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Burntrubber87
Getting up steam
Getting up steam



Joined: Aug 12, 2010
Posts: 10
Location: NY

PostPosted: Fri Aug 13, 2010 3:08 pm Reply with quote Back to top

Hey guys..Saw an add for a '80 CB750 on craigslist for $350. So I pondered it for about a week while I gathered some money together. I called the guy up 2 days ago and ask him whats the lowest he'd take? He said $150..so I went on my way (150 mile round trip) to go pick it up. When I got there I got the shock of a lifetime. The CB fired right up..runs pretty good..a few dead spots but apparently the charging system isn't charging correctly so it killed its battery and only starts if you run it off something alittle more substanstial like a car battery.

I talked him down to $100. javascript:emoticon('Twisted Evil')
Then..as I was loading the '80 onto my truck..I was told there was a parts bike in back that was in "rough shape."..I was debating even going back there, but I went for a walk with him and sure enough it was a stripped down '79 CB750F Super Sport..he gave it to me for free..motors seized up and its missing its back tires and a bunch of electrical parts and it has no title. Here are the pics-
Image
Image

Is it ok to ask a couple questions here..? well here goes..
-Can I swap the forks over from the 750F SS? so I get a cool front wheel and dual discs?
-The 750F SS gauge cluster should work on the '80 right? they look just about the same.
-Where can I find some info about aftermarket rear shocks?(i'm a big dude..i'm about half-way to 2/3 through the shock travel just sitting on the bike)
-Would I be able to just buy a '79 750F SS rear wheel to use the rear discs or would that require swapping over the swingarm and everything? would that be worth it?
 
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pd750
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Joined: Aug 01, 2007
Posts: 25067
Location: Waldron , Arkansas

PostPosted: Fri Aug 13, 2010 4:19 pm Reply with quote Back to top

Welcome to the site Burntrubber87 ... Smile

I'd say you got a deal Very Happy

Yes to those questions .

Plenty of aftermarket choices for shocks , too . I'm sure a few of the guys will offer suggestions .

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Please put the year and model of your bike in the signature section on your profile / member account page and set \"Always attach signature \" to YES . Just below the Reply box , check the box in front of \"Attach signature (signatures can be changed in profile)\" .

1982 CB750C (Sold) Haven\'t found another , yet . 
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Frank
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Joined: Feb 27, 2010
Posts: 14379
Location: Eufaula, Oklahoma

PostPosted: Fri Aug 13, 2010 6:04 pm Reply with quote Back to top

Howdy, great deal!

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You meet the nicest people on a Honda I sold my bike but I still have a 750 and a 900 that I will fix up some day. Right now I´m learning about Goldwings 
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jk333
Feel the Power
Feel the Power



Joined: Apr 29, 2008
Posts: 958
Location: WA

PostPosted: Fri Aug 13, 2010 8:53 pm Reply with quote Back to top

Burntrubber87 wrote:


Is it ok to ask a couple questions here..? well here goes..
-Can I swap the forks over from the 750F SS? so I get a cool front wheel and dual discs?
-The 750F SS gauge cluster should work on the '80 right? they look just about the same.
-Where can I find some info about aftermarket rear shocks?(i'm a big dude..i'm about half-way to 2/3 through the shock travel just sitting on the bike)
-Would I be able to just buy a '79 750F SS rear wheel to use the rear discs or would that require swapping over the swingarm and everything? would that be worth it?


I dont know about the spacing, but the forks and gauges should swap (the forks are 35mm just like the K) Try ebay for the shocks, they can get pricey pretty quick. You have to swap the swing arm as well as the rear master cylinder, brake line, caliper, etc.

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81 CB750C

Mirage Paint
Drag Bars
Rearsets
Spin On Adapter w/ Oil Cooler
Custom Seat
4 into 4 Exhaust
And Much More... 
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genesound
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Joined: Jul 24, 2007
Posts: 44788
Location: Studio City, CA

PostPosted: Sat Aug 14, 2010 1:43 am Reply with quote Back to top

Scooooore! Laughing

Welcome to here wave

Please read all the suggested stuff.

_________________
NMT - New Member Thread, a Must Read, click here!!! - Information For New and Veteran Members.
Contains SITE RULES, how to enter required bike information in your signature, thread and picture posting...
Also some important DOHC wrenching tips, and some other information, shop manuals.
Kindly read this linked thread with the rules before posting
pictures or asking lots of questions that are already answered in it.

ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
81 CB900C, 83 CB1000C. 
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Dodgerfan
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Joined: Dec 29, 2007
Posts: 1063
Location: Bullhead City, AZ

PostPosted: Sat Aug 14, 2010 2:38 am Reply with quote Back to top

Welcome

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1980 CB900C 
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CjKit
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Joined: Mar 09, 2010
Posts: 1303
Location: London, UK

PostPosted: Sat Aug 14, 2010 5:22 pm Reply with quote Back to top

yeah that
That is definitely what I'd call a good deal!!! Very Happy

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82 CB900FC
CjKitPhoto 
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Burntrubber87
Getting up steam
Getting up steam



Joined: Aug 12, 2010
Posts: 10
Location: NY

PostPosted: Mon Aug 16, 2010 8:01 pm Reply with quote Back to top

So..I think I figured my problem (Hopefully) Both of the brushes on the generator are less than 1/2" long..one is less than a 1/4". Found that out after I made the video. If you want to hassle me about jumping it from the truck and jumping the relay go ahead..i'm trying to figure out if the bike is worth putting money into it.

If you can't see what the dvom says its 12.4-12.6(not charging) and it won't go any higher. I've still got a few more tests to do, but I'm concerned with the noise.

http://www.youtube.com/watch?v=J03MTZlIWrA

Around 0:49 in the vid you'll hear a clackety clack clack..I hope..no..I PRAY its the valve are so out of whack it sounds like a washing machine full of marbles. 26,000 miles. But the weird thing is..it goes away if you hit the throttle, or at least quiets down alot compared to a low idle..keep in mind I just got this bike going and I haven't had the chance to completely bring it up to temperature with brand new fresh oil.

Be nice..i did only pay $100 for two bikes.


Last edited by Burntrubber87 on Mon Aug 16, 2010 8:11 pm; edited 1 time in total 
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genesound
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Joined: Jul 24, 2007
Posts: 44788
Location: Studio City, CA

PostPosted: Mon Aug 16, 2010 8:09 pm Reply with quote Back to top

Sounds to me like it's only running on 2 cylinders. Do all 4 head pipes get hot?

That noise may have just been clutch basket or cam chain noise. You have to get it running better before you can get critical on that.

_________________
NMT - New Member Thread, a Must Read, click here!!! - Information For New and Veteran Members.
Contains SITE RULES, how to enter required bike information in your signature, thread and picture posting...
Also some important DOHC wrenching tips, and some other information, shop manuals.
Kindly read this linked thread with the rules before posting
pictures or asking lots of questions that are already answered in it.

ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
81 CB900C, 83 CB1000C. 
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Burntrubber87
Getting up steam
Getting up steam



Joined: Aug 12, 2010
Posts: 10
Location: NY

PostPosted: Mon Aug 16, 2010 8:16 pm Reply with quote Back to top

Yeah, They're all getting hot and they all seem to be around the same temp. At the very end of the video I hit it a couple times and it sounds healthy (to me..might sound different on video.) I think i'm going to do a compression test before I start spending money on batteries, charging components and etc.
 
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genesound
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Joined: Jul 24, 2007
Posts: 44788
Location: Studio City, CA

PostPosted: Mon Aug 16, 2010 8:18 pm Reply with quote Back to top

Good idea. Be sure to do it with the throttle wide open. Wouldn't hurt to make sure the carb slides open properly too.

_________________
NMT - New Member Thread, a Must Read, click here!!! - Information For New and Veteran Members.
Contains SITE RULES, how to enter required bike information in your signature, thread and picture posting...
Also some important DOHC wrenching tips, and some other information, shop manuals.
Kindly read this linked thread with the rules before posting
pictures or asking lots of questions that are already answered in it.

ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
81 CB900C, 83 CB1000C. 
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Burntrubber87
Getting up steam
Getting up steam



Joined: Aug 12, 2010
Posts: 10
Location: NY

PostPosted: Mon Aug 16, 2010 8:44 pm Reply with quote Back to top

YES! just found the problem.
Tested the resistance on the rotor on the '80 that isn't charging. It read .3-.4ohms. Then I checked the rotor on the '79 and it was 4.7 ohms. so..next question is..how hard is it to get that rotor off and can I use the one off from my '79 CB750F SS on the '80 CB750K?
 
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genesound
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Joined: Jul 24, 2007
Posts: 44788
Location: Studio City, CA

PostPosted: Mon Aug 16, 2010 8:51 pm Reply with quote Back to top

Use the rear axle.

http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&p=97456#97456

Use the search engine and put in "remove and rotor and axle" and select "search for all terms"

_________________
NMT - New Member Thread, a Must Read, click here!!! - Information For New and Veteran Members.
Contains SITE RULES, how to enter required bike information in your signature, thread and picture posting...
Also some important DOHC wrenching tips, and some other information, shop manuals.
Kindly read this linked thread with the rules before posting
pictures or asking lots of questions that are already answered in it.

ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
81 CB900C, 83 CB1000C. 
View user's profile Send private message Send e-mail Visit poster's website
Burntrubber87
Getting up steam
Getting up steam



Joined: Aug 12, 2010
Posts: 10
Location: NY

PostPosted: Mon Aug 16, 2010 9:15 pm Reply with quote Back to top

Thanks a lot, gene. you've been helpful.
So take out the rear axle, thread it onto the rotor and smack it, take the slack out, smack it, repeat? I'll have to give it a shot..Hopefully my Ford wrench (5lbs Estwing mallet) is up to the challenge.
 
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genesound
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Joined: Jul 24, 2007
Posts: 44788
Location: Studio City, CA

PostPosted: Mon Aug 16, 2010 9:17 pm Reply with quote Back to top

Ought to do it. Smile

_________________
NMT - New Member Thread, a Must Read, click here!!! - Information For New and Veteran Members.
Contains SITE RULES, how to enter required bike information in your signature, thread and picture posting...
Also some important DOHC wrenching tips, and some other information, shop manuals.
Kindly read this linked thread with the rules before posting
pictures or asking lots of questions that are already answered in it.

ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
81 CB900C, 83 CB1000C. 
View user's profile Send private message Send e-mail Visit poster's website
Burntrubber87
Getting up steam
Getting up steam



Joined: Aug 12, 2010
Posts: 10
Location: NY

PostPosted: Wed Aug 18, 2010 10:30 am Reply with quote Back to top

Well, I got the rotor off the '80 and the rotor off the '79 with the axle. Just as an FYI for everyone..use a socket on the end of the axleshaft when you're hammering it..I mushroomed out the bolt head on mine and had to file it back straight. Worked like a charm though. Bike is still not charging though..I bench tested the two regulator/rectifiers resistance between the three yellow wires and the green and red and both of the had resistance of about 4.5ish-5.0 - 40 ohms.

I'm beginning to think the kid who had the bike put the parts RR on the '80 with the rotor still shorted and it fried that one also..leaving both effectively fubar.

So can I bypass the regulator (Ground the white wire on the harness.) with the RR messed up? does it bypass everything is what i'm asking.

Can I test the wires coming out of the stator to see if there is voltage coming out of there? (i'm guessing its going to be AC)
 
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genesound
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Joined: Jul 24, 2007
Posts: 44788
Location: Studio City, CA

PostPosted: Wed Aug 18, 2010 11:51 am Reply with quote Back to top

You can stick straight pins in the black and white wires if you don't have sharp probes on your meter. Then measure the voltage to the rotor at 3 grand, it should be over 12 v. Be sure you don't short out those connections though... if the regulator wasn't fried before, that would do it.

The best way to full field the rotor is to disconnect the black and white wires from the R/R and feed the rotor battery voltage directly with a 10A fuse inline. Don't apply voltage when it's not running though and don't leave it hooked up full fielded too long either.

http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&p=141368&highlight=full+field#141368

_________________
NMT - New Member Thread, a Must Read, click here!!! - Information For New and Veteran Members.
Contains SITE RULES, how to enter required bike information in your signature, thread and picture posting...
Also some important DOHC wrenching tips, and some other information, shop manuals.
Kindly read this linked thread with the rules before posting
pictures or asking lots of questions that are already answered in it.

ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
81 CB900C, 83 CB1000C. 
View user's profile Send private message Send e-mail Visit poster's website
Burntrubber87
Getting up steam
Getting up steam



Joined: Aug 12, 2010
Posts: 10
Location: NY

PostPosted: Wed Aug 18, 2010 1:33 pm Reply with quote Back to top

Ok, i'm gonna go try and full field the rotor. What wire do you feed voltage into and do you have to ground the other wire? (white/black?)
..Might just T-pin the white and black with it hooked up and check v.
 
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