Topic: My bike wont stay running without choke up...

[Black Hercules]

Sohc4 world, whats up, Im having an issue with my 78 cb750k , I just installed my carbs back in the bike last week after a small cleaning. now when I start my bike with choke and after 20 mins of warming up I try to push choke back down , and bike
just dies, I pull choke back up and the starts and stays on, I was riding the bike like this last night , but I want to see if you guy's can give me any suggestions, on what might be possible  causing my sweet cb750 A.K.A BLACK HERCULES to act up, I know the name of my bike seems a little weird, but Im sure Im not the only guy here naming there bikes silly names. Please Help, Raul N.Y.C

Also I forgot to mention one more thing , my garage was smelling heavy with fuel fumes. Could that be Im running Rich, I adjusted my gas srcerws 1 and a half turn...............

[Gordon]

Yes, it's running rich because you have to leave the choke on for it to keep running. 

I know this sounds like a dumb question, but have you tried turning in the idle stop screw?

[Black Hercules]

No I have not , and thanks I will try that.....

[beta1042]

I had the same problem last year.  Final solution was to take the carbs off again and reclean them.  I found a clogged jet that I swore I cleaned the first time.  Once I cleaned that out I put it back together and it ran like a charm.  Unfortunately no silver bullet so it may mean you check the jets again, but you can do that by just taking off the bowls.  A little less labor intensive.

Good Luck.

Danny

[333]

I'd clean or replace the spark plugs,too.  They have to be fouled if you run the choke for that long.  And those screws you've adjusted are air screws.  The gas is fixed by a specific size jets, idle and main. 

[BobbyR]

Raul, I have the same bike and you are running too lean. By using the choke you restricting the air which produces a richer mixture. Running lean can come from having an air leak in the carb rubbers or plugged idle jets. On the 77-78 750s the idle mixture screws are mixture screws unlike the earlier carbs. The 1 1/2 turns was probably a wink and nod to the EPA. Spray some carb cleaner around he boots when she is running and see if you can hear a difference in the engine, you have a leak. If that is good play with the mixture screws and see of that helps. If that is of no help, you may need to clean out those jets. Actually it could be all of those.

[jdpas29]

my bike had the same problem when i first got i partially running.

my solution was to do an entire tune up

set the breaker point gap.  set the valve gaps.  make sure you don't have any leaks around the rubbers.  make sure your airbox is set up right for air flow and replace the filter if not clean.  your air mix screws need to be set as well as the idle.  if you don't have vacuum gauges go ahead and buy them.  replace the spark plugs or just clean them up if they look good.  make sure your battery is fully charged.

i'm sure i left out some stuff but...  i have the same year model and everything so i'd be happy to help.

[ANVkevin]

I'm having almost the same issues with my '77 CB750K. But not to that extent. It runs without the choke after warm, but it runs alot better choked. It also has a silly name, Sweet Pea. I just wish it ran alittle sweeter.

[Black Hercules]

Thanks guy's for the replys.. let me tell you what I did, I just took off carbs a few weeks ago , and I just removed my bowls and
clean them , because there was crud inside them, I also removed choke valves clean them, also pilot screws as well cleaned and put back  and I thought that was my problem,  I  was going to
take all 4 carbs apart , but I got cold feet, I never worked on bikes in my life Im the type of person if I see someone helping me that knows what they are doing then I quickly pick up the technic, but with all the manules and sohc4 resources I was afraid that  the bike was never going to start if would had taken the carbs apart .So I just replaced bowls back into carbs, and I adjusted the pilot screws (4 screws )1 and half turn and I put carburator back on the bike, I also
put new spark plugs because I did not installed new ones when I got bike last year. Sorry for the long reply, but I have to come clean. So I started bike last week and it sounded awosome,the only problem then was the choke when push down , bike would fade and shut off , so I road the bike with the choke up around my way and and coming back home bike did not feel right any more it was slight hesitent on take off's every time that I stopped, but then once I switched gears it was O.K. So when I posted
this problem ,GORDON was my first reply that I got , and he mention about the stop idle screw and I was like YEAH I forgot to adjust that like the manule said and I stated bike choke up let it warmed up for 10 mins , then pushed choke down and bike was going to die, but as soon as I increased Idel screw I got bike to stay running, but then it started to slightly back fire,and I was like #$%*
I can not get this machine right, so today I removed all 4 plugs clean them , #4 was kinda white and the rest where black, because I know I was running with choke up, I put the plugs back and decided to go for another ride this time on the highway, I was doing 50MPH and it felt like it had alot of power left, but I held back because Im still not used too the bike, so as soon as I got off exit I stopped at red light and the bike kept reved up to 2 , 3 rpm it took a long time to rev back down to 1 rpm. I also got pulled over the the police and got 3 tickets one for vertical license plate second for no inspection and third for no Motorcycle license I only have my permit,but I know a few officers that could help me out on the tickets.. Way to go Right.. Nice.. any way I guess to put long story short Im going to dismantle the carbs and I think that Im going to do it right this time... Thanks for reading my post. so know the bike revs up high and it takes along time to come back down, I know carbs have to come out , but please reply back with suggestions, thank you once again guys you have been alot of help...

[upperlake04]

Herc - I can't diagnose your bikes problem like some here can but I've just been through a month of head scratching and trying different things to stop the same high idle you have. It turned out to be a combination of two things. 1- some of the  carb boots, both the carb/air box and the carb/engine side were leaking air.  2- the carbs were not synchronized which caused one or more cylinders to pull harder. 
  Once this was sorted out, the rpms  dropped down quickly and made the idle  smooth and steady. Keep at it, do one thing at a time and see what effect it has, then move on to the next. You'll get it, its not voodoo. 

[Black Hercules]

 Thanks upperlake04 I think that Im going to start with new rubbers on the carbs and air filter box

Herc - I can't diagnose your bikes problem like some here can but I've just been through a month of head scratching and trying different things to stop the same high idle you have. It turned out to be a combination of two things. 1- some of the  carb boots, both the carb/air box and the carb/engine side were leaking air.  2- the carbs were not synchronized which caused one or more cylinders to pull harder. 
  Once this was sorted out, the rpms  dropped down quickly and made the idle  smooth and steady. Keep at it, do one thing at a time and see what effect it has, then move on to the next. You'll get it, its not voodoo.