Topic: Calling on Plug Readers

[BrickWoll]

All,

Just put brand new NGK D7EA plugs in my '77 CB550K3 in the latest effort to diagnose why it's still not running smoothly after timing and vacuum sync looked dead on.  Pulled them immediately after a 20 min ride.

Clearly #4 is fouling (wet), but it looks like all are blackening more than they should be after one ride. 

Setup:
Jets: 42 / 110
Fuel Screw: 1 turn out.
Intake: Pods (filtered breadbox with velo stacks on order)
Exhaust 4 --> 1

Where should I look for #4 issues when all carb settings are the same?  Anything else look like trouble?

Greatly appreciate any thoughts.

[PeWe]

Carb 4 can have a floading float. Clear tube procedure will tell. Fuel level should be ca: 2-4 mm under bowl gasket.

[pjlogue]

A #42 slow jet is on the rich side but what is more important is where your needle height is.  Should be 2nd-3rd position from top of needle.  As Peewee said, check your fuel  level height with clear tube as well.

The idle air screw is also very important.  It is relevant for much more than just idle.  As the throttle is opened the idle air screws % contribution drops off.  Even at 1/4 throttle it is contributing a fair % of the mixture to the engine.  At 1/4 throttle you are getting into interstate speeds.

Check for intake air leaks on # 4.  (you should check ALL intake boots for leaks)  with the engine warmed up and idling spray carb cleaner around each rubber seal.  Carb to rubber and rubber to intake spigot.  A change in idle will indicate an air leak.  An air leak will cause that cylinder to run rich.  (opposite of conventional thought)

-P.

[BrickWoll]

Carb 4 can have a floading float. Clear tube procedure will tell. Fuel level should be ca: 2-4 mm under bowl gasket.

Thanks PeWe, I've done the clear tube many times on these PDs, but one more couldn't hurt.  I've finally come to a place where none are leaking, so I'm confident fuel level in 4 is not too high.  Clearly floats / needles are among the things that could differ between each carb so worth another look.

A #42 slow jet is on the rich side but what is more important is where your needle height is.  Should be 2nd-3rd position from top of needle.  As Peewee said, check your fuel  level height with clear tube as well.
The idle air screw is also very important.  It is relevant for much more than just idle.  As the throttle is opened the idle air screws % contribution drops off.  Even at 1/4 throttle it is contributing a fair % of the mixture to the engine.  At 1/4 throttle you are getting into interstate speeds.

Check for intake air leaks on # 4.  (you should check ALL intake boots for leaks)  with the engine warmed up and idling spray carb cleaner around each rubber seal.  Carb to rubber and rubber to intake spigot.  A change in idle will indicate an air leak.  An air leak will cause that cylinder to run rich.  (opposite of conventional thought)

-P.

Thanks. Forgot to mention needle is at position 3.  If that was an issue, wouldn't all plugs show the same rich condition?  Air leak is a good thought.  Boots are new and soft.  Manifold rings are also new from a recent top-end rebuild.  A quick spray test should reveal any issues.  I'm particularly focused on the idle screws.  On the PD46A it's on the engine side of the carb.  As I understand it, it works the OPPOSITE of an air screw on the filter side: restricts fuel flow, not air flow.  I'll keep at it.

[TwoTired]

Have marked your throttle so you can note which fuel metering device is dominant?
The main jet controls mixture from 3/4 to WOT.  The slide needle diameter and taper angle dominate mixture from 1/4 to 3/4 throttle position.  (You can make a gross adjustment of this with clip position in the slides.) The pilot circuit dominates mixture from idle to 1/4 throttle position.  You may have used all three circuits during your ride with a combination of too rich to too lean or just right for any of the metering devices.

Certainly, number 4 shows an aberration that needs a correction first. Quite possibly a float level issue, or even a choke plate not synced with the others, runner leak, emulsion tube blockage, even a cam or valve issue.  The carbs are the last thing to tweak AFTER all the mechanicals are verified and the entire 3k tuneup schedule is performed.

Then you do a Dyno or test track procedure to find what carb circuits at given throttle positions either show on the exhaust sniffer or deposit patterns show up on the spark plugs.
You do know this hunting for correction is a direct result of your engineering change to intake and exhaust, right?

Are you willing to pay dyno fees?
Do you have a test track where you can safely wail on the motor and a supply of fresh clean plugs to read after each run at specific throttle positions?

Or do you expect to make random changes to main, needle, and pilot circuit, to stumble upon something you can live with?

Cheers,

[BrickWoll]

Have marked your throttle so you can note which fuel metering device is dominant?
The main jet controls mixture from 3/4 to WOT.  The slide needle diameter and taper angle dominate mixture from 1/4 to 3/4 throttle position.  (You can make a gross adjustment of this with clip position in the slides.) The pilot circuit dominates mixture from idle to 1/4 throttle position.  You may have used all three circuits during your ride with a combination of too rich to too lean or just right for any of the metering devices.

Certainly, number 4 shows an aberration that needs a correction first. Quite possibly a float level issue, or even a choke plate not synced with the others, runner leak, emulsion tube blockage, even a cam or valve issue.  The carbs are the last thing to tweak AFTER all the mechanicals are verified and the entire 3k tuneup schedule is performed.

Then you do a Dyno or test track procedure to find what carb circuits at given throttle positions either show on the exhaust sniffer or deposit patterns show up on the spark plugs.
You do know this hunting for correction is a direct result of your engineering change to intake and exhaust, right?

Are you willing to pay dyno fees?
Do you have a test track where you can safely wail on the motor and a supply of fresh clean plugs to read after each run at specific throttle positions?

Or do you expect to make random changes to main, needle, and pilot circuit, to stumble upon something you can live with?

Cheers,

Thanks for the detailed response, TwoTired.  Agreed, I used all circuits during the test ride, making discerning which was causing the rich condition impossible.  I appreciate the suggested order of diagnostics. 

RE: "You do know this hunting for correction is a direct result of your engineering change to intake and exhaust, right?" - I purchased the bike with the exhaust and pods so while I didn't initiate this design change, I accept it.  I have also learned much about the perils of these changes from this forum.  I am changing out the pods for a filtered breadbox to get closer to the orig intake for this reason.

RE: "Are you willing to pay dyno fees?" - Absolutely, if it helps me understand how to pinpoint the issue.

RE: "Do you have a test track where you can safely wail on the motor and a supply of fresh clean plugs to read after each run at specific throttle positions?" - I do! But not likely an option for me.  I will have to exhaust more diagnostic methods before taking this step.

RE: "Or do you expect to make random changes to main, needle, and pilot circuit, to stumble upon something you can live with?" - Nope.  I wouldn't be on here if random changes were of any interest.  I'd like to think every change I've made is a result of information I've received here or elsewhere.  I've certainly come across results that I don't understand, but this only prompts more investigation and testing.  With the help of posts like yours and others, I'll get there!