Topic: Carb Wizards... I need your sacred wisdom

[Adam_F]

Man - I am no carb wizard for sure - but I just went through almost the exact same thing on my CB550 - #1 was running cool; plug would get wet and black; would sputter and spit until higher revs.

Thought for sure it was ignition or coils or something as I had just gone through the carbs. Checked plug wires, got new caps, etc. etc etc.

What it finally ended up fixing it was raising the needles by one notch. I thought they were in stock - and technically they were - only 77 CB550 came w both 42 and 38 slow jets, and mine happened to have 42 slows, which meant that stock was actually not center notch, but 2nd from the top.

Anyway - point being - I don't know why #1 really seemed to be the only cylinder affected when all the needles were out, but just throwing that experience at you in case it gives you any clues.

Like you, I cleaned by GD slow jet on #1 about a million times, checked my floats, float valves - changed the points, checked the coils, etc. etc. etc. and was about to pull my hair out - then just tried the needles for a WTF sort of thing - and presto - bike fired on all four and has run perfect ever since.

Hmmm... Thanks so much for that.  From the look of your avatar, you have a 550k, correct.  I have the F and believe that we have different carb models (mine are the 069a).  Wonder if that would make any difference.  I've had the bike for a while and ran everything stock for years with no issues...  I'm going to try replacing the caps and checking coilds... and if all else fails, will take your advice and try moving the needles.

[lucky]

Did you remove the idle jets and look through them as you held them up to the light?

Sure did.  I also carefully ran a high e guitar string through all the tiny holes to make sure they were not blocked.  All of the jets from each carb are stock and appear original.  Float heights are all properly set at the point just before they compress the spring/needle. 

Somehow either too much fuel is still getting in, or there's just not enough spark to ignite it.  I just ordered new spark plug caps and plan on trimming the wires back 1/4 inch.  If that doesn't make a difference, I can test the ohm of the coils and potentially replace them.  If THAT still doesn't work... then.... well, no idea

Thanks for the suggestions though!

A question..
Did you put the guitar string through the central hole of the jet too?
When you set the float height did you do it by the book or did you use the so called "clear tube method"?

As far as the spark, did you clip a timing light on to each spark plug wire and check to see if the spark was consistant?

[Adam_F]

Did you remove the idle jets and look through them as you held them up to the light?

Sure did.  I also carefully ran a high e guitar string through all the tiny holes to make sure they were not blocked.  All of the jets from each carb are stock and appear original.  Float heights are all properly set at the point just before they compress the spring/needle. 

Somehow either too much fuel is still getting in, or there's just not enough spark to ignite it.  I just ordered new spark plug caps and plan on trimming the wires back 1/4 inch.  If that doesn't make a difference, I can test the ohm of the coils and potentially replace them.  If THAT still doesn't work... then.... well, no idea

Thanks for the suggestions though!

A question..
Did you put the guitar string through the central hole of the jet too?
When you set the float height did you do it by the book or did you use the so called "clear tube method"?

As far as the spark, did you clip a timing light on to each spark plug wire and check to see if the spark was consistant?

Hey Lucky.  Yeah, I ran the guitar string down the center as well and made sure I could see light through.  I only had to adjust the float on carb #4 a couple mms.  I measured by the book.... carbs on there sides to the point just before the needle/spring is compressed.  They all measured out at 22mm (stock setting) and I have no issues with the others. 

I don't have a timing light as I have dyna s ignition and haven't needed to set points, but I should pick one up.  Can you point me in the direction of any info on how to check for consistent spark and or checking my coils?  I used an ohm meter to check the caps (ordered new ones because the numbers were a tad higher than spec (over 10) and cap #4 was melted inside from arching).  Any idea how to use an ohm meter to check the coils (or is that even possible)?

Thanks!

[TwoTired]

Coil primary resistance is just under 5 ohms.  Coil secondary resistance is right around 15K ohms.  Coils unconnected to anything else.

[Adam_F]

Coil primary resistance is just under 5 ohms.  Coil secondary resistance is right around 15K ohms.  Coils unconnected to anything else.

Thanks TT.  Please bear with my ignorance / noobness...  So with the plug caps OFF the coils, can I simply touch the ends of the wires from each coil (1 and 4, 2 and 3) to the black and red tips of the ohm/micrometer to get a reading?  If so, should that reading be 5, 15, something else?  I read your post in the faq section about testing for spark, but alas remain a bit confused.  I'm admittedly more of a visual learner, so I appreciate any further explanation/help...

EDIT>>> I have dyna s ignition... no points

[Adam_F]

Found this great video:

https://www.youtube.com/watch?v=rRQ45lT2d3c

My question is...  To check the secondary coil, does the cap need to be attached to the end of the wire, or could he have done the test without the cap by putting the multimeter directly onto the wire?

[BobbyR]

Coil primary resistance is just under 5 ohms.  Coil secondary resistance is right around 15K ohms.  Coils unconnected to anything else.

EDIT>>> I have dyna s ignition... no points

Dynas have a habit of dropping out one side when heated. Pretty common.

[TwoTired]

So with the plug caps OFF the coils, can I simply touch the ends of the wires from each coil (1 and 4, 2 and 3) to the black and red tips of the ohm/micrometer to get a reading?  If so, should that reading be 5, 15, something else? 

Primary wires are Black.wht to blue or Black/wht to Yellow.  ~ 5 ohms on the ohmmeter.

The coil's spark leads are the secondary connections.  Ends of leads with no plug caps should read ~ 15,000 ohms.

Different meters can have different control functions and display details.  I don't know what particular meter you are using.  But, they all come with operating instructions.

[scottly]

  If #1 repeatedly soots up, then fix the carb issue related to it; float height, dropped jet, emulsion tube, etc.

1+ Also, do a "clear tube" check of the actual fuel level in the float bowl. Setting the float height when the tang just touches the spring-loaded needle plunger assumes the spring has a certain tension. A weak spring will cause a higher fuel level in the float bowl, and the only way to check this is with the clear tube.

[joesmotos]

I had a 750 once that idled like what you describe,turned out a couple of the float needle/seat assemblies were weak,it didnt leak fuel out the overflow but i think maybe the little springs inside the float needles were weak enough to just allow enough extra fuel to seep by to make the bike run richer on a couple of cylinders.after i replaced all 4 needle seat assemblies,there was no more problem.All the plugs burned the same and it idled clean.

Just an idea

[scottly]

It was a K7 750 in my case, that I bought as a parts bike. The 2 center carbs were overflowing when the seller tried to demonstrate the bike, and I used that as a bargaining chip. I originally suspected the floats had become less buoyant, but much later found the weak springs. If the carb bank is flipped upside-down, so the weight of the floats is compressing the springs, there is a significant difference in float height between 1/4 and 2/3. 

[joesmotos]

Yeah the flipping them upside down thing would be a indicator of what i was talking about..when i set float levels i usually have the carbs laying on their sides,with the needles just gently touching the float tang..i use one of those cheapie float level gauges from K&L or Motion pro(probably the same tool) that spans over the float and is adjustable..it has graduations on it but i also use a vernier caliper to double check the height..

[scottly]

The clear tube doesn't lie; it's the only true check of the fuel level in the bowls.

[BobbyR]

The clear tube method will tell you the actual fuel level in the bowls. I had a bowl that was lower than the others causing a popping on decel. When originally set up I had measured them and if they were brand new I suppose that would be it. I was able to sneak that bowl off and tweak it. recheck it and all is good.
The science of the clear tube method is sound, fluids seek their own level. It is a good check and prevents you from taking the whole rack down for no reason, or something simple. 

[Deltarider]

Found this great video:

https://www.youtube.com/watch?v=rRQ45lT2d3c

The guy in the vid doesn't know what he's talking about. What's the point trying to read impedance between HT lead and primary if the two in their original design aren't even connected?

[Honda-Rog]

This issue sounds very similar to mine on my CB500 -

http://forums.sohc4.net/index.php?topic=138656.msg1579451#msg1579451

- still haven't found the answer, done everything by the book.

Hope we get there in the end.

[TwoTired]

Found this great video:

https://www.youtube.com/watch?v=rRQ45lT2d3c

My question is...  To check the secondary coil, does the cap need to be attached to the end of the wire, or could he have done the test without the cap by putting the multimeter directly onto the wire?

Delta is correct.
This video is for testing single output coils.  SOHC4 coils are dual output and are tested differently.  Specifically, the primary and secondaries are isolated on our dual output coils.  If you diagnose our dual output coils using the method in this video, every single one will test bad, even if they function perfectly.

[Adam_F]

The clear tube method will tell you the actual fuel level in the bowls. I had a bowl that was lower than the others causing a popping on decel. When originally set up I had measured them and if they were brand new I suppose that would be it. I was able to sneak that bowl off and tweak it. recheck it and all is good.
The science of the clear tube method is sound, fluids seek their own level. It is a good check and prevents you from taking the whole rack down for no reason, or something simple. 

  If #1 repeatedly soots up, then fix the carb issue related to it; float height, dropped jet, emulsion tube, etc.

1+ Also, do a "clear tube" check of the actual fuel level in the float bowl. Setting the float height when the tang just touches the spring-loaded needle plunger assumes the spring has a certain tension. A weak spring will cause a higher fuel level in the float bowl, and the only way to check this is with the clear tube.

This makes a lot of sense.  I'm planning on checking the coils this afternoon, but either way, I will do the clear tube method to see if that spring is weaker than the others.  That would actually make a lot of sense as even when the bike was running really well, I always had some issues with #1 running a bit richer.  I've heard that aftermarket carb parts are garbage, so hopefully there are OEM replacements for those springs...?

Found this great video:

https://www.youtube.com/watch?v=rRQ45lT2d3c

My question is...  To check the secondary coil, does the cap need to be attached to the end of the wire, or could he have done the test without the cap by putting the multimeter directly onto the wire?

Delta is correct.
This video is for testing single output coils.  SOHC4 coils are dual output and are tested differently.  Specifically, the primary and secondaries are isolated on our dual output coils.  If you diagnose our dual output coils using the method in this video, every single one will test bad, even if they function perfectly.

Good to know.  Thanks for the great info Two Tired and Delta. 

This issue sounds very similar to mine on my CB500 -

http://forums.sohc4.net/index.php?topic=138656.msg1579451#msg1579451

- still haven't found the answer, done everything by the book.

Hope we get there in the end.

Yep!  Been watching your thread closely as it seems like our problems are very similar.  Lets figure this out!  Its summer and I just wanna riiiiiiiide 

[joesmotos]

The springs are actually made into the body of the little needle so theres nothing you can do but replace them.The needle and seat assemblies that i bought were generic,not OEM Honda..they worked just fine for me.Perhaps its the other parts that come in an overhaul kit that are suspect by many,i really dont know.Think i spent under 40$ for all 4 assemblies,but its been a few years..i think they were Keyster parts...

[scottly]

Don't bother checking the coils; you obviously have a carburetor issue. Ignition problems don't cause spark plugs to turn black. Fix the carb, replace any blackened plug with a brand new one, and see how the bike runs.

[billingstitan]

What it finally ended up fixing it was raising the needles by one notch. I thought they were in stock - and technically they were - only 77 CB550 came w both 42 and 38 slow jets, and mine happened to have 42 slows, which meant that stock was actually not center notch, but 2nd from the top.

Hmmm... Thanks so much for that.  From the look of your avatar, you have a 550k, correct.  I have the F and believe that we have different carb models (mine are the 069a).  Wonder if that would make any difference.  I've had the bike for a while and ran everything stock for years with no issues...  I'm going to try replacing the caps and checking coilds... and if all else fails, will take your advice and try moving the needles.

Hope you have some luck - and yes, I've got two 550k's.

Just to clarify - I'm not suggesting you change your needle height ... more just empathizing, and letting you know I got on the track of coil/ignition sleuthing after thinking I had tried everything on my carb (and in truth - I almost had - everything except the needles).

Anyway - I was certain it had to be in the coils or ignition because it was only a single cylinder being affected - when in fact it ended up being the carbs    I didn't even have any hope when I adjusted the needles - just was something else to try, and then, voila!

Just keep plugging away, bro - you'll get that AHA moment if you keep at it, then it will be that much sweeter when it's finally running right!! 

[Adam_F]

Just keep plugging away, bro - you'll get that AHA moment if you keep at it, then it will be that much sweeter when it's finally running right!! 

Thanks man.  I just clipped 1/4 inch of each coil wires and put in new NGK spark plug caps.  They're 5k ohm and my old ones were 10k....  Not sure what kind of difference that makes....  I don't want to jinx myself, but the bike is running great now!  Could be that I just had a case of the ol' weak spark.  Cheap and easy fix. 

I did notice that I have an air leak right where my muffler and headers meet.  I'm not sure exactly how the effects running conditions, but I'm ordering a new muffler gasket as we speak. 

Thanks again everyone for all your help and suggestions.  I'll report back if things go awry (fingers crossed).

[Adam_F]

Don't bother checking the coils; you obviously have a carburetor issue. Ignition problems don't cause spark plugs to turn black. Fix the carb, replace any blackened plug with a brand new one, and see how the bike runs.

I had a 750 once that idled like what you describe,turned out a couple of the float needle/seat assemblies were weak,it didnt leak fuel out the overflow but i think maybe the little springs inside the float needles were weak enough to just allow enough extra fuel to seep by to make the bike run richer on a couple of cylinders.after i replaced all 4 needle seat assemblies,there was no more problem.All the plugs burned the same and it idled clean.

Just an idea

Thanks guys.  After I clipped the cables back 1/4" and replaced the spark plug boots the bike ran perfectly for a few long runs.  Then the idle issue reappeared a couple days later.  I have new float needles and seats on the way, so I'll report back after those are installed.  While I have the carbs off (again), I'm going to figure out an easy way to do the clear tube method for checking the fuel levels.  My carbs 069A don't drain out of the overflow tubes, but rather a separate drain screw.  The float needles are really the last stop on my carb check list as I've really been through every other detail a few times now. 

[flybox1]

for your clear tube method, you'll need to heat and stretch a section of clear tubing, or cut it at a taper to jamb or twist it in the drain screw hole, before turning on your fuel at the tank.
the 350F drain is the same.

[goldarrow]

read here about clear tube checking float level.   i'm sure there are other easy ways too

http://forums.sohc4.net/index.php?topic=135470.25