Topic: idles high after long ride, or highway ride. ideas???

[shizzomynizzo]

so when i ride the bike, it runs fine in the city. Intermittently it wont drop idle below 2000-2500 at some stop lights. I turn the idle screw down and the it drops. It does the same thing if i really get up on it hard for a while and then stop anywhere or when im on the highway for 10 minutes or so. as soon as it cools, it starts up and idles fine, but not when it has been driven and is hot.

Carbs are the first thing that comes to mind, just cleaned them 3 times in the last week alone, along with setting the floats today. I read a few other threads and have seen that the most common response is adjust the carbs. Well what do I adjust? should I basically start from scratch and adjust every screw to factory spec? I don't believe the carbs are original to the 1974 550 that I have. The book says set float to 22 mm and the floats I have won't go near 22mm, so I set them at 12.5mm and seem to work fine, except for the idle at stoplights. so I really cannot follow the repair manual.

From what I have read and experience, it seems that one of the carbs is holding up the idle because it is going into "needle jet range". this means i should play with the idle mixture screws for each carb? 

I am new to the honda carbonated engines, not that i'm a master mechanic on anything else either, and really need some help here.

Thanks in advance for your input 

[jmckinne]

It is normal for the idle to go up somewhat as the engine warms but yours is going to high. You don't mention where your idle starts at...?

Mine starts at about 900 and when fully warm it ends at 1000-1100. When it does grow by more it is almost always tamed by a carb sync I find.

You mention cleaning your carbs and setting the mixtures but you don't mention doing a synch. Get them synced up, set a decent idle to start with and then see if it will hold a nice lower idle <= 1200.

[shizzomynizzo]

it starts at around 1100, and idles very nicely.

I have been having problems with it keeping power through the rpm's too. I think it might be a fuel delivery problem. I have rebuilt the petcock, but theres still something wrong with it.

from what i read in other posts, it is a good idea to check the gas cap for a breather hole...I don't see one. does anyone know where it is located? could it be in the seal itself?

Thanks again

[Hush]

OK I'll bite, how about checking your cables are free and not squished against the frame somewhere, favourite place for this to happen is under your tank or badly threaded through the frame, I've found them twisted through the triple tree too so don't expect the PO to have got it all right just cos it was that way when you got it.
Is the choke being fully released when you open it (sounds dumb eh but when you open the chokes it's for running without the choke).
One of the the things to check if you can is the position of the choke butterflies, loosen the wee screws that hold them on the axle and then let them close fully, now tighten the screws while it is in that position, this will line all your choke butterflies up so they have the same closing gap.

[shizzomynizzo]

The choke is fully functional and shuts off when pushed down. I inspected to make sure they were closing when the carbs were off. the throttle cables are new and both set per the manual.

The only thing I have not done is adjust the carbs. I will have to break down and sync them.

I have never done it before, and it cannot be too easy. I will look into it on tuesday after school. I know I came across a few posts about this. It seems that syncing can solve many problems 

Thanks guys I really appreciate it

[Hush]

I definately recommend the sync job, makes a lot of evils go away, quietened my bike right down, could well be one of your carbs is set higher than the rest so the whole motor will be pulling against its self........well worth getting a shop to do it if you aren't sure.

[Scrubs]

+1 on carb sync. Stncing the carb allows the engine to run smoother at lower RPM's

One correct way of setting the Idle is to go for a long ride to get the engine fully up to temp
or in your case - where it is idling the highest - then set the tickover to the correct speed.
If your plugs/filter are good and carbs are synced etc... It should start fine and stay at
the RPM constantly may need a little throttle to keep her running for first minute.

By the way have you tried that already? not the carb sync and stuff but just setting the idle
when it's completely hot. You may find you have to tickle the throttle to keep her
running initially until the engine warms- but if you are riding her as soon as you start
her like most people that should be no problem and once it gets hot it will be running
at the correct rpm.

Much better than fiddling with it to idle fully then constantly slowing it down.

[jmckinne]

I will have to break down and sync them.

shizzo-

Yep, your range of movement is too much.

You don't have to break them down to sync them tho. You would for a "bench-sync" but that just lines them up mechanically with a drill bit spacer etc. That is usually done just to rough sync them after a rebuild.

What you really want to do is get a manometer and give them a proper dynamic syncing. The manometer measures actual flow thru the carbs when the bike is running and warm. Search on "carb synch tool". You can make your own or buy one - or take your bike to a shop of course.

[Johnny5]

Do you notice the bike running better cold or after it's warmed up? There could be plugged jets or something causing the bike to run lean or rich. Probably more on the lean side since the idle goes high after it's warmed.

Maybe a sticky carb slide too?

[shizzomynizzo]

I just pulled the carbs off 3 times this week. Gas tank was rusted so I know they needed cleaning.

first time i just pulled the bowls removed the floats and sprayed everything off. the bike ran but still idled bad and had bad hesitation.
second time i adjusted the floats pulled the jets and soaked everything in a gallon of carb cleaner. one of the needles was sticking, because gas was pouring out the overflow intermittently while running and anytime I would stop.
third time i redjuated the floats, and again pulled the jets and everything else and cleaned it very thoroughly.

It runs like a 7 on a scale of  1-10. no gas hemorrhaging from the carbs anymore at all. idles great when cold, or after a long ride and sitting in the driveway, maybe 10 - 15 minutes.

I agree that I think one of the carbs is going into jet needle range and holding the idle high.

I'll start reading how to build a sync (manometer) tool. I'm not a rocket scientist, but I'm sure I can figure it out

Thanks everyone