Topic: Concidering an 81 CB900F

[mgbgt89]

I got offered one today at work. He said it ran until he bought a Harley a few years ago, then parked it and hasn't ridden it much since. He said i could have it for 500 bucks. This will be the THIRD bike i have gotten just from people noticing my 350 and saying I've got an old honda sitting in my barn....

Seems like a good deal, Are there any common problems on these? Things to look for that are specific to the DOHC bikes? I'm actually trying to get a friend of mine to buy it, I gave him first dibs since he doesn't have a bike currently. If he doesn't go for it, I'll just have to find somewhere to put this one.

[Markcb750]

I think they are great bikes, some bad press on the DOHC motor not being as reliable. I have seen several around, and I chased several around Charlotte in the $1500 range for something that ran.  2500 for a well maintained bike.

Good luck

wish I was closer...

[Alan F.]

www.CB1100f.net will have every bit of info you'll need.
Get it running and get 2 grand for it in the spring.
-Alan

[Retro Rocket]

I had a red and white F2 900 and loved it, it needed a bit of work tomake it handle but it was a good strong bike for me..

Mick

[bill440cars]

       Never had a 900, but have an 80' CB750K (same basic engine) and it's a pretty good runner.

[mgbgt89]

Went with my friend last night when he bought it. Great shape, came with a trunk. It was parked in 1993. We got it home, and pulled the carbs to clean them, and they were pretty much spotless, but had some sort of oil in the bowls. No varnish at all.

We'll be replacing the fuel lines and trying to start it today.

[Alan F.]

Any possibility of pics or a video?

[mgbgt89]

Should have took one tonight, we fired it for the first time. Settled down to a nice idle. Very smooth running bike, even with dirty plugs and no airbox. It has to be the worst possible airbox to get on and off. You have to leave the box on, pull the carbs, then the box comes out.

I steered him away from pods after my bad experiences. He's going to make some sort of custom aluminum airbox for it and try to mimic the amount of air restriction the stock one has, just in a more manageable shape.

It has the usual issues of a bike sitting for 17 years, gunked up brakes, rusty tank and cables, but really doesn't need much at all. We found maintence records in the back of the book that came with it. Very well maintained by both PO's. I wish my bikes came together this easy.

[mgbgt89]

And yes.. He said it ran "A few years ago"

It was last plated in 1993.  I was 4 years old in 1993. I guess most of my lifetime counts as "a few" years to some people.

[Alan F.]

He's going to make some sort of custom aluminum airbox for it and try to mimic the amount of air restriction the stock one has, just in a more manageable shape.

Not air restriction, but internal volume.  Size matters when it comes to an airbox.  I might be fabbing one up for a CM400 I'll be making a project out of later on, I think I'll be measuring the volume of the stock airbox by filling it with ping pong balls or something that will acurately represent the volume, then fill my cardboard mockup with the same number of balls to check for similar enough capacity. (ping pong balls won't blow the side off of a cardboard mockup...)
Give considerable thought to your design to keep the bike running as intended, and while you're at it maybe you can design your airbox around an inexpensive and universally available automotive air filter too.
-Alan

[tbpmusic]

It has to be the worst possible airbox to get on and off. You have to leave the box on, pull the carbs, then the box comes out.

I steered him away from pods after my bad experiences. He's going to make some sort of custom aluminum airbox for it and try to mimic the amount of air restriction the stock one has, just in a more manageable shape.

Those DOHC Fours really prefer the stock air filter setup. As mentioned, the plenum (airbox) is highly engineered.
Anything else leads to hard times for you.

The filters are commonly available and cheap, just stick with the stock setup - my 2 cents worth FWIW......

[mgbgt89]

Ah.. Didn't realize it was a volume issue. Well in that case we'll be keeping the stock one. It's massive, and a pain in the ass to get on and off. That was the only reason i was thinking about ditching it.

[6adan]

I have a 81 750K and you are right about tha airbox it is just a pain to get on and off but it has to be there to run right.I had to buy a special screwdriver to adjust the carbs.

[bucky katt]

does it have the dual range gearbox?

[bill440cars]

does it have the dual range gearbox?

  Jeff, I think I'm right in saying that only the 900C had the dual range gearbox.

[mgbgt89]

Not a dual range, those were only on the customs. I've always wanted to ride one of those though. Anyone know how those work? Twin shifters?

[Markcb750]

I test rode a couple 900 customs, the H/L is a second lever. Not good for 1low to 1high to 2low... It is meant for selecting depending on driving conditions, like the front cog on your 10 speed bicycle.

[Tnutz]

basically a 2 speed primary drive.  KEEP THAT AIRBOX.  those cv's just refuse to run right without it.

[mgbgt89]

I think we may be having a timing issue. The carbs are very clean. So i don't think it is that. I'm also fairly certain the accelerator pump is working. When it hits about 5500-6000 rpm it's like it hits a brick wall. It will rev higher though with the choke slightly on. This was told to me over the phone. Just doing a quick search online, this is when the timing should be in full advance. I've never messed with CDI ignitions. Where do i start? Farthest i've been into them is looking at the pickups on my 650 when i had the cover off. Same as setting points just without the gapping?

After work tomorrow i'll go pick up my timing light from my girlfriend take it over there and see if my theory is right.

Also, I need help. There have been words thrown around the shop of "Ratting it out" and "Raking the front end". I explained to him about how this was honda's sport bike of the day, and that chopping it would make about as much sense as chopping a CBR. Not to mention the destruction of a part of honda history. I read the 900F's finished 1-2-3 at daytona in 82? Don't get me wrong, i actually like bobbers. Jreichs bike on here is one of my favorite on the site. I just think a 900F bobbed out would look like #$%*.