Honda Hawk CB400 carb question

indy452May 29, 2007

Hello, I'm not sure how active this forum is but I have a question for the mechanics out there.

I have an older 1978 Honda Hawk CB400A.

My carbs are both leaking from the overflow tube. I go to the Honda dealer and buy the new needles for the carbs and I realize unlike alot of carberated engines this needle did not come with a matching seat. The manual says to replace needle when a groove has formed in the needle. I did and so now I'm wondering before I reinstall the carbs if the new needles alone will be enough to stop the leaking?

It also says that you must replace the carb body if the seat is bad. The needles were twenty bucks apiece I can't imagine what the body must go for. Crazy prices for Honda parts.

I love this bike as it runs like a champ other than the leaking gas. I'd hate to give it up now when gas is at a premium. Can some one help advise me?

Thanks, Neal

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Nevermind, I realize this is not a "mechanical" type of forum.

I've answered my own question anyway.


    Bookmark   May 31, 2007 at 11:38PM
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It's not so much that it's not a mechanical forum, but it just doesn't have a lot of traffic.

So, what was the answer???

    Bookmark   June 5, 2007 at 3:57PM
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"So, what was the answer???"

"I'm wondering before I reinstall the carbs if the new needles alone will be enough to stop the leaking?"

I used a tight wound Q tip, the ones on a wooden stick, and spun a little valve lapping in the brass seats and polished them real good and then reinstalled the needles and float and then back together again.

The leaking has stopped for now but for how long? Nobody knows. I prefer to leave the carbs ON the machine though.
What a pain.

I think you are right about the lack of traffic.


    Bookmark   June 9, 2007 at 12:28AM
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I agree this forum has not much traffic. It is kinda new and it is seems quite tough to get much motorcycle traffic on a general interest forum like this.

BTW a couple years ago I sold off my 1976 CB400f. And just because I think it is still a wonderful looking bike, here is a pic I took of it.

    Bookmark   June 9, 2007 at 10:36AM
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Love that vintage bike look! Sweet to me.

Mine is a twin but I did not know Honda produced a quad that small. Very neat machine. How did it run?


    Bookmark   June 10, 2007 at 12:15AM
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It ran fine. It is quick for a 37 bhp, 400lb machine. On a good day it could hit 100 mph. Handling was its forte. Really stable.
IIRC it was the first Honda with a 4 into 1 header. It also has a 6 speed transmission.
The 400 cc engine was the punched out version. In the early 70's Honda made a 350 cc four cylinder version.
Back in the 60's Honda had a 250cc 6 cylinder race bike called the RC166.

    Bookmark   June 10, 2007 at 10:14PM
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I read an interview with the mechanic that supported the RC166 when it was being raced. He said that working on the engine was more like working on a watch than on a motorcycle. All of the parts were tiny and you're more likely need tweezers than pliers to get things in and out.

    Bookmark   June 12, 2007 at 11:00AM
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Replacing the float needles may have improved the problem. However, the cleaning you did on the seat may have had as much effect as new needles. Examine the needle tip under magification. These should be smooth and free of nicks, burrs, and grooves. If the needles and seats are in good shape, look elsewhere.

Two common sources of bowl flooding are 1) float level too high, and 2) sinking floats. When you had the carburator apart, shake the float and listen to it. If you hear fliud sloshing around in it, it is leaky.

I'm not sure what kind of needles your bike uses: solid metal needles or elastomer tipped. The float level is easy set for solid needles, but the elastomer tipped ones require some 'fiddling'. You may think that the elastomer tipped needle and float has been set to a proper height only to find that the tip takes a set and allows the fuel level to rise.

Also, don't forget to shut off the fuel valve when shutting down the machine for a period time greater than 15 minutes.

    Bookmark   July 18, 2007 at 1:36AM
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The 4-cylinder 350 CB Honda was a heavy for the engine size and a dog. It was slow and cunbersome. I had a twin cylinder 350 that ran circles around those, but admittedly, the twin was a vibrator; The foot peg was bolted to the bottom of the engine case and it could break capillaries in your feet.

The later 4 cylinder 400 CC Honda CBF was a marvel compared to the older 350 4 cy. It was reasonable fast, smooth, and handled well.

    Bookmark   April 13, 2010 at 1:23AM
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I had the same problem and tried all the things mentioned above. Nothing seemed to help. I noticed that the gas appeared to be coming from around the area where the aluminum tube connects the two carbs. So I took the carbs off and took off the brackets holding them together and separated them. There is an o-ring at each end of the tube where it enters the carb body. They were definitely deteriorated and flattened. I replaced both of them and have had no more gas leaks. I hope this helps you.

    Bookmark   March 17, 2011 at 1:20PM
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I just re-aquired a 1976 Honda Hawk that I bought new for my first bike in 76. The problem is the only other owner worked at J.P.L. in Pasadena Ca. and figured if he could send a space ship to the moon he could dismantle the bike and put it back together again, he couldn't. The bike is in many different boxes. I am experienced in automotive repair but almost no experience in bikes. I would prefer to do the work myself, but need advice and maybe help from time to time. Is there a Honda Hawk club or any bike club that I could contact?

    Bookmark   May 15, 2011 at 3:09PM
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Basically each float bowl will have a drain that you can put a hose on at the center of the bottom of the float bowl and then there will be a screw on the side to open and close the drain, it's possible that the oring on one of your drain screws is leaking and that's the leaky tube. But it could also be that the 83 carbs had individual overflow tubes for each carb in which case the problem would have to be either a stuck float or a float that's set way too high , if this is the case the carbs have to come out and apart. I would first verify if it's just a leaky drain or if those are actually overflow tubes. You can adjust the small tang on the float up or down to where the float assy is level when held upside down.The clearance on the the valves have a specific range on the intake and exhaust.


    Bookmark   April 25, 2012 at 10:16PM
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