1980 DOHC Cb750 stalling out without choke.

[NotoriousVICb750]

Hey everyone, new rider here, novice at motorcycle maintenance but I have the help around me luckily. Just scored this ride as my first, when the bike was checked out everything was great. It was driven back for me to my place on freeway for 30-40 minutes with no issues smooth ride all together. Now, a week later, starting up the bike with choke on it starts to idle at 2k rpm then the longer it goes it slowly moves up to 4k after being warmed up for 5 minutes. Choke gets pressed back in and it stalls in a matter of seconds. Tank has plenty of fuel, does the same with the fuel tab on “On and Res.” Not sure if this is normal or not while idle but, some white smoke does seem to come out of the 4 header intakes after being warmed up. Any ideas on where to start or what this issues seems to be. Feel free to let me know, thank you for your time.

 

[NotoriousVICb750]

Hey everyone, new rider here, novice at motorcycle maintenance but I have the help around me luckily. Just scored this ride as my first, when the bike was checked out everything was great. It was driven back for me to my place on freeway for 30-40 minutes with no issues smooth ride all together. Now, a week later, starting up the bike with choke on it starts to idle at 2k rpm then the longer it goes it slowly moves up to 4k after being warmed up for 5 minutes. Choke gets pressed back in and it stalls in a matter of seconds. Tank has plenty of fuel, does the same with the fuel tab on “On and Res.” Not sure if this is normal or not while idle but, some white smoke does seem to come out of the 4 header intakes after being warmed up. Any ideas on where to start or what this issues seems to be. Feel free to let me know, thank you for your time.

For more information it all checked out when the bike was bought and it worked beautifully. It was dropped once it was in my driveway while it was off as I lost my balance and it fell onto the side without the kickstand. Gasoline did spill a bit , it was around 30 seconds max of the motorcycle being on its side.

 

[SenseAmidMadness]

What kind of gas did it have in it? E10?

Could be as simple as the idle isn't set high enough, but with the dry and hot environment of SoCal the gas could have also evaporated out fast and semi-clogged the pilot jets in just a week.

 

[NotoriousVICb750]

What kind of gas did it have in it? E10?

Could be as simple as the idle isn't set high enough, but with the dry and hot environment of SoCal the gas could have also evaporated out fast and semi-clogged the pilot jets in just a week.

Thank you for replying, not sure what kind of gas is in there , owner filled up a full tank before I picked it up , still lots of gas left. I was sitting earlier thinking about the issue and yeah it could be that with the drop I did , it may have tweaked the level of the idle screw. It has been hot lately but I haven’t ran the bike up until 2 days ago when I went to do some low speed parking lot practicing(my first bike so I’m learning to ride on it/get comfortable ) that is when I couldn’t run it without choke on. It’s under a cover but still outside. Moved the bike into my parking spot that’s under a roof.

 

[SenseAmidMadness]

The idle speed screw is right in the middle of all four carbs, sticking down between the bowls for #2 and #3. Look in there with a flashlight and then feel around for it to remember where it is. You can reach it with a gloved hand while the bike is running -- sometimes I reach down there while I'm idling at a stoplight and turn it a bit.
Start up the bike again, and as you slowly remove choke, tighten the screw a half-turn at a time. You want it to be idling around 1100rpm with the choke off once it's fully warm.

 

[NotoriousVICb750]

Wi

The idle speed screw is right in the middle of all four carbs, sticking down between the bowls for #2 and #3. Look in there with a flashlight and then feel around for it to remember where it is. You can reach it with a gloved hand while the bike is running -- sometimes I reach down there while I'm idling at a stoplight and turn it a bit.
Start up the bike again, and as you slowly remove choke, tighten the screw a half-turn at a time. You want it to be idling around 1100rpm with the choke off once it's fully warm.

Ill be doing this for sure , read that this is the most common fix for lean running engines but I’ll also check the air filter before in case that can be the simple problem too.

 

[brettp]

A non idling bike is likely pilot jets, too. If the tank is dirty and/or there was no fuel filter on it, you could have junk in your carbs.