Topic: #4 cylinder won't fire -- tried all the standard checks

[db22]

For some reason beyond my limited knowledge, the #4 cylinder on my 1975 CB550 won't fire.  The carbs are PD46As -- some PO fitted them, or maybe the engine is a '77.  I removed the carbs a couple of days ago to install new bowl gaskets and reset the float height to the correct 14.5mm, and when I put the carb rack back, #4 played dead.  I removed the plug, inserted it into the boot, and cranked the engine while touching the plug to a valve cover, and there is a healthy-looking spark.  I can feel suction when I put my hand over the carb intake, and gas spills out the intake when I cover it while the engine is cranking or running (the airbox is removed to make it easier to pull the carbs).  I removed the carb rack again and checked both jets for obstructions, and noted that the moving parts seem to be free when the throttle is moved.  The float valve seems to move properly when I move the float up and down.  All the air screws were opened to 1.5 turns before reinstalling.  I even removed the intake valve cover and turned the engine over -- the valve seems to move normally.

The one thing that bothers me is that the plug is not very wet with gas.  What should I check to be certain that gas is getting into the cyclinder?  Or, is there some other thing I am missing?

[MoMo]

Was the bike running on all four cylinders before you removed the carbs? The thumb over the plug hole is not really an adequate check, buy a compression gauge and check all 4 cylinders.  You have spark but if the plug cap is not fully contacting the plug wire what you see could be misleading. Good compression, spark at the right time and fuel in the correct mixture and it should fire up...Larry

[moham]

#4 was firing before you had the rack off? if so, i agree with johnie...you may have inadvertently helped some bit of gunk move into a bad spot when pulling the rack. i think the next step is to have them off for a proper cleaning/de-gunking before moving on. if you can't verify the last time this was done, then you have to assume they need it. do as you did before with all of the float height adjustments etc, and then see where you stand.

if #4 was firing before you had the carbs off to replace the gaskets, i think it is much less likely to be the plug boot (although this is a common issue)

[db22]

Ah well -- off they come again.  Yes, #4 was firing before I pulled the carbs.  I had first adjusted the floats to the Clymer manual spec of 22mm, and the idle was mighty rough.  At 14.5mm, it promises to be a lot smoother -- if I can just get #4 to burn gasoline again.  Perhaps a closer look at the valve controlled by the float -- everything else seems to be clear.

Off to the garage... thank you for the advice!

[daley]

I had the same problem only mine was #2. Come to find out that the new bowl gasket was slightly wider and was holding the float up so no gas could get into the bowl. I put the old gasket back in and that fixed the problem. Hope it is that easy for you. daley.

[TwoTired]

Maybe it is time to do an actual fuel level test?
Put clear tubing on the bottom drain hose and run it up the side of the bowl.  Open the drain valve, and the fuel will rise to what the level is inside.  Should be 1-2mm below the gasket mating surface with carbs upright.

If nothing else, it will confirm that the float height was set properly and eliminate that as a possible problem cause.

Cheers,

[db22]

I had the same problem only mine was #2. Come to find out that the new bowl gasket was slightly wider and was holding the float up so no gas could get into the bowl. I put the old gasket back in and that fixed the problem. Hope it is that easy for you. daley.

Ah HA!  Yes, the new bowl gaskets are really just o-rings, and are considerably thicker than the old molded gaskets.  After the struggle to get them to stay put in the groove on the lip of the bowls, I'd hate to pull them out.  I wonder if simply adjustng the float height to make up for the thicker gasket might help. 

Two Tired, you always come through with the advice most likely to solve the problem . . . I think I can scare up some clear fuel line somewhere.  Thanks to all for the help!

[db22]

TT: I couldn't find any line that was a good fit on the drain nipple, but with a leaky length of clear line, it looks as if fuel is not rising in the bowls -- yep, bowls, plural: #3 has now gone on strike.  However, when I drain the bowls to take the carb rack back to the bench, there seems to be a full bowl of gas present in each carb.

I removed the bowls and checked the stand pipe and drain with wire and compressed air -- clear.  What could be stopping the flow of fuel?  How can I check the passage from the fuel intake nipple to the carbs?  This is a PD46A rack -- there is only one fuel intake. 

daley: went back to the original gaskets, no change.

Getting ticked off!  The sun is out, temps here are above 50F; riding weather has finally arrived in Wisconsin.  The old saw about ignorance being bliss doesn't apply to motorcycle carburetors. . . .

[TwoTired]

I'm going to ask if you have installed the floats upside down?
The large flat area goes to the bottom of the carbs.  The rounded portion goes up.

[db22]

TT: Floats are flat-side down.  I have made so many assempbly mistakes in my misadventures with machines that I actually thought to make note of the correct orientation before removing them.  Once in a while, the slow kid in the class manages to get the right answer.

Last time I had the carbs off, I shot carb cleaner into the fuel intake nipple.  Bowls were removed.  Sure enough, it dribbled equally from all four carbs.  A nice single-cylinder bike is starting to look good about now...

[Spanner 1]

#4 and now #3 wont fire/run = no fuel !!! Clean the fuel supply from the tank to the carbs... namely the petcock and it's filter and possibly the tank cap vent... your fuel is only 'trickling' down to your carbs  ... will make a 1 cyl. out of a 4 cyl  motor PDQ.

[1timduke]

I'm going to ask if you have installed the floats upside down?
The large flat area goes to the bottom of the carbs.  The rounded portion goes up.

TT: Floats are flat-side down.  I have made so many assempbly mistakes in my misadventures with machines that I actually thought to make note of the correct orientation before removing them.  Once in a while, the slow kid in the class manages to get the right answer.

Last time I had the carbs off, I shot carb cleaner into the fuel intake nipple.  Bowls were removed.  Sure enough, it dribbled equally from all four carbs.  A nice single-cylinder bike is starting to look good about now...

Wait a minute... flat side down if the carbs are upside down??? Or, flat side up if the carbs are upside down???   I only make this observation be cause I am also sometimes a little slow.   

I'm battling a #2 right now and yes, a single cylinder bike sounds awesome to me right now as well.

Is this cylinder firing at all?   If a slow jet is clogged you may be able to get life out of it at higher RPMs.   Possible something could have gone up in it and clogged it during all the activities.   Rev it up and see if the pipe heats up.  Also, is the fuel clean when you take the bowls off?   

I haven't been on in awhile but there's a place somewhere on this site that shows engine serial #'s and corresponding years and carb #'s and such.   Track down exactly what you have if you haven't already.    Those charts come in handy, I spent years w/ the wrong set of carbs.   See, I told you I was a little slow sometimes!

-Tim

[db22]

Tim: Flat side up with the carbs upside-down, as they were when I first removed the bowls.  In other words, flat side down when installed on the bike.  Most of the pins were difficult to remove, leading me to believe that they had never been removed before, so this is how they were assembled at the factory. 
Spanner: Fuel flows freely, from the petcock to the bowls, and I now see gas on the the plugs when removed.  The bike is in the garage, on the centerstand.

I have reached the point where I need to walk away from it and stop letting it get to me.  Maybe later in the week, things will go better.  I do have other issues to deal with beside getting my bike to run.

[db22]

Problems are cascading: now, no cylnder will fire, and there is no spark in #1, which leads me to believe that there is no juice going to the plugs at all.  This is baffling, since 1 and 4 fire together, and 2 and 3 fire together.  First, 4 quit, then 3.  Why would that happen, when 1 and 2 were still lighting up?

Plus, I can't get #4 plug back in the cylinder.  It wants to cross-thread, will not seat.  Brought metal shavings up last time I tried to turn it in, so quit immediately.

I'll consult a troubleshooting chart for ignition problems.  In spite of the spark I saw from #4 initially, perhaps it was too weak to fire the cylinder.  But first, how can I get the plug back in #4 properly?

Thank you all for your help and advice!

[Duke McDukiedook]

Work from the top of the spark/fuel chain from the top tank/battery and cross off working components as you go down the chain ending utimately at the cylinders. This has to be done when you are having what appears to be multiple problems.
 

[db22]

Industrial: Yup, that's what it'll take.  As for my cross-threading spark plug -- should I try to locate a tap and chase the threads?  I worry about metal shavings in the cylinder.  Is a metric spark plug tap soemthing I might find at an auto parts store, or are the threads standard for bikes and cars?  I'm on new terrirtory here, for me -- steep learning curve!!

Thank you!

[Duke McDukiedook]

Start all plugs by hand if you can to make sure this type of thing doesn't happen. Hopefully you can get it going by hand and didn't do any real damage. If not, you might have to put a helicoil or some other type of thread insert in.

Others will chime in with more info on your plug problem probably.

[TwoTired]

Lots of cross threaded spark plugs could have been avoided by using the stock spark plug tool that came with the Honda tool kit.

I subtract at least $50 from purchase price if that tool kit is missing, btw.

You don't want a tap fro thread correction. It cuts off more metal.  You want a thread chaser which will push the metal back into proper position.

With either, you put heavy grease on the tool to bring any metal bits back out with the tool.

12 mm threads.

For the spark issues, verify the points gap and timing.  And, that the points haven't formed crusties that stop power flow.

Then check the spark leads for cracks which will let the spark jump to engine case.

Having said that...
  If there is a bulidup of carbon on the spark plug insulators inside, the spark energy just flows through the carbon trail rather than jump the gap.

Cheers,

[db22]

By careful hand-threading, I got the plug back straight in #4.  TT, you are right -- my metric plug socket starts 'em out crooked in #1 and #4.  Seated the plug with the tool from my '68 CT-90's factory kit.  I didn't realize tha value of the tool kits that come with motorcycles. 

The work week and other responsibilities will keep me out of the garage for a while.  Took the CT-90 to work yesterday -- quite thrilling to ride a 180-pound bike in 50MPH traffic!  Thank goodness for tailwinds...

[Duanob]

Sounds like you got a bevy of problems but back to the original. I've had more problems with my slow jets than anything else on my bike. It's a 76 550K with OEM 022a/087 carbs. I've had three cylinders not fire off at different times. I get spark and compression and gas in the float bowls. All three times I take the bowl off, take out the pilot jet clean it, blow canned air up inot the carb where the pilot jet goes, put it back together using permatex #2 gasket sealer in the bowl gasket groove to get the gasket to stay in place. Wipe any excess off. And voila! She fires up and burns hot on all cylinders. That is until it sets for a while then I start the process all over again.

Stupid gas! We pay extra for gasoline that is crap in quality. That's where I place the blame. I finally drained my tank and all 4 float bowls and had some murkey white crap in it. When it dries it turns to a whiter powdery substance that covers and plugs everything. The gas was only a few months old. I can't even imagine a bike that sits for years with the same gas in it.

[TwoTired]

Stupid gas! We pay extra for gasoline that is crap in quality. That's where I place the blame. I finally drained my tank and all 4 float bowls and had some murkey white crap in it. When it dries it turns to a whiter powdery substance that covers and plugs everything. The gas was only a few months old. I can't even imagine a bike that sits for years with the same gas in it.

It's part of a greater plan to stimulate the economy (equals: extract more money from the populace).
It used to be corporation that would design in "planed obsolescence" so consumers would have to purchase replacements.  Now the government has gotten into the act to increase costs for the consumer and user of products.  You either pay more to keep the old stuff working or you pay more to replace it with new.

Oh, and the "murkey white crap" is the result of condensation or water added to the the gasohol.
Modern vehicles have a fuel tank vapor return system that helps keep humidified air out of the fuel containment vessel.  Yet another reason to replace old with new, paying extra taxes, and supporting the tax income base on the workers who make the new product.

I'm waiting for new legislation mandating blood banks only use rocks as a source of stocked inventory.

Cheers!!!

[db22]

I have reinstalled my carefully cleaned and checked carbs and hooked up control cables, and am looking at this from an ignition point of view.  When the key is turned, the system lights up normally.  All indicators work, headlight works, starter turns over vigorously.

There is no spark in any of the plugs I have tested.  Looking at the 36-year-old wires leading from the battery forward to the plugs, it looks like the bullet connectors are sealed in little clear-plastic covers, but I pulled and pushed on each one to check the fit.  Wires to the solenoid, starter switch, and coils seem to be fixed tightly in place.  I did find a stray wire some PO had attached to the battery-in side of the solenoid, probably to power some device long since removed.  I took it off, accidentally touching the engine, which caused some sparking.  However, when the nut on the solenoid was re-tightened, all seemed well -- no change in the behavior of the system.  I have pushed all the plugs together to be sure they are connected -- I suppose I should separate them and use compressed air, but garage time is short this week.  I unscrewed the spark plug caps and re-screwed them on, but have not trimmed the wires back.  Is there a particular way to trim plug wires?  I have heard auto wires are made of some special material, not just insulated copper, like a common eletrical wire.

Next, I will remove the points cover and start looking at the connections there, and try the test procedures in the manuals.  Is there a component that might have failed, causing first partial, and then total, failure of the ignition system?  Searching SOHC4, I have found that the coils are durable items and are unlikely to have failed, particularly both at once.  I keep hoping to find some broken wire or dangling connector that is causing the trouble. 

[Duke McDukiedook]

Make sure there are no breaks or frays in the spark plug wires. With your setup you will be alright with rubber over copper wire (stock). You never really mentioned your ignition system- is it a Dyna or after market ignition or is it points? You might have bad condensors on your points plate.

You will want to run resistance tests on your coils also.

[db22]

Industrial: Ignition is stock points & condensers.  Will a cheapo mutlitester do the resistance test on the coils?  I just downloaded the Honda serice manual, and haven't had much time to read up on this.  "Noob" barely describes my greenhorn status with wrench and gauge.  Thanks!!!

[Duanob]

I think I would start with a voltage test at the coils first. Check the small wires going into the coils for roughly 12 volts with kill switch on/ignition switch on. If yes, then your problem lies between your coils and your spark plugs. Do a resistance test on the coils. If no, then work your way back towards the points plate. You may end up going all the way to the kill switch or ignition switch. It sounds like a bad connection supplying juice to both coils.