Topic: Carb Servicing

[jimbo]

Some of you might remember, I brought a 74 CB550 back from the dead.  Well, I've never really been happy with the carb performance since I rebuilt them.  I have another set of carbs off that I'm thinking about giving another shot to rebuilding.  Any suggestions or tips?  Where I am now is, the bike is running way way too rich.  Choke doesn't even make a difference.  One cylinder is blowing wet.  I have to baby the throttle or it bogs down.  I actually thought about having our local Honda dealer do the rebuild but all they wanted to do is sell me a new bike.  I don't want a new bike, I like mine.    Here's a pic of what the carbs look like inside the bowls.

[damn_yankee]

Are you sure the choke is opening?

[TwoTired]

Carbs are sensitive to specific details.
In no particular order, here are some things to address during a rebuild.

All passageways must be clear and flowing for both fuel jets and the air jets.
The float height must be set correctly.
The float valves must operate properly.
All emulsion tubes behind the jets must be clear. (Often overlooked.)
They must be fed clean fuel without lumps larger than 0.016 inch.
The jets should not be damaged by random enlargement during cleaning.
The orings on the main jet and float valve body must be resilient enough to seal.
Each carb should have the same parts and settings as the others.
The air screws should be set for the same opening adjustment.
The air filter should be clean and free flowing.
The slides should be adjusted for the same opening on each carb.

Carbs are sometimes blamed for ignition or other mechanical issues.
All periodic tuneup items should be addressed before placing deserved curses on the carbs.

Tell us which of the above wasn't addressed in the last carb rebuild.

Why do you think a rebuild of another carb set will be more successful than your current ones?

Why don't people put their location in their bios?

Cheers,

[750goes]

TT,
I was just going to mention all that stuff... but not in the same way...

[dusterdude]

Carbs are sensitive to specific details.
In no particular order, here are some things to address during a rebuild.

All passageways must be clear and flowing for both fuel jets and the air jets.
The float height must be set correctly.
The float valves must operate properly.
All emulsion tubes behind the jets must be clear. (Often overlooked.)
They must be fed clean fuel without lumps larger than 0.016 inch.
The jets should not be damaged by random enlargement during cleaning.
The orings on the main jet and float valve body must be resilient enough to seal.
Each carb should have the same parts and settings as the others.
The air screws should be set for the same opening adjustment.
The air filter should be clean and free flowing.
The slides should be adjusted for the same opening on each carb.

Carbs are sometimes blamed for ignition or other mechanical issues.
All periodic tuneup items should be addressed before placing deserved curses on the carbs.

Tell us which of the above wasn't addressed in the last carb rebuild.

Why do you think a rebuild of another carb set will be more successful than your current ones?

Why don't people put their location in their bios?

Cheers,

because they are hiding from the fbi.

[clarkjh]

because they are hiding from the fbi.

For them its easyer to spend money and trace the IP address to your door.

Jimbo

Don't feel bad, I rebuilt my carbs over the summer, the bike is now in pieces for complete cleaning, painting, ect.  I plan on stripping the carbs again because I don't feel I did it right the first time.   That and I think I'll try to beat Bob W on how many times I can remove and install my carbs

James

[jimbo]

Carbs are sensitive to specific details.
In no particular order, here are some things to address during a rebuild.

All passageways must be clear and flowing for both fuel jets and the air jets.
The float height must be set correctly.
The float valves must operate properly.
All emulsion tubes behind the jets must be clear. (Often overlooked.)
They must be fed clean fuel without lumps larger than 0.016 inch.
The jets should not be damaged by random enlargement during cleaning.
The orings on the main jet and float valve body must be resilient enough to seal.
Each carb should have the same parts and settings as the others.
The air screws should be set for the same opening adjustment.
The air filter should be clean and free flowing.
The slides should be adjusted for the same opening on each carb.

Carbs are sometimes blamed for ignition or other mechanical issues.
All periodic tuneup items should be addressed before placing deserved curses on the carbs.

Tell us which of the above wasn't addressed in the last carb rebuild.

Why do you think a rebuild of another carb set will be more successful than your current ones?

Why don't people put their location in their bios?

Cheers,

I started out by disassembling all carbs, keeping them with thier respective parts in little bins.  One by one, I soaked them for about 48 hours in berrymans (man, that is some nasty stuff)  After removing them from the soak, I sprayed them out with spray carb cleaner then, blew them out with forced air.  I bough kits from partsnmore which contained bowl gasket, all jets and needle valve and slide needle along with air mixture screw.  I installed all new parts (except floats).  I adjusted all floats (Can't remember the height I used) and reinstalled.  Once reassembled, I adjusted the air mixture by bottoming out the screw, then backing it out 1 & 1/4 turns.  Once all 4 carbs were cleaned, I bench synced them by using a 1/4" drill bit.  I adjusted the idle screw to where the very left carb would just barely scrape the drill bit when inserted.  One by one, I adjusted the remaining three until all were within the same gap.  Then, I backed my idle back in so it woundn't run away when I started it.  I installed a new air filter and fuel lines.  Also installed new plugs and adjusted the valves.

At first, it would start on it's own after some cranking and run rough.  It would smooth out a little as it warmed up.  I never was able to use the choke effectivly.  It would make no difference at all as to the starting of the bike.  Once running, if I over accellerated, it would just bog down and I would have to clutch in and rev a little and let her catch her breath before continuing on.  Thinking there may be a problem with my new air filter, I removed it to see if it did any better but it really didn't make a difference.

Now, it won't start unless I give it a shot of ether before I try.  Without the ether, it will run the battery down and still not start.  It will crank and almost catch but never fully hit.  Once started, it will run about the same as always.

The set of carbs that I am going to try next are the orginal carbs off the 74 engine.  The ones I rebuilt first were off of a 76 550 but I didn't think it would make a difference.  Now, I'm not so sure.

One thing I did not do was sync the carbs on the bike with a set of gauges.  It was running so poorly, I didn't think it would make a diffence.

One cylinder has always blown wet out of the pipe.  I believe it is fuel.  Bike also smokes like it is too rich.  I did test each spark plug to see if it got fire and all 4 cylinders sparked when I removed them and grounded them.

I was thinking about converting to electronic ignition to see if that helps but, I think I'm getting good fire.

Whew, that is a lot but that is everything I know or remember about my situation.  If I've missed something, let me know.  I'm a fair car mechanic but this has me whooped.  I greatly appreciate any advice.

[jimbo]

Are you sure the choke is opening?

Yea, I can see the butterflies move when I move the choke lever.

[TwoTired]

Okay, much better description.  Here's a few things.
You may have more than one problem now since symptoms have recently changed.

Note that a rich running engines will deposit soot onto the plugs.  When the center electrode insulator gets enough carbon on it, the spark follows the carbon path instead of jumping the gap.  Sometime there will be a very tiny spark between the electrode and the carbon path but it is really not enough to properly ignite the gas mixture.  Might be for ether, though.  Much lower flashpoint.

I noticed no mention of emulsion tube cleaning.  The slow jet has it attached, so the replacement should be clean.  But, the one behind the main also must be clean as it adds air to the mix before going to the slide needle and into the carb bore.  If this air supply is shut off by plugged emulsion tube holes or preceeding air jet, it could cause rich running.

The idle screw's factory settings assume an engine with stock exhaust and filtration.  If these are aftermarket items, most likely the idle screws will need to be differenet than the factory.  These are most effective for closed to 1/4 throttle openings as is the entire slow jet system.  so don't expect much mixture impact from the slow or air bleeds once the throttles are opened past 1/4 of the overall opening.

For 1/4 to 3/4 throttle openings the main needles dominate the mixture settings (The emulsion tubes are ahead of these).  Not all slide needles have the same diameter or taper profile.  If your "kit" supplied new ones did they have the same dimensions as the old ones?  If not, you can, at least, expect to hunt for the correct needle height position to give you correct mixtures for the midrange operation.
You didn't say what needle height you selected during the rebuild.

Might be nice to know how the carbs were originally set up.  On each carb body mount flange, top right side, there is a stamping for set up.  I am aware of 627B, 022A, and 069A.  Are both your sets the same?

Float height, if set for too high a fuel level, might allow raw gas to flow into the carb bores.  If excessive, the cylinder won't fire and will simply pump the gas into the exhaust.

When the bike does run, do all the exhaust head pipes feel the same temp (flash touch).  Colder ones point to problems with that cylinder/carb, so you can narrow your focus.

Any chance of getting compression test numbers?

Cheers,

[jimbo]

Okay, much better description.  Here's a few things.
You may have more than one problem now since symptoms have recently changed.

Note that a rich running engines will deposit soot onto the plugs.  When the center electrode insulator gets enough carbon on it, the spark follows the carbon path instead of jumping the gap.  Sometime there will be a very tiny spark between the electrode and the carbon path but it is really not enough to properly ignite the gas mixture.  Might be for ether, though.  Much lower flashpoint.

I noticed no mention of emulsion tube cleaning.  The slow jet has it attached, so the replacement should be clean.  But, the one behind the main also must be clean as it adds air to the mix before going to the slide needle and into the carb bore.  If this air supply is shut off by plugged emulsion tube holes or preceeding air jet, it could cause rich running.

The idle screw's factory settings assume an engine with stock exhaust and filtration.  If these are aftermarket items, most likely the idle screws will need to be differenet than the factory.  These are most effective for closed to 1/4 throttle openings as is the entire slow jet system.  so don't expect much mixture impact from the slow or air bleeds once the throttles are opened past 1/4 of the overall opening.

For 1/4 to 3/4 throttle openings the main needles dominate the mixture settings (The emulsion tubes are ahead of these).  Not all slide needles have the same diameter or taper profile.  If your "kit" supplied new ones did they have the same dimensions as the old ones?  If not, you can, at least, expect to hunt for the correct needle height position to give you correct mixtures for the midrange operation.
You didn't say what needle height you selected during the rebuild.

Might be nice to know how the carbs were originally set up.  On each carb body mount flange, top right side, there is a stamping for set up.  I am aware of 627B, 022A, and 069A.  Are both your sets the same?

Float height, if set for too high a fuel level, might allow raw gas to flow into the carb bores.  If excessive, the cylinder won't fire and will simply pump the gas into the exhaust.

When the bike does run, do all the exhaust head pipes feel the same temp (flash touch).  Colder ones point to problems with that cylinder/carb, so you can narrow your focus.

Any chance of getting compression test numbers?

Cheers,

Sorry for the delay in replying.  Darned work.    Thanks for the detailed reply.  As for the spark plugs, you're dead on.  I am getting heavy soot deposits so that even further confirms my rich condition.  The first set I put in were Champions but I read hear that they were not real well liked in the SOHC/4 so I went back to the NGK.

I did replace the slow jet but I'm not sure about the emulsion tube behind the main jet.  I wasn't too happy with my carb soak.  I used Berrymans and let each carb soak for a couple of days but even then, I still had a good bit of varnish still on them.  They even felt a little slimy afterwards.  I used a spray cleaner to finish them up after the soak.  I've since read about a carb cleaner by Yamaha that people claim does a much better job.  If I do pull them back off, I may use it instead.  I remember back in the day, I used to be able to get a real good cleaner but alas, the EPA has regulated it back to the weaker stuff out today.

I am running the factory airbox with the original 4-4 exhaust.  When I did the rebuild, the original needles were set to the middle notch.  I used the same on the new ones.  I can't remember the numbers on the needles but I believe I still have the old ones, I'll check on that.  You know, it would be nice to be able to get at the needles with the carbs on.    If you know a trick for this, I'm all ears.  I'll check the numbers on the flanges tomorrow and post them.  I haven't done a compression test yet but I may try to pick up a guage and grab the numbers tomorrow while I'm out working on it.

You've given me a few things to check so I'll get busy on my homework and post the results.  I have another engine in storage with only 7000 miles on it.  It's the engine out of the 76 that the carbs came off of.  The last time I checked it out, it cranked over real nice, no odd noises or anything.  I may clean my spare carbs up and try them on this engine.  It would be nice to have a running engine spare just in case I needed it.

Thanks again!!!

[mrbreeze]

Check your float bowls.Turn the petcock on...go in the house grab a brewski or whatever.Come back out and turn the petcock off.Now get a small jar and drain each bowl one at a time.You are looking to see if you have the same amount of gas in each bowl.Even if you set the floats to spec,I have seen situations where 1 or 2 carbs are getting too much fuel.If you did everything else that Too Tired said...You should at least be in the ballpark for it to run.Good luck dude.

[tatanka]

Something I read on the HondaChopper Board for cleaning the carbs....boil them in lemon juice!
Don't have to disassemble and won't eat up rubber parts. You can do this with the complete rack or single carb.

Place in longated pan for (complete rack) or small pan (for single).  Put in enough juice to cover carb and let begin boil. Add carb/s and boil for 30 min.  Remove carbs, rinse with water, blow out all passages and body.
Was told that it works great.
I'm gonna give it a try, can't hurt anything.

tatanka

[Bob Wessner]

This is a new one. Interesting, you will have to let us know how it goes. I would guess the rinsing should very thorough to remove any residual sugars. Also assuming the lemon juice should be pulp-free. 

[theunrulychef]

As an added bonus, you can poach a side of salmon while you're cleaning your carbs - just add a bay leaf & some peppercorn. 

We used to use lemon juice & salt to bleach wood work surfaces in a kitchen I worked at.  I wonder if adding salt would help the action of the lemon juice?  Please let us know how it goes as I really hate the caustic stuff & I still have something in my slows.

Also, I would do this in the garage as the smell of boiling lemon juice for 30 minutes will be pretty strong.

[SteveD CB500F]

That much lemon juice probably costs more than carb cleaner!  (unless you live where the lemons grow...)

[Frankenkit]

Any new news on how this worked?  I'm not too excited about using heavy duty chemicals on my carbs if I don't have to...