Topic: CB500 carburetor - Found what was broken and why I can't pass emissions (PICS)

[seventythreecb]

Bike: 71 Honda CB500 - airbox gone, 115 jets on open pipes. #$%* of a PO.
I tried to pass emissions and have failed.  Always toooo rich. A friend helped me take off and open up my carbs. Low a behold I found what is pictured below. The stem of the #3 carb sat for too long with gas and deteriorated. 

I need the help of this gigantic community to figure out what to do.
1. Replace carbs with brand new set.... I'm broke and spent all my money fixing what the PO did to this bike.
2. Replace #3 carb..... Would it be smart for a relative novice to break these carbs apart and replace the #3 carb with a spare carb i have?
3. Just replace all the jet with 110 and try emissions again... I think the #3 carb will cont to suck up as much gas as the bowl can hold.

[MoMo]

It looks as though gas will seep around the O-ring so either get the carb body repaired or replace it with the one you have. It is not all that difficult to do, take your time and some photos before...Larry

[haill]

jb weld the stem and jet back in place together.
 set all the floats to 22mm be very accurate with the set-up of the floats for they really affect the mixture.
 ride it for the season.
find yourself some new carbs when you can afford.

[motosan]

In my opinion being able to inspect carb parts is a great basic skill.  There are LOTS of information in this forum about how to take these carbs apart.  It's easy, just follow the steps and take photos if you feel uncomfortable.

It might also help if you can provide exactly what you have done to the bike to "fix what the PO did", in addition to the general condition of the bike performance.

Is the bike running fine?  (i.e. doe it idle steadily?  does it hesitate? when does it hesitate? does engine sound fine?)  How did you find it was running rich?  What are the colors of all spark plugs?  Oil leakage anywhere?  Vacuum leakage anywhere?  Do all 4 headers get equally hot?  any weird sound?  Are the carbs synchronized?   Has it gone though the basic maintenance?

Check all the jets to see if there are no clogs, the float height are done correctly, and if the float actually floats also.  I might be wrong but if the #3 was indeed running way too rich, the bike's general performance would be noticeably "less than optimal"......

   

[flybox1]

JBWeld it if you want to have to do it right/again later because it broke again, or pieces of it have clogged your carb.
Or...
Contact forum member harisuluv and see if he has another #3 carb that you can put in there...and be done with it

[RAFster122s]

I think I would want to make the jet removeable so it could be salvaged when the body is recycled.
If it is a Kiehlin jet it is worth saving if undamaged.

[Jerry Rxman Griffin aka MuthaF'er]

Looked hosed to me.

[Bankerdanny]

Since you have the spare carb, swap it out. It isn't that hard.

Take pictures before you pull the carbs off the rack and maybe a few drawing to help you remember which tubes and srews go where.

Take your time and it should be an medium difficulty weekend project.

[HondaMan]

This is like detective work, but will solve it for the short term: the O-ring on the mainjet is a 1.0mm cross-section (I think the whole size is 4.0x1.0mm). See if you can find one that is a 1.1mm or 1.2mm thicker O-ring. This will seal up the gap for a while. This would then be one of the following sizes:

4.1 x 1.2mm
4.1 x 1.1mm
4.0x1.1mm
4.0x1.2mm (tough to fit, will be a real squeeze!)

[seventythreecb]

Thanks everyone for your help and advice.

Motosan, to answer your questions:
PO repairs: throttle return cable (missing), Re-wire of ENTIRE bike, his "creativity" was my demise (done professionally, cause I'm not that smart), replace ignition switch, replace all brake lines, rebuilt disc calipers/new pads. Replaced caps/cord/plugs.

"Is the bike running fine?(i.e. doe it idle steadily? mostly stable, requires 1/2 choke  does it hesitate?sometimes the throttle is not responsive then it engine just kicks in. somewhere around end of 2nd gear  when does it hesitate? does engine sound fine?I believe so )  How did you find it was running rich?  emissions reportWhat are the colors of all spark plugs? recently replaced and now with very slight carbon buildup. All fairly equal Oil leakage anywhere?  1-2 drops per 24-24hrVacuum leakage anywhere?  not that i am awareDo all 4 headers get equally hot?  any weird sound?  Are the carbs synchronized?  yup Has it gone though the basic maintenance? done everything in the manual

First and only cb500 i've ever riden so i do not know if the ride is less than optimal.

Here my two spare carb housings. Not sure which one is better... Opinions???


Thanks again for all the help and advice.


Patrick

[motosan]

"Is the bike running fine?(i.e. dose it idle steadily? mostly stable, requires 1/2 choke

Do you need 1/2 choke to stabilize idling even when the engine is at operating temp?  Does the engine stall without it?

[HondaMan]

This sounds suspiciously like the most-overlooked item on the CB500/550 inlet systems! Did you replace the O-rings that are in those castings between the carbs and the head? They are the same size at the ones on the valve caps. (I have a whole BAG of them, if you need them). They are easy to replace. If they leak vacuum, the engine runs rich but oddly also needs choke to run below 2000 RPM, very common. To replace them, just unbolt the castings from the head, slide the carb set back a little, pick the old ones out and slide the new ones in,, tighten gently until snug. I think Honda calls them the 30.8x3.1mm O-ring, better known as the valve cap O-ring.

[seventythreecb]

Motasan:
Will over corse of about 15sec idle will slow then engine will die. If I move choke to 1/2 prior to the idle cutting out it returns to normal..

This does not quite make sense to me.... This means,to me, that there is not enough gas making it to the cylinder to mix with an open choke "amount" of air... But I am alway had too much unburned gas at emission testing and I thought that was due to the eroded main jet housing

Thoughts??

Domo arigato Motosan


Hondaman,
When I took the carbs off the bike I did not notice any O-rings in the area you describe. If you had a picture of the part or exactly where it should be, I would be appreciative. If there missing, I will need them...

thanks for sharing your knowledge and experience

Patrick

Patrick

[harisuluv]

I can tell by looking at your spares they are #2 and #4. You need #3. 

I'm not far from you, in tucson. If you need a body just give me the casting number, mail to Phoenix is usually next day or sometimes two days.

[seventythreecb]

Harisuluv,
I was afraid someone was going to say that. Dern....
Well thanks for letting me know before I started taking things apart.
Looked at your rebuilt page... purty carbs..

Sent you a pm about the 3rd carb body you mentioned
thanks,
Patrick

[motosan]

Will over corse of about 15sec idle will slow then engine will die. If I move choke to 1/2 prior to the idle cutting out it returns to normal..

This sounds suspiciously like the most-overlooked item on the CB500/550 inlet systems! Did you replace the O-rings that are in those castings between the carbs and the head? They are the same size at the ones on the valve caps.

Hondaman, I read many of your posts before i started on my 550k3.  It's cool to see a man with unique skill set!.  Your posts helped a lot too, so let me thank you here. 

Now...back to the issue.....I'm right behind Hondaman....I've started thinking this sounds more like vacuum leak actually and possibly also wrong slow jet size and idle mixture screw turns.

Do you have the service manual and the part list?  They are here. ->>http://tinyurl.com/muohrrd  and http://tinyurl.com/lqknpnm.  What Hondaman is referring to is on page 14 #21 on the part list.  I didn't have a picture of them but it would look like this.  ->> http://www.ebay.com/itm/75-HONDA-CB550-SUPER-SPORT-INTAKE-MANIFOLD-A-/280874382374.   The top side (the nasty look side) would connect to the motor and the other side is to the carb).

So I think the first thing I really think you should do is to check for any vacuum leakage.  I think people here would agree that doing that is by far the cheapest and (arguably) the best way to start troubleshooting.

You have a can of carb cleaner or wd-40 right?  All you gotta do is spray it.  All connection points should be checked, so....the 4 O-rings and the both ends of the carb rubber boots on the motor side (not the air box side)...totalling 12 points.   And listen for any RPM change.  It could go either up or down and could be very little.  If it changes only a little, spray more/longer to see what happens.  Just watch for the paint if you are using carb cleaner.     

Lastly, what pilot/slow jet size do you have?  how many turns on the idle mixture screw?

oh i forgot to mention, have a good ventilation!  Don't go killing the brain cells by breathing carb cleaner fumes in

[HondaMan]

oh i forgot to mention, have a good ventilation!  Don't go killing the brain cells by breathing carb cleaner fumes in

If you do, you fall in love with...the SOHC4!

[seventythreecb]

Hondaman,
I've already got the bug.. inhaling any MORE fumes would do little to decrease the obsession.

Motosan,
Thanks for the info and explanation. The carb is off the bike at the moment and will not be back on until this weekend. I will most definetly check for a vacum leak. I have the manual from the first link but the second in not working. Page 14 of the first manual talks about brake boosters. If you could find a picture I would really appreciate it. I am not exacetly sure where you are directing me to spray.
the the ring you are reffering to this rubber boot that connects the carb to the head? I circled what i'm talking about

Thanks again

Patrick

[harisuluv]

That circle has half the aluminum manifold on the right side. It is separate from the head. You will see where it is bolted on. There are 4 orings for each manifold between it and the head.

[HondaMan]

Here's an exploded view of the similar 550 head (don't hold that against it?). the O-rings are #15 in the image.

[Randy]

what sucks is that you need to pass emissions.. california doesn't have that.. But we don't really have guns either..

[motosan]

I'm on roll for messing things up!  (first my speedometer plate and the links haha).  I'm glad to know being in nirvana on carb cleaner fume is rather mandatory here  .

You should check out one the sticky posts in the SOHC/4 Bikes (should be the 2nd from the top in this board), which has pretty much everything you need to have that would

http://forums.sohc4.net/index.php?topic=17788.0

Now....did you see the picture Hondaman showed you?  Notice the 2 parts that these 4 o-rings belong to.  That's what harisuluv is referring to.  In the picture you posted, you should see these parts bolted on with 2 nuts to the engine on the left of the circle. 

Since you have the carbs off, just take these parts off and check the o-rings.  If they are stuck/hard, you probably should change them.  They are cheap.

To check these o-rings at idle, you'll be spraying where these parts contact the engine. The idea here is to "try" to get combustibles like carb cleaners to sneak by the seal.  You have the rubber boots i was referring to circled right   You'll spray where the rubber meets the metal on both ends of these boots.  (again, you can ignore the 4 boots on the air filter side)

Before you put the carbs back on, make sure to check/tell us what pilot/slow jet size you have.  The number should be engraved on the side or the top.  And how many turns on the fuel/air mixture screw you have.  If you aren't sure which screws, check the service manual or the owner's manual.

By the way, do you have the original air box and filter?

[seventythreecb]

Motosan,
the sticky has been very helpful other things, but the one that i thought would be helpful:
"Honda CB 750 550 500 400 350 Carburetor Rebuilding Site"
is not very functional.. none the links work and there is not too much info on the site.

I plan on checking out the o-rings on saturday when i have a few hours off. I will also have a few minutes to look at the jets and let y'all know what's the values are. I am positive that my main jets are 115's.

Is there a way to tell the number of turns on the fuel/air mixture screw without the bike running? if not I should have a enough time to get her together this weekend.

Original box is gone.  I know it runs better, but that ship has sailed.


Thanks again for all the help, I really, really appreciate it.

Patrick

[HondaMan]

I plan on checking out the o-rings on saturday when i have a few hours off. I will also have a few minutes to look at the jets and let y'all know what's the values are. I am positive that my main jets are 115's.

Is there a way to tell the number of turns on the fuel/air mixture screw without the bike running? if not I should have a enough time to get her together this weekend.
 

Those are mighty big jets for a 500! They should be more #100, possibly #105.

The air screws: just gently bottom them out and back them back out to spec. Their seats are soft aluminum, so don't crank them down or the seats will get opened up more: in that case, you have to open the screws LESS to make up for the wider seat.

[motosan]

Is there a way to tell the number of turns on the fuel/air mixture screw without the bike running? if not I should have a enough time to get her together this weekend.

Yup easy.  You know which one I'm talking about, right?  if not...just start "tightening" all screws on outside the carb body.  If it tightens easily, that's probably it.  It it doesn't it's either a fuel drain screw or a vacuum port screw.  Now, once it starts turning, start counting how many 1/2 turns you get.  (that's what I do).   Like Hondaman said, do it lightly and stop just when it won't go any further. 

By the way, I think you should also look into the 3rd carb with the broken off main jet holder.  How much shorter is the damaged main jet holder compared to others?