DanDeZinna
CB750 Enthusiast
The o rings ended up being in there. I purchased a kit that had all replacement jets and O rings
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1980 Honda CB750F Runs with choke then dies with choke off.
- Thread starter DanDeZinna
- Start date
Yes, nothing worse than spending time to help someone and getting no reply back. Granted, some are not used to using the internet or forums. Need more interest in this forum too.
DanDeZinna
CB750 Enthusiast
Thanks man! I really appreciate other people taking the time to read and help diagnose issues I haven’t experienced that other people have! This has been a great forum so far!
DanDeZinna
CB750 Enthusiast
Update for everyone following!
Today I reinstalled the carbs with brand new intake manifold boots and hooked everything up. The bike fired right up with choke and then idled up to about 2,000rpm. I pushed the choke in the bike died right away again. I started it back up and set the idle to about 1200rpm and the bike ran but would die when I gave it throttle. I let it warm up and kept trying with same results so I’m pretty sure I have the fuel/air mixture screws set to rich at 3 turns out. I read some forums that recommend this setting and was worth a shot. Tomorrow I’m going to sync the carbs up again and turn the fuel / mixture screws in to 2 turns out and see how it responds. I’ll keep everyone updated!
Today I reinstalled the carbs with brand new intake manifold boots and hooked everything up. The bike fired right up with choke and then idled up to about 2,000rpm. I pushed the choke in the bike died right away again. I started it back up and set the idle to about 1200rpm and the bike ran but would die when I gave it throttle. I let it warm up and kept trying with same results so I’m pretty sure I have the fuel/air mixture screws set to rich at 3 turns out. I read some forums that recommend this setting and was worth a shot. Tomorrow I’m going to sync the carbs up again and turn the fuel / mixture screws in to 2 turns out and see how it responds. I’ll keep everyone updated!
Do your mixture adjustment before you sync the carbs.
Your accelerator pump(s) may need to get some fuel in them. I've had to twist the throttle a number of times before they would start to squirt fuel. With the bike off, twist the throttle 15-20 times. Ought to do it.
May not solve your issue, but an easy thing to do.
May not solve your issue, but an easy thing to do.
DanDeZinna
CB750 Enthusiast
Another small update!
Adjusted mixture screws a 1/2 turn at a time and monitored running. I went from 3 turns out to 2 turns out and the bike started to back fire really bad so I guess to lean. Also the bike wouldn't rev out much or at all . You twist the throttle and it just bogs and slowly revs up. Then takes forever to get back down to idle. I think I may be pulling the carbs back out and going through them again! Not really sure what steps to take next
Adjusted mixture screws a 1/2 turn at a time and monitored running. I went from 3 turns out to 2 turns out and the bike started to back fire really bad so I guess to lean. Also the bike wouldn't rev out much or at all . You twist the throttle and it just bogs and slowly revs up. Then takes forever to get back down to idle. I think I may be pulling the carbs back out and going through them again! Not really sure what steps to take next
DanDeZinna
CB750 Enthusiast
Thank you Brett!! I definitely gave this a shot and didn’t seem to make a difference.
Hanging in the rev range before coming back to idle is indicative of a lean condition or carbs being out of sync.
Have you check for cracked boots between the carb and engine? Synced the carbs?
Have you check for cracked boots between the carb and engine? Synced the carbs?
DanDeZinna
CB750 Enthusiast
I just installed brand new intake boots between the engine and the carbs! Haven’t synced the carbs yet! Was trying to get mixture set correctly then sync but couldn’t find the sweet spot since it won’t rev out!
Do you have the gauges on it now while you are doing this? If not put them on and see what you got.
DanDeZinna
CB750 Enthusiast
I currently don’t have them on but I’ll put them on and see what they’re showing! I’m going to set my mixture screws to 3 1/4 turns out and hook them up! I’ll report back with what I find!
Did you mean 2 1/4¿
DanDeZinna
CB750 Enthusiast
Yes sorry! I’m going to set them at 2 1/4 turns and go from there! Is that what you would normally set them too or around that?
Yeah. Curious what your vacuum gauges are going to show
DanDeZinna
CB750 Enthusiast
I will hook them up tomorrow!! My bike is at my work!
DanDeZinna
CB750 Enthusiast
Another update!
Was able to continue with troubleshooting and adjustments. I started off with adjusting the fuel mixture screws to 2 1/2 turns out and it still seemed pretty lean. So I went to 3 turns out and the bike started to actually run better but still not great as in idle was ehh but would kinda rev out but still bogging. I went to 3 1/4 turns out and it got better and the bike actually wanted to try and idle. So I stuck the sync gauges on and it was pretty out of sync. I got them relatively synced up and the bike started to idle and kinda rev out, but still not great. (The bike was at operating temp). I may do some more adjustments with the fuel mixture screws to see if that helps make a difference with throttle response. I feel like I’m on the right track but still not there. My battery died and couldn’t get it started back up so I think I have an issue with the charging system. I’m away for work for 3 weeks so I’ll attempt some more tinkering when I get back!
Was able to continue with troubleshooting and adjustments. I started off with adjusting the fuel mixture screws to 2 1/2 turns out and it still seemed pretty lean. So I went to 3 turns out and the bike started to actually run better but still not great as in idle was ehh but would kinda rev out but still bogging. I went to 3 1/4 turns out and it got better and the bike actually wanted to try and idle. So I stuck the sync gauges on and it was pretty out of sync. I got them relatively synced up and the bike started to idle and kinda rev out, but still not great. (The bike was at operating temp). I may do some more adjustments with the fuel mixture screws to see if that helps make a difference with throttle response. I feel like I’m on the right track but still not there. My battery died and couldn’t get it started back up so I think I have an issue with the charging system. I’m away for work for 3 weeks so I’ll attempt some more tinkering when I get back!
If your bike was at idle for most of the sync process, the bike won't charge the battery. It needs some throttle and RPMs to charge. I have a battery tender connection on mine that I can easily hook up to help the battery if I'm idling it long. And while we're on the topic, put a fan in front of the motor while doing that, they're air cooled.
Keep in mind, the mixture screw is only going to influence the idle. For revving the bike, we're looking at needles and main jets.
Keep us updated.
Keep in mind, the mixture screw is only going to influence the idle. For revving the bike, we're looking at needles and main jets.
Keep us updated.
