Topic: 72 CB500 Idle Hanging

[blakesommers77]

Hey everyone, I'll try and be as complete as possible. 72CB 500 Four with the 4 to 2 exhaust no baffles or anything from (Honda I think) and pods. ( I know it was a bad idea.)

The bike will only idle if I set the idle fairly high (1500 RPMS) Any lower and it will just die. Any little backfire out of the back of the carbs will shut her down. If I set it to idle high and crack the throttle the idle will hang at about 3k and climb fairly quickly to around 5k. If this happens at a light a little clutch slip will stop it.

I can post a video later if it would be helpful.
The bike used to fall on its face and sputter at about 5k if I got into the throttle at all so I rejetted from the stock 100 main to a 125 and it pulls hard all the way to redline with no problem or hesitation. I tried to replace the pilot with a 55 from DCC but they sent the wrong size so the stock 40 is still in there.

Off the line it really wants to bog down even with the throttle being applied. ( Can clarify in video if need be.

What has been done;
Carbs Cleaned
No blocked jets
Floats are not overflowing so that little valve is working as it should or at least I assume. I forget the name... Little pointy thing haha.
Synced to a 1/8th inch bit. (Carb 4 moved a little but it had same issues right after being synced...
Points system has been gone through.
Intake boots look ok.

Possible issues;
Spark plug wires are #$%*ed! But all cylinders are firing. (Amazingly)
Float levels have not been set yet. Is 22mm correct? Where do you measure from?
Air leak?


Is this really an issue of the pilot jet being super super lean?


-Blake

[blakesommers77]

Any input?

Sent from my SCH-I545 using Tapatalk

[turboed13b]

First your mains are way too high a cb500 needs only 105 maybe a 110 but very rarely.

Stay with the 40 slows the reason you are not idling is because you have the idle screw open too far causing loss of vacuum and a lean condition. Switching to 105 mains may sort out the issue if not then you have to drop the needle one slot.


Also setting the float height should be the first thing to do.

[BomberMann650]

A solid vacuum sync and a double check of the points timing helped my 550's idle come down.  A little fine tuning of the fuel mix screw helped things some more.

[blakesommers77]

First your mains are way too high a cb500 needs only 105 maybe a 110 but very rarely.

Stay with the 40 slows the reason you are not idling is because you have the idle screw open too far causing loss of vacuum and a lean condition. Switching to 105 mains may sort out the issue if not then you have to drop the needle one slot.


Also setting the float height should be the first thing to do.

Interesting, even with 100 mains it fell flat on its face the second you got into it a little. figured 105 would not make enough of a difference. Correct me if I'm wrong. The main (even if it is too big) should not effect the idle. I was under the impression the pilot was responsible for that? I should have mentioned that the clips are in the stock position. I'll look into that.

I will set the float hit this evening once I'm off work. Vacuum gauge is on its way right now.

Thanks!

[harisuluv]

With pods you are never going to get close to running well without changing the needle position.

You have focused on the main jet and pilot, however the needle is also just a fuel metering device.  But it's arguably the most important, and has an effect at all ranges.  You completely overlooked it.

Standard starting point for pods and your bike is:

110 mains
40 slow
Needle clip LOWERED one notch (same as raising the needle one notch)
Air screw 1.5 out to start then adjust as necessary.

P.S.  Where on earth did you come up with 125 main and 55 slow?  Do not listen to them anymore.

[blakesommers77]

With pods you are never going to get close to running well without changing the needle position.

You have focused on the main jet and pilot, however the needle is also just a fuel metering device.  But it's arguably the most important, and has an effect at all ranges.  You completely overlooked it.

Standard starting point for pods and your bike is:

110 mains
40 slow
Needle clip LOWERED one notch (same as raising the needle one notch)
Air screw 1.5 out to start then adjust as necessary.

P.S.  Where on earth did you come up with 125 main and 55 slow?  Do not listen to them anymore.

hahaha! This forum actually I've been lurking forever trying to figure out these stupid things.

I'll change the clip position tomorrow morning and report back my findings. Would a video be of any help or is everyone pretty certain the clip position is the best spot to start? Still curious as to my question about the main jet... " The main (even if it is too big) should not effect the idle. I was under the impression the pilot was responsible for that?"

[harisuluv]

A video would always help, it's information, and everything we say is based on what you provide us with.  A video would only benefit you.

Your main jet is a problem.  It is not a problem for ONLY the idle, but you need to acknowledge that main is way too big.  Let it go.

While you're in there, take care of all the other stuff that you neglected, i.e. float height (22mm), check for air leaks, etc.  THEN do your vacuum sync, no sense in syncing them, then changing everything to the proper settings, then having to sync them again.

And this is all under the assumption that your incredibly broad, blanket terms like "cleaned carbs" means that there are no issues regarding that.  Keep in mind these types of threads often hit 3-4 pages and end with "runs great after I cleaned the carbs again!"
 
P.S  Honda never made a 4-2 exhaust for that bike, stock is 4-4.

[blakesommers77]

A video would always help, it's information, and everything we say is based on what you provide us with.  A video would only benefit you.

Your main jet is a problem.  It is not a problem for ONLY the idle, but you need to acknowledge that main is way too big.  Let it go.

While you're in there, take care of all the other stuff that you neglected, i.e. float height (22mm), check for air leaks, etc.  THEN do your vacuum sync, no sense in syncing them, then changing everything to the proper settings, then having to sync them again.

And this is all under the assumption that your incredibly broad, blanket terms like "cleaned carbs" means that there are no issues regarding that.  Keep in mind these types of threads often hit 3-4 pages and end with "runs great after I cleaned the carbs again!"
 
P.S  Honda never made a 4-2 exhaust for that bike, stock is 4-4.

Lol I'm not holding onto the main jet... obviously it's too big. Realized that pretty quick. All I asked was for someone to address my question.....
Gonna be a few days until I can sync. Meantime I'll check out the floats and clip position. I can assure you the carbs are clean.
These bikes are a little different than what I'm used to working on. 18 years of racing motocross... Never dealt with 4 carbs.

A video would always help, it's information, and everything we say is based on what you provide us with.  A video would only benefit you.

Your main jet is a problem.  It is not a problem for ONLY the idle, but you need to acknowledge that main is way too big.  Let it go.

While you're in there, take care of all the other stuff that you neglected, i.e. float height (22mm), check for air leaks, etc.  THEN do your vacuum sync, no sense in syncing them, then changing everything to the proper settings, then having to sync them again.

And this is all under the assumption that your incredibly broad, blanket terms like "cleaned carbs" means that there are no issues regarding that.  Keep in mind these types of threads often hit 3-4 pages and end with "runs great after I cleaned the carbs again!"
 
P.S  Honda never made a 4-2 exhaust for that bike, stock is 4-4.

Sent from my SCH-I545 using Tapatalk

[turboed13b]

All my bikes needed the needle dropped(or e-clip up one notch) because adding pods actually richens the mid range mixture.

Main jet does affect idle as does needle position try pulling out the main and see if the bike will even start or let alone idle.

[blakesommers77]

All my bikes needed the needle dropped(or e-clip up one notch) because adding pods actually richens the mid range mixture.

Main jet does affect idle as does needle position try pulling out the main and see if the bike will even start or let alone idle.

haha good to know. Thanks man.

-Blake

[alacrity]

When you cleaned the carbs, did you remove the emulsion rubes and check that every passage and orifice is completely clear like factory new?  Did you examine each pilot jet to be sure that each was flowing properly ?  These things have tiny little paths and channels and it's super ez for crap to get in there or just varnish to form.
And of course you are 100% certain your fuel tank doesn't have rusty diarrhea that is scooting past a failing screen in the Petcock, right? Because it would be silly to dump that sort of thing into "clean" carbs...where the stickygummyrusty particles will seek a perch in your pilot jets and emulsion tubes.

It sounds like you have the fuel/air version of atherosclerosis...
I could be wrong- wouldn't be the first time.

[blakesommers77]

The tank needs work but for tackling the idle issues I have not been running the gas through the tank. Gas is coming from a clean source...

[blakesommers77]

Carbs were gutted and cleaned. Hell, I'd eat off them

[calj737]

Blake - just to be 100% clear, you did pull and clean the emulsion tubes? A
Acuity asked about it, and you mentioned cleaning the jets, but not the emulsion tubes. Lots of folks miss them and you can not clean them unless you have actually pulled them and cleaned them outside of the carb.

Pay close attention to the advice from Harisuluv, he will not be wrong on these carbs.

[blakesommers77]

I checked with a friend of mine who did the initial deep clean and according to him he did. When I came across this bike there was probably a 1/4 inch of just crap built up everywhere in these carbs. He had them for a few days and did a good overhaul on them while I was out of town. I'll gladly pull them apart to make sure but given his experience it would be silly for him to skip that. Never know though and only one way to know for sure. I personally have cleaned the float bowl valve, all the jets, made sure the floats are not hanging like they were before, installed new gaskets on the float bowls, old ones were barely present and rejetted the main to the massive 125
Might have to wait till this weekend to pull everything apart. Been sick for a week and work is kicking my butt right now. Thanks for the help everyone. I do appreciate it.

Blake

Sent from my SCH-I545 using Tapatalk

[blakesommers77]

As promised here is a video. I would talk through it but I do not have a voice at the moment so sorry about that. Idles fine on its own when its not 100% warmed up. Just to show the problem I bumped the idle up a little and it hangs as it would if the bike were to be at operating temp and I adjusted the idle so it would stay alive at a light. Hope that makes sense.