Topic: Hanging idle....I'm done

[wolfejm]

I very much appreciate this thread and everyone who contributed because I recently bought a '72 CB500 K1, it has this EXACT same problem. I think I can fix it. THANKS!!!

[Scott S]

I very much appreciate this thread and everyone who contributed because I recently bought a '72 CB500 K1, it has this EXACT same problem. I think I can fix it. THANKS!!!

 That's why we're here! I appreciate it,  too. I couldn't have figured it out without the help of the forum.

[Kevnz]

Congrats on seeing it through to a happy conclusion. I'm sure it will feel SO much better having gone through so much grief to get it right.
Enjoy the ride, you've earned it.

[Deltarider]

... and sync screws are now at 4-5 threads out. ...

That seems more like it.

... Mixture screws are at 3/4 turn from seated. ...

I wouldn't be surprised you can lean out a bit here. However, when revved, rpm must drop instantly to idle when throttle is closed. Read: snap, without any hesitation. Under load, whilst accelerating, bike must pick up smoothly without wheezing (driveability).

[Scott S]

 That's why I ended up at 3/4 turns. One turn and it would lag a bit, fall a little slower to idle. One and a half turns actually mimicked the hanging idle effect. I richened it up until it ran the best.

[grcamna2]

That's why I ended up at 3/4 turns. One turn and it would lag a bit, fall a little slower to idle. One and a half turns actually mimicked the hanging idle effect. I richened it up until it ran the best.

That pilot jet 'circuit' which controls the 0-1/8 throttle position responses is very sensitive,seems more difficult to do with 'air screws' at the back of the carbs than fuel metering 'mixture screws' that are at the front of carbs.
I used to spend plenty of my own time tweaking each individual pilot screw when installing DynoJet kits for a couple special customer's vintage bikes:some would respond better with #1-1.25 turns out,#2-1.10 turns,#3-1.35 turns and #4-1 turn out,or many other variations.This was when I had plenty of time and a good fan blowing on the bike:it could take an extra 1/2 hr on a bike to make it smooth as silk.No shop would do that if they had a backlog of work.When I tried to make them all exactly the same amount of turns out without really fine-tuning each screw it was acceptable but not optimum,imo. 

[bender01]

Are you still going to sell it?

[Maraakate]

That's why I ended up at 3/4 turns. One turn and it would lag a bit, fall a little slower to idle. One and a half turns actually mimicked the hanging idle effect. I richened it up until it ran the best.

That pilot jet 'circuit' which controls the 0-1/8 throttle position responses is very sensitive,seems more difficult to do with 'air screws' at the back of the carbs than fuel metering 'mixture screws' that are at the front of carbs.
I used to spend plenty of my own time tweaking each individual pilot screw when installing DynoJet kits for a couple special customer's vintage bikes:some would respond better with #1-1.25 turns out,#2-1.10 turns,#3-1.35 turns and #4-1 turn out,or many other variations.This was when I had plenty of time and a good fan blowing on the bike:it could take an extra 1/2 hr on a bike to make it smooth as silk.No shop would do that if they had a backlog of work.When I tried to make them all exactly the same amount of turns out without really fine-tuning each screw it was acceptable but not optimum,imo. 

How do you detect the differences to know it's dialed in?  With a portable tach on the cylinder you are tuning?

[grcamna2]

That's why I ended up at 3/4 turns. One turn and it would lag a bit, fall a little slower to idle. One and a half turns actually mimicked the hanging idle effect. I richened it up until it ran the best.

That pilot jet 'circuit' which controls the 0-1/8 throttle position responses is very sensitive,seems more difficult to do with 'air screws' at the back of the carbs than fuel metering 'mixture screws' that are at the front of carbs.
I used to spend plenty of my own time tweaking each individual pilot screw when installing DynoJet kits for a couple special customer's vintage bikes:some would respond better with #1-1.25 turns out,#2-1.10 turns,#3-1.35 turns and #4-1 turn out,or many other variations.This was when I had plenty of time and a good fan blowing on the bike:it could take an extra 1/2 hr on a bike to make it smooth as silk.No shop would do that if they had a backlog of work.When I tried to make them all exactly the same amount of turns out without really fine-tuning each screw it was acceptable but not optimum,imo. 

How do you detect the differences to know it's dialed in?  With a portable tach on the cylinder you are tuning?

Yes,
And 4) accurate vacuum gauges along with an accurate electronic tachometer.I still have the gauges but my tachometer is broken:an Electro Specialties unit I bought from K&L  back in the 90's.The unit has a large analog face,worked nice for a while.. I'm looking for a good digital unit.

[Scott S]

Are you still going to sell it?

 Already off to her new owner.

[seanbarney41]

Are you still going to sell it?

 Already off to her new owner.

geez dude?...are you sending Deltarider his cut?

[slopps]

Scott, could you possibly clarify how you measure the 49mm?
I'm trying mine now (similar issues in different thread about high rpms when I first start the bike until it warms up), and with the idle screw turned all the way in I cant even get close to 49mm:

[Scott S]

 Measure from the top of that white line you drew to the upper red line. The German manual pics show it using the bottom of the holder for the push cable (your upper red line, which is correct) and the bottom of the bell crank (which would sort of align with the upper white line in your pic).


 I screwed in the big, main idle screw to get the 49mm. Then I lowered all of the slides on the bench using a 5/64 drill bit. Loosen the lock nuts on the sync screws a good bit and lower the slide(s) until you can't pull out the drill bit. Carefully....don't clamp down on the bit. Then raise the slide just enough that the bit pulls out with the slightest drag, almost like a feeler gauge. Lock set screw. Repeat.
 

[Deltarider]

geez dude?...are you sending Deltarider his cut?

Too much honour, Sean, too much honour. Credit where due. All the effort was by Gruzzel. I merely passed on his findings. To quote my favourite philosopher Manuel: I know nooothing! "He's from Barcelona, you know." Let me confess that, unlike others maybe, I was born a 100% ignorant, so I can only pass on what I've learned or read elsewhere. I know, it's a serious shortcoming, but... as long as I mention the source..., I guess it's allright. Back to the subject. I have several paper manuals. A quick scan learned me that the Haynes manual (at least in the Dutch translation) mentions a distance of 40 mm ± 1,5 instead of the 49 in the Honda Shop manual. Now a '9' instead of an '0' is a plausible typo. Interesting. Maybe one of you guys is in the position to check if that 40 mm will make more sense of the original fig.5 on p.8 of the Honda Service Manual CB500-550 (shown below). If so we could edit that page 8 very easily.

[maxheadflow]

I used to tune these things from 69 to about 81 professionally.  Most of the work was 73 to 79, with 90% of the work was in Honda dealerships.   We never used the process in the manual.  Last shop I worked in typically had 4 guys doing street bikes and one guy that specialized in ATCs.   There was a few years at different times when I was the service manager. Don't don't that against me.

Or process for syncing the carbs was different than the manual.  The service included all the lubes, fastener tightening, oil change up front. Sorry didn't warm the bike up for the oil change unless it came in warm. Cam chain and valve adjustments. Timing was next always done with a timing light to check the advance mechanisms as many times the mechanism would need a tweak. We usually didn't clip the springs, we'd just squash the hook a little to get the tension right.  Settings were done with the tank off and fuel from a bottle with a hose.

When it cam to syncing carbs, we used vacuum gauges which were connected even before the timing was set. Motor was already warmed up from setting the timing. Timing has to be correct before using the gauges.

Anyway our process for setting the synch was to open the throttle to about 4000 rpm, and balance there then check at idle to see that they were still equal. Once the adjustments were close, we'd blip the throttle and let the throttle snap shut to see of the sync shifted. On the 500/550 carbs, they would often change slightly due to the complexity of the mechanisms.  We would then go through and set pilot mixture and recheck sync.   Seems like a long process but it really only took a few minutes.

[Deltarider]

... We usually didn't clip the springs, we'd just squash the hook a little to get the tension right.

That would be my approach. I never quite understood this clipping the springs thing. One: I don't know what advancer it is about: the TOYO one, the Hitachi or both. Second: so far I have not read one positive post like 'wow, what a difference that made', at least, not where it concerned a CB500/550. But maybe I have missed it. I have two TOYO (= TEC) advancers and not one has springs that show sloppiness to a degree that it worries me. If they would, I'd tweak the hook just like you used to do (close ups below).

... O(u)r process for syncing the carbs was different than the manual. ...  was to open the throttle to about 4000 rpm, and balance there then check at idle to see that they were still equal.

4000 rpm is a bit high IMO. Working on a standard CB500/550, I wouldn't go higher than say 2700 rpm where these bikes will have reached full advance.

...  We would then go through and set pilot mixture and recheck sync. ...

I doubt that will result in much change in the vacuum, but that's just me, unless you mean to reset all 4 idle screws and not individually tweak one against the other.

[maxheadflow]

... We usually didn't clip the springs, we'd just squash the hook a little to get the tension right.

That would be my approach. I never quite understood this clipping the springs thing. One: I don't know what advancer it is about: the TOYO one, the Hitachi or both. Second: so far I have not read one positive post like 'wow, what a difference that made', at least, not where it concerned a CB500/550. But maybe I have missed it. I have two TOYO (= TEC) advancers and not one has springs that show sloppiness to a degree that it worries me. If they would, I'd tweak the hook just like you used to do (close ups below).

... O(u)r process for syncing the carbs was different than the manual. ...  was to open the throttle to about 4000 rpm, and balance there then check at idle to see that they were still equal.

4000 rpm is a bit high IMO. Working on a standard CB500/550, I wouldn't go higher than say 2700 rpm where these bikes will have reached full advance.

...  We would then go through and set pilot mixture and recheck sync. ...

I doubt that will result in much change in the vacuum, but that's just me, unless you mean to reset all 4 idle screws and not individually tweak one against the other.

I'll admit that it the time, we really didn't pay much attention to what brand advancer was in the bikes. We just tweaked them as necessary.  We'd pull them apart and clean if necessary.  If someone had been in there and screwed up the screws, they got a hole new points plate assy as they were only a buck or 2 more than points and condenser.  IIRC most of the stuff was Nippon Denso. Bikes were still new and parts plentiful.

When doing the sync, the advance is not the main reason for picking a higher RPM, the vacuum reading is the main reason.  Higher RPMs draw more vacuum. Using more of the scale allows for the reading to me more precise.   For example  + or -1 inch is less error at 20 in-hg than the same + or - 1 at 10 in-hg.

Didn't use vacuum to to set idle air mixture, used exhaust sound on individual adjustments.  Better mixture might pull a little more vacuum on 1 cylinder.

[Deltarider]

I had the impression you guys choose 4000 rpm (for other bikes than SOHC CBs?) to eliminate any side effects of a possibly irregular advancer. Hence my suggestion for 2700 rpm for when a CB500/550 is involved. Actually the few times I have synched CB500/550s using gauges, I choose a raised idle of around 1500 rpm. I don't understand how you have reached a higher vacuum at higher rpms. I've always had the highest vacuum at or near idle.

... A quick scan learned me that the Haynes manual (at least in the Dutch translation) mentions a distance of 40 mm ± 1,5 instead of the 49 in the Honda Shop manual. ...

Can anyone check if this '40' appears also in the English edition of Haynes?

[maxheadflow]

I had the impression you guys choose 4000 rpm (for other bikes than SOHC CBs?) to eliminate any side effects of a possibly irregular advancer. Hence my suggestion for 2700 rpm for when a CB500/550 is involved. Actually the few times I have synched CB500/550s using gauges, I choose a raised idle of around 1500 rpm. I don't understand how you have reached a higher vacuum at higher rpms. I've always had the highest vacuum at or near idle.

When you crack the throttle, vacuum will drop for sure but as the motor reaches steady RPM, vacuum increases to steady state.  With motor has a redline of 9500, do you think it will run efficiently at idle?  These motors don't have cams that open exhaust or close intake valves at BDC. Intakes close later and exhausts open earlier. 

[PeWe]

This is a good example for Hondaman's next book!

[Erny]

Scott, are you sure that, before the synching, you had the correct position to start from?
For some reason p.8 is missing in almost all internet copies of the Shop Manual Honda CB500-550.
The page deals with the carburetor adjustment. Recently somebody on the German forum has clarified what was somewhat confusing in that particular page and left many of us puzzling. Although the text is in German, the modified pic makes clear what Honda ment.

reopening this thread, as I'm working on the same topic - adjusting carbs 069A after rebuild

I wanted to use mentioned "german method", but I failed, I'm unable to adjust buttferly into position using trottle stop screw, on maximum I can reach max ~38mm, see photo.

Either something is wrong (but what?) or I misunderstood method where I should measure 49mm?

Adjusters are 4-5 threads out of nut see pic

[Redline it]

Throttle cables are routed correctly? Experiment by closing (fully) and opening one individual airscrew at the time and see if that changes RPM. The one that doesn't change RPM has a suspect idle circuit. I'm with Rob to start rich. I know Amercan Honda suggests to have airscrews two turns out. The rest of the world has one turn out. What happens with a partially closed choke (or partly covered airfilter case for that matter)? Your EI does not happen to be a programmable type, does it?

I would check out what Deltarider said and add to be sure you have enough free play in the cables.  Slight  binding can cause an idle hang.  I had this on my 750 when I tried to remove all "slop" from the cables.

-P.

that would explain why the changes  happen when the clutch is disengaged. i just went through the same thing and have for long time on and off. this time it would hang if the  bars  were moved in minutely different angle. i'd adjust the freeplay and nothing, then i got lucky and found out that the cable adjuster locknut when snugged up would angle the cable into the cam run just enough to do make the hang. it was such a slight difference to make the effect. those cables last forever, but they can get touchy, and stuck in their way.

[Scott S]

Scott, are you sure that, before the synching, you had the correct position to start from?
For some reason p.8 is missing in almost all internet copies of the Shop Manual Honda CB500-550.
The page deals with the carburetor adjustment. Recently somebody on the German forum has clarified what was somewhat confusing in that particular page and left many of us puzzling. Although the text is in German, the modified pic makes clear what Honda ment.

reopening this thread, as I'm working on the same topic - adjusting carbs 069A after rebuild

I wanted to use mentioned "german method", but I failed, I'm unable to adjust buttferly into position using trottle stop screw, on maximum I can reach max ~38mm, see photo.

Either something is wrong (but what?) or I misunderstood method where I should measure 49mm?

Adjusters are 4-5 threads out of nut see pic

 Lower the slides with the adjusters so that you can get the 49mm.

[Scott S]

 Well, I finally got up the gumption to fire up the '71 CB500 today. Before installing the carbs, I set the carb linkage to the 49mm discussed earlier in this thread. I checked the main jet O-rings and they were tight, so I didn't change them.
 The bike fired right up (after sitting for 25 years) and....you guessed it: HANGING IDLE!!!

 This is why I stopped working on bikes for so long.

 I'm running points and set them statically. I put the timing light on it and it's close enough that it's not an issue. I will be converting to electronic soon, so I didn't mess with it.

 I didn't sync the carbs since I'm assuming they will be coming back off.

 I do have some questions about the 49mm setting.
 I took pics BEFORE the carbs were rebuilt and you can still see the factory marks. It was mentioned earlier, on a different bike, that too many threads were showing on the sync screws. But look at how many are on here from the factory.

 When set to 49mm, I have to screw the main idle screw WAY in. It feels like it's too much, but that is what is required to get the 49mm. After achieving that, I bench synced the carbs.

 After bench syncing them, the sync screws look WAY different than the factory settings.

 I have a set of HondaMan's O-rings. I will be pulling the @#$&^* carbs and installing those. I will be going back closer to the factory settings on the sync screws and see what happens.
 I'm open to other suggestions.
 On a positive not, it runs well, with no smoke, leaks or funny noises!

 * First pics are before; factory settings. Middle pic shows the rack as delivered from OldSkoolCarbs (looking like factory settings Later pics are with the 49mm setting *

[Korven]

offtopic: what are those exhaust in your first picture? Look great.
ontopic:The metal bracket between the sync screws looks slightly bent. I have not read the entire thread, but did you experiment with slightly bigger jets? (Its just me thinking it might be the modern fuel that causes bike to run slight lean on idle.)