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Old 07-25-2014, 11:40 PM   #1
NighthawkSWN
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My $500 project - Honda Nighthawk S

I bought this a few weeks ago and had hopes of having is running with new plugs, tank cleaning and a little luck. I was able to get it to fire over but could not get it to run. I had accepted the fact that I would have to clean the carburetors (which I was really dreading). I took the carbs off tonight and was surprised that I did not find them full of junk.
I have basic kits with gaskets and float needle but am looking for any guidance in making sure I get this right the first time.
Any hints, tips and insights would be greatly appreciated.
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Old 07-25-2014, 11:53 PM   #2
El Pachuco
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Have a read here.........

http://www.zrxoa.org/forums/showthre...light=pine-sol
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Old 07-26-2014, 06:24 AM   #3
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Likely the pilots are plugged/restricted.
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Old 07-26-2014, 06:40 AM   #4
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I second the idea that the pilots are clogged. Neat bike. The first street bike I rode was one of these. Keep an eye out for a broken starter/generator chain. They seemed to be the reliability weak point on these bikes.
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Old 07-26-2014, 07:57 AM   #5
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Clean every passage, orifice or anything that looks like it might be. Spray through every hole. Replace the pilot jets if you can, if you can't, remove them and clean them. Avoid running a wire or drill through them, they are precision made and very tiny.
It's critical that they be very clean.
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Old 07-26-2014, 11:11 AM   #6
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Thanks for your input. I will keep you posted on my progress.
I am reading my manual and it mentions pilot screws but does not have a good photo of them. It seems that the caps will not come off without removing the bracket and I really was hoping to not have to break the assembly apart...
Any idea what the pilot screws look like? Are they a jet with small orfices?
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Old 07-26-2014, 11:53 AM   #7
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Yes. Usually they have a slot so you can turn them like a screw. They are often stuck so be careful, the metal is fairly soft brass and they strip easily. Use a good screwdriver that fits the slot.
May have to use a little heat but if you do, make sure there are no rubber parts left in the carb.
Just being able to see day light thru the orifice may not be enough, the passage is so small that even a thin film left in there will change how the bike idles, if it will.
Should be in the bowl, or in the carb body above the bowl. It's not a screw on the outside, like a mixture screw.
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Last edited by bumblebee; 07-26-2014 at 11:57 AM.
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Old 07-26-2014, 11:55 AM   #8
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Look forward to reading your progress. I have a couple of old bikes that I'm wrestling with...
Just found out yesterday that my "new" 1974 GT380 has a broken points drive gear. It's on order, who knows how long that will take.
Oh well, the joy of old bikes.
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Old 07-26-2014, 09:18 PM   #9
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Quote:
Originally Posted by NighthawkSWN View Post
Thanks for your input. I will keep you posted on my progress.
I am reading my manual and it mentions pilot screws but does not have a good photo of them. It seems that the caps will not come off without removing the bracket and I really was hoping to not have to break the assembly apart...
Any idea what the pilot screws look like? Are they a jet with small orfices?
Pilot screws? there are pilot jets and there are air/mixture screws but I have never heard of pilot screws. looking at the pic you posted in your opening post, you have already removed the main jet and the pilot jet. The main is the bigger one that came out of the hole nearest the bottom of the picture and the pilot jet is the much smaller one that came from the hole nearest the top of the picture. The air mixture screw is hiding underneath the aluminum plug all the way at the top of the picture and is on the outside of the carburetor's bowl. you will have to remove the aluminum plug to access the mixture screw, for cleaning.
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Old 07-26-2014, 09:28 PM   #10
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If you decide to remove the bracket to remove the plugs and air screws, be sure to run each air screw in until it very lightly bottoms out (seats), while counting and logging how many turns out it was to begin with. That is where you will want to set them at after a good cleaning. Each screw may be set just a little differently than the other. DO NOT TIGHTEN THE AIR SCREW. THAT WILL CAUSE MAJOR DAMAGE TO THE SCREWS AND CARBS!.

there is a screw with a very fragile needle, a washer, a spring and an O-ring in the assembly. Be careful to note the orientation of all the parts and be careful to not damage the needle or the O-ring.
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Old 08-01-2014, 08:34 AM   #11
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I reassembled my carburetors last night and will see if I can get the bike running this weekend. I soaked the carbs for 24 hours and blew out all passages with compressed air before reassembling them. I am not as intimidated about the carburetors now that I have worked with them and plan to rebuild the other set of carbs I have from my parts bike just to have them available if needed.
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Old 08-01-2014, 08:42 AM   #12
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There ya go. Sometimes you gotta just go for it
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Old 08-01-2014, 11:49 PM   #13
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I made some progress with the carburetors as I did get the bike to idle. I am not out of the woods yet as she did not want to rev up and sounds like it has a miss. I cannot get the short video I shot to upload as it is a .MOV file which is a invalid file type
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Old 08-03-2014, 11:08 AM   #14
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With troubleshooting help from AKS Racing and Poor Kid, I have gotten the bike to run better and am even able to rev the engine. Still suffering a fuel feed issue and will continue to push forward.
I shoot video through my Iphone but can't seem to post them here. Anyone have tips on how to convert the video to a usable file?
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Old 08-03-2014, 11:33 AM   #15
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That was my first street bike . Loved that bike.
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Old 08-04-2014, 12:24 PM   #16
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Quote:
Originally Posted by NighthawkSWN View Post
With troubleshooting help from AKS Racing and Poor Kid, I have gotten the bike to run better and am even able to rev the engine. Still suffering a fuel feed issue and will continue to push forward.
I shoot video through my Iphone but can't seem to post them here. Anyone have tips on how to convert the video to a usable file?
upload it to youtube first, then paste the youtube link here. YT should do any necessary conversion for you.
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Old 08-04-2014, 03:14 PM   #17
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do you have the original air box and all of it's components in place?
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Old 08-04-2014, 09:35 PM   #18
NighthawkSWN
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Yes I am using the OEM air box. Continued to have a issue with cylinders not firing and think my coil pack was going out. I replaced the coil pack from my parts bike and all exhaust pipes are getting hot. Evidently the other one was only working intermittently.
I look at the K&L catalog but did not see any replacements for the 84-86 CB700SC.
Anyone know of a source for these as it probably would be smart to replace them
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Old 08-09-2014, 07:00 PM   #19
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I have gotten it to fire on all 4 cylinders and idle but still need to get the pilot screws situated as it still does not rev up....
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