cooled off) and see if there is sediment in them.  If I find sediment, I am inclined to boil/rebuild the carbs (would CB550F rebuild kit be appropriate since it has the MAC single exhaust/header?).  And, I would be synchronizing the carbs.

So what I am planning to do (before carb rebuild):

check/set the points
drain the carb bowls
clean/check the spark plugs.  What is correct gap?

If this doesn't solve the mystery, then:

Rebuild/boil carbs
Synchronize the carbs.

[TedH]

I've cleaned and verified the plug gap @ .025".  New NGKs in spring '10 per PO.  NGK D7EA. 

I also drained the carbs.  No sediment.  I'm going to clean/check the point gap next...

[mlinder]

Which 2 stop firing?

[TedH]

It is running on three cyl's.

I checked the exhaust pipes and #2 cyl is consistently cooler than 1, 3 and 4.  I've already trimmed off the end of the spark plug wire as it was very loose where the boot plugs into it.  That didn't solve it completely as it still runs cooler than the other three.  It is firing as I have a spark tester and have detected spark on all four cyl's.

I am going to next test the resistance on all four cylinders' coils/wires/boots to see if any are far from specs.  I have a needle type ohm/voltage tester.

Then, if they check out, I'll see if swapping a fresh spark plug in solves it; perhaps the insulator is cracked (very remote possibility).

Last resort, pull the carbs and clean/adjust/synchronize.

[TedH]

I note there is a lone narrow hose that originates on the #2 carburetor body and 'hangs' down near where the four overflow hoses attach to the carb bowls and snake toward the rear fender.  I don't recall seeing this lone hose 'unattached' on my '76 CB550F but it is 2 years newer. 

PO said he installed an aftermarket petcock.  Is this lone hose a vacuum signal hose for the OEM petcock?  I note that I have a similar hose on my Yamaha 850 Midnight Special that triggers the OEM petcock fuel flow using a vacuum signal; secondary to the fuel hose.

[TwoTired]

I note there is a lone narrow hose that originates on the #2 carburetor body and 'hangs' down near where the four overflow hoses attach to the carb bowls and snake toward the rear fender. ... Is this lone hose a vacuum signal hose for the OEM petcock?

The hose is a carb bowl vent.  It supplies the pressure to push the fuel through the metering orifices in the carbs.
Is is most certainly NOT a vacuum hose.  And, the original fuel valve did not have vacuum shut off.

If you have a head pipe that is cooler than the others, and it does this at idle speeds, it is most likely the pilot jet clogged up.
These are pressed into the carb bodies on the PD style carbs.

Cheers,

[TedH]

What's the best solution?  Boil the carb?  Are these jets removable?  I've rebuilt 750K carbs and was able to remove the (three?) jets that are inserted into the carb bodies from 'inside/under' the fuel bowl covers (working on the carbs upside down on a work bench).  I've not had to rebuild CB550 carbs before.

[Kframe]

No I don't think that jet comes out. 
Shouldn't have to though.

Give each carb a good soak in Berryman's or Gunk or some other suitable can of toxic waste and use some compressed air and some strands of copper from a lamp or speaker wire. 

To eliminate an electrical problem, swap your #2 and #3 plug wires and see if the problem switches sides. 
They run off the same coil (as do 1 and 4). 
-K

[TedH]

Good idea.  I'll do that swap in the morning before I pull the carbs for soaking.  I did find that the spark boots on #1 and #2 were both loose and the wires pulled out of them easily so I trimmed 1/4"-5/16" from the wires and re-inserted into the boots; the wires now seem snugger in the boots and #2 header gets warm to touch but still not burning hot as 1, 3 and 4 pipes.

I have a gallon of 'gunk' cleaner on the shelf in my garage.  Was going to just boil the carb in a pot of white vinegar though since I had used the 'gunk' to clean rollerblade bearings years ago   and it's not moved from the shelf since then.  I suppose the bearings crud (sand/soil) has settled/dissolved by now though.  

It runs poorly under load too.  It is evident from the engine performance that it is 'down' on power when I attempt to accelerate.  The missing cylinder is apparent.

[Kframe]

Good idea.  I'll do that swap in the morning before I pull the carbs for soaking.  I did find that the spark boots on #1 and #2 were both loose and the wires pulled out of them easily so I trimmed 1/4"-5/16" from the wires and re-inserted into the boots; the wires now seem snugger in the boots and #2 header gets warm to touch but still not burning hot as 1, 3 and 4 pipes.

I have a gallon of 'gunk' cleaner on the shelf in my garage.  Was going to just boil the carb in a pot of white vinegar though since I had used the 'gunk' to clean rollerblade bearings years ago   and it's not moved from the shelf since then.  I suppose the bearings crud (sand/soil) has settled/dissolved by now though.  

It runs poorly under load too.  It is evident from the engine performance that it is 'down' on power when I attempt to accelerate.  The missing cylinder is apparent.

Yeah try the wire swap, might save you a carb rack pull. 

You could always pour that can of gunk through a triple layer of t-shirt into a clean can, should filter most of the sediment.
I don't know about boiling in acetic acid (vinegar), might do odd things to the cast aluminum carb body.  I'd worry most about etching the bore that the slide slides in, and the jet seats, and the bowl/body junction surface and .....   just don't do it.

-K

[TedH]

ok.  The vinegar was suggested (as was lemon oil) for boiling to remove hard to remove deposits from carburetor bodies.  Also, sonic cleaning was suggested for the same issue (not sure how that works). 

I'll strain the gunk with an old cotton t-shirt before I use it to soak the carbs.  I have an air compressor with the air nozzle.

[Kframe]

Ultrasonic cleaning uses powerful microvibrations (and sometimes heat) rather than just chemicals to loosen and carry away crud. 
Some places like NAPA or Autozone have a shop in back and will do this for your parts.  Some are just stores with no ability or knowledge about these things.

Sounds like you're set up.  Don't forget eye protection and gloves (I'm a nurse, and I see lots of eye injuries that a $2 pair of safety glasses could prevent).

-K

[TwoTired]

The pilot jet can be removed from the carb bodies.  They are swagged in and can be pulled out with pliers.

The removed jet can be immersed in carb cleaner.  I don't like to use acids in carbs as that attacks metals and dissolves them.  You can't put that removed metal back.  It is why carb cleaners are offered for sale.
After you can see light though the pilots tap them back into their seated position.

Cheers,

[Kframe]

The pilot jet can be removed from the carb bodies.  They are swagged in and can be pulled out with pliers.

The removed jet can be immersed in carb cleaner.  I don't like to use acids in carbs as that attacks metals and dissolves them.  You can't put that removed metal back.  It is why carb cleaners are offered for sale.
After you can see light though the pilots tap them back into their seated position.

Cheers,

Ah, good to know!  Thanks! 
Of course, I'm sure it needs to be pulled straight out, avoiding wiggling and mucking up the hole.
I could see that going wrong quickly if they were corroded and stuck!
 
-K

[TedH]

The performance problem is now solved.  The #2 float level was WAY out of tolerances.  I suspect I know why now that I've let it sit for a while... after I rode it.  It was hanging about 3/4" lower than the other three floats.  Confirmed height of #1 and #3 and set #2 to match.  Bike now runs smooth and has 100% power.  

So, why was #2 float set to essentially starve the carb?  It leaks!!!  I have to figure out if it is the carb body, a sealing surface or a hose... BUT I had a puddle under the bike last night after I took it for a short ride and didn't turn off the petcock. 

The plot thickens...

[TedH]

The performance problem is now solved.  The #2 float level was WAY out of tolerances.  I suspect I know why now that I've let it sit for a while... after I rode it.  It was hanging about 3/4" lower than the other three floats.  Confirmed height of #1 and #3 and set #2 to match.  Bike now runs smooth and has 100% power.  

So, why was #2 float set to essentially starve the carb?  It leaks!!!  I have to figure out if it is the carb body, a sealing surface or a hose... BUT I had a puddle under the bike last night after I took it for a short ride and didn't turn off the petcock. 

The plot thickens...

I hope it isn't a carburetor body/casting issue...

[TwoTired]

Check the float bowl stand pipe for cracks?

[TedH]

Will do.  Also going to check the needle valves.  It appears to be #2 carb only (for now).

[flybox1]

did you measure/set your floats, or did you just eyeball them?
no where in this thread do you indicate anythign more than a carb dip cleaning.
MOST carbs wont get clean enough with just a dip/US cleaning.
since you re-set #2 float height, is it now too high, and overflowing out the standpipe?
doubt its leaking from a crack since it didnt leak before...unless ya cracked it removing a bowl. 

take the bowl off and fill it with water, to a point just below the top of the standpipe.
support it on a chunk of cardboard, and come back in 30.  no wet spot, and its prob your float height still off.  wet spot, and you may have some fixn to do.

[TedH]

I measured the revised float setting.  However, I will remove and remeasure as removal of the carbs is not nearly as involved since the bike has pod filters instead of an air box.  As I mentioned, the float was set so low/high that it cut flow off early when the bike was running.  Therefore, I suspect it was set such that it prevented the gas from rising to a point where it became a problem.

Once I found the float set so incorrectly, I realized there was not a need for a dip/cleaning to solve the rough running.  It runs fine now... just have the #2 carb leak that wasn't there before.  I adapted what I did given what I discovered when I pulled the #2 bowl cover.  I don't see any sense in doing something that isn't necessary just because I originally intended/stated that I would.

[flybox1]

 I don't see any sense in doing something that isn't necessary just because I originally intended/stated that I would.

+1
just hoping to save ya future issues that can be prevented with an extra 30 minutes spent being more detailed.  if the carbs are off, why not go thru them?
you stated the tank was near empty. did you drain and rinse it before filling it with fresh gas?
any sediment in there will be suspended when you fill up, and if you have a aged PC screen ,that stuff makes a bee-line right for your bowls.

[TedH]

#2 carb was actually cleaner than the neighboring #1/#3.  I cleaned the bowls and inspected the jets that are easily removed.  I'll take a look at the rest more closely.  Had the carbs not leaked after I reassembled, I'd not have gone back in this one more time.  Now that I am, gonna take a closer look to see what could be contributing in addition to the float level.  Also, before I pull the carbs, I'm going to turn the petcock on and watch where the gas comes from; could just be loose bowl seal that got out of sorts.  I tried setting the carb bodies down on the float bowls and then tightening but one may still have popped out of the grooves.  Those seals don't stay put very well.

[flybox1]

when you turn on the gas, do it slowly, have a rubber mallet handy, and smack the bowls to get the floats to release and shut off fuel

if your floats are set to spec, and you are getting:

A: overflow out the overflow drain tube, it might be cracked, or something might be blocking the float valve from closing as it should (clean it and check for sediment in your tank)

B: overflow at the oring/bowl gasket seam, then a o-ring might be pinched and see A above.
O-rings tend to swell when they contact gas.  let them dry really well before reinstalling. they'll shrink back down to size and may stay put better with a dab of superglue in the corners easing reinstallation of your bowls.

[TedH]

I just now started the bike and let it idle both on the side stand and level.  No leak.  However, I did manage to switch the #2 and #3 bowls (the drain screw location is the tip-off) when I had them off Tuesday so I'll need to pull and switch them. 

I'll observe the carbs today when running the bike in my garage to see if, from exterior, I can detect the leak source.  I'm watching the overflow tubes to see if the fuel is coming out of them OR if from the carb body.  I know that I had to put hose clamps on the fuel hose as it wasn't fitting perfectly on the carb and petcock.  With the inline screen-style filter (no in-tank screen).  Fuel tank is clean of sediment.  I drained the fuel tank Tuesday and the gas was clear with no sediment settling in the gas can.  When I removed the petcock, there was no junk on or in it.  The in-line screen is also clean of any debris.

[TedH]

The carbs stopped leaking.  I suspect the float got hung up initially after I installed everything.  I still need to swap the #2 and #3 bowls as I switched them by accident when I assembled Tuesday. 

I'll be running some SeaFoam through the tank for next 2-3 to remove any 'crud' that may be causing things to stick.

I took the bike out twice this evening and, during and after both rides, there was no indication of leaking from the carb bodies OR from the overflow lines.