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Why were you revving the piss out of your engine? You read the vacuum at idle, and when you did let it idle the vacuum readings looked good. The carb sync does nothing with fuel entering the engine. It sets the level of the slides, so that each cylinder is operating at the same power. Also when you rev an engine the vacuum will go down, so don't worry about that. As for the cold knock, it could be too thick of oil, or piston slap. I would change the oil to 10w-40, and give it a try.
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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Yes knocks, or something that sounds like the cam chain eating the engine at idle, and then going away as the engine builds up RPM is a tell of being out of sync. As for 7-9lbs. That is right in spec. If the carb boots were leaking it would not affect setting the sync, it would present itself in a whole different set of problems, kike a high idle. And as I said "the engine will loose vacuum as it is revved up" This is normal. That is how the vacuum operated hood scoops on the old GM Muscle Cars worked. When the engine was revved, the vacuum would drop, and the spring on the mechanism would be able to pull the flap open. It is also why they used vacuum cans on cars. They would do the reverse of an air compressor. Instead of holding compressed air, they would hold vacuum for when the engine was operating at wide open throttle to operate vacuum assisted devices on the cars, such as power brakes.
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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If you have the little plastic restrictors in line with your vacuumlines to the carbs, they will give you a "false" reading on actual PSI of vacuum. What you are looking for with the meters is to have them all read as close to the same as practical. Overall vacuum levels are not important.
Check it at idle, then when it's reading ~equal across the gauges, try it at 2000rpm and see if they are still in line. Then try it again at ~4000rpm. You may have to tweak it a bit to get a good overall sync at different RPM levels. My Shadow is just a bit "lumpy" at idle, but smooths out nicely once I get on the throttle.
Chances are you won't get it perfect everywhere. Like most things in life, it's a compromise. Do the best you can, and when you get it, go out and ride. Therapy is expensive, wind in the hair is cheap.
Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.
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Vacuum operated wiper blades on an old Rambler were an adventure going uphill in a driving rainstorm. Especially if the engine had low facuum to start with. Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.
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So, if you take 1 and 2 offline, what happens? Is it the same thing? How about if you switch 1 & 4 and 2 & 3? Does the problem move? What do the spark plugs look like on the insulators right after initial start up but before all cylinders fire?
What spark plugs do you have? Manual lists D8EA as the stock plug. D9 plugs are colder which can make initial starting more difficult.
I think we need to know if the problem moves if wires are changed.
Have you done a compression test? I don't see why it would matter but it would remove 1 more variable.
The ride IS the adventure. The destination is just to get gas!
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I'd go with idea #2: normal petrol issue.
DOHC or SOHC, these are some cold natured pigs. Give her some love and learn what she likes when she's cold. Runs good once its warm? Thats all you can ask for IMO. Baby her when she's cold, wring her neck once she warms up. That's what I do.
Keep in mind how teeny tiny the amount of fuel these engines burn at idle. Its amazing they does as well as they do when cold. Give it a few more pumps on the throttle for cold starts. Maybe a lil extra fuel may help the others light off a little earlier.
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Those are super rich, like "I am surprised it started" rich. When cold, choke is a way of life, even when over rich.
So, if this issue only happens on 3 and 4, then the carbs on those 2 have some sort of issue. Have you checked float height with the carbs on and fuel in the bowls? What jets are installed? How far out are the fuel screws? How did you clean the idle jets? If they had a hard blockage, air and carb cleaner does not always get it out.
The ride IS the adventure. The destination is just to get gas!
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gkmaia wrote
That is why I am selling my super fancy master powerful Ducati to keep this old bitch!
I got nothing but respect for this guy...
I couldn't see the plugs before on my phone. Im with Rerun. Thats terribly rich.
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Any reason why the jets are bigger? I would drop the idle jets back down, if not stock, probably 70 then.
Mains might be fine but wait on those till idle circuit is working better.
The ride IS the adventure. The destination is just to get gas!
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I don't know the exact metering ratios but with the fuel screws, out is richer and in is leaner. They do offer a fairly wide range of tuning though. I don't know how far the cv carbs go but mine will allow a person to drop in an 836 kit without having to rejet at all.
I would certainly try the original jets, I know pods usually require more but things are way too rich right now. If the originals are too lean, you at least know it is somewhere in the middle. The exhaust I almost never factor in unless it is a very open pipe such as a drag pipe.
The ride IS the adventure. The destination is just to get gas!
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+1 on Re-Run's post as it pertains to the jets and stuff.
You can always go back to the factory defaults regarding jet size, mixture screw, etc. Even if you have different air filters, pipes, whatever... I think the Honda engineers put those values in as the middle of the sweet spot for a running engine.
Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.
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It usually shouldn't be unless you made changes to the slides. At least that is how my carbs work. Changing jets should mess with your sync.
The ride IS the adventure. The destination is just to get gas!
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