|
|
|
|
Hi all, got the '81 cb750 going, bought a carpy pipe, lots of cool shit. However, as I was idling the bike to cure the clear coat on the new pipe, the bike started to rev up high, like past 3 grand, and wouldn't drop down, even after snapping the throttle and stuff. It idled beautifully at 1000 rpm for about 2 or 3 minutes, then just randomly started to rev. I shut it off and let it cool down for 10 minutes. Started it up again after, no problem, and idled great for another 2-3 minutes, then did the same thing. Any ideas? As well, when I got the bike, #3 carb was leaking, like pouring, so I pulled the carbs off, tore them all apart, cleaned the shit out of them, then rebuilt them. Put in a new rubber tip needle from vintagecb750s.com to stop the leak. It didn't... I guess it's leaking at the seat, because it just drips out the overflow all the time. The seats aren't replaceable as far as I know, does anyone know if I can fix this, or do I need a whole new carb? Thanks in advance for your help, I know how amazing all you are at knowing what to do and giving advice 
-sean
1981 cb750K
1977 Maico aw400
1975 MR50
1970 Hodaka Super Rat
1972 Hodaka ace100
|
|
|
Do you have adjustable floats? They should be adjusted to 15.5mm from the base (where the bowl sits on) to the top of the float. Maybe your float has a small hole in it? You can polish the needle seats with brasso (cut a Q-tip on one side and put it in a drill and go for it!) Makes it nice and shiny and clean!
I think the high idle thing is a vacuum leak somewhere
Have you messed with the idle adjustment knob at the bottom of the carbs?
1981 SS with Kerker 4-1 exhaust and extremely attractive rider.
|
|
|
No, floats are not adjustable. Alright, I'll try the q tip thing! Any ideas where the vacuum problem might be coming from? Thanks so much. Yeah I got the idle dialed with that knob. Do you think the pipe leaned the bike out enough to be a problem?
-sean On 2013-04-26, at 9:13 PM, "Johnnylevi [via Honda CB750'S]" < [hidden email]> wrote:
Do you have adjustable floats? They should be adjusted to 15.5mm from the base (where the bowl sits on) to the top of the float. Maybe your float has a small hole in it? You can polish the needle seats with brasso (cut a Q-tip on one side and put it in a drill and go for it!) Makes it nice and shiny and clean!
I think the high idle thing is a vacuum leak somewhere
Have you messed with the idle adjustment knob at the bottom of the carbs?
1981 SS
To unsubscribe from Idling Problem While Warming & Carb Leaking, click here.
NAML
|
|
|
Check for a vacuum leak by spraying a flammable aerosol (unlit propane torch, wd-40, etc) around the carb insulators. That is a likely source of your vacuum leak. You should be able to isolate it to at least the left or right side of the bike (carbs 1-2 or 3-4). Lots of places they could be leaking. Cracked old insulators are the usual culprit, but it could be leaking via a loose carb sync vacuum sensor screw or even somewhere inside the carb.
1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals
My wife's recipe website that I'm trying to help promote: Strawberries for supper. Yes, I am a lucky man.
|
|
|
Mine did the same thing and it was just a float sticking. Tapped on the side of the suspect bowl and idle dropped and leak quit. I assume some of the excess gas was flowing into the chamber as well as the overflow causing the idle to rise. Two Sea Foam treatments later it hasn't happened again.
|
|
|
Shit eh alright. The float isn't sticking, I believe the seat is just worn. I hate to sound like a newbtard, but what part are you calling the insulator? Do you mean like the air boots? I think they all look good, I'll check them out though for sure! Why do you think it would only do this once warm?
-sean
On 2013-04-26, at 10:16 PM, "seestheday [via Honda CB750'S]" < [hidden email]> wrote:
Check for a vacuum leak by spraying a flammable aerosol (unlit propane torch, wd-40, etc) around the carb insulators. That is a likely source of your vacuum leak. You should be able to isolate it to at least the left or right side of the bike (carbs 1-2 or 3-4). Lots of places they could be leaking. Cracked old insulators are the usual culprit, but it could be leaking via a loose carb sync vacuum sensor screw or even somewhere inside the carb.
1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals
My wife's recipe website that I'm trying to help promote: BuffyAndGeorge.com. Yes, I am a lucky man.
To unsubscribe from Idling Problem While Warming & Carb Leaking, click here.
NAML
|
|
|
Insulators connect the carbs to the head. Sent from my BlackBerry device
Shit eh alright. The float isn't sticking, I believe the seat is just worn. I hate to sound like a newbtard, but what part are you calling the insulator? Do you mean like the air boots? I think they all look good, I'll check them out though for sure! Why do you think it would only do this once warm?
-sean
On 2013-04-26, at 10:16 PM, "seestheday [via Honda CB750'S]" < [hidden email]> wrote:
Check for a vacuum leak by spraying a flammable aerosol (unlit propane torch, wd-40, etc) around the carb insulators. That is a likely source of your vacuum leak. You should be able to isolate it to at least the left or right side of the bike (carbs 1-2 or 3-4). Lots of places they could be leaking. Cracked old insulators are the usual culprit, but it could be leaking via a loose carb sync vacuum sensor screw or even somewhere inside the carb.
1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals
My wife's recipe website that I'm trying to help promote: BuffyAndGeorge.com. Yes, I am a lucky man.
To unsubscribe from Idling Problem While Warming & Carb Leaking, click here.
NAML
To unsubscribe from Idling Problem While Warming & Carb Leaking, click here.
NAML
1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals
My wife's recipe website that I'm trying to help promote: Strawberries for supper. Yes, I am a lucky man.
|
|
|
Ok that's what I thought you meant, thanks so much
-sean On 2013-04-27, at 12:22 AM, "seestheday [via Honda CB750'S]" < [hidden email]> wrote:
Insulators connect the carbs to the head. Sent from my BlackBerry device
Shit eh alright. The float isn't sticking, I believe the seat is just worn. I hate to sound like a newbtard, but what part are you calling the insulator? Do you mean like the air boots? I think they all look good, I'll check them out though for sure! Why do you think it would only do this once warm?
-sean
On 2013-04-26, at 10:16 PM, "seestheday [via Honda CB750'S]" < [hidden email]> wrote:
Check for a vacuum leak by spraying a flammable aerosol (unlit propane torch, wd-40, etc) around the carb insulators. That is a likely source of your vacuum leak. You should be able to isolate it to at least the left or right side of the bike (carbs 1-2 or 3-4). Lots of places they could be leaking. Cracked old insulators are the usual culprit, but it could be leaking via a loose carb sync vacuum sensor screw or even somewhere inside the carb.
1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals
My wife's recipe website that I'm trying to help promote: BuffyAndGeorge.com. Yes, I am a lucky man.
To unsubscribe from Idling Problem While Warming & Carb Leaking, click here.
NAML
To unsubscribe from Idling Problem While Warming & Carb Leaking, click here.
NAML
1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals
My wife's recipe website that I'm trying to help promote: BuffyAndGeorge.com. Yes, I am a lucky man.
To unsubscribe from Idling Problem While Warming & Carb Leaking, click here.
NAML
|
|
|
2stroker_4_life wrote
No, floats are not adjustable. Alright, I'll try the q tip thing! Any ideas where the vacuum problem might be coming from? Thanks so much. Yeah I got the idle dialed with that knob. Do you think the pipe leaned the bike out enough to be a problem?
While you've got the carbs out, check the overflow tubes for cracks. That can cause leaking as well. Some guys have had good results fixing cracked overflow tubes with JB weld.
You should be able to adjust the float by bending the tang if needed. Check the FSM or other threads on this board.
Good luck.
Livin' my life like a song.
1985 Honda Rebel 250 - "Birdie"
1979 CB750K - "Behemoth"
|
|
|
Floats on the 81 aren't adjustable. I think it was only the 79 dohc that had adjustable ones.
1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals
My wife's recipe website that I'm trying to help promote: Strawberries for supper. Yes, I am a lucky man.
|
|
|
Rubber tip needles are NOT interchangeable with metal needles!
The angle of the seat is completely different.
On a Roadstar Adventure.
|
|
|
You cannot just bolt on a new exhaust and not expect to have to make adjustments.
IT may be lean but not from an air leak.
What year?
What kind of intake system?
Are the jets stock?
On a Roadstar Adventure.
|
|
|
Alright guys, I think I have done something. Started the bike up again today, same thing happened, but rather than turning it off I just turned the idle down back to where it's supposed to be. Came up to about 2k again, so turned we down a bit more so she idles around 12. Ran for prob 10 minutes after that no problem, so maybe it's fixed. I'm worried that it won't start cold now though because the idle is turned so low. Thoughts? I have no idea what jets are in it, all the markings are off the main jets. When I got the bike it had an aftermarket 4-2 on it, so it may already be leaned out. It has stock airbox and filter, and it's an 81 750K. Float level isn't adjustable, the whole float is plastic including the tab the needle sits in. Put new rubber tipped needle in to replace old rubber tipped needle, so no mess up there. Haven't tried the q tip trick yet, hate taking those facking carbs off and back on again...should I put some autosol or equivalent on the q tip? Thanks everybody for your help!!
-sean On 2013-04-28, at 6:59 PM, "Lucky 1 [via Honda CB750'S]" < [hidden email]> wrote:
You cannot just bolt on a new exhaust and not expect to have to make adjustments.
IT may be lean but not from an air leak.
What year?
What kind of intake system?
Are the jets stock?
Working on a CB750 Digger named Rover
To unsubscribe from Idling Problem While Warming & Carb Leaking, click here.
NAML
|
|
|
Are you starting it with the choke on? When you use the choke the mechanism actually pulls the throttle open a little bit. The amount that it opens the throttle is adjustable. Yours may be set too low.
1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals
My wife's recipe website that I'm trying to help promote: Strawberries for supper. Yes, I am a lucky man.
|
|
|
2stroker_4_life wrote
Alright guys, I think I have done something. ..............
Haven't tried the q tip trick yet, hate taking those facking carbs off and back on again...should I put some autosol or equivalent on the q tip? Thanks everybody for your help!!
I've used Autosol on mine with no problems Just flush well with carb cleaner when you're done.
Livin' my life like a song.
1985 Honda Rebel 250 - "Birdie"
1979 CB750K - "Behemoth"
|
|
|
Just when it's cold. I would like to try to adjust that though it doesn't make it rev up too much. Where is that adjustment?
-sean On 2013-04-30, at 8:05 AM, "seestheday [via Honda CB750'S]" < [hidden email]> wrote:
Are you starting it with the choke on? When you use the choke the mechanism actually pulls the throttle open a little bit. The amount that it opens the throttle is adjustable. Yours may be set too low.
1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals
My wife's recipe website that I'm trying to help promote: BuffyAndGeorge.com. Yes, I am a lucky man.
To unsubscribe from Idling Problem While Warming & Carb Leaking, click here.
NAML
|
|
|
You have to remove the carbs and bend a tab. Details and pics are in the MacGregor carb cleaning manual.
By cold, do you mean when it's really cold outside, or when the engine hasn't been running for a while.
There is no reason why you wouldn't use the choke to start the bike when the engine hasn't been running for a while. If you don't need to then you're probably running too rich.
1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals
My wife's recipe website that I'm trying to help promote: Strawberries for supper. Yes, I am a lucky man.
|
|
|
By cold I mean hasn't been running for like a day. I started it up today, about 24h since last time I had it running. Pulled the choke and it fired up instantly. Idled around 1500 with the choke on and about 700 with it off right after it was warm enough to do so. Does it sound fixed?
-sean
On 2013-04-30, at 12:12 PM, "seestheday [via Honda CB750'S]" < [hidden email]> wrote:
You have to remove the carbs and bend a tab. Details and pics are in the MacGregor carb cleaning manual.
By cold, do you mean when it's really cold outside, or when the engine hasn't been running for a while.
There is no reason why you wouldn't use the choke to start the bike when the engine hasn't been running for a while. If you don't need to then you're probably running too rich.
1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals
My wife's recipe website that I'm trying to help promote: BuffyAndGeorge.com. Yes, I am a lucky man.
To unsubscribe from Idling Problem While Warming & Carb Leaking, click here.
NAML
|
|
|
dude, 700 is a very low idle. Mine would stall if it were idling that low.
If I were you I wouldn't worry about it, although you might want to check your plugs to make sure you aren't running too rich.
1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals
My wife's recipe website that I'm trying to help promote: Strawberries for supper. Yes, I am a lucky man.
|
|
|
It will idle as low as 500, the things a tractor! I will check the plugs, that's something I didn't expect, putting an open exhaust on it and being too rich...ahahaha
-sean On 2013-04-30, at 9:34 PM, "seestheday [via Honda CB750'S]" < [hidden email]> wrote:
dude, 700 is a very low idle. Mine would stall if it were idling that low.
If I were you I wouldn't worry about it, although you might want to check your plugs to make sure you aren't running too rich.
1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals
My wife's recipe website that I'm trying to help promote: BuffyAndGeorge.com. Yes, I am a lucky man.
To unsubscribe from Idling Problem While Warming & Carb Leaking, click here.
NAML
|
|
Locked
