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internal leaking carbs?

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croker4352

internal leaking carbs?

Having an issue with starting after sitting over night and a idle issue.

Idle-I can raise the idle via the adjustment knob but I can't lower the idle below 1250, not a big inconvenience but thinking it's related to main problems.

After sitting for a few hours or especially noticeable over night, I have hard starts. I have figured out the best way is to crank with full choke, even then its only idling at 1k for about 15 secs before it pops up to 3k and the bike runs fine. I having a feeling the carbs have a slight internal gas leak and its a flooded until it burns of the extra fuel and idls fine again. Possible? Thoughts?

Also having an occasional hesitation when going from idle to blipping the throttle, so bad at times it has stalled the bike out.

Also noticed, the throttle, will snap shut nice, but the front cable has a SLIGHT pull on it. If I rotate the throttle forward I can see the front cable just alittle slack and the front linkage move up just a little. It's had to explain but I took a video in case nobody can understand how I tried to explain it.

Any thoughts on my issues? Related?

shinyribs

Re: internal leaking carbs?

Administrator

Sounds like the symptoms of a vacuum leak.

There is an adjustment in the throttle cable to fix your slack issue. It's in the cable itself a few inches from the throttle housing.

croker4352

Re: internal leaking carbs?

how Would the vacuum leak cause the bike to have hard starts for only the first 20 secs or so?

Lucky 1

Re: internal leaking carbs?

In reply to this post by croker4352

What motorcycle????

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TOOLS1

Re: internal leaking carbs?

Administrator

In reply to this post by croker4352

croker4352 wrote

how Would the vacuum leak cause the bike to have hard starts for only the first 20 secs or so?

For the same reason that engines run better as they warm up.
TOOLS

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croker4352

Re: internal leaking carbs?

In reply to this post by Lucky 1

82 nighthawk 750.

I found that if I turn off the fuel a block away from my house and burn our stone of the fuel left on the carbs it does have better stats. That's what led me to think it's leaking somewhere internally. But I'm no expert on carbs by any means. I will take another shot at adjusting the cables today. I spent over an hour lubing and getting to adjusting them yesterday with no progress.

TOOLS1

Re: internal leaking carbs?

Administrator

The idle problem is more then likely a vacuum leak at the rubber boots between the carbs, and the head.
The cable could be either an adjustment, or the "push" cable is broken.
The fuel leak is a needle valve not seating. The valve could be bad, the seat could be dirty, the float could be out of adjustment, the float could be sticking on the pivot pin, or the float could be bad.
TOOLS

seestheday

Re: internal leaking carbs?

In reply to this post by croker4352

I forget, do you still have your SOS on your nighthawk? Those cause notoriously hard starts, and may not be related to the vacuum leak.

1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals

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Johnnylevi

Re: internal leaking carbs?

In reply to this post by croker4352

the blipping sounds like a rich mixture to me, but check your floats and your boots like tools was saying. You can check for vacuum leak by spraying carb cleaner around the boots and if the idle goes up for a sec youve got a leak. I think theres something thats nicer on rubber that you can use, but I've used it once or twice and my boots are fine.

1981 SS with Kerker 4-1 exhaust and extremely attractive rider.

croker4352

Re: internal leaking carbs?

No SOS on it, I tightened the boots, still no fix, sprayed starting fluid sound the boots and couldn't find a leak. Idle still won't go below 1250! A vacuum lake would make sense on that though... If I hooked my vacuum gauges up to the block think it would help show what cylinder I had the leak?