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Discussion Starter #1 (Edited)
Hello All

I have recently purchased a 1971 Honda CB450 as my first motorcycle. The bike was not running when I purchased it (thought I was led to believe otherwise), however this didn't bother me as I had planned to do a near full restoration to the bike within the next year or so. I had done a lot of work on cars, mostly Volkswagen, before now and so I'm not to familiar with the make up of a bike. I have created this thread for a few reasons, those being:

-To show off my motorcycle and the work I plan on doing to it.
-To get help with certain problems that occur, when needed.
-As a sort of reference to others who have just purchased a bike for the first time and plan to fix theirs up as well.

I noticed these older Honda motorcycles are pretty popular machines, so I hope it helps a few people, and that some people can help me! I plan on doing many things, such as rewiring, replacing clutch, replacing exhaust, general cleaning, replacing parts that are broken or worn as I see them, replacing electric push starter, re-painting, and changing air filters. Maybe, and probably, many more things as well!

*EDIT* I anyone wants to download the manual I did for this bike, here is the link: http://www.mediafire.com/?jnyzijmfydw

First off; the bike:



For a short history of what has happened with the bike since I have purchased it, I took it home and it did not run. The previous owner did tell me that it ran, and ran quite well. Foolishly I believed him. I was in quite a hurry when I went 3 hours out of town to pick it up. I had to get my friends truck, which I had borrowed, back to her by the time she had to work. He never started the bike infront of me, but I guess thats my fault. Kids - make sure when you buy your first bike it runs before you spend $1000CND!

I got it home, tried to fire it up with the electric starter, nothing happened. Right from the start, the push start was dead. Not a big deal I figure, because I didn't plan on using the push start anyways. I give it a few kicks and nothing happens there either. I did a few tests such as testing the battery, changing the gas, cleaning the gas filter, and a spark plug test. For those who don't know, that consists of removing the spark plug, and holding the tip to the engine case, or another metal surface and seeing if you can see a spark. To me, the spark plugs looked incredibly weak compared to what I was used to seeing on cars. So I changed the spark plugs and voila! The bike was running.

Now comes the road test. I decided to drive the bike around for a few hours to get a good feel for it. cruising along residential streets was fine, but when I got into a more commercial area with my first red light, it died at the light. At first I thought I had an idle problem, so I adjusted the idle pins to the point where it was idling at around 3000rpms - which is not an ideal place to have it. Later, after some more general riding, I noticed it only seemed to die if the clutch was in, however didn't die if only left in neutral. Through that reasoning I have decided the clutch must be replaced. For the next few days, I just kept it in high revs while at lights.

All is fine and dandy, until it rains one night, and I am unable to use the bike so it sits for a day. I tried to get her going the next day, and I noticed something:

The air jet (centered in the picture) was sticking out, which I never noticed before and thought may have been a problem. Especially after turning the gas on, giving it a kick, and watching this happen:

I think its safe to assume that gas exiting the vehicle is usually not a good sign.

Since posting on another thread, and a further examination of the bike, THIS IS NORMAL! The air jet protruding, anyways. The gas leak - not so much.
*EDIT* Picture of the side of the left carburetor, showing the air jet you couldn't see without the other carburetor off:


I think this is either a mixture problem, or a float isn't working properly in the carburetor. Any one have any ideas?
 

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Discussion Starter #2
I am going to wait for my new air filters to arrive in the mail before putting the carburetor back on and fixing that problem, however any advice would be greatly appreciated!

Now, while removing the old air filters, I stumbled across a little silver box and I'm not sure what it does. I was planning on taking it off along with the little passage connecting the two air filters, however I now don't think that would be such a good idea:


If I shouldn't take off the silver piece under the battery, is there anywhere I could remount it that anyone could suggest?
 

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Visually it looks like a great bike to start with. I bet she'll be up and running in no time. I look forward to following your progress.
 

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Discussion Starter #4
Anyone know if it would be a problem to chop off the oval part above the mysterious silver box and just mount it RIGHT under the battery?

Just something small and cosmetic I did while waiting for my new air filters to arrive:
Before:

(If you can't tell, those covers aren't the original ones from the bike. By the looks of it, the previous owner replaced them with ones taken from a dirt bike.)

After:


I'm not sure whether I am going to look for the original covers, or leave them blank. I may also just purchase brand new front shocks eventually, also, so I will probably leave them like this for quite some time.
 

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Discussion Starter #5
Just as an update:
My new air filters have arrived in the mail today - unfortunately I was out when the delivery man came to my house so I will have to pick them up tomorrow. I'll be throwing them on and updating this thread with some new pictures during the process. Lets hope its not actually going to be pouring rain tomorrow the the weather man says.
 

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my '74 cb450 did not come with turn signals. i hooked some up, and they turn on but do not flash. i have been flashing them, when needed, via the switch. i'm not too interested in turn signals as i think they mostly clutter up a bike, but it is the law here in ohio, and i like to avoid talking to the police whenever possible. some flush mounts may be in my future...
anyway, i recently bought a 72model cb450 for parts and noticed the same mysterious box you speak of mounted under the battery. this box is missing on my '74.
i believe this box to be the turn signal relay/flasher. it should not be a problem for you to remount it.

the fork boots are also missing on my '74, and the fork seals leak horribly. i think that once i replace the seals i'll be installing the boots i have off of the '72 for some added protection, since i ride a lot of dusty gravel roads.

good luck.
 

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Discussion Starter #8
So its pretty miserable out today. I am probably not going to finish installing the new air filters. I put one on, mainly just to see how it looked. The battery is in the way of the other one so the next day that isn't pouring rain I'll probably find a way to remount the battery (along with that mysterious silver box piece).

Anyways, here is the left side of the bike with the air filter on:

 

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Discussion Starter #10
I know what my parts are.

So, back to the leaky carb problem; Does anyone know what to adjust so that the carb gets lets gas?
 

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First, that oval box is a bridge between the stock air filters, there to make sure there is no drop in air pressure when one cylinder pulls air in.
Leaky carbs mean floats not shutting of the flow of gas when the bowl is full. This could be caused by floats that don't float, worn or dirty float valve parts, loose valve body, or just mis-adjusted float height.
 

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Discussion Starter #12
How would I go about adjusting float height? I know that the float does float, and it doesn't stick.
 

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The float has a little brass tab that presses against the float valve needle. To adjust the height, you carefully bend that tab, in your case, toward the body of the carb so that it pushes the needle against the seat sooner. You can often do this with a very small screwdriver.
 

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To measure the correct float height, using a thin piece of sheet metal, or very stiff cardboard (the plastic-coated kind that small tools come on works), and make a U-shaped cutout that will bridge the float from one side of the bowl seat to the other. You will be measuring from the portion that crosses from one side to the other, so make sure it is square to the sides. With the carb turned so that the float chamber is vertical, with the valve at the top, you measure the distance from the bowl seat to the bottom of the float itself, with the float just resting against the needle. That distance should be 20mm, or about 25/32 inch.
 

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Discussion Starter #15
So I have adjusted the float height and it has stopped leaking gas. However she isn't kicking over yet. May be partially because its getting a bit chilly out, but I'm thinking it must be because of the new air filters. Anything you should change when you get new air filters?
 

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Usually, when changing from a factory airbox to pod filters, the first order of business is to re-jet the carbs richer to allow for the increase in air.
Not sure what you have done in detail to alter your air-flow though.

Eric
 

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Discussion Starter #17
I really haven't done anything.

this mountain of information that comes along with Carburetors is quite alot to get a grasp on in the short time I've been working with them. Re-jet; do you mean to purchase a carb kit or adjust them or something entirely different?
 

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Typically, you go higher on the main jet orifice by going to a higher numbered jet. (it can be anywhere from 5-20 sizes larger depending on your combination of mods including exhaust)
Also, you raise the needle jet one or two notches. If it has one.
And, the pilot jet needs to be slightly richer.

Eric
 

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Needing to re-jet shouldn't keep the engine from starting; it would just run a little lean.
You do, however, need to use the choke to get it to pop, then quickly take the choke off as you keep it running with the throttle. At least, that's how I start my CB450.
 

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About Carburetors

The following was copied from the Xbikes.com forum and was written by Len (known as "Chacal" on that forum) who runs a business of supplying hard to get Yamaha XJ model parts and special tools. His post contains a lot of great information and most of it applies to the Keihin Carbs on your Honda 450 (even though it was written for the Hitachi and Mikuni carbs that were used by Yamaha on the XJ series of bikes). I copied and pasted here because it saves me much time and a lot of two finger typing trying to give you an accurate explanation of what carburetors do:

THE SECRET LIFE OF CARBURETORS:


A/K/A CARB THEORY AND OPERATION MADE EASY:



Or, why carbs suck:

At first glance, you might read the title of this article and say "so what?" You're not really interested in why carbs operate as they do; you just want them to perform properly.


But wait, grasshopper: in order for you to appreciate both the what and the why of proper carb rebuilding techniques, then you need to also have a basic understanding of what a carb is trying to do, so you'll have a clearer understanding of why you need to pay close attention to what might seem like the incredibly picky details and procedures that are recommended as part of a proper carb rebuilding process.......which you can read all about here:

xjbikes.com/Forums/vie...14692.html

But before you go there, please continue reading here......




I'm Already Denying It; I Should Have Been A Politician:

We started out by saying that "carbs suck". Well, as we all know, that's not really true. It's the engine that sucks, and it's that "vacuum signal" from the engine----that "suck"----that controls and tells the carb "when" and "how much" they're needed to do in order to correctly perform their dirty, fuel-and-airish deeds.

And if your carbs are not ready to properly respond, or if they tend to respond in a non-appropriate or non-reliable or non-coordinated manner to that sucky signal, well, that's the root of all evil, now isn't it?




Nature Abhors One: All About A Vacuum:

Actually, there's no such thing as a "vacuum" in nature (no, not even in the new lightweight 8-pound Oreck model that you can try at home for FREE! for 30-days........), but there are areas of higher or lower fluid pressure........."higher" or "lower" being meaningful only in comparison to some other nearby or related area........and what everyone likes to refer to as a "vacuum" really means "an area of lower pressure".

Areas of low pressure----just like you see and hear about on TV when the weather-person is talking about weather systems (and a hurricane, as you may know, is the "mother of all low-pressure areas")----will "draw in" a fluid---and physically-speaking, air is a type of "fluid"----from the surrounding areas of "higher pressure". Note that we haven't said anything at all about HOW MUCH pressure we're talking about.......nothing about p.s.i . or inches-of-vacuum or the like.......no, all that matters is that one area is at a lower relative pressure to some other area.


Now, in an engine, the monster that is responsible for the creation of a "lower pressure area" is the piston and it's cylinder. As the piston is mechanically (via the crankshaft and the connecting rod) drawn down into the bowels of the cylinder, the ring-tight seal of the piston to the cylinder walls evacuates the area of the cylinder above it. Well, even the word "evacuate" isn't good, so let's try this: when a piston is at the very top of it's stroke, and before the piston moves down into the cylinder, there was, let's say, 3cc's of total area between the top of the piston dome and the cylinder head combustion chamber. And, there was 3cc's total volume of air in that space, too.


Good. Now let's say the piston moved all the way down to the bottom of that cylinder. Now, there's maybe 120cc's of total area in that cylinder (between the top of the piston dome and the cylinder head combustion chamber), but still only 3cc's of air volume to fill this newly expanded area! That air thus becomes "thinned", in essence, and now we ram head-on into one of the basic laws of physics:

A fluid (and once again, air is a "fluid" in physical terms) will undergo a decrease in pressure as it expands or is "thinned".


Hey, I didn't make up the laws of physics, I'm just reporting them.......


So the downward movement of the piston within the cylinder "stretches" and "thins" the amount of air that's in the cylinder. And this "thinned" air loses pressure.

Bingo! A "low pressure area" has been created. Your piston, in a conspiritorial bond with both it's rings, the cylinder walls, and the cylinder head, in a plot worthy of a Tom Clancey novel, has just created a "vacuum", better thought of as an "area of low pressure".




An Army of Air On The March and Spoiling for a Low-Pressure Fight:

Now, in the presence of this developing low pressure area within the cylinder, what happens? Well, my-oh-my, an intake valve opens! And that intake valve opens up a sealed route through the intake passage in the cylinder head, and then into the intake manifolds, and which continues on into the carb throat (and beyond). And guess what? This entire air supply in the cylinder head passage, and in the intake manifold, and thus in the carb throat (and beyond, all that way back to your airbox boots, the air box itself, and finally to the air outside the airbox, too) "feels" the presence of this low pressure area inside the cylinder, and like the greedy beast that nature is.....abhorring such vacuums with a passion and a universal vengance......seeks to invade this low pressure area and "fill it up" until the low pressure area is no more, and the air pressure throughout this air supply chain is equalized.


So, an air stream----an invisible little river of air----within the atmosphere, thru the air box, the airbox boots, thru the carb throat, the intake manifolds, the cylinder head passage, and on into the cylinder, is created. An airflow. A flow of air.

And in case you weren't fully pumped yet, well hang on, 'cause this is where things really get moving.......literally!




Here's Where the Plot Thins:

This moving column of air, created by the opened intake valve that exposes that low-pressure area inside the cylinder, makes that afore-mentioned Law of Physics----just like a restored XJ-series motorcycle----fully growl to life again, and actually do something useful. Recall:

A fluid will undergo a decrease in pressure as it expands......

and because we can re-write that Law above to read as:

A moving column of air, which is the same as an expanding volume of air, will undergo a decrease in pressure as it moves (and, you actually get even more bang for your buck: the faster that air moves, the less pressure it exerts).


A decrease in air pressure. Wow! It's just what the doctored ordered!! Inside the carb throat, that is...........


Why? Because we've got this big puddle of fuel sitting there in the bottom of the carb float bowl, all dressed up with no way to go where we want it to go (inside the cylinder).


(Continued next post)
 
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