'78 CB400TII "Lucy" (NEW PIPES!!!)
- Thread starter yayuppp
- Start date
Re: '78 CB400TII "Lucy" (post christmas)
Got my new tank in and lowered the gauges.
(for some reason it looks fuzzy to me ??? )
Anyways I'm having issues getting it to idle.
Starts with full choke and will idle, barely. Almost like it's running on one. Give it some gas and things start to sound better. But I still have to play with the throttle constantly to keep it alive. Do that for about 30 seconds then release the choke. It revs up to somewhere around 5k and dies. I havn't got a chance to sync the carbs. Hopefully my buddy will bring his syncer over this weekend.
Any ideas fellows?
Got my new tank in and lowered the gauges.
(for some reason it looks fuzzy to me ??? )
Anyways I'm having issues getting it to idle.
Starts with full choke and will idle, barely. Almost like it's running on one. Give it some gas and things start to sound better. But I still have to play with the throttle constantly to keep it alive. Do that for about 30 seconds then release the choke. It revs up to somewhere around 5k and dies. I havn't got a chance to sync the carbs. Hopefully my buddy will bring his syncer over this weekend.
Any ideas fellows?
MotorbikeBruno
Over 1,000 Posts
Re: '78 CB400TII "Lucy" (idle woes)
That's questionable at best, how much did you up the mains and pilots, and if they aren't mechanical carbs where the slides are moved solely by a cable...(which they aren't) idling is that much harder if everything isn't PERFECT including synchronizing the two sides.
Edit: That left gauge looks awesome.
That's questionable at best, how much did you up the mains and pilots, and if they aren't mechanical carbs where the slides are moved solely by a cable...(which they aren't) idling is that much harder if everything isn't PERFECT including synchronizing the two sides.
Edit: That left gauge looks awesome.
Maritime
Over 10,000 Posts
Re: '78 CB400TII "Lucy" (idle woes)
These carbs don't have slides, they are butterfly. You can pull them and bench since them easily, at least get both butterflies to move at the same time. Pods don't effect idle very much, mufflers will a bit. Take the carbs off together on the rack. look into them and turn the throttle control and see if both butterflys open at the same time. Your idle control screw adjusts how much the butterflies sit open when you let go of the throttle. You can start with it having them slightly open but you can;t make final adjustments until the bike is fully warmed up. These bikes are lean and cold blooded from factory so choke needs to stay on for a few minutes before they will idle correctly. They aren't the kind you use choke to start them shut it off and go, I generally have to use full choke, fires, then when idle climbs I slowly push it in until it levels again approx 1200rpm, then as bike gets warmer it will climb again and I push in the choke some more unitl it it all the way in, 2-3 minutes on a cool day, 5 mins on cold day and maybe 1-2 minutes in July. If I need to ride right away, leave choke on halfway and I get 2-3 miles and the bike tells me it no longer needs choke. THis is all after overnight sit. if I just rode it less than an hour ago, it never needs choke. You should not need to go higher than 80 on the slow jet, may need to go as high as 140 on the fast. Also this is all when I was running pods and emgo shorties. I since put some briggs style lawnmower mufflers in the ends of them to quite the bike downa nd I no longer need to choke it as long, so with your open headers, you may need to choke it for a lot longer.
These carbs don't have slides, they are butterfly. You can pull them and bench since them easily, at least get both butterflies to move at the same time. Pods don't effect idle very much, mufflers will a bit. Take the carbs off together on the rack. look into them and turn the throttle control and see if both butterflys open at the same time. Your idle control screw adjusts how much the butterflies sit open when you let go of the throttle. You can start with it having them slightly open but you can;t make final adjustments until the bike is fully warmed up. These bikes are lean and cold blooded from factory so choke needs to stay on for a few minutes before they will idle correctly. They aren't the kind you use choke to start them shut it off and go, I generally have to use full choke, fires, then when idle climbs I slowly push it in until it levels again approx 1200rpm, then as bike gets warmer it will climb again and I push in the choke some more unitl it it all the way in, 2-3 minutes on a cool day, 5 mins on cold day and maybe 1-2 minutes in July. If I need to ride right away, leave choke on halfway and I get 2-3 miles and the bike tells me it no longer needs choke. THis is all after overnight sit. if I just rode it less than an hour ago, it never needs choke. You should not need to go higher than 80 on the slow jet, may need to go as high as 140 on the fast. Also this is all when I was running pods and emgo shorties. I since put some briggs style lawnmower mufflers in the ends of them to quite the bike downa nd I no longer need to choke it as long, so with your open headers, you may need to choke it for a lot longer.
MotorbikeBruno
Over 1,000 Posts
Re: '78 CB400TII "Lucy" (idle woes)
Maritime, I thought these were similar to the goldwing carbs where they are almost a CV carb without the rubber diaphragm. maybe I'm wrong? (I'm ok with that, always willing to learn) 8)
Maritime, I thought these were similar to the goldwing carbs where they are almost a CV carb without the rubber diaphragm. maybe I'm wrong? (I'm ok with that, always willing to learn) 8)
Maritime
Over 10,000 Posts
Re: '78 CB400TII "Lucy" (idle woes)
Actualy you are kind of right and I am a bit wrong, I was forgetting the 78-79 are different from the 80-81, Mine have a booster pump in them that these may not. I was speaking from foggy memory from 3 years ago last time I was in them. I will be re-learing them again when I have time to tune them again after adding the baffles.
Actualy you are kind of right and I am a bit wrong, I was forgetting the 78-79 are different from the 80-81, Mine have a booster pump in them that these may not. I was speaking from foggy memory from 3 years ago last time I was in them. I will be re-learing them again when I have time to tune them again after adding the baffles.
Maritime
Over 10,000 Posts
Re: '78 CB400TII "Lucy" (idle woes)
I guess they have what looks like a slide that is vacuum operated and the butterflys open and close to change the vacuum? I am used to calling "slide carbs" the ones with the cable attached directly to the slide and it being pulled up by the cable and pushed back by the spring. I call these type butterfly because when you look into the mouth of the intake and atuate the mechanism the butterfly pivots and lets more air in.
I guess they have what looks like a slide that is vacuum operated and the butterflys open and close to change the vacuum? I am used to calling "slide carbs" the ones with the cable attached directly to the slide and it being pulled up by the cable and pushed back by the spring. I call these type butterfly because when you look into the mouth of the intake and atuate the mechanism the butterfly pivots and lets more air in.
MotorbikeBruno
Over 1,000 Posts
Re: '78 CB400TII "Lucy" (idle woes)
And if you have already gone up a set of pilots and still can't get that idle down, you will have to shim your main needle with little washers or move it UP (towards the sky so-to-speak) one or two notches if it has them. Although, this is only needed provided you already took care of your air leaks if there was any.
And if you have already gone up a set of pilots and still can't get that idle down, you will have to shim your main needle with little washers or move it UP (towards the sky so-to-speak) one or two notches if it has them. Although, this is only needed provided you already took care of your air leaks if there was any.
Re: '78 CB400TII "Lucy" (idle woes)
I went from a 110 to a 120. So, that's 78(or 72)/120. I bench synced the carbs. Mixtures at 1.5 out.
Now it's idling on one(drive side) cyclinder. Give it throttle and the other one fires up; let off and the whole thing dies. So I backed out the second mixture out another .5, nothing.
I noticed I have a float the droops down more than the other, when the carbs are upside down. Big problem?
I went from a 110 to a 120. So, that's 78(or 72)/120. I bench synced the carbs. Mixtures at 1.5 out.
Now it's idling on one(drive side) cyclinder. Give it throttle and the other one fires up; let off and the whole thing dies. So I backed out the second mixture out another .5, nothing.
I noticed I have a float the droops down more than the other, when the carbs are upside down. Big problem?
MotorbikeBruno
Over 1,000 Posts
Re: '78 CB400TII "Lucy" (idle woes)
So you went from 78 pilot to 120? Or you went from 78 mains to 120? (sorry, just want to verify)
Have you pulled the air screws and made sure there is an o-ring (in good condition) around it. I had a bike that was driving me nuts, then I pulled the air screw and found a washer in there....missing the O-rings under them. Ran much better after that!
One more thing, did you open your fuel tank filler lid to see if it was venting well enough?
As for the float, when upside down you are putting pressure on the little spring in the bottom of the float needle. If one droops because the spring is being loaded, and the other doesn't droop because the spring isn't working, that could be a problem too.
So you went from 78 pilot to 120? Or you went from 78 mains to 120? (sorry, just want to verify)
Have you pulled the air screws and made sure there is an o-ring (in good condition) around it. I had a bike that was driving me nuts, then I pulled the air screw and found a washer in there....missing the O-rings under them. Ran much better after that!
One more thing, did you open your fuel tank filler lid to see if it was venting well enough?
As for the float, when upside down you are putting pressure on the little spring in the bottom of the float needle. If one droops because the spring is being loaded, and the other doesn't droop because the spring isn't working, that could be a problem too.
MotorbikeBruno
Over 1,000 Posts
Re: '78 CB400TII "Lucy" (idle woes)
Well the easiest way to find out the float is to get a cup of gas, put it in there and weigh it down with something, walk away for10 min, let the weight off of it, and if it floats your are generally safe, I say this because if it floats but when you pick it up and it's much heavier...there's fuel in there
Theres a pilot jet (idle jet) middle jet (secondary jet) and main jet on yours. If I remember right. The main jet should be the 110 that you changed to 120. Thats only really in use above 1/4 throttle or so. The secondary jet is short and fat, screws into the top of one of the spots, should be 78 or something close to that. And your pilot jet is UNDER a plug of some sort, might be black rubber plug, or white hard plastic plug with o-ring, again I can't remember off the top of my head. When unscrewed, it will be longer and very skinny compared to the others. If you don't have a plug over your pilot jet circuit (the only tube that doesn't have threads in it, so the plug will fit nicely) it will run like crap. Take a picture of the insides of your carbs and we'll get to the bottom of this.
Well the easiest way to find out the float is to get a cup of gas, put it in there and weigh it down with something, walk away for10 min, let the weight off of it, and if it floats your are generally safe, I say this because if it floats but when you pick it up and it's much heavier...there's fuel in there
Theres a pilot jet (idle jet) middle jet (secondary jet) and main jet on yours. If I remember right. The main jet should be the 110 that you changed to 120. Thats only really in use above 1/4 throttle or so. The secondary jet is short and fat, screws into the top of one of the spots, should be 78 or something close to that. And your pilot jet is UNDER a plug of some sort, might be black rubber plug, or white hard plastic plug with o-ring, again I can't remember off the top of my head. When unscrewed, it will be longer and very skinny compared to the others. If you don't have a plug over your pilot jet circuit (the only tube that doesn't have threads in it, so the plug will fit nicely) it will run like crap. Take a picture of the insides of your carbs and we'll get to the bottom of this.
