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First post, I'm learning a lot here already.
I have a '78 CB750F Super Sport, it is in extremely clean condition, no rust, no old cables, etc... and it does not seem to want to start in temps below ~52 degrees. Once it's warm it idles great, and it runs great in all gears. The previous owner put a Dyna system in, and I'm wondering if that may be the cause of the problem. Battery is strong, carbs have been recently cleaned/synced, new spark plugs.
I have to hold down the elec start for a long time (when it's cold) while the engine is trying to start. One trick that seems to help is to adjust the idle speed to much faster than it should be. I do this just when I'm trying to start the bike, I have to slow down the idle speed once it warms up(otherwise it would be idling at ~2500RPMs).
I'm pretty new to maintenance/adjustments... but I was planning on trying to diagnose the problem by taking the carbs apart, checking the timing, float levels, etc.. I was just wondering if anyone has advice in where to start?
Thanks in advance
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Administrator
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Is your choke working properly? Check to make sure it is closing. Also, even though you have just had the carbs cleaned, your pilot jets might still be plugged. I have seen this several times on these keyhole carbs.
TOOLS
Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
Darkwing Duck: The worst part of public transportation is the Public.
"That is awesome shit there" Re-Run
"Fear nothing, attack everything" Eric Berry
" Oh, you read that on the internet? Clearly it IS a massive problem. Of course it CAN’t be normal operation."
1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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Now that you mention it, the choke seems to lag a bit when the bike is warm... takes a second for it to actually do anything. And it really doesn't seem to be helping the bike start in the cold. How would I go about adjusting that?
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Administrator
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If it is just an adjustment, you can loosen the screw that holds the cable to the carb, and pull up on the cable casing while tightening the screw back up. However you really need to look in the back of the carbs to make sure they are closing properly. I have seen the linkage messed up between the two sets after being put back together after a rebuild.
TOOLS
Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
Darkwing Duck: The worst part of public transportation is the Public.
"That is awesome shit there" Re-Run
"Fear nothing, attack everything" Eric Berry
" Oh, you read that on the internet? Clearly it IS a massive problem. Of course it CAN’t be normal operation."
1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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Thanks. To check and see if the carbs are closing properly, do I need to remove the carbs? Also is that a separate issue from pilot jets? Forgive my ignorance.
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Administrator
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No, just remove the airbox. the choke actuates the flaps. They should close virtually all the way when the choke knob is pulled.
Does the bike start and then die right away? if so, then the fast idle cam is probably not adjusted right and you would need to hold the throttle to keep rpm up until you have it adjusted.
During the time you have the airbox off, twist the throttle and make sure fuel shoots out of the 4 brass nozzles to verify the accel pump is working.
The ride IS the adventure. The destination is just to get gas!
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Administrator
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The pilot jets are a totally different system on the carbs. Here is a link to a tutorial on how to remove them for cleaning. http://honda-cb750-s.456789.n3.nabble.com/Removing-pressed-in-Pilot-Jets-from-Keyhole-carbs-td4036674.html They are impossible to clean without removing them.
TOOLS
Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
Darkwing Duck: The worst part of public transportation is the Public.
"That is awesome shit there" Re-Run
"Fear nothing, attack everything" Eric Berry
" Oh, you read that on the internet? Clearly it IS a massive problem. Of course it CAN’t be normal operation."
1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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Thanks guys, I might try adjusting the fast idle, and checking to see if the choke is working properly. If that doesn't work, get into the carbs.
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Administrator
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I like to start with easy things first, especially if doing them prepares me for going in further. 
The ride IS the adventure. The destination is just to get gas!
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