1982 Honda 450 Nighthawk carb problems

[Arnii]

Hi guys,

my name is Arndt and I'm a 20 year old from Germany. I'm in Florida doing a volunteer service for a year. Recently I bought my first bike, a 1982 Honda Nighthawk 450. I like the bike a lot but I have noticed some rideability problems. I experience a feeling of lean and surging carburetion in the midrange. The bike starts up very well and once I hit 3000- 3500 rpm the bike runs great as well. It's just the time from approximately 2000rpm to 3000rpm where I experience "acceleration holes". That's maybe the best way to describe it.

I searched online for similar problems at other bikes and found this:

http://www.hondanighthawks.net/article450SB.jpg
http://www.hondanighthawks.net/82_450_CarbSB.pdf
http://www.hondanighthawks.net/needles.jpg

My problem seems to be known for the 450 Nighthawks made in 1982. I would love to solve this problem by myself and feel confident doing it but I talked to a motorcycle  garage close by and they told me that the jet needle itself probably won't solve the problem because the jet, or the part where the needle goes into, mostly is torn out and too wide so that it needs to be replaced too. Is that correct?
Is the new needle the same size like the original one?

The manual in the second link I shared doesn't seem too difficult but I just can't find the right jet needle.
Has anybody of you guys ever had the same problems with a 450 Nighthawk and can give me some advice.

I would really appreciate it,

Thank you

Arnii

[Arnii]

Anybody who can help me? At least show me a store where I can get those needles?

[Bumblebee]

Stay away from the parts cannon for now. You don't need parts until you know for certain you need parts and it's too early to tell yet.

Check my response to the PM you sent.

Anyone else, start talking if you can help here.

[TDodge7]

It sounds like you're having a lean flat spot as you get off of the pilot jets and onto the needle jets, If your needles aren't adjustable I would try putting a small washer under them to richen your mid range a bit and see if that helps any. That is assuming that your carbs are 100% clean of course.

[cjbear11]

I would start by giving your carbs a good cleaning. They might just be dirty. If that doesn't help, then you can either shim your needle or look into different jet sizes. Most carbs have a flat spot somewhere in the power band, but you need to start with a clean sheet of paper so-to-speak. i.e. a good cleaning.

[Bumblebee]

Clean everything to set a valid base reference point.
Then, if necessary, start making alterations.

And clean, gap spark plugs and inspect wires as well. Ya never know and it's dirt simple to do.

[jerjohn]

When I installed a 2-1 exhaust on my 86 450 I got a really bad lean spot around the same rpm range. Go to radio shack and get some #4 washers, take the needle out as illustrated in the linked diagram, and raise the needles a bit buy using one washer on each needle. Do a search on the forum for "washer mod" to find better instructions.

[edac]

Seafoam and good quality gas.

[Bumblebee]

When I installed a 2-1 exhaust on my 86 450 I got a really bad lean spot around the same rpm range. Go to radio shack and get some #4 washers, take the needle out as illustrated in the linked diagram, and raise the needles a bit buy using one washer on each needle.

That might be good in the long run however when you have a mechanical problem, it is far better to return things to normal conditions by taking things back to original THEN if necessary start adding unknown variables to refine details. I seriously doubt honda built, much less successfully sold, a motorcycle that the power drops out in the mid power range.

It's entirely possible this could be nothing more than a single sticking vacuum piston or a little crud in one of the jet holes.

[jerjohn]

I guess I misunderstood the post. According to the links honda did in fact sale a bike with bad performance that required a modification to remedy it. I was under the impression that his bike wasnt fixed (wouldnt be the first vehicle to miss a recall) and that he was trying to fix the factory caused problem. Of course make sure the carbs are clean and working properly, but if they require an upgraded needle no longer available, then the washer mod is a solution.

[usbigred]

If cleaning the carbs doesn't fix the problem, I just ordered and received the 61C needle jets mentioned in the Honda Service Bulletin from www.westernhillshondayamaha.com last week.  They are discontinued from Honda, but Western Hills had them.  I paid $20.99 each plus shipping.  The part number has been changed to 16113-MC0-305.  Haven't put them in yet, so don't know if it it will fix my problem, which sounds similar to yours.  I'm planning on doing a complete carb rebuild as well, being that I'm the original owner of a 1982 CB450SC with 6000 miles on it and have never cleaned or taken apart the carbs.  I bought new oem gasket kits and K&L accelerator pump/air cut-off valves, being that after thirty years, I was concerned that all the rubber products were probably starting to dry rot.  I hope the K&L products last as long as the oem stuff, being that my son gets his license next year and wants to ride the bike for another 30 years.

[bobkids]

If cleaning the carbs doesn't fix the problem, I just ordered and received the 61C needle jets mentioned in the Honda Service Bulletin from www.westernhillshondayamaha.com last week.  They are discontinued from Honda, but Western Hills had them.  I paid $20.99 each plus shipping.  The part number has been changed to 16113-MC0-305.  Haven't put them in yet, so don't know if it it will fix my problem, which sounds similar to yours.  I'm planning on doing a complete carb rebuild as well, being that I'm the original owner of a 1982 CB450SC with 6000 miles on it and have never cleaned or taken apart the carbs.  I bought new oem gasket kits and K&L accelerator pump/air cut-off valves, being that after thirty years, I was concerned that all the rubber products were probably starting to dry rot.  I hope the K&L products last as long as the oem stuff, being that my son gets his license next year and wants to ride the bike for another 30 years.

Did the needles fix your lean spot?  I just ordered mine.  I just wondered what else you my have done to fix this problem.

[usbigred]

The 61C needles definitely helped.  I also rebuilt the carbs at the same time, so it could have been a combination of both, but since I rode it out of the showroom in '82, the bike always had a lean spot at around 2500-3000 rpm's.  It definitely doesn't anymore.

[timsonic]

I've got the same exact bike and have probably pulled the carbs a dozen times in the last few years for various tinkering.  The problem you describe will be helped a bit by the newer needles but it's far more likely to be a cleaning issue.  Pull 'em out and be prepared to spend a few hours spraying carb cleaner into various nooks and crannies (once you've gotten all the plastic off of course- and careful to keep track of which jet is which- they all look the same unless you've got really good eyes).  I also had good luck with a small shim on the needle jets but that also required making a bit of extra room under the retainer screw.  Once I got the newer needles I still ended up with a tiny shim and one # up on each of the jets in combo with a K/N filter.  Runs like a top now.

[PTwin]

It sounds like you're having a lean flat spot as you get off of the pilot jets and onto the needle jets, If your needles aren't adjustable I would try putting a small washer under them to richen your mid range a bit and see if that helps any. That is assuming that your carbs are 100% clean of course.

I agree with this. I had the same problem with my -85 450 NH. There was a flat spot somewhere below 3000..3500 rpm. It was like a little hesitation while opening throttle lightly in city traffic speeds. If you opened up quickly no problems at all. I don't know which needles I have maybe those 61C but I put first one washer under the flange of the needles and tried. Little bit better but still something like to go or not to go. Then I put 2 washers and all the problems went away. The gas mileage was about 4 liters/100 km and after mod 4.2. I ride all the time the same roads and old man's riding style is more or less the same. But putting the washers under the needle flanges in 450 case needs care. The needles are locked with needle set screw. If you rise needles (with washers) you can't tighten the set screws against the needle's flange. You have to secure the screws somehow not to open by vibration. The point is that the needles have to hang freely. I tightened the set screw just lightly against the needle and took back a little until the needle was hanging freely. Finally I pushed a narrow slice of rubber gas tube (3 mm lice) against the set screw's head. The rubber tube seem to hold quite well the set screw in place.

But before making any mods the basic things have to be right. Clean carbs, really clean carbs, ignition working as it should do etc.. I did this and have rode now maybe 2000 miles and still think it was right thing to do.

PTwin

[bobkids]

Ok, I have the same bike (1982 Honda CB450SC Nighthawk) and after cleaning the carbs I had the same hesitation at mid throttle.  I cleaned them twice and then found this thread.  I ordered the 61C needles and installed them.  WHAT A DIFFERENCE!!!!!! The bike runs great now with no hesitation anywhere along the powerband.  I highly recommend that you get those needles if you have the original 61A (printed on them).  You will be very satisfied.  But again, like someone said, everything else has to be spotless clean in the carbs for it to run well.  Also check your air filter.  (Mine was missing when I bought the bike.)