Newbie about to start my first build - '82 Honda CB450 Nighthawk

squizzymchaggis

squizzymchaggis

Active Member
Hello to all! I'm new here and about to jump in with both feet and start my first attempt at this. Here is how the it looks now. Rough but I've seen worse and I named it "The Ugly Duckling. It starts and will stay running but won't rev over about 3500 rpm without dying. Once I turn it off I have to cut the gas off or the carb will start leaking out of the overflow. And I think it has a electrical short someplace since sometimes when I go to start it absolutely nothing happens. Then after trying several times suddenly it will start turning over. Its like there is a bad electrical connection someplace between the ignition switch and the starter. Anyway, I will be posting pics as I go and I welcome any hints, tips, tricks, or ideas that anybody feels inclined to throw at me.
 

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cool bike one of the best ever of that series.here is some sage advice do not do a single solitary thing to it as far as cosmetic or "stance" changes ..until you get it tuned like a swiss watch, running perfect and have put a few thousand miles on it.go ahead and get new tires and go thru the brakes for safety checks,inspect the drivechain cahnge oil adjust valves all that stuff...
 
xb33bsa said:
cool bike one of the best ever of that series.here is some sage advice do not do a single solitary thing to it as far as cosmetic or "stance" changes ..until you get it tuned like a swiss watch, running perfect and have put a few thousand miles on it.go ahead and get new tires and go thru the brakes for safety checks,inspect the drivechain cahnge oil adjust valves all that stuff...
Click to expand...

+1
 
xb33bsa, thanks for the advice. I've been read a lot of theads on here and I have seen that same thing shared a lot of times by a lot of people, and it makes sense. Oddly enough, the tires are in great shape and look pretty new. My first plan is to address the not revving above 3500. I know it sat for a while so I'm assuming it needs a the carbs rebuilt. Once I have it running well I will check stuff like the brakes and start putting some miles on it. I was thinking about getting a set of Mikuni VM32 carbs and putting those on rather than rebuiding what is on there now. The main reason is that in the box of extra parts that came with it were two other sets of carbs, including what looks like the originals, so I have no idea what is on there now. At least if I put some new ones on I know what I am dealing with from there.
 
The overflowing carb is a sticking float. used to happen on my CM. sometimes a tap on the carb will free it. or it is crud in your float needle valve seat, a good cleaning will stop it all together. Like XB said do all the maintenance stuff first. Valves are easy to set, but follow specs as these bikes are supposed to have some valve click when set right. Folks like to set them tighter to quiet them down and then they burn the valves out. IF you don't know much about jetting, keep the airbox as these carbs will run with K&N's but take a lot of trial and error tuning to run right. Electrical on these is usually corrosion, What I did to exercise the gremlins on my CM is I went through every single connection and switch, took it apart, cleaned it, di-electric greased it and put it back together, then fixed any questionable wires. after that I never got stranded or had it not start sometimes or had random lights stop working. The Starter button can be taken apart and cleaned and is usually why you have the problem you are having.

Cheers
 
do not try to put mikunis on it !!! keep it stock rebuild what you have make it like new and do not be afraid to spend money on the stock carbs and keep the airbox 100% stock unless you do not want to ride this season
the mikuni sellers will tell you they are pre-jetted ,that is a filthy lie >:( and unless you are an EXPERT tuner with years of experience you will never get it running anywhere near as good as stock
one of the first things you should do on a fully warmed up engine is an accurate cylinder compression test throttles wide open do thi sright away before you do almost anything else
 
Maritime and xb33bsa, thanks! I had assumed the leaking carb was a sticking float so it sounds like my first step should be cleaned the existing carbs so that it will rev without dying and then move on to a compression test. It also sounds like I need to follow Maritime's plan on checking all the switches and connections. The good thing is that I have a '80 CB900 that is all stock and running great so I still have something to ride while I play with this one.
 
do the compression test now it doesn't need to run right only be fully warmed up
it is always nice to know the condition of the motor and if the results are good it is a great feeling to encourage further work ! if the results are poor well then you got some decisions to make
 
Good idea on compression check, set the valves first though on a stone cold motor, compression check, then move forward. good thing about these motors if you need to do the pistons and rings the whole top end can be done with motor in frame but I doubt you will need to.
 
Sounds good. Thanks for the guidance. Now to find out specs on the valves and compression and go from there. Much more interesting than work, lol.
 
The manual for this bike is downloadable from a few places. Google it and you should be able to get a PDF has everything you need to know.
 
Sorry if this sounds like a stupid question, but just to make sure I understand how to do the compression test... I let the bike warm up to normal temp, turn it off, remove the spark plug and screw in the gauge, then crank the engine to see how much compression is build up, then repeat on the other cylinder?
 
Pretty much except a few things. Pull the plug wires from the other cylinder when testing to make sure it doesn't try to start. Also make sure the throttle is wide open when cranking to get a correct reading.
 
get new sparkplugs a few sets you can get them at any suto parts store no need for the expesive stuff ,standard ngk is perfect
and very important,get new sparkplug wire caps trim the wire back a 1/4'' when putting them on the wires
 
I put mikuni carbs on my 82 cm450 and I love them you will have to tune them. As someone before stated prejetted is a lie. You will have to spend some time and a some cash on jets but to me it was worth it. Once I hade them jetted in and tuned I have not looked back.
 
Thanks XB. I had thought about the new plugs but not the new plug wire caps. I really appreciate the guidance! I'm planning to making a stop on the way home to pick up a compression tester and plugs, so I'll add the caps to the list.

And thanks for the info on the Mikuni carbs, JG. I'm still thinking about them but it will be down the road a ways. I have seen several posts on here saying the same thing about them. I know that they will take time and work, and I totally understand what XB was saying. I've got to get the engine running right so that it purrs before I even begin to think about taking the step with the carbs. Otherwise I will never get the new carbs tuned and the engine running right at the same time.
 
Just out of curiosity I decided to do the compression test before checking the valves and then again afterward. I just finished the test before checking them and the results were 150 on the right cylinder and 155 on the left. Now to check and adjust the valves and do it again.
 
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