Topic: Help with CB500f carb tuning

[MotorFist]

Hi everyone!
It's about time to start riding here in Idaho so I cleaned my carbs yesterday and in the process adjusted float height to the 22mm the manual suggests. They were all off quite a bit as I have never adjusted them before. They were around 18mm give or take 1mm.
I also changed the pilot jets as I could just not seem to get them clean no matter how much a soaked and sprayed and blew compressed air through them.
 I replaced the needle and seats too as all the old ones showed wear on the needles.

The bike has stock air box with lid removed and Marving exhaust. I am running stock jetting. #40 pilots and 100 mains.

When I rode it last summer it ran pretty good but I have always had a hanging high idle problem. Now it is MUCH worse. My Carbtune is at a buddies house and I will get it back tomorrow and sync the carbs. Hopefully that will help a bit. I may be jumping the gun by even asking questions before I sync the carbs but thought I'd give it a shot.

I attached pictures of what the plugs look like after a WFO plug chop. The electrodes look lean to me but the rings look ok? Except number 2 plug. It's less lean than the others. I didn't have a lean issue last summer. If anything it seemed fat on the top end. I am now thinking that was due to bad float heights and needle valves that were grooved.

Is it possible that syncing the carbs can help with my new lean problem? What do you think of the plug color?

Thanks in advance for your feedback!
Josh

[Vinhead1957]

I'm thinking you have one carb not working properly

[flybox1]

with your 4 into 1 exhaust, and ? intake(cant tell what you have in the pic)...They all look lean. 
dont do your carb sync until you have done your valve adjustment, set your timing/advance, and adjusted your cam chain.
oil/oil filter/air filter changed recently?
once this is done, and if you STILL have a hanging idle, verify you have no vacuum leaks
lean + hanging idle makes me think vacuum leak.
if your WOT chop comes back again looking like that, and all the above has been done, you'll need to up jet size until its right, then address the mid range chop and needle clip position.

[iron_worker]

Is it a hanging ilde or just an idle that is way too high and never comes down no matter what? I hanging idle means you rev it up and it hangs there for a while and comes down.

I ask because if the idle is too high at all times it may be that you have the sync adjusters too far in and the slides are not bottoming out anymore.

What was your method of bench syncing the carbs?

IW

[Scott S]

I also changed the pilot jets as I could just not seem to get them clean no matter how much a soaked and sprayed and blew compressed air through them.
 

When I rode it last summer it ran pretty good but I have always had a hanging high idle problem. 

 And therein lies your problem. I went through the SAME thing on my CB500. It's the poorly designed aftermarket pilot jets.



 They're too short and don't stay submerged in the fuel in the float bowls. The holes are not the correct size nor are they spaced properly. You're idle is hanging because it's lean. It's lean because the pilot jets are crap.
 Find some genuine Keihin jets and try....I bet it will solve your problems.

[MoMo]

If you have those short jets you need to get rid of them asap.   Sync does not affect mixture...Larry

[MotorFist]

Thanks for the reply guys!
I actually didn't use those short jets. They looked looked wrong so I didn't use them.
After looking at some other topics regarding carb sync I think I am ready to go take another crack at it right now

[MotorFist]

Is it a hanging ilde or just an idle that is way too high and never comes down no matter what? I hanging idle means you rev it up and it hangs there for a while and comes down.

I ask because if the idle is too high at all times it may be that you have the sync adjusters too far in and the slides are not bottoming out anymore.

What was your method of bench syncing the carbs?

IW

Well the correct answer about bench syncing is: I didn't. Then when I saw your post tonight I pulled them again and benched synced using the 1/8" drill bit method. After that I was able to use my carbtune. I bought a carbtune but I am pretty green with it.

So my problem now is my idle. Sometimes it hangs at 2,000 rpm and then falls really low and stalls the motor. Sometimes it will hang at 2000 rpm and then climb to 4000!
Bad news is it didn't use to have a climbing idle. It would just hang at stop lights etc. when I went through my carbs, the float height was way off spec. None of them were equal but they were all around 18mm. I adjusted them to 22mm.  I wonder if this could be part of my new problem?

I live at 4800 feet and am running the stock main jet size of 100 and a foam filter in the stock air box with no lid. I wouldn't think I'm too lean but obviously I am missing something. I used to work at a Yamaha dealership as a teen and they would always drop the main jet two sizes for our elevation when they would set up a new unit.

It may also be worth noting I never ride below 4800 feet. We usually ride the twisty mountain roads nearby which climb up to 6500 on the top of the passes.


When I had my carbs off, I checked my air box boots and intake boots and didn't see and cracks or loose clamps. Even though the clamps aren't loose, I did see some grime that concerns me about leaks. I attached a picture and you can see grime on both ends of the intake manifold. All clamps and nuts are tight.

I really appreciate the replies so far and hope you keep the coming!
Thanks,
Josh

[MotorFist]

Ok so I took a little video too. Albeit not a very good one. The idle self increases to 4000 rpm then I use the choke to drop it to 2000 where it hangs for a moment and then drops again.

Maybe this will help some of you smart guys help me diagnose?
Thanks

http://youtu.be/ilD2wSjhrHk

[dave500]

if everything else is solid replacing the o rings at the manifold to head might be worth doing,they get rock hard and stay flat,you should be able to wrangle them in without removing the rack fully.

[iron_worker]

Agreed. Check again for vacuum leaks. Take a propane torch *not lit but with the valve open* and allow some propane to flow around the carb intake boots with the engine idling. If the idle suddenly rises then you've found your leak point.

IW

[MotorFist]

Thank you both for the suggestions. I like the propane idea. I didn't want to use carb cleaner very badly and this sounds much less messy and damaging.

[flybox1]

WD-40 works just as well, too, but I prefer carb cleaner as it doesnt leave anything to clean up 

[MotorFist]

I was under the impression wd-40 was changed a few years back and is no longer flammable?

I do have lots of carb cleaner though

[MotorFist]

Well I sprayed carb cleaner to no end and couldn't find any leaks so that is ruled out. I did however notice the throttle lever that the cables hook to on the carbs was not in the right spot. Basically if the throttle grip was pushed forward, the throttle lever on the carb rack was still at least a quarter inch for hitting the eccentric pin.
So I fiddled with that and found some immediate improvements but still had a hanging idle. Just for curiously sake I gently pushed down on the big cap nuts that at next to the throttle sync adjusters. Low and behold! When I pushed down on all for of them my idle dropper to normal. Push a little hard and the slides fully closed and shut off the bike.

So it appears my slides aren't going back down all the way. I feel like a major jackass because I was lazy when I cleaned my carbs and didn't pull the slide assemblies out.

So I pulled one slide assembly out before I called it a night in the garage. It looked a little dirty but not enough to make it stick it I think? I will see what the other three look like tomorrow night.

For reference, the needle I pulled out says 272304 and the clip is in the position of one up from the bottom. What should it be on a 72 500?

Also if my other slides look as clean as the first, what else could be the culprit that is keeping my slides returning home? Do the springs on the throttle lever stretch over time? It feels plenty stiff when I move the throttle lever by hand. I wish I would have paid closer attention to see if the idle was hanging after a throttle snap or just when it was twisted and let go gently. I'm still learning...

[dave500]

that clip should be in the middle,its common for people to richen it like yours when a 4-1 pipe is fitted as a matter of course,most run fine with it left in the stock position.

[Scott S]

 If you didn't pull the slides, is it safe to assume you didn't pull the emulsion tubes? They're designed to drop out from the bottom after removing the main jet, but most of the time they get so cruddy you have to push them out from the top.
 If you're going to remove the slides, save yourself some headache and push the emulsion tubes out and clean them. They're probably not the cause of the hanging idle, but the bike idles and runs much better when they're clean. Use a wooden dowel or chopstick to push them out.

[Duanob]

Agreed. Check again for vacuum leaks. Take a propane torch *not lit but with the valve open* and allow some propane to flow around the carb intake boots with the engine idling. If the idle suddenly rises then you've found your leak point.

IW

Ah never heard of the propane torch method. Someone else mentioned using a propane torch on their carbs I thought they were nuts!

[iron_worker]

If your slides were very sticky and your return spring was weak it could possibly cause the whole thing to hang open slightly. It's definitely something to check. Especially if you were able to close them off my by hand.

x2 on cleaning the emulsion tubes if you're pulling the carbs anyway.

IW

[MotorFist]

Well here I am again, scratching my head. I still can get this sorted out

I pulled the slides and emulsion tubes and cleaned them. Two of the emulsion tubes had a lot of gunk built up on the outside of them but the holes down the sides of them we are clear. I cleaned them all up and adjusted the needle clips to the middle position.
Put it all back together and no change.

Tried carb cleaner again for vacuum leaks with no results again.

The only thing I have gained with the bike through all this is it starts and idles much better than before. That goes for a warm or cold motor. But as soon as I start twisting the throttle, the hanging idle and occasional climbing idle starts.

Something I noticed is that when I first start the bike with a cold motor, the problems don't occur. It's only as the bike warms up. I know I read something in the carb FAQ about that. I better have a look again.

Also I can get the carbs synced and then snap the throttle a few times, and it becomes mildly out of sync again.

[dave500]

if the all of the carb passages also havent been blown through with compressed air any trouble from crud/dirt will remain,if the tubes had crud the carbs will aswell,the discharge port for the idle jet in the carb body isnt much larger than the actuall tiny jet itself!carbs cant be too clean,,also go right over your ignition,make sure the advancer isnt sticking.

[MotorFist]

Thanks Dave. I did blow it out and the carbs seem to be clean. How do I check to see if my ignition advancer is sticking?

I just read the FAQ on checking timing and I used the spark method and it all lines up. But that doesn't mean that it might not stick?

[MotorFist]

I also just noticed that my 2&3 pipe have blued a lot more than 1&4. This is a new development. I remember being happy with how even they were last summer/fall.

[K3Owner]

Interesting video. I would attribute unstable idle to vacuum leaks or improper mixture but a blip on the throttle that hangs at 4000 would lead me to overly tight cable or at least something in the throttle mechanism. You say that you push on the mechanism and the idle returns to normal and you've removed the slides to check for sticking. I think you're at least in the proper area - almost definitely mechanical. You should find what is holding that throttle high. Ever disconnect the throttle cable fully to remove it from the equation? Sorry I can't be there to help.

[dave500]

if you have a strobe light,a simple rev up will show if the bleeding advancer is working or nought,,cafe racer lip alwright.what you #$%*in well lookinat you bleedin geezer?you wanna get funny boyo?