Topic: newcomer: 76' 750f high idle (4000 rpms) when warm

[Andrew Foss]

hey everyone,
i have been reading through pages for a while but have not come to my specific problem (did a search too). i just bought a 76' cb750f and have been riding it around town for a while. today i ran into a little probblem. After filling up, once the bike warmed up it idled at around 4000 rpms. i just can't seem to get the idle to go down. I know absolutly nothing about carbs but the PO told me that he had them jetted for the pod filters he installed. i checked the intake manifold everywhere i could think of for leaks (wd-40 spray) but could not find any indication of a leak. it seems like a very simple and manual problem (something hanging up the throttle) the throttle arm does not come back all the way to the stopper (the screw on the right hand side between the two carbs) but i could not find anyhting hanging up the arm when i took the tank off. i tried pushing the throttle forward but that would not bring it down either.
   I am also having another problem with the bike stalling out. When i first start the bike (choked) it holds a low idle speed and will rev. once it runs smoothly and i ease off the choke the bike stalls out if i give it quick throtle, it will rev all the way with slower throtle but stumbles when i open it quickly. once it gets fully warmed up it starts the high idle crap. any help appreciated (i am reading through my repair manual to try to gain some insight about the carbs but i think this mught just be a cable adjustment problem.)
-andrew

[dusterdude]

have you tried to reset your idle speed when the bike is warm?

[GroovieGhoulie]

I had the same problem.  Bike ran good when cold but when hot would idle high.  I set the idle when warm as per the manual, and just give it an extra minute in the morning to wake up.

[cben750f0]

just a question, if you can get it to lower at the carbs, you havent got the cables too tight?, or when you have balanced the carbs, not given yourself enough adjustment?, or are you sucking some air somewere... just a thought?..

peace

[Andrew Foss]

just a question, if you can get it to lower at the carbs, you havent got the cables too tight?, or when you have balanced the carbs, not given yourself enough adjustment?, or are you sucking some air somewere... just a thought?..

peace

i cant get it to lower from the carbs, but i am thinking that i need to get it warmed up and adjust the cables. the return cable looks a little loose so it might just need adjustment. i just dont understand why it just started doing this today, possibly because i just got the bike and had been riding it on reserve until today? ill look at it tomorow afternoon and post what i have figured out.
-andrew

[Bean]

I'm curious if your problem was resolved by setting the idel while warm. I am having the same problem with my BRAND NEW '72 CB350F that I rode for the first time today (first bike, first post on here...)

I have to start the bike on choke and give it gas since pulling the choke lever up doesn't give more throttle (I didn't have needle nosed pliers small or long enough on me to adjust that nut in there).

After running the engine chocked for a minute I can un-choke it by pushing the lever down (choke open according to the lever, terminology seem a bit weird to me but I'm pretty sure I'm operating the choke lever correctly).

The bike idles pretty well at about 1100 though it farts/putt-putts" quite a bit. If I rev it very high it has trouble returning to that idle and ends up stalling if I don't give it more throttle to sorta catch it.

After riding the bike up and down my street it started idling at about 3500 rpm.

Tomorrow when the suns come up I'll take a look at the throttle cable. The RPM's went down by a couple hundred when I rotated the throttle forward past its resting no throttle position. I'll try adjusting the idle screw as well but I imagine it'll be tough to warm the engine up at first. Though maybe I'll just have to choke it at first for more than 10 seconds? I really hope it's simple. I do have to clean out the carbs but I was hoping to put that off till post-awesome-riding-weather-season. The overflow tubes from the carbs did leak quite a bit of fuel yesterday when I ran it, they didn't today though *shrug*.

This being my first post on here I'll hold back mentioning or asking about the many other things on my mind. I'm extremely excited having my first bike and riding it on the road for the first time.

[oldbiker]

If the throttle does not return to the stop, I'll make a bet that your throttle cables are not adjusted properly. Set them according to the manual. Next warm the bike up and use the throttle stop adjuster to get it to idle at about 1200rpm. You may find that cold starting is now a bit off but this can be adjusted at the choke lever mechanism.