1980 CB900F Build

Tim of all trades

New Member
I've had this bike in my shed for 6 years and I didn't even own it when it first got to my place. since then I have moved house 3 times and been very busy between being away with work and being a good husband and father.
 

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Tim of all trades

New Member
It ran! my mate who bought it rode up and down the street but it didn't have front brakes and the rear was not working great either. I do have a short video of that moment (maybe I will upload it to youtube and post a link)
After letting me have a quick turn it was time to start work on it. Because my mate lived in an apartment and my wife is very understanding it was decided it would be built in my garage.
So first thing we did was park it up on the center stand and strip it down.

If you look carefully there is a CD250 in the background that belongs to my brother that I had my first go at tinkering with. Also my other mate used my compressor to spray his tank and it was still hung up.
 

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Tim of all trades

New Member
The project paused here. I moved house then my mate and I went away for work, I went home after only a month and he had to stay for another 6 months and because he is a top bloke he said I could have the bike!
When I got home I put the donk in my trailer and took it to get soda blasted. You can see it was painted with a brush and if the duct tape wasn't holding the valve cover on you could see it was not painted down the middle because the brush the PO used wouldn't have reached in that far.
Also the carbies are in need of a clean.
 

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Tim of all trades

New Member
The engine after soda blasting was great! it did however reveal that the bike had an accident at some point in its mysterious life because there was a crack that had been metal puttied up on the bottom of the front left engine cover. (not pictured)
I painted the motor except for the parts that I would be polishing.
 

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Tim of all trades

New Member
I got new tyres, shocks, headlight, front indicators, fork seals, clip-ons and somewhat reassembled the bike. I built a seat pan out of a street sign and duct taped some foam to it. I also welded on a tab to the rear hoop to mount the number plate
I then built a box for the battery to live in and promptly chucked my cheap stick welder in the bin as I'd had enough of shitty looking welds.
My lovely wife decided I needed a good mig welder for my birthday.

Bike is starting to look pretty damn good here if you ask me.
 

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Tim of all trades

New Member
I'm not really confident in my wiring abilities so I took the bike into a mates workshop and he helped me with the spaghetti monster, unfortunately he was all about just getting everything hooked up no matter how messy or what length wire was used. He didn't even get the Acewell gauge working properly! So after getting it home and doing some research I decided to rip all the wiring out and start again myself. I just had to buy some Moto gadget products so it was a bit easier.
I got the M-Unit, M-button, and a 3 Button switch for each handle bar. The wife wasn't really happy with how much all that cost until I did a price comparison with getting an auto-elec to build and fit a custom harness that wouldn't even have as many functions or as nice minimal controls.
 

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Tim of all trades

New Member
Ok, we are nearly live with this build. I moved house again and started the most intense employment I have ever done including non stop 7 days a week of 16 hr days doing physically demanding work. So there was absolutely no progress on the bike for a solid year as I ran myself into the ground and as I watched all my mates getting divorced from this ridiculous new job I got super lucky and snapped my femur into 3 pieces. Now I've had some time off and when I was able to walk again I started working on the 900 that had been so neglected.

I got the wiring sorted and kicked the bike in the guts and it coughed to life! ...then died. I took out all the spark plugs and cleaned them up with some wet'n'dry and tried again and it worked so much better! The valve cover wasn't torqued down so some oil dripped out the top and ran all down the motor.
The battery isn't charging and after taking it into a shop yesterday the bloke said "its dropped a cell" he put it on charge and I will go check it after lunch today and if its still cactus I will buy a new one. Meanwhile I checked the stator and reg/rec with my multi-meter, checked the brushes and all the connections for continuity and they all seem fine so I really don't know why it not charging. Thats what led me to modify a wiring diagram of the bike to try and work out what else it could be and I put it up on this site in the electrical section and some one has already pointed out a few problems with the diagram and my wiring for me to address.
 

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Tim of all trades

New Member
POD FILTERS!!! The only thing my mate bought for this bike before he gave it to me was the pod filters, that led me to throwing out the air-box in one of my house removals. Little did we know what fun getting a bike with CV carbies on it to run well with pod filters would be. Talk about a can of worms! anyway my "solution" was to put rubber boots on the carb intake and drill holes for a balancing pipe between them so it acts like an air-box and lets the pressure level out between the 4 carbies as well as making a velocity stack shape similar to what was in the factory air-box so the turbulent air from the pod filters goes into more of a laminar flow. What ever the outcome is i'm not claiming anything and i'm not trying to shave tenths off a second on any lap times. I want to ride and enjoy this bike. If I wanted to go fast I would buy the S1000rr that I have been eyeing off....
 

crazypj

Split personality, I fake being smart
Find a stock airbox or fit different carbs, The $200.00 (US) Dynojet carb kit may work (never tried one) but without some serious modification to carb bodies it will never run right. It isn't that tey are CV carbs but the specific type of CV carb.Even Honda knew tey screwed up when the couldn't get factory race bikes to run properly with 'stock' carbs for Superbike series in the 1980's. As your in Oz you may find someone who understands CX500 carbsand knows how to mod them. mods won't be the same but will be similar.
BTW, any 'job' where breaking femur, in 3 places is deemed 'lucky' is probably not a good place to be, no matter how well it pays (16 hr days, 7 days a week you better be a millionaire after a year)
Oh, is rear tyre fitted properly now?
The cheap pods are more trouble than they are worth (you have the cheap pods, looking at pics)
K&N 'oval will be a lot better, those actually restrict airflow at high rpm
Usual reason for bad charging is bad earths (ground connections) You'll ave to fit extra leads from crankcase to frame and probably from frame to forks to make sure headlight gets full voltage (even with all te ground leads Honda fitted)
 

Tim of all trades

New Member
so the bike starts and runs (even if its not charging yet) the only thing stopping me doing a test lap of the block is a complete lack of brakes. Old me would have done it but you should ask how I broke my leg... anyway I'm not getting on the bike until the front and rear brakes are working at 100%
I bought some nice braided lines to get rid of the old rubber ones. I've heard that is the best thing to do. (other then a modern fork conversion which is a future job)
When I took the front calipers off I did notice that the mounting threads had stripped out, I drilled and heli-coiled them to good as new.
I pulled apart the front master I got from the wreckers and checked it and put it back together, I couldn't get pressure from it even though it looked good! many frustrating hours later I pulled it apart and figured out I put the piston back in the wrong way! Idiot!
The front calipers will need a rebuild new pistons as they are super mega pitted.
The rear calipers are good but the master cylinder needs a rebuild and I couldn't get the piston out. It was stuck solid! I managed to hammer it in further to try and free it up but that didn't work so I tried 150psi of air shot into the return hole. That also didn't work because the piston had been hammered too far in by some idiot!
I soaked it in apple cider vinegar over night and it still wouldn't budge. so to get it this morning I drill a hole in the piston, tapped it with an M6 and put a bolt with washer and nut on it to screw it out. I found this solution on a forum last night but didn't find any vids or pics so I thought I would share mine.
 

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crazypj

Split personality, I fake being smart
Back in te day........'they all do that sir' then collapse laughing around the corner. I moved to Suzuki deal across the street and ended up working on Honda's again ;D
 

Tim of all trades

New Member
1: stuck piston
2: 5mm drill bit
3: 6mm tap ready to go into the new hole
4: bolt long enough to screw into hole with thread sticking out for nut and washer
5: success! I twisted the nut and there is piston sticking out. (nut and washer removed for picture only)
 

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Tim of all trades

New Member
crazypj said:
Find a stock airbox or fit different carbs, The $200.00 (US) Dynojet carb kit may work (never tried one) but without some serious modification to carb bodies it will never run right. It isn't that tey are CV carbs but the specific type of CV carb.Even Honda knew tey screwed up when the couldn't get factory race bikes to run properly with 'stock' carbs for Superbike series in the 1980's. As your in Oz you may find someone who understands CX500 carbsand knows how to mod them. mods won't be the same but will be similar.
Oh, is rear tyre fitted properly now?
The cheap pods are more trouble than they are worth (you have the cheap pods, looking at pics)
K&N 'oval will be a lot better, those actually restrict airflow at high rpm
Usual reason for bad charging is bad earths (ground connections) You'll ave to fit extra leads from crankcase to frame and probably from frame to forks to make sure headlight gets full voltage (even with all te ground leads Honda fitted)
HAHA! yes the tire is fitted the right way now. Thanks man, that's some interesting info on the history of those carbs with the whole superbike thing. I didn't know any of that (prob because I wasn't born then). And yeah they are the cheap pod filters and I had even written that they were cheap shitty ones in the build thread but then deleted that part because I want to show my mate this page without pointing out the only thing he did was shit.

Earthing you say? I do have a solid connection for my headlights and all my switches by running the earth leads back to an earthing block under the tank (pictured) the only reason I haven't got a more updated photo of that is because i'm a bit embarrassed that I have tech-screwed that block to the frame. And only because one of my other mates kept my tap and die set (except the M6) that I lent him and an M6 bolt is too big for that application. I will go pick up my new battery now and put it in and check if its charging, if its not I will try adding some more earth straps to the crank case. I just really want it to look neat and to not have to take any paint off my beautiful frame or motor.
 

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Tim of all trades

New Member
Also I will need everyone that reads this to help me convince my wife I need new carbies, because the bike technically is running and the Mikuni or Keihin carbies are between $1300 and $2000! Considering how much I paid for the bike I don't know how I will justify that...
 

Tim of all trades

New Member
Work has been slow because my garage has no A/C and it was bloody 45 degrees! (if your in the Bahamas, Belize, the Cayman Islands, Palau or the United States that's 113)
But, I have the new battery and its filling with delicious electricity water as I write this. Can't wait to see if the charging problem magically fixed itself!
Also this battery has 20 less Amps or cranks or something? The bloke at battery world assures me that it wont matter. Is he full of shit? I only agreed to buy it because I also figured a smaller battery would be easier to charge.
 

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