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Author Topic: CB550 Bobber-Junkyard Dog  (Read 14158 times)

Offline john83

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CB550 Bobber-Junkyard Dog
« on: Jan 24, 2018, 21:24:07 »
I've always wanted a hard tail bobber chopper. Last week I saw this hard tail frame on the local CL. Seller said he was selling it because the motor had locked up and he'd gone on to different things, it had a CB500 motor in it. I happen to have CB550 that I was working on making a cafe racer out of but the project is stalled and I've sort of lost interest. So what's gonna happen is I'm going to stick my motor in this thing and see try to get it going. There are some interesting things going on with this thing to sort out.

The hardtail looks to be well done, the welds all look very solid. All the factory welds seem to have been smoothed down and blended in. It had a cool purple paint job with some pin striping but it's been in the weather and has quite a few nicks in it. The fuel tank is actually below the seat and used to be a fire extinguisher. There's a tap the bottom of the tank and a small vacuum operated pump that apparently gets fuel up to the carburetors. The seller said it worked pretty well before the engine seized. The front end doesn't look like it came from a 500 or 550, due to the Comstar wheels and trailing bake caliper. Maybe from a 650?

So the plan to begin with is to get my engine in the frame and see if I can get it to run. From there we will see.
« Last Edit: Aug 23, 2018, 22:48:31 by john83 »

Offline Hurco550

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Re: CB550 Bobber
« Reply #1 on: Jan 24, 2018, 21:25:22 »
This is stupid. Ill watch :)

Sent from my SM-G920V using Tapatalk

"If you just picked up a drug habbit instead of a kawasaki triple at least you could get high while you waste money"
~ bradj
1988 tw200, the swamp donkey: http://www.dotheton.com/forum/index.php?topic=75455.0
2006 Suzuki DR650 Adventure monowheel trailer build: http://www.dotheton.com/forum/index.php?topic=75033.0
1976 BMW R90/6 farkilitious: http://www.dotheton.com/forum/index.php?topic=74349.msg882477#msg882477
1975 RD350 Road Racer: http://www.dotheton.com/forum/index.php?topic=70652.msg833688#msg833688
1976 GT250 Rebuild: http://www.dotheton.com/forum/index.php?topic=64973.new#new
Full Custom Pit Bike: http://www.dotheton.com/forum/index.php?topic=66954.new#new
1971 Yamaha 90cc twin HS1: http://www.dotheton.com/forum/index.php?topic=70498.0
"much ingenuity with a little money is more profitable and amusing than much money without ingenuity" - Arnold Bennet

Offline john83

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Re: CB550 Bobber
« Reply #2 on: Jan 24, 2018, 21:37:08 »
I'm sure things are gonna get a bit silly.

Offline canyoncarver

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Re: CB550 Bobber
« Reply #3 on: Jan 24, 2018, 23:18:14 »
What a cool frame.  I'm in.

Offline Hurco550

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Re: CB550 Bobber
« Reply #4 on: Jan 24, 2018, 23:35:06 »
I think the chipped up frame paint is cool myself. Throw a lump in it and ride it as is. That's my meaningless vote anyways ;)

Sent from my SM-G920V using Tapatalk

"If you just picked up a drug habbit instead of a kawasaki triple at least you could get high while you waste money"
~ bradj
1988 tw200, the swamp donkey: http://www.dotheton.com/forum/index.php?topic=75455.0
2006 Suzuki DR650 Adventure monowheel trailer build: http://www.dotheton.com/forum/index.php?topic=75033.0
1976 BMW R90/6 farkilitious: http://www.dotheton.com/forum/index.php?topic=74349.msg882477#msg882477
1975 RD350 Road Racer: http://www.dotheton.com/forum/index.php?topic=70652.msg833688#msg833688
1976 GT250 Rebuild: http://www.dotheton.com/forum/index.php?topic=64973.new#new
Full Custom Pit Bike: http://www.dotheton.com/forum/index.php?topic=66954.new#new
1971 Yamaha 90cc twin HS1: http://www.dotheton.com/forum/index.php?topic=70498.0
"much ingenuity with a little money is more profitable and amusing than much money without ingenuity" - Arnold Bennet

Offline WhyNot

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Re: CB550 Bobber
« Reply #5 on: Jan 25, 2018, 07:58:36 »
Hardtails, they seem to be popping up all over the place.

I just picked up a SL350 frame, that I intend to hardtail it, if I can.............

I think what Hurco550 said is exactly what I would do, and sounds like sound advice.

I'm watching this, hope I can get something started with my frame.
1975 CB750K5
1974 CB350F

Offline irk miller

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Re: CB550 Bobber
« Reply #6 on: Jan 25, 2018, 08:13:41 »
I still don't know what to think of that fuel tank.  And put shocks on it.  That would make it unique. 

Offline john83

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Re: CB550 Bobber
« Reply #7 on: Jan 25, 2018, 21:59:06 »
Of course since I got it home I've had no time to get out to the garage. I did get the engine out of the cafe frame and moved over toward the bobber. Once I get the lump in there I'm gonna let the avionics tech at work perform some magic on the wiring. I'm definitely gonna give it a go with it's current fuel situation. I may eventually want to make some changes but for the mean time the goal is just to ride it.

Offline Hurco550

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Re: CB550 Bobber
« Reply #8 on: Jan 25, 2018, 22:10:14 »
I was thinking about the conversation about fuel pumps and carburetors and needle seats etc etc tonight while I was pulling this carburetor apart to rebuild it. It is a Tillotson brand carburetor, this particular one was used on a 1972 boa ski snowmobile. They're kind of a neat little deal. There is no Bowl, but instead where the bowl would be is actually an integrated fuel pump that runs on vacuum Pulses from the crank. It still uses a needle in a seat just like a normal carburetor would. Just something to think about

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« Last Edit: Jan 25, 2018, 22:14:18 by Hurco550 »
"If you just picked up a drug habbit instead of a kawasaki triple at least you could get high while you waste money"
~ bradj
1988 tw200, the swamp donkey: http://www.dotheton.com/forum/index.php?topic=75455.0
2006 Suzuki DR650 Adventure monowheel trailer build: http://www.dotheton.com/forum/index.php?topic=75033.0
1976 BMW R90/6 farkilitious: http://www.dotheton.com/forum/index.php?topic=74349.msg882477#msg882477
1975 RD350 Road Racer: http://www.dotheton.com/forum/index.php?topic=70652.msg833688#msg833688
1976 GT250 Rebuild: http://www.dotheton.com/forum/index.php?topic=64973.new#new
Full Custom Pit Bike: http://www.dotheton.com/forum/index.php?topic=66954.new#new
1971 Yamaha 90cc twin HS1: http://www.dotheton.com/forum/index.php?topic=70498.0
"much ingenuity with a little money is more profitable and amusing than much money without ingenuity" - Arnold Bennet

Offline john83

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Re: CB550 Bobber
« Reply #9 on: Jan 25, 2018, 22:24:11 »
I was doing a little reading about vacuum operated fuel pumps. Seems they're pretty common on lawn mowers when tank is located lower than the carb. That would make sense since mine has a Briggs and Stratton logo on it, also says Mikuni though. Seems they are usually operated by vacuum pulses from the crank acting on bellows like Levi mentioned. Not sure exactly how mine works yet since it doesn't have a vacuum line running to it. It does have a return line back into the tank, that might address Kileys concern about excess fuel overcoming the floats and flooding the carbs. I guess we will see.