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1979 Cb750

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750Diamond

1979 Cb750

Hey guys, this is my migraine making motorcycle, so I just bought her last year, got a great summers riding out of her. In the winter I took her apart to do some adjusting, clean the carbs all the good stuff. So I put her back together a month ago and I noticed when she idles she slowly starts to die and when I took her out for a ride my rpms were so high it was like cruise control was on. Whenever I grabbed the clutch the rpms would increase to about 5000. Cracking the throttle brought it back down to the normal 1100, also braking then downshifting would keep the rpms down when I pulled the clutch. So I was thinking maybe a vacuum leak, found a tear in one of the air boots. Replaced those, still having this problem. Recently discovered that I have an exhaust leak coming straight out of my engine, I've ordered new crush gaskets and new sets of the joint pipe collars. You guys think this will fix my problem? Or is there something deeper?

TOOLS1

Re: 1979 Cb750

Administrator

Exhaust leak will not affect the engine running, you still have a vacuum leak somewhere.
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)

750Diamond

Re: 1979 Cb750

Thanks for the respond, I've tested for a vacuum leak before but I wasn't getting any kind of response to my tests. Time to get back in it and find that leak.

TOOLS1

Re: 1979 Cb750

Administrator

The WD-40, carb cleaner, starting fluid does not always show the vacuum leak. Sometimes they are inside the carb. Check all the rubber components in the carb.
TOOLS

750Diamond

Re: 1979 Cb750

Well shucks, that's probably the problem then, I rebuilt a rack of carbs that had been sitting around for years so I probably missed something. My other carbeurators had 2 jet needles that were stripped on top. You think drilling those out with reverse threads would work without damaging the carb?

TOOLS1

Re: 1979 Cb750

Administrator

Not if you are very careful about it.
TOOLS

750Diamond

Re: 1979 Cb750

Last question, a vacuum leak inside of the carbs, what exactly am I looking for, missed rubber o ring? There just doesn't seem to be a lot inside..

On Jun 5, 2017 4:25 PM, "TOOLS1 [via Vintage and Classic Honda's]" <[hidden email]> wrote:

Not if you are very careful about it.
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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TOOLS1

Re: 1979 Cb750

Administrator

That or one not fitting properly.
TOOLS