Topic: Dead cylinder, rough running

[dr. destructo]

I have a 76 550.  I just got my bike running again after a few years off the road.  I noticed the engine runs rough and is slow to rev up when you snap the throttle in neutral.  I used a infrared temp gun pointing on the header pipes near the cylinders, 3 cylinders were in the 300 deg range, but cylinder #2 was 150 deg.   When first trying to get the engine to run, i couldnt get it started at all.  I found that the spark plugs were black and filthy and cruddy.  So i used a wire wheel on a die grinder to clean them up. Then the engine fired up easily. 

So i dont think its the plugs.  So then I tried wiggling the spark plug connector while the engine was running on cylinder #2, and the wire came out of the boot.  I tried stuffing the wire back in the boot, but I definately dont think its making a great connection in there.  But that spark plug wire was definately supplying some great spark, I saw first hand a 1/2 spark from the wire to the engine.  So after running the engine after jamming the plug wire back in the boot,, the header pipe temperature never rose above 150 deg, again while the others were 300 deg+. 

Now a few years back, I remember the engine having a sudden dieing problem and it started leaking fuel out one of the over flow tubes on the carbs.  I remember diagnosing one of the needle/seats was leaking, but I dont remember on what carburator it was.  I even ordered the parts, and never installed them before my little accident.

Do you guys have any suggestions on diagnosing a possible leaking needle/seat problem?  Now its not so bad that any fuel is leaking out of any overflow tubes, the engine just isnt running right.

thanks for your suggestions

[TwoTired]

Probably have some fuel contamination.  And, or gunked up carbs.  The carbs fuel bowls are vented and evaporation leaves behind gummy or hard deposits depending on how long it's been sitting.

Anyway this can cause plugged slow jets (.016 in diameter) sticking float valves, sticking float, etc.

Rust scale from the fuel tank can also cause problems by blocking a jet or preventing the float valve from closing.

If it is just evaporative deposits, you may get by with a cheap flushing.  At the bottom of each float bowl on the carb is a drain screw.  Open this and catch what comes out of each carb.  Chunks and flakes are a problem.  Replace the drain screws and remove the fuel line from the tank petcock.  Fill the carbs with Yamaha Carb cleaner (won't damage internal orings) and allow to sit over night.  Then drain and flush the carbs again with gas tank fuel.  If you are lucky, number two will work okay again.  If not, you will have to remove the float bowl and the slow jet to verify it is clear.  It is a bit of a contortion to do this on number two.  I sometimes take off number one float bowl, too, just so I can see more of what I am doing with number 2.
Also, when you look into the carb bowl it will be pretty obvious if a more thorough carb cleaning is warranted.
Anyway, if you're lucky it should work again as before.  Other wise and carb bank removal and cleaning will need to be performed with all new internal orings (available from Honda).

The spark plug cap is supposed to screw onto the ignition wire.  Righty-tighty.  If it won't go tight, trim off a 1/4 inch or so from the ignition lead so it will screw on tight and make a good connection.

Cheers,

[dr. destructo]

thanks twotired for your reply.

I decided to remove the carbs.  I had a hard time getting the air filter intake boots off from the air box , resulting in little room to get the carbs out? i must be missing something obvious to make it easier...

carb 2 and all the other carbs had plenty of gunk/debris in the float bowls.  Im really glad i removed them. I used fine lapping compound to "lightly" lap the needle/seat together on carbs 1 and 2 because i found their overflow tubes had both been recently leaking fuel.   I removed every jet and every component I could under the float bowl cover and cleaned with carb cleaner and sprayed out with compressed air.  I used a wire to clean the slow jets.  Put the carbs back on the engine, but didnt bother with the hassle of any air filter components temporarily..

Started it up, it sounds like its running on all 4, it revs up with much more authority now in neutral.  It actually seems to idle ok, and that was with a cold engine.   But, I immediately took it out a back alley and ran it back and forth, getting only up to 2nd gear, and a friend said when i got on it hard, the exhaust created a huge black cloud behind me.  So when he told me that, sitting there in neutral, I revved it up really high, and sure enough it just bellows out black smoke.  Now, this was all on less than a 2 minute test drive after just playing with the carbs that were sitting for 3 years.  Could this just be a cold motor? Or could it just be running too rich from not having the air filter assembly on? or do I just need to try to run it longer to see if it will clear itself out.  ?

[TwoTired]

I decided to remove the carbs.  I had a hard time getting the air filter intake boots off from the air box , resulting in little room to get the carbs out? i must be missing something obvious to make it easier...

Remove the band clamps off the air plenum couplers.  And, remove the bolts that anchor the air filter box.  The extra 3/8 inch and floppy rubber bits help quite a bit.

I used a wire to clean the slow jets. 

The slow jets are only about 0.016 inch in diameter down deep in the hole.  Did your wire make that orifice bigger?

Started it up, it sounds like its running on all 4, it revs up with much more authority now in neutral.  It actually seems to idle ok, and that was with a cold engine.   But, I immediately took it out a back alley and ran it back and forth, getting only up to 2nd gear, and a friend said when i got on it hard, the exhaust created a huge black cloud behind me.  So when he told me that, sitting there in neutral, I revved it up really high, and sure enough it just bellows out black smoke.  Now, this was all on less than a 2 minute test drive after just playing with the carbs that were sitting for 3 years.  Could this just be a cold motor? Or could it just be running too rich from not having the air filter assembly on? or do I just need to try to run it longer to see if it will clear itself out.  ?

A cold motor should need choke until it warms up.  It is very inefficient when cold and doesn't burn all the fuel provided.

An air filter adds restriction and should make it run richer.

What setting did you use for the Idle Air Bleed Screws?

Random thoughts...
Soot does build up in the exhaust system.  And condensation glues it into position.  Exhaust pulses and heat can knock it loose and blow it out the back end. (so to speak  )

There are two air jets in each carb, one for the slow system and one for the main throttle valve.  Restrictions in these and the carbs can run rich.
Both the slow jet and the throttle valve have emulsion tubes.  These are pipes with cross drilled holes that add air (from the air jet) to the fuel before it gets to the carb throat.  Restrictions or blockages in these cross drilled holes can make the carbs run rich.

A high level of the fuel in the carb bowl can make them run too rich.  What float height setting did you use?

Check your choke linkage so that all the butterflies open fully.

Sounds like you're making good progress!

Cheers,

[dr. destructo]

for cleaning the slow speed jets, I used a wire thats used in the auto industry a lot for wiring tags to parts, perhaps for warranty returns and such at dealers.  I dont know its thickness, except that it was thin enough to fit all the way thru the slow speed jet without too much difficulty, I dont believe i opened that jet up too bad the way i cleaned it.
Im not even sure how I would measure any damage done via incorrectly cleaning? its such a small diameter and with the air holes,, how would you even go about trying to measure this?

This morning I let the bike run in idle for a while, and it ran so rich my eyes were burning.  Eventually it would just die, but it always easily restarts. 

Well, later today I decided to remove the carbs again.  Im glad i left off the air plenum/filter assy.  It took only a few minuts to get the carbs on my box again.  anyway.. Now that you mention it, I did not inspect the emulsion tubes under the main jets.  one of them accidentally fell out, that one i checked, but tomorrow i will check the other 3. 

well, as my screen name suggests, this second attempt didnt go without any upsets. I couldnt remove the float pin on carb 4, so i tried using a spring loaded center punch , not smart.  it slipped off and forced its energy into the needle/seat/float tab area.  I dont think theres any damage done other than messing up my float setting.  Actually, I moronically didnt bother to check the float height on my initial carb cleaning.  Nor did I bother to check the upper half of the carb- the air side.  All I did was take off the float bowl because I was ASSuming to find some clogged jets.  I also dont want to have to re sync the carbs so I didnt make any adjustments to any adjusting screws.  I guess i was going on the idea that the bike was running great 3 years ago before my chain broke,, and now has been sitting forever. 

So now the carbs are back off.  Im trying to set the floats to 22 mm.  Im using a small pocket ruler with the sliding clip to measure float height... how do you check float height again?  Im no expert on carbs, and my clymer manual obviously is not dumbed down enough for me on their explanation of float setting.  with the carbs in their normal upright position, do I raise the float until i feel the needle seat, but still not compress the needle spring?..because the way the book reads it says as soon as the float tang touches the spring loaded tip of the needle, thats where i stop and check/adjust.  Im confused.  If thats right,, my fload setting was no where near 22mm.  I almost need a third arm to hold the carb bank upright, try to carefully lift up the float, and then adjust??

all the guys at work love the way this motor sounds, Ill love the way it rides if I can get these carbs going right!
thanks for your time and expertise ...ps I  used the search feature for adjusting floats on 550,, I guess im the only moron with this specific question, i didnt see any answers.

[TwoTired]

Most of the stuff that gums up with neglect is below the throttle bore.  I have often cleaned carb banks without separating the carbs or messing with the slides or their settings.  Therefore, the carb synch is undisturbed when done this way.  I will add, though, that this is no guarantee that carb sync isn't helpful.  The idle mixture screw settings do not comprise a carb synch.  These set idle mixtures.  You can just turn them in till lightly seated and count the number of turns to find or create an even setting across the carb bank.

You've already found the main jet emulsion tubes.  Check them all for clean and spiffy.
The idle jet emulsion tubes are attached to each slow jet (unscrews).  They are small but the holes need to be cleaned, anyway.

The air jets are found at the entrance mouth of the carbs.  There are two.  One for the slow circuit and one for the main/throttle valve.

The can of seafoam has a small tube with it.  Squirting fluid into the one of the air jets, you should find it exits several places; where the slow jet goes in, a small hole in the throttle bore, and if the idle screw is removed, that hole too.

The other air jet should flow fluid to where the main throttle valve emulsion tube sits.

The float setting is the measured position from the carb body bowl flange to the lowest part of the float.  The measurement is taken with the valve fully seated, the spring pin uncompressed, and the float actuating tang just touching the spring pin.  It is possible to make this measurement in any orientation.  However, many find it convenient to measure while the carbs are on their sides so the float valve remains stationary in it's seat, and the floats tend to remain in the position they are placed during the measurement.

Measuring orifice holes can be done with jet gauges.  Or, the shanks of tiny drill bits can be used.  Your slow jets should be #38, or 0.38 mm, or 0.01496063 inch.  A #80 drill bit shank should pass through. A #79 drill bit shank should not.

Happy wrenching!