Topic: Off idle hesitation 75 CB 550 K

[hereforever23]

Forgot to attach the image

[TwoTired]

Is it a trick of photography or does the rightmost tube have some enlarged bleed holes?   Would that one correspond the slightly leaner deposit spark plug?
Checked the holes with a drill bit shank?

Be sure to note any differences between the keyster slow jet emulsion tube holes and the genuine Keihin.

What float height setting have you set?   Dropping the fuel level should lean the entire operating range.

Is the annoying hesitation RPM specific or throttle position specific?

Is your fuel ethanol blended, or have any additives in it?

Valves adjusted per spec?  Timing at book value?  And, have you checked the advance curve?

[hereforever23]

Yes I think the middle holes on each side of the rightmost tube have slightly enlarged holes.  I don't have any small drill bits to check size right now.

The float height is at 22mm

Fuel has ethanol, 87 octane

Valves recently adjusted and spot on.  Timing and advance I should probably check since I had a shop do that for me in the fall and I never rechecked
Thanks

[hereforever23]

OK, so I rechecked and adjusted static timing- I don't have a strobe
Gap was set right but 2/3 was slightly retarded

I took the points plate off and cleaned up everything in there, regreased the cam and checked to make sure the advancer mechanism was working properly.  It was pretty clean and springs seemed in good shape- I am not sure how to check it beyond making sure it was springing back properly.

I cleaned out all the passages again really well with carb cleaner and forced air.  It seemed like there was a little debris in there that I missed the first time around but I'm not sure.

Also I scored the missing parts of the stock air box I didn't already have and put that all together with a foam UNI filter
I'm hoping once I get the OEM jets in there with everything returned to stock my problems will clear up...

[hereforever23]

Here's an update on my tuning-

I started with-
1975 CB550 K
4-2 exhaust
stock needle, 4th position from top
K&N mono filter
100 Keyster main jets
38 Keyster pilot jets

After thorough re-cleaning of carbs, set static timing, valve adjustment, synch-ed carbs , installed stock air box with UNI filter it seems to be running much better.  I think a combination of 2-3 timing slightly off, air passageways possibly being not sparkling clean & aftermarket jets was making the bike run a bit rich

Unfortuately now I am developing some oil leaks which I will start a new thread about

[hereforever23]

Another update-

After re-checking timing, valve adjustment, carb sync, bringing air filter and all jets to stock
I still have a bit of hesitation from idle after the bike warms up.  I am also getting some popping from the exhaust on deceleration.  There is a slight exhaust leak - I can feel some air coming from between the mufflers and the headers. I assume this is causing the popping on decel.

When I took the mufflers off I found there is no gasket or any material in the collar where the muffler slips over the headers.  I did not thoroughly check for leaking where the headers meet the cylinder head but I plan on replacing those gaskets when I seal up the leaks by the collar.  Was planning to just use Permatex ultra copper to create a seal.  Is there a cleaner/better solution?

Would the exhaust leak be causing the bike to run rich at idle thus causing the hesitation?

[TwoTired]

After re-checking timing, valve adjustment, carb sync, bringing air filter and all jets to stock
I still have a bit of hesitation from idle after the bike warms up.  I am also getting some popping from the exhaust on deceleration.  There is a slight exhaust leak - I can feel some air coming from between the mufflers and the headers. I assume this is causing the popping on decel.

Quite possibly.

When I took the mufflers off I found there is no gasket or any material in the collar where the muffler slips over the headers.  I did not thoroughly check for leaking where the headers meet the cylinder head but I plan on replacing those gaskets when I seal up the leaks by the collar. 

The crush gaskets used there, are usually copper colored, but blackened during use.  Point of a screwdriver should scribe the carbon to show copper.  The gasket must be dug out of the pocket for renewal.

Was planning to just use Permatex ultra copper to create a seal.  Is there a cleaner/better solution?

Permatex would be a hack, best employed after the apocalypse.  Buy some new crush gaskets.  ...and don't let the muffler system be supported only by the header flange bolts during assembly or they will crush unevenly and leak just as bad as before renewing if not worse.

Would the exhaust leak be causing the bike to run rich at idle thus causing the hesitation?

No.

Go back and reset the pilot screws.  These screws are adjusted to obtain smooth acceleration when the throttle is opened.

If the factory setting of 1 1/2 turns out from seated doesn't cure the hesitation.  The begin with them at 2 turns out and perform the following test.

Mark your throttle so you can determine the halfway twist point.
Operate the bike, select top gear, and ride a short distance so that the engine is at idle RPM. Snap the throttle to the half way point.  The engine should smoothly pick up speed without stumble or wheeze.   There won't be a lot of power or torque down that low in top gear.  But it should try to do what was commanded without complaint.  If it does stumble, then turn all the screws inward (022a carbs) about 1/8 turn and repeat the test recursively until you can get the desired response. 

If you turn the pilot screws in too far, you can grab more throttle than 1/2 twist.  But, then you run the risk of carbon fouling the plugs during periods of idle, and creating stumble from misfires during acceleration as the plugs clean themselves.

[hereforever23]

Was planning to just use Permatex ultra copper to create a seal.  Is there a cleaner/better solution?

Permatex would be a hack, best employed after the apocalypse.  Buy some new crush gaskets.  ...and don't let the muffler system be supported only by the header flange bolts during assembly or they will crush unevenly and leak just as bad as before renewing if not worse.

I think I was unclear.  I was planning to freshen up with new crush gaskets under the headers.  Then Permatex at the collar where the header meets the muffler.  There is no gasket here and I feel some leaking coming from this collar.  Not sure how I would otherwise seal up this point.

Go back and reset the pilot screws.  These screws are adjusted to obtain smooth acceleration when the throttle is opened.

If the factory setting of 1 1/2 turns out from seated doesn't cure the hesitation.  The begin with them at 2 turns out and perform the following test.

Mark your throttle so you can determine the halfway twist point.
Operate the bike, select top gear, and ride a short distance so that the engine is at idle RPM. Snap the throttle to the half way point.  The engine should smoothly pick up speed without stumble or wheeze.   There won't be a lot of power or torque down that low in top gear.  But it should try to do what was commanded without complaint.  If it does stumble, then turn all the screws inward (022a carbs) about 1/8 turn and repeat the test recursively until you can get the desired response. 

If you turn the pilot screws in too far, you can grab more throttle than 1/2 twist.  But, then you run the risk of carbon fouling the plugs during periods of idle, and creating stumble from misfires during acceleration as the plugs clean themselves.

Thanks, I will try this test and report back.

[hereforever23]

I did the test TT recommended and it seems that 1 1/8- 1 1/4 turns is a better setting than the 2 turns out that I had the air screws set at.  I was sure that it was running a bit rich off idle since the hesitation got worse as the bike warms up and to me it "felt" like a rich sort of blubbering.  Thank you very much for all your help, Lloyd

I've got the new crush copper gaskets installed now and sealed up the muffler collars. I'm giving it 24 hrs to dry and hoping to be running good as new now

[Bankerdanny]

You should not need a gasket or sealer between the clamps and the pipes. The flanged edge of the pipes seals against the crush washers. If you still have a leak after installing new crush washers the problem is there. The clamps only touch the outside of the flange, not the exhaust port. Sealing there doesn't do anything but make it harder to remove the clamps if you need to.

Our 550 carbs don't have an accelerator pump, there will always be a slight hesitation when opening the throttle until the fuel flow catches up with the airflow. This is more pronounced when you grab a big handful of throttle, but may be noticeable even if you roll it open smoothly.

[hereforever23]

You should not need a gasket or sealer between the clamps and the pipes. The flanged edge of the pipes seals against the crush washers. If you still have a leak after installing new crush washers the problem is there. The clamps only touch the outside of the flange, not the exhaust port. Sealing there doesn't do anything but make it harder to remove the clamps if you need to.

I did not add any sealant at the head.  The noticeable leaking was coming from the collars where the muffler meet the header.  So sealant was added only on the one header where I felt some leaking and found dark soot where it meets the muffler.

Since I already had half of the exhaust system off, I figured I might as well freshen up with new crush washers to make sure everything was healthy.

[Bankerdanny]

I didn't compose my sentence well. I meant sealant between the clamp and the flange.

If a new crush gasket doesn't fix the leak on it's own then you need to check the flange to make sure its intact and not excessively deformed, and the port itself and make sure that there isn't a crack or a piece of carbon or something preventing the washer from sealing properly against the port or the pipe flange from making a uniform connection with the gasket.

[hereforever23]

I think we are still talking about two different locations on the exhaust set up.  I am not talking about adding sealant anywhere near the flange or the clamp attaching the header to the head.  I'm talking about the other end of the header where it meets the slip-on 2 into 1 mufflers on each side of my Jardine 4 into 2 setup.

[Bankerdanny]

Oh, yes, we are talking two different points. Very poor reading job on my part as you were very clear about which point you were referring to.

[TwoTired]

...there will always be a slight hesitation when opening the throttle until the fuel flow catches up with the airflow. This is more pronounced when you grab a big handful of throttle, but may be noticeable even if you roll it open smoothly.

I must disagree with these statements.  And, I have several examples of CB550 that put up a good argument.

[hereforever23]

The hesitation has not gone away.

It comes on after the bike has warmed up for about 15-20 minutes and is from closed to about 1/8 throttle.  Once warm, I am also still getting some popping from the exhaust pipes.  When I make adjustments to the air mix screws starting from 2 turns out and going richer 1/8 turn at a time I can't be sure it is really getting any better.  When I get to 3/4 turns out it is really blubbery from closed throttle.  The bike pulls very smoothly at all other throttle settings.  It sort of feels like the fuel supply is starving off idle once it warms up.

Only today, it occurred to me that the fuel line routing might be an issue.  The bike is a 75 but the tank is 78 with a 78 petcock.  The petcock has one barb that goes to a T splitting into 2 hoses to the carbs.  The hose was sort of looping around, not a direct downward flow.  I tried shortening the hoses and getting them so that they only run downwards from the petcock to the carbs but that did not make the problem go away.  The fuel lines run relatively close to the cylinder head and get hot...I used the bracket in between the 2 holes where the fuel lines run into the carbs to keep the line back but the hoses still get hot.  There are no kinks in the fuel lines anywhere

[hereforever23]

I think I finally got rid of the annoying hesitation.

I took the carbs off once again and cleaned out all the passageways again.  I ran new fuel line as efficiently as I could to the petcock.  Set air screws at 1 1/2 turns out and put in new gapped plugs.  I also fitted the K&N mono filter back on.   I'm still getting a little popping on deceleration but the plugs look nice and tan and the bike pulls strongly and smoothly through all throttle settings.

[TwoTired]

Popping on decel is usually a lean idle setting, as that is where the slides are positioned during decel.

Try turning the pilot screws inward about 1/8 to 1/4 turn.  You should be able to grab more throttle for low RPM pickup as well.