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Author Topic: 1978 CB750k Project - Where to Start?  (Read 424 times)

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Offline Gonzo750

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1978 CB750k Project - Where to Start?
« on: January 08, 2019, 03:02:29 pm »
Hello Everyone!

I've jut bought a heck of a project bike. It's a 1978 CB750k.

What I know so far: It turns, it has compression (allegedly), But it has no oil pressure. The seller gave me an extra oil pump to see if that'd solve the issue. The reason stated for selling was because it's a full service shop and they can't waist their resources on a project bike like this. The fuel tank needs to be replaced (or welded together for that matter). There's rust and dirt and grime all over. Brakes are non-existent. Wiring is a mess. Signs of being dropped on the points cover and gauges. The bike basically seems to need to rebuilt near entirely. The most positive note I see is the shifter feels good and seems to go through the gears easily.

My question is, where do I even start and how should I go about this project? I don't want to get deep in cash and then figure out it's not going to work out. Also let me know what tools I absolutely need to get going, and what I'd need to finish it all.

I thank you all in advance! It will be my first project, and bike, ever. Hopefully I can get this stallion back to glory!


1978 CB750k - Barn Find

Online efletche

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Re: 1978 CB750k Project - Where to Start?
« Reply #1 on: January 08, 2019, 03:22:30 pm »
Are those passenger floor boards for sale???

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Offline Stev-o

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Re: 1978 CB750k Project - Where to Start?
« Reply #2 on: January 08, 2019, 03:27:02 pm »
First off, welcome Gonzo.

You sure picked a winner for your first bike!   The first thing I would do is check the engine for compression and do a leak down test.

You'll need the testers for this.  Why do you think it has no compression? It appears the spark plugs are in place, that would be rare to zero compression. Maybe it's "stuck"?  Can you kick it over?

What is your budget?  Are you prepared to sink $1000-1500 into this bike if it does indeed need motor work? Rebuilding a motor is not cheap if done properly. And if you do it, do it right or it may just end up being a waste of time and money.

Appears you have a mixture of parts - early tank and later carbs.  Nice exhaust btw...

'74 "Big Bang" Honda 750K [836].....'71 Honda 750K project.....'76 Honda 550F.....K3 Park Racer.....K5 Fiddy Dolla Special!......CB500 Fiddy Dolla Special too!!............plus plus plus.........

Offline Gonzo750

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Re: 1978 CB750k Project - Where to Start?
« Reply #3 on: January 08, 2019, 03:30:18 pm »
Are those passenger floor boards for sale???

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I won't be using them so sure! Haha. They mount right over the standard passenger pegs.
1978 CB750k - Barn Find

Offline Gonzo750

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Re: 1978 CB750k Project - Where to Start?
« Reply #4 on: January 08, 2019, 03:39:29 pm »
First off, welcome Gonzo.

You sure picked a winner for your first bike!   The first thing I would do is check the engine for compression and do a leak down test.

You'll need the testers for this.  Why do you think it has no compression? It appears the spark plugs are in place, that would be rare to zero compression. Maybe it's "stuck"?  Can you kick it over?

What is your budget?  Are you prepared to sink $1000-1500 into this bike if it does indeed need motor work? Rebuilding a motor is not cheap if done properly. And if you do it, do it right or it may just end up being a waste of time and money.

Appears you have a mixture of parts - early tank and later carbs.  Nice exhaust btw...



It does have compression. I say allegedly because that's through the word of the seller; I just haven't officially tested it myself. When I bought it, they turned the engine freely with the kick start and I could hear it has compression.

What it doesn't have is oil pressure, and they couldn't get it to start. I've already bought new spark plugs, so they're in line to be replaced. My guess is the oil pump must be stuck.

Would I need to get battery power and a turned on key to start? Or can I soley get it started by kick? ( I ask b/c I don't necessarily want to shell out a good set of change for a battery if I don't have to.)

I currently have my overall budget at around $2500 over the span of a good period. Also, I'm at school right now and my house is 100 miles away, so it's going to be a weekend only project.
1978 CB750k - Barn Find

Online efletche

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Re: 1978 CB750k Project - Where to Start?
« Reply #5 on: January 08, 2019, 03:41:21 pm »
Give me a price for them???

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Online efletche

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Re: 1978 CB750k Project - Where to Start?
« Reply #6 on: January 08, 2019, 03:42:22 pm »
Remember all the things you won't use is for sale, people will vye

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Offline Gonzo750

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Re: 1978 CB750k Project - Where to Start?
« Reply #7 on: January 08, 2019, 03:54:06 pm »
Give me a price for them???

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Sent you a PM
1978 CB750k - Barn Find

Offline calj737

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Re: 1978 CB750k Project - Where to Start?
« Reply #8 on: January 08, 2019, 05:49:26 pm »
You can get the bike to start with the kicker once the RUN switch is ON, and the ignition switch is activated. If you don’t have a key or ignition switch, jumper wires will make it go.
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Offline beemerbum

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Re: 1978 CB750k Project - Where to Start?
« Reply #9 on: January 08, 2019, 06:00:59 pm »
Looks like you got a good seat. A little rust on the fittings, no problem to remove

Offline seanbarney41

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Re: 1978 CB750k Project - Where to Start?
« Reply #10 on: January 08, 2019, 06:29:39 pm »
You can get the bike to start with the kicker once the RUN switch is ON, and the ignition switch is activated. If you don’t have a key or ignition switch, jumper wires will make it go.
battery is gonna have to have at least 9 or 10 volts for it to kickstart
If it works good, it looks good...

Offline ekpent

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Re: 1978 CB750k Project - Where to Start?
« Reply #11 on: January 08, 2019, 07:27:58 pm »
 Oil pump would not stick as its all mechanical pretty much. What would worry me is that it was run if indeed there was a problem with the oil pressure and the cam and top end got dry. Good place to start if your leaving the engine in is to drop the oil pan and look for sludge and debri on the screen and shavings of metal in the bottom.

Offline Bankerdanny

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Re: 1978 CB750k Project - Where to Start?
« Reply #12 on: January 09, 2019, 02:58:08 pm »
If they can't get it to start and it doesn't have a battery to spin the engine how do they know it doesn't have oil pressure?

You can use a car battery or jump box to spin the engine, just don't try to jump from a running car/truck.
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Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki 80 (K11 probably, it's been 30 years), '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline MauiK3

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Re: 1978 CB750k Project - Where to Start?
« Reply #13 on: January 09, 2019, 03:05:21 pm »
If there is the correct amount of oil in it, remove the plugs, get some power to the starter and spin it, it will take a minute or so to show pressure on the gauge but I bet it will come up. Kicking it over will not produce any apparent pressure on the gauge unless you can kick fast and long.
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Offline calj737

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Re: 1978 CB750k Project - Where to Start?
« Reply #14 on: January 09, 2019, 03:50:25 pm »
You can use a car battery or jump box to spin the engine, just don't try to jump from a running car/truck.
Not a thing in the world wrong with jumping a 12v bike from a running, 12v car. That is a myth that needs to be quieted. The bike will only request what it needs, paying no attention to what is available at the car (just like your home on the power company grid  ;) )
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Offline Gonzo750

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Re: 1978 CB750k Project - Where to Start?
« Reply #15 on: January 09, 2019, 05:19:17 pm »
Ok, so it seems like you guys are suggesting to basically just start from the top and diagnose everything myself?

It does seem like they replaced the oil when I looked at the dipstick and it was clear.

If I don't have a battery, or charger, what's the easiest and most affordable way of jumping it?
1978 CB750k - Barn Find

Offline calj737

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Re: 1978 CB750k Project - Where to Start?
« Reply #16 on: January 09, 2019, 05:21:27 pm »
You need a battery or a jump box to excite the coils. Whether or not you use the electric start or kick start is up to you from there.
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Offline Bankerdanny

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Re: 1978 CB750k Project - Where to Start?
« Reply #17 on: January 09, 2019, 07:56:45 pm »
Ok, so it seems like you guys are suggesting to basically just start from the top and diagnose everything myself?

It does seem like they replaced the oil when I looked at the dipstick and it was clear.

If I don't have a battery, or charger, what's the easiest and most affordable way of jumping it?

Like I said, the battery from your car will work fine. The bike is a 12V system just like your car.
"The problem with quotes on the Internet is that you never know if they're true" - Abraham Lincoln

Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki 80 (K11 probably, it's been 30 years), '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline Gonzo750

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Re: 1978 CB750k Project - Where to Start?
« Reply #18 on: January 10, 2019, 08:38:19 am »
Okay so here's the plan:

1. Check in the oil pan (if the oil was replaced before and it's clean may I reuse?)
2. Check the Oil pump (both original and spare), replace if need be.
3. Replace spark plugs
4. Make sure carbs are clean (previous owner already did but just to double check)
5. Jump and check for spark
6. Jump and see if it fires
7. If all is well, go from there and project is on

Let me know if I'm missing anything here or if you have any different way. Thank you all for the responses!
1978 CB750k - Barn Find

Offline ekpent

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Re: 1978 CB750k Project - Where to Start?
« Reply #19 on: January 10, 2019, 11:47:25 am »
 I think it would be pretty rare to have 2 oil pumps be bad enough that they would not work. I've had many 750's and never had a bad pump on any of them. I think I would try to start it up first and look for circulation quickly in the oil tank with a flashlight and look for oil in the top end through some tappet covers.If nothing happens quickly oil wise shut her down.

Offline Bankerdanny

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Re: 1978 CB750k Project - Where to Start?
« Reply #20 on: January 10, 2019, 07:28:29 pm »
 You can re-use the old oil but make sure whatever you drain it into is absolutely clean.
"The problem with quotes on the Internet is that you never know if they're true" - Abraham Lincoln

Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki 80 (K11 probably, it's been 30 years), '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline rotortiller

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Re: 1978 CB750k Project - Where to Start?
« Reply #21 on: January 11, 2019, 05:07:03 pm »
First thing I'd do is pull the carbs and float bowls to see if it's gummed up and check for float valve leaks/ correct level. I'd use a small aux gas tank. Once done I'd check the ignition for correct spark, make sure there is oil in the tank and try to fire the mother up with the kickstarter. If the sucker starts with oil pressure then I'd check the cam/valve area for lube. At this point you will have a better idea of how big a POS the engine is. Lots of ways to kick the kat, just look for snakes along the way.

 

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