Topic: high idle after warm up

[neonknight]

did a forum search and found stuff on this topic, but maybe not the exact same circumstances...

i have a 73 cb500F and for a little while it has been idling high at stop lights after warming up. before, i'd just wick the throttle and it'd go back down to 1300. now it's staying above 2200 and if i wick the throttle, it stays high and sometimes escalates. at stop lights, i turn my idle screw to bring it down... which is successful, but directly after, giving it some gas, the idle goes back up to 2200 and stays there. the snap back on my throttle seems to be fine... doesn't seem to be sticking... carb issue?

[Deltarider]

If you haven't change things yourself, look for airleaks. When idling, spray brakecleaner (some use WD-40) around the boots between carbs and engine. If RPM change, there's a leak. O-rings between the intake manifold and the engine are also suspect. Check the ignition timing and certainly the advancer.

If you have changed things: what position are your airscrews in? You could be the victim of false information. Recently I saw some pages out of a booklet with specs (American Honda Company 1977) that advises 2 turns out. That's even half a turn more than the 1¹/₂ out, which was already a mistake, IMO. It should be 1 ⁺/_- ¹/₈. Unless American Honda Company counts 180⁰ per turn. That would be the same as our 1 turn out.
This 1¹/₂ or two turns out seems only to occur in USA. Maybe a mistake is copied, maybe Honda America had to comply with pollution regulations at idle. I don't know. Are you satisfied with how your bike accelerates?

[Old Scrambler]

Read the threads about the Hanging Idle.................Your fuel level is likely too high in the bowls.........and you may have miss-matched parts regarding jets, emulsifier tubes, and jet needles.

[Deltarider]

Your fuel level is likely too high in the bowls.........

I don't think so. When the slides are in their normal position at idle, more fuel will not bring a higher idle, but rather a lower.

[neonknight]

If you haven't change things yourself, look for airleaks. When idling, spray brakecleaner (some use WD-40) around the boots between carbs and engine. If RPM change, there's a leak. O-rings between the intake manifold and the engine are also suspect. Check the ignition timing and certainly the advancer.

If you have changed things: what position are your airscrews in? You could be the victim of false information. Recently I saw some pages out of a booklet with specs (American Honda Company 1977) that advises 2 turns out. That's even half a turn more than the 1¹/₂ out, which was already a mistake, IMO. It should be 1 ⁺/_- ¹/₈. Unless American Honda Company counts 180⁰ per turn. That would be the same as our 1 turn out.
This 1¹/₂ or two turns out seems only to occur in USA. Maybe a mistake is copied, maybe Honda America had to comply with pollution regulations at idle. I don't know. Are you satisfied with how your bike accelerates?

Thanks, I'll search for airleaks first. As far as acceleration, it seems to pick up power noticably at higher rpms -- off the line, it seems to lurch a little bit...

[KingCustomCycles.com]

If you haven't change things yourself, look for airleaks. When idling, spray brakecleaner (some use WD-40) around the boots between carbs and engine. If RPM change, there's a leak. O-rings between the intake manifold and the engine are also suspect. Check the ignition timing and certainly the advancer.

If you have changed things: what position are your airscrews in? You could be the victim of false information. Recently I saw some pages out of a booklet with specs (American Honda Company 1977) that advises 2 turns out. That's even half a turn more than the 1¹/₂ out, which was already a mistake, IMO. It should be 1 ⁺/_- ¹/₈. Unless American Honda Company counts 180⁰ per turn. That would be the same as our 1 turn out.
This 1¹/₂ or two turns out seems only to occur in USA. Maybe a mistake is copied, maybe Honda America had to comply with pollution regulations at idle. I don't know. Are you satisfied with how your bike accelerates?

Thanks, I'll search for airleaks first. As far as acceleration, it seems to pick up power noticably at higher rpms -- off the line, it seems to lurch a little bit...

classic induction leak.............

[neonknight]

sprayed wd-40 on the carb boots, and didn't notice any change in idle. right at 1300. i guess i could get it to the point where it's idling high and spray again, but wouldn't you notice a difference either way?

[neonknight]

CORRECTION: i sprayed a little more wd-40 this time and it sputters a bit when spraying carb# 3. this means i have to replace the boot?

[Hondawggie]

Bingo.

Me?  I'm replacing all 4 boots and associated o-rings, not just the bad one, if one of them leaks.  They're not too expensive, and if one has aged to the point of leaking can the others be far behind.  Plus if you do all 4 you may never need to worry about it again.

One other thing to consider (and you probably already know this), warm the engine up for 10 minutes before attempting to set the idle.

If you start the bike up and let it run for a only a minute or so, then adjust the idle so that the engine idles at 1k rpm +/- after only a couple minutes of engine running, once the motor warms up it will give a very similar symptom to what you're describing -- at stop lights, *after you've been riding several minutes,* it will idle too high.

Sounds like you may have found a leak too.

[neonknight]

Bingo.

Me?  I'm replacing all 4 boots and associated o-rings, not just the bad one, if one of them leaks.  They're not too expensive, and if one has aged to the point of leaking can the others be far behind.  Plus if you do all 4 you may never need to worry about it again.

One other thing to consider (and you probably already know this), warm the engine up for 10 minutes before attempting to set the idle.

If you start the bike up and let it run for a only a minute or so, then adjust the idle so that the engine idles at 1k rpm +/- after only a couple minutes of engine running, once the motor warms up it will give a very similar symptom to what you're describing -- at stop lights, *after you've been riding several minutes,* it will idle too high.

Sounds like you may have found a leak too.

Ok Thanks! I'll look into getting a set of boots and o rings.