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Hi guys, looking for some help.
I have had my bike for a couple years with no issues. My problem started with a needle valve issue with fuel coming out of the overflow. I decided at that point to do a cleaning of all 4 carbs (bank assembled) and new needle valves. After cleaning I decided to include the air cut bypass during assembly. I backed out the pilot needle 3-1/2 turns. Bike Runs but is lean at idle even after warm up. I checked for leaks at the intake boots but found none. At this point i figured there must be something clogged in the fixed idle jet. Removed the carbs again and cleaned them again and made sure I could run a wire down the fixed passage and blow cleaner through the circuit. I reinstalled them and had the same problem. Bike is lean. No matter how much I back out the pilot needle it is lean. Any ideas to my problem. The only thing I changed is the air cut bypass. Should I not bypass the air cut? Anyone else had this problem? Any help would be appreciated. Thanks
-stock jets 68 primary, 102 secondary
-stock air box/filter
-exhaust is stock 4x4 but previous owner cut most of the mufflers off
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This reads like you read and followed the carb cleaning manual well.
Backing out the fuel/mix screw should fix this if your idle jet is truly clean. Sucks that it is pressed in on your model.
Are you running the stock airbox? Did you bypass the SOS and made sure to have the vacuum teat plugged, but the breather open (plastic "T" in between 2-3)?
Also, to confirm - you held one finger over the mainjet hole, another over the lower air cutoff hole, and then sprayed cleaner through the slow speed emulsion tube. When you did this you got bubble out of the pilot screw tube and the little tiny metering holes? The carb cleaner spray straw will have to be wrapped with electrical tape to get a snug fit.
There is a way to drill and pull the pressed in slow speed emulsion tubes out, but damn, that is some tricky stuff I wouldn't want to try if you don't have a spare set of carbs.
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.
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Thanks for the reply,
I have stock air box, although some of the air box rubber boots are cracked from pulling carbs in and out, not sure if that has an affect or not. I don't have SOS, I don't think I have a vacuum teat either? Plastic T is open. I was able to get spray out of the pilot screw port and small hole inside the carb body in front of the butterfly.
I'm not sure what to try next...
On Tue, May 28, 2013 at 9:23 PM, seestheday [via Honda CB750'S] <[hidden email]> wrote:
This reads like you read and followed the carb cleaning manual well.
Backing out the fuel/mix screw should fix this if your idle jet is truly clean. Sucks that it is pressed in on your model.
Are you running the stock airbox? Did you bypass the SOS and made sure to have the vacuum teat plugged, but the breather open (plastic "T" in between 2-3)?
Also, to confirm - you held one finger over the mainjet hole, another over the lower air cutoff hole, and then sprayed cleaner through the slow speed emulsion tube. When you did this you got bubble out of the pilot screw tube and the little tiny metering holes? The carb cleaner spray straw will have to be wrapped with electrical tape to get a snug fit.
There is a way to drill and pull the pressed in slow speed emulsion tubes out, but damn, that is some tricky stuff I wouldn't want to try if you don't have a spare set of carbs.
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.
My cb750 video site
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yes, I think the SOS only came about in 1981.
You say that your rubber boots that are going into the airbox are torn. That might be your issue. The rubber boots act like velocity stacks that pull non turbulent air from within the airbox. If you have rips/cracks messing up how air is getting pulled in it could cause some cylinders to run lean.
Can you fix the cracks with some silicone or even tape to see if it helps your lean condition?
Those boots are supposed to be quite supple, so it's probably time you replaced them anyways.
Also, how are your insulators? The parts going from your carbs to the engine. They often crack and have leaks if they're old, although that causes a high idle, not usually a lean condition.
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.
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Thanks for info. Where can I get the rubber boots?
Sent from my iPhone On May 29, 2013, at 9:42 AM, "seestheday [via Honda CB750'S]" < [hidden email]> wrote:
yes, I think the SOS only came about in 1981.
You say that your rubber boots that are going into the airbox are torn. That might be your issue. The rubber boots act like velocity stacks that pull non turbulent air from within the airbox. If you have rips/cracks messing up how air is getting pulled in it could cause some cylinders to run lean.
Can you fix the cracks with some silicone or even tape to see if it helps your lean condition?
Those boots are supposed to be quite supple, so it's probably time you replaced them anyways.
Also, how are your insulators? The parts going from your carbs to the engine. They often crack and have leaks if they're old, although that causes a high idle, not usually a lean condition.
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.
My cb750 video site
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