Topic: gas overflow belching after idle 76 cb 550

[KevinD]

So, I picked up this cb550 4 months ago and have been taking it out every weekend riding two to four hours a weekend.  The bike sat for a couple months from the time I bought it till I started riding that much.  I had no idea that a sitting bike can screw up the carbs (receipts show that it had a carb rebuilt a couple months before purchase).  I switched the exhaust after purchasing it from a four into two to a four into one.  Besides that just an oil job and spark plugs.  The bike was running rough (power fluctuation from four to seven grand on the rpm) so I am not sure how much the pipe conversion can contribute to the rough running.  Anyway, I have been doing a heavy rotation of seafoam trying to avoid another 500.00 carb re-clean.  Tonight the bike sounded perfect on the idle and I am hoping for the best on the seafoam carb treatment but what has been happening since I bought the bike is that after it idles I let it set for a min without shutting off the fuel and half the times it will beltch a few ounces of fuel after I shut off the engine through a single carb drain hose.  I am wondering what all of this may point to.  I have only done around 30 miles since the seafoam but have been idling it after work every day with heavy seafoam in the gas for around 5 min each day.  Any info on my approach and the gas beltch would be greatly appreciated.  Thanks for any and all info in advance.

[mrfish2]

If you have gas pissing out of the overflow tube them that means you have a stuck float, a stuck float needle, or the o-ring around the float seat isn't sealing off like it should. Take the bowl off the offending carb (assuming this is only happening to one carb) and verify that everything is moving like it should. Pictures of this would help tremendously.

[KevinD]

Thanks Mr Fish for the reply.  Whats odd is that it belches a couple ounces than that's it.  It seems like the flow would keep rolling until I shut off the petcock.  Anyway, I have had to tap that carb on the bottom to get it to fire in the past (chekcing the pipes one was cool so a tap on the carb and all good) the seafoam has resolved that issue.  I was thinking maybe if it were a float needle sticking the seafoam could resolve that as well?  Wishful thinking?  I am trying to avoid removing the carbs if possible and approaching the bowl from the bottom sounds like a bad idea.  Any other ideas on the whole of the initial post about power fluctuation.  I just am having a hard time facing the fact that a couple months sitting after a full carb rehaul will destroy the carb system again with out any other resolve other than coughing up a few hundies more.  Maybe I am living in denial.  I am going for a long ass ride tomorrow to try to run this carb cleaner though.  Oh yeah one other thing it was having an issue of stalling out once a ride when pulling the clutch in and during down shift while not feeding gas for stop.  Started right back up but nerve racking for a newb.

[RAFster122s]

Changing the exhaust would affect your carb tuning at least a little , if not a lot. It depends upon the pipe design.  It sounds like the mixture is way off in the mid-range. If you are going to own a 70s bike you are going to have to either learn how to maintain it, or find someone who can do so. So, you have to decide if you can afford to have others handle the repairs.

I would recommend that you pull the carb rack and be certain of the jets in the carbs as well as bench sync on your carbs. It sounds like your float or float valve is sticking.  It may be fouling on a gasket for the float bowl or assembled incorrectly. 
If you are running lean a long hard ride could cause damage.  Depending upon your definition of hard riding.  SeaFoam can help carbs that are properly adjusted and hrlp stabilize the fuel and aid in carb health. Problem is that your carbs aren't.
You don't wanna have to tear down the motor because you ran it excessive lean and holed a piston or siezed the motor from overheating caused by running too lean.

Check the timing and points adjustment and the dwell setting to see that it is set correctly.  You also should check the valve lash to see if it is contributing to your issues.
Plug chop with new plugs to get a reading of the burn to see if it is lean is advised. You are going to need several new sets of plugs to check the reading after adjusting things systematically.

David

[Deltarider]

I would recommend that you pull the carb rack

Not necessary to fix a float. As a matter of fact on these oldstyle Keihins you can do all carb maintenance with the rack in situ. Just take your time and do it in the right mood. If you've done it once, it is pretty easy to do. In this forum people are pulling racks like mad.
Tip: If you have the bowl(s) removed, on assembly replace the screws by little ss allen screws. So much easier. Everything you do here after removing the bowls (floats, main jets, pilot jets, emulsion tubes) does not require synchronisation afterwards,
BTW, which carb is pissing gas?

[KevinD]

Delta I believe the carb that is doing the brief gas vomit is the third.  Thanks for the heads up and info RAF. 

[RAFster122s]

Delta, he's already been told once to pull the offfending carb bowl and he doesn't want to do that or pull the rack. So, he can choose to try and fix it with SeaFoam when it requires a visual inspection.  So, unless he has xray vision he will continue to have issues until they kill the motor. 
Pulling a bowl is possible and common with the carbs still in place, saves you from fighting old stiff carb to intake boots. Unless they are new.

[Deltarider]

Delta I believe the carb that is doing the brief gas vomit is the third.  Thanks for the heads up and info RAF.

 I was hoping it was #1 or #4. I personally would do it like this. Remove #4 bowl and it's float and then move on to #3. Keep parts of each individual carb separated.

For who is interested, below you'll find the directions for a complete inspection.
1. Unscrew the 4 floatbowl screws (later to be replaced by same size allen screws)
2. Pull floatbowl carefully downwards in a straight line. If you number the floatbowls 1,2,3 and 4, you can use them as containers for all the brass parts of that particular carb.
3. Remove springleaf
4. remove float by carefully(!) extracting it's swingpin. Do not exercise force. Some manage to break their whatever it is called (towers?). If the swingpin is hard to extract, spray some WD-40. Caution: whilst removing the float, have your free hand cupped under it to collect the tiny floatneedle that will fall down. Don't loose it! They are expensive.
5. Pull the main jet using your thumb and finger. Some wiggling does it.
6. After removing the main jets twist the throttle wide open in order to raise the needles and with your free hand insert from below a match or wooden toothpick into the needle jets (aka emulsion tubes). When that is snug in the needle jet, cant or turn the wooden toothpick a mm or so and you can wiggle the emulsion tube out easily. Some WD-40 at forehand can help. Essential in this procedure is that you open the throttle to raise the needles. BTW, sometimes the needle jets just drop by themselves after the main jets is removed so start with your hand cupped under it.
7. use a small screwdriver 'slid in sideways (horizontally)' to unscrew the slow jet. Think first and make sure you turn it in the right direction. Gently!
8. All parts go in 1,2,3,4, numbered floatbowls or little containers
9. Now all parts can be inspected and cleaned. Also carefully inspect the tiny O-rings that seal the main jets.
10. The airscrews (in the sides of the carbs) can be removed at all times. Caution: do not loose the little spring under them. On these carbs they don't have tiny O-rings.
11. Back to the carbbodies. Use a can carbcleaner with a straw and spray from below the carbbodies upwards in all it's orifices. Don't forget the openings where the airscrews sat.
12. Install in reverse order. Do not overtighten the slow jets!
13. Install floatbowl using new little allen screws instead of the old dreadful crosshead screws. Much easier for future removals.

You need to be at ease and well concentrated. Don't hurry. On a CB500 carb #1 and #2 are a bit harder due to the presence of the clutchcable. Make it a Zen exercise (that's how Soichiro designed motorcycles, with Zen). I can do it blindfolded and after the first time so can you.
This method can be exercised with 022A, 069A, 087A, 627B, 649A carbs.

[becken]

IF you should decide to pull the carburetors, replace the o-rings between the head and the intake manifolds. They will harden and leak after time. It would be a good time to install new rubbers between manifolds and carburetors. This won't help your overflow problem, but may head off future problems IF you decide to pull the carburetors.

[KevinD]

Thanks Delta.  I will check out the process of going through four to get to the third and follow your notes.  I do have a clymer manual (which I have heard is crap really) and you tube to fill in most questions.  Thanks again.   I have no problem pulling a couple carb bowls to fix the issue.  Although "I have already been told once" I do feel I know my limitations at this point and a full carb removal, breakdown, clean and re-assembly, sync and plug chop and adjust is a little past my current comfort level, patience and tool set.  I have read a ton of posts where people are ready to throw in the towel due to weeks of trouble shooting that does not pay off when it comes to problematic carbs.  Perfect riding weather is here in AZ and I want to get in some riding.  Sometimes, just sometimes, it is a simple fix that someone has dealt with and can share, other times you pay a professional.  I was thinking of buying a cheap bike in the  near future to do a full tear down to gain some knowledge gradually (riding should be part of this equation as well, right).  Thanks again for all the info!

Becken you posted while I was typing this.  Thanks for the heads up and I will reveiw ALL of this when I do attempt a carb rebuild in the future = thanks again.

[harisuluv]

Where in arizona are you? (Tucson here)

[KevinD]

I am in PHX - Tempe.  So, just got back from a three hour ride.  I am a nube so bare with me.  The bike seemed to run great today.  The thing I found is that going from 6k rpm to clutch pulled in just downshifting it stalled once.  I found that letting the rpm drop with speed down around 4k then clutch would allow the engine to go to a good 1.5 k idle.  Is this the norm (lowering the rpm instead of balls out to clutch while just downshifting?).  I only have around 600 miles on this thing since I picked it up.  So far I have redone the shock seals, put on a lower profile bar (it was steel but had to do the drill and re-run of the electronics). Switched the pipes from a four to two - to a four to one (new crush gaskets) with a short muffler that definitly raises the decibles but seems to sound good (It is a 9" carpy muffler with very little in the way of a baffle large exit port)  I have heard a little light popping on deceleration but nothing like a backfire.  Replaced the stock brake lines to a steel braided line (seems like decent stopping power) and a new seat.  Since I have not ridden anything else I am not sure what to compare it all to.    Oh yeah no gas beltcing anywhere on the ride today.  As I have said multiple times and will continue - thank you guys for the info and trust me once I get more tech knowledge under my belt I will be sure to post more on the responses other than questions but considering the knowledge available here I will leave it to the pros for a while.

[harisuluv]

You might want to do a vacuum sync and see if that helps. 

[Deltarider]

Becken you posted while I was typing this.  Thanks for the heads up and I will reveiw ALL of this when I do attempt a carb rebuild in the future = thanks again.

Most important is to be in the right mood (Zen and the Art of Motorcycle Maintenance, remember?).
Sometimes I must say to myself 'better not now' when there's is maintenance to be done, like when I'm stressed or in a hurry. I then postpone it to the moment I'm calm and have plenty of time. So if you unscrew #4 carb for the first time, take your time, concentrate and act without haste and do each step carefully. The parts involved are small and delicate but it is a very good exercise. If you feel you become nervous or irritated, stop, have a rest and/or a coffee. If you do it right, you'll feel like a succesful surgeon. Learning can be so rewarding.

[KevinD]

Hey Deltarider, Did you post a video on YouTube where this is the starting point to all mechanical approach to these bikes is reading "Zen and the Art of Motorcycle Maintenance".  I have been going through those videos and they are great for people new to bikes.  I am picking up the book for sure.  Very cool.  If you were not involved with the vids thanks for the reminder on the book.  As I said earlier since I do not want to be down a long time I am thinking of picking up another bike to test and figure things out.  This site, repair manuals and you tube definitely brings this to a possible hobby that is pretty realistic and enjoyable. 

[Redline it]

Delta I believe the carb that is doing the brief gas vomit is the third.  Thanks for the heads up and info RAF.

 I was hoping it was #1 or #4. I personally would do it like this. Remove #4 bowl and it's float and then move on to #3. Keep parts of each individual carb separated.

For who is interested, below you'll find the directions for a complete inspection.
1. Unscrew the 4 floatbowl screws (later to be replaced by same size allen screws)
2. Pull floatbowl carefully downwards in a straight line. If you number the floatbowls 1,2,3 and 4, you can use them as containers for all the brass parts of that particular carb.
3. Remove springleaf
4. remove float by carefully(!) extracting it's swingpin. Do not exercise force. Some manage to break their whatever it is called (towers?). If the swingpin is hard to extract, spray some WD-40. Caution: whilst removing the float, have your free hand cupped under it to collect the tiny floatneedle that will fall down. Don't loose it! They are expensive.
5. Pull the main jet using your thumb and finger. Some wiggling does it.
6. After removing the main jets twist the throttle wide open in order to raise the needles and with your free hand insert from below a match or wooden toothpick into the needle jets (aka emulsion tubes). When that is snug in the needle jet, cant or turn the wooden toothpick a mm or so and you can wiggle the emulsion tube out easily. Some WD-40 at forehand can help. Essential in this procedure is that you open the throttle to raise the needles. BTW, sometimes the needle jets just drop by themselves after the main jets is removed so start with your hand cupped under it.
7. use a small screwdriver 'slid in sideways (horizontally)' to unscrew the slow jet. Think first and make sure you turn it in the right direction. Gently!
8. All parts go in 1,2,3,4, numbered floatbowls or little containers
9. Now all parts can be inspected and cleaned. Also carefully inspect the tiny O-rings that seal the main jets.
10. The airscrews (in the sides of the carbs) can be removed at all times. Caution: do not loose the little spring under them. On these carbs they don't have tiny O-rings.
11. Back to the carbbodies. Use a can carbcleaner with a straw and spray from below the carbbodies upwards in all it's orifices. Don't forget the openings where the airscrews sat.
12. Install in reverse order. Do not overtighten the slow jets!
13. Install floatbowl using new little allen screws instead of the old dreadful crosshead screws. Much easier for future removals.

You need to be at ease and well concentrated. Don't hurry. On a CB500 carb #1 and #2 are a bit harder due to the presence of the clutchcable. Make it a Zen exercise (that's how Soichiro designed motorcycles, with Zen). I can do it blindfolded and after the first time so can you.
This method can be exercised with 022A, 069A, 087A, 627B, 649A carbs.

you know what's really strange, i had the parts all in little bins buried under tools for 4 years (because a slide got stuck from sitting 5yrs before that,)I pulled the stuck slide carb off and broke into another bank of carbs to replace it. Bench testing the float levels, took 20 times of removing bowls and just slightly changing the float lever, cleaning the seats and jet, it'd have one carb overflowing then that carb would get no flow 20 times they'd rotate in which wasn't working. Or they'd appear to be set, I'd put them on and one would be stuck open, or not getting any gas. After a month... The 21st try I poured all the parts in a pile, and randomly picked all jets and floats out of 8 carb sets and eyeballed, no measuring the now changed floats, I was out of my mind insane, ready to give up and put them in the recycle can bag, and they worked, just like that. Onto bench sync like the manual says for open throttle measurement, because I added a strange carb, put the carbs back on, it ran like crap, tried it again it ran like crap. top linkage for the one carb was way different than the other 3, and at the bottom stop the one was way off. The top was in specs. Instead of using the drill procedure, I tried it again with just eyeballing the sunlight gap and got it as close as I could in one try, put it on, ran excellent. I have no idea, why, or how.