Topic: #4 Cylinder Not Firing-Figuring out why-CB550K1

[DustyRags]

Woooo! Yeah, those points are a PITA to get right at first. Glad you made headway, and I hope it stays!

[iron_worker]

Might need to try something more flamable like ether before you notice a difference in idle when checking for vacuum leaks.

IW

[saxamaphone]

I think I'm slowly making headway here.  After I synced the carbs I still was having a hanging idle.  I'd blip the throttle and it would stay high.  Throttle cables are lubed and they snap back no problem.  I tightened the clamps around the intake ports as tight as I possible could and it seemed like it went away, but then it came back after 5 mins.  If I moved the air cleaner around (Uni stock replacement) it seemed to change the idle.

I took off my spark advance to make sure it was working properly and gave it a bit of 20-50 oil on the pivot points.  It was very clean and was working ok.

The hanging idle seems much better but now it's blowing smoke out of the exhaust, especially when I rev it.  It's light grey in colour.  I'm hoping this is because it's burning off carbon deposits.

It idles nicely at 1000rpms but if I blip the throttle it stutters when it gets back down.

I'll need to track down a propane torch in order to use that to find any vacuum leaks.

When I got the bike it was missing this part below, any opinions on wether that would make a huge difference?  I've been looking on ebay for a year and they almost never come up, and when they do, it's with the entire air cleaning assembly for an arm and a leg.

It's the middle piece here:

[saxamaphone]

Forget what I said about making headway.

I rechecked the timing yesterday after cleaning the spark advance and noticed the the #4 cylinder shows that it skips an occasional firing.  With the timing gun there are intermittent breaks in the flashes.  The rest of the cylinders fire steadily.

With brand new coils, wires and caps any idea what could cause that?

[TwoTired]

I realize I'm late to the party.  Is the original subject question still valid?
An aid to problem solving is a concise statement about the symptom(s) you wish to alleviate.

I rechecked the timing yesterday after cleaning the spark advance and noticed the the #4 cylinder shows that it skips an occasional firing.  With the timing gun there are intermittent breaks in the flashes.  The rest of the cylinders fire steadily.

With brand new coils, wires and caps any idea what could cause that?

Half of the spark plugs fire in reverse polarity.  Some timing light triggers are sensitive to polarity.
Do you HEAR misfires in conjunction with the missed light flashes?

Have you looked at the spark plug deposits lately?  Any sort of carbon trail on the center electrode insulator will effect the voltage developed in the coil.  If a spark plug is shorting, the effective gap is smaller for the dual output circuit, and the current flow stops voltage development for that firing cycle.

Idle hang:
  Can you physically close all the slides with the idle knob backed out?  To set idle with knob, it must have full authority to close off the inlet air supply.  The individual slide adjusters can be skewed to prevent this important function.


The part in the picture is the engine breather/water separator.  Yes the bike will run ok with out it, until the engine vapors foul the air filter.
However, that part also registers the filter for proper mounting inside the filter box.  How are you presently holding the filter in the proper position?

[saxamaphone]

Hi and thanks for your reply. 

The original problem was that cylinder #4 wasn't firing.  It would come and go.  It wasn't firing due to the fouled plug.  Since then I've been trying to figure out why the plug keeps getting fouled, so the original question is still valid.

As I see it now, there are two problems:  the #4 cylinder has plenty of spark and will fire with a new plug but it gets fouled quickly and stops firing.  The second problem would be the hanging idle before and after I've synced the carbs.

One thing I wrote earlier in the thread that may be valid is that the #4 cylinder's compression is 130 compared to the rest being right on 150psi.  Adding a bit of oil to #4 cylinder brought the compression up to 150.

Up to this point:
-I've cleaned and re-cleaned the carburetors (all stock jets and set floats.  Checked for sticky valve)
-new boots (the ones from the plenum)
-new air filter (Uni stock replacement)
-new Mac 4-1 exhaust
-cleaned all of the electrical connections on the bike
-new battery
-new hondaman blade style fuse box
-new points/condensers
-new dyna 5ohm coils/wires/caps
-new D7EA plugs/gapped (I've replaced #4 a few times this summer trying to solve the problem)
-valves adjusted
-adjusted cam chain tension
-gapped points and set timing with strobe (idle and advance are dead on)
-Vacuum synced carburetors (a few times after I go and readjust things because I'm at a loss)
 

Concerning the timing light skips, I do hear a slight stumble in the idle at the same time.  The consistent skips I see with the timing light are only on that cylinder, all others are steady.

I looked at the #4 spark plug two days ago and it was the same as what's been happening all along,dry black fouling.  A new plug gets fouled within 20 minutes of riding.  Here's the one from two days ago (I found it difficult to get a photo that captured the detail).

Idle hang:
  Can you physically close all the slides with the idle knob backed out?  To set idle with knob, it must have full authority to close off the inlet air supply.  The individual slide adjusters can be skewed to prevent this important function.

I can't say for sure at the moment because I haven't bench synced them since the spring.  I can get the bike to die while idling if I back out the idle knob if that's any indication.  It will idle well at 1000 rmps but a throttle blip will cause the idle to hang.  Throttle cables are lubed and snap back.  Can you screw the adjusters down until they bottom out then back them off a bit?  If so, should the idle knob be at middle position roughly?

I've tightened the intake manifold boots as much as possible (which seemed to help the idle hang for a bit) but I have yet to try using a propane torch around them to help find leaks (I don't have a torch at the moment).  The boots have no cracks and seem to be in good shape.

However, that part also registers the filter for proper mounting inside the filter box.  How are you presently holding the filter in the proper position?

The air filter housing is being held to the plenum with a zip tie.  My bike came with no spring (behind the air filter), no tool tray, no engine breather/water separator and no hardware to attach the housing together.  The air filter itself sits snugly onto the plenum and doesn't move by itself.

Sorry for the long post.  Any help or suggestions are greatly appreciated.

   

[TwoTired]

If the other cylinders are keeping their plugs clean, you can put the sooty one in one of those to clean it.  Flogging the motor helps this.  A bit of fun, too.  The cylinders reach their highest temps when the motor is working hard.  And the plugs can then clean deposits off their tips.  Over rich mixtures cool the chamber, preventing the self cleaning process.

How much in volume is a "bit" of oil for the compression test?  Did you add the same amount to the other cylinders to see what effect that volume of oil had on them?

Since # 4 carb is responsible for delivering fuel to the cylinder, and there is too much of it, it seems likely that it isn't working as the others do.  I'd focus on finding out what that difference is.

Did you record the number on the slide needles?  Did you check the needle jet orifice size?  These can be damaged by aggressive removal attempts.

Did you verify the air jet passage to the main emulsion tube, or the air jet and passage that feeds the pilot jet?

Are all the jets the same brand?

Have you verified that the fuel level is the same in each carb bowl?

Concerning the timing light skips, I do hear a slight stumble in the idle at the same time.  The consistent skips I see with the timing light are only on that cylinder, all others are steady.

Does this happen with a brand new plug in #4 also?  If only with a sooty plug, I already explained why that can be so.

[thep1pe]

Regards the strobe light skipping, I have found that connecting the light to a spare battery cures this. I have the air cleaner part you need, but I am in the UK so shipping might be a problem.

[ANDY W]

Have you checked the #4 float is floating properly?

[saxamaphone]

I'll try switching the plug around.  I'll enjoy it.

When I did a compression test, I added about 2 tsp to #4 only since the rest were at an even compression.  I had thought perhaps stuck rings but haven't taken the head off to see for myself.  Someone suggested that if that were the case, riding it for awhile might help them.  With the #4 cylinder problem, I haven't been able to do much riding.

For the slide needles, they are clipped on the 4th from the top position. 
To be honest, all the times I've had the carbs apart, I don't think I've noticed the number on the needle itself.  The rest of jets are stock sizes and not marked up.  Maybe it's time to take them apart again.

I did not check the needle jet orifice size.  What would be the best technique to do so?  I cleaned the emulsion tubes and they were in good condition.

Last time I cleaned the carbs this summer, the air passages were free but I think I'll take the carbs off tomorrow and double check everything you've been asking.  I also have some new o-rings I'll put on the jets.

The jets are all the same brand.

I've read about verifying the fuel level in the bowl using clear tubing.  I'd like to do that but I'm not sure how to solidly attach some clear tubing to the drain of these 022A carbs.

As for the timing light skips, it was doing it with a new plug the other day. I just went and tried it with a new plug now and it's not skipping...

I did notice just now that when I revved it so the spark advance was fully advanced, mostly the advance would stay in the correct place accept occasionally it would it would drop back for a split second and then quickly go back to full advance even though the throttle had remained steady.  I just cleaned and checked the spark advance a few days ago.  I'm sure it's been doing this all along.

thep1pe, I tried the light with a spare battery and with the one on the bike and found there to be no difference for me at least.

Funny coincidence, I'm going to be in the UK for a week mid-September.  Mostly around London. 

Thanks to you both.

[saxamaphone]

Hi award550, I've made sure the float is set properly and not sticking.  There's no liquid in the floats.  I'll try letting it float in some liquid and see how it does.  If I can figure out how to check the gas level in the bowl using the clear tube method, that should show me.

[TwoTired]

There was a clever post a while back regarding the clear tube method.
He found some hard plastic tubing slightly larger than the drain hole in the float bowl, and would fit onto some clear tubing.
 He gently heated the plastic tube in the center until it became soft and then pulled it apart.  This extruded the plastic and it tapered to a point, or at least reduced in diameter.  Cutting it at the tapered section, resulted in two cone tips that would wedge/screw into the drain holes of the bowls.
Run the flex clear tube up the side of the bowls and turn on the gas.  Nice sight gauge for seeing the internal level of the fuel inside the bowls.


Each piston displaces 544cc/4 = 136cc, 9:1 compression means the compression chamber is about 15cc.  2 tsp of oil = 9.8 cc.  So, you removed 2/3 of the space in which to compress the gas.  I'd say that's ample reason for the pressure to come up all by itself regardless of ring seal issues.  I expect if you had oiled the other cylinders similarly, they would have come up in pressure as well.

You only need a few drops in small engines to form a temporary aid in ring seal and not effect the absolute pressure increase by changing the compression ratio.
Many will recommend a leak down tester in place of the common pressure tester, as it relies less on operator knowledge for a truly informative test.

I measured my slide needle jets using the shanks of a numbered drill bit set.  From memory they were 2.60mm (0.102").  So I found a drill that would just fit (#38) where the next size up (#37) wouldn't.  You can measure the shanks with a micrometer or dial vernier to check their size/labels.
This drill bit size chart might be handy for you.
http://bobmay.astronomy.net/misc/drillchart.htm

[saxamaphone]

Hi Lloyd, thanks very much for the information.  It makes complete sense.  For some reason I'm not getting emails from the forum so I apologize for not replying earlier.

A few days ago I ran into a bunch of 550K0 parts for very cheap.  I dismantled the engine I got here http://forums.sohc4.net/index.php?topic=130186.0

I measured the ring gap of the top and middle rings an inch into the bottom of the cylinders for the engine I just got and they measured .013", just at the max they give in the shop manual. 

I decided I'd take a look into my engine that has been fouling plugs and not firing.  I left it in the frame and went down to the crankcase. 

I'm thinking I found why I'm fouling plugs.  The piston ring gaps from my engine are enormous!  Almost a quarter inch I'd say.



I put the rings from the K0 engine I just got into the cylinder and they measured 0.014", just outside the max.

I'll have to get the bores measured I guess and see if they've worn too much.  Any guesses if it's the rings or the bore?

The pistons for both engines are standard size.  Here's some other photos just for kicks.

So many spiders in this engine!  Even a bunch of cricket carcasses.













The cylinders look good to me and you can't feel any abnormalities with your finger.

[DustyRags]

Welcome back!

So- I can't remember, but did you ever do a compression test on that bike?

[saxamaphone]

Hey Dusty, I did do a compression test.  They were low across the board, 135 if I recall.  When I added a bit of oil in the spark plug hole the compression went up to 150.  The other day I figured I'd tried everything that's been recommended outside of the engine so it was time to take a look inside.  I was hoping to a find stuck rings and that'd be that.

The rings are obviously worn out with that huge gap.  I used mineral spirits in the valve ports to see if they were leaking.  The mineral spirits started going down slowly after 30mins in 2 of the 4.

I don't have a bore gauge so I'm trying to find a shop that will measure the bores and see if that's a problem as well.  Just ordered a gasket kit so I'll be ready when it's time to put it back together.

[DustyRags]

Huh, with gaps like that I'd expect the compression to be super low... shows what I know!

[saxamaphone]

Hey guys, hope all of you in the US are having a good Thanksgiving so far. 

I've run into something that's baffling me:  I measured my new (to me) cylinders with a telescoping gauge and a dial caliper (exact to 0.001 inches).  I measured them quite a few times in 3 places and they turned out to be within specs of the service manual.  The original cylinders that came with the engine were good as well except for one so I decided I'd use the new cylinders.

The old rings had a gap of 0.013" so I thought it would be logical to get new rings, gaskets, and cam chain, then put it back together using the new cylinders.

I just got new standard sized rings and I'm finding that they have a larger gap in the cylinders (0.0015") than the old ones, which makes them no longer in the standard range but still within the serviceable limit. 

I don't get it.  I thought they'd be fitting tighter.  Any ideas?

Cheers

[Trad]

Hey guys, hope all of you in the US are having a good Thanksgiving so far. 

I've run into something that's baffling me:  I measured my new (to me) cylinders with a telescoping gauge and a dial caliper (exact to 0.001 inches).  I measured them quite a few times in 3 places and they turned out to be within specs of the service manual.  The original cylinders that came with the engine were good as well except for one so I decided I'd use the new cylinders.

The old rings had a gap of 0.013" so I thought it would be logical to get new rings, gaskets, and cam chain, then put it back together using the new cylinders.

I just got new standard sized rings and I'm finding that they have a larger gap in the cylinders (0.0015") than the old ones, which makes them no longer in the standard range but still within the serviceable limit. 

I don't get it.  I thought they'd be fitting tighter.  Any ideas?

Cheers

Hey saxamaphone,

I am in Edmonton as well and also have a 550. (currently rebuilding with a 572 Kit). Cool to find another enthusiast.

I wouldn't worry about that small difference in ring gap at all. Think of how much better it's going to run than with the massive gaps you previously had. That is crazy. haha

[saxamaphone]

Hey guys, hope all of you in the US are having a good Thanksgiving so far. 

I've run into something that's baffling me:  I measured my new (to me) cylinders with a telescoping gauge and a dial caliper (exact to 0.001 inches).  I measured them quite a few times in 3 places and they turned out to be within specs of the service manual.  The original cylinders that came with the engine were good as well except for one so I decided I'd use the new cylinders.

The old rings had a gap of 0.013" so I thought it would be logical to get new rings, gaskets, and cam chain, then put it back together using the new cylinders.

I just got new standard sized rings and I'm finding that they have a larger gap in the cylinders (0.0015") than the old ones, which makes them no longer in the standard range but still within the serviceable limit. 

I don't get it.  I thought they'd be fitting tighter.  Any ideas?

Cheers

Hey saxamaphone,

I am in Edmonton as well and also have a 550. (currently rebuilding with a 572 Kit). Cool to find another enthusiast.

I wouldn't worry about that small difference in ring gap at all. Think of how much better it's going to run than with the massive gaps you previously had. That is crazy. haha

Hey Trad, great to hear from you and glad there's another member here in Edmonton. Your build sounds very cool and hopefully I'll see it in town sometime.

For some reason I was under the impression new rings would equal smaller gap then older still-ok rings. I'll need to lap the valves and get the surfaces good and clean.  Always seems to be the hardest part!

Cheers