Author Topic: CB750K4 New project  (Read 12168 times)

Offline Rob62

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Re: CB750K4 New project
« Reply #120 on: July 22, 2018, 05:25:43 PM »
Thanks K2.. i wanted to see if anybody could shed some light before i tried the other way round as i dont want to cause damage but i think its the only other option.... The other doubt thats now creeping into my mind is the big square metal mounts on the coils which are earths right?, since they are mounted to the frame they must be?... its just that none of the diagrams I’ve looked at show any earths on the coils and when i connect all the wires up with the coils just sitting there not screwed down onto the frame bracket, the fuse doesn’t blow....

What a frustrating day, and to cap it all off i managed to stand up next to the bike, hook the clutch lever around my brand new foooking expensive varifocals and knock them lense down onto the floor and scratch the lenses..... grrrrrr

Offline K2-K6

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Re: CB750K4 New project
« Reply #121 on: July 22, 2018, 05:59:41 PM »
As I understand it the main, structural, earth on the coils is the neg side of the High Tension circuit that completes the spark circuit. 

The low tension, low voltage side of the coil is effectively separate and just connected via the wires you describe through both the supply positive and negative switching by the points.

Offline Rob62

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Re: CB750K4 New project
« Reply #122 on: July 22, 2018, 09:03:50 PM »
Ok...the solution. First off as many of you no doubt already know, the big iron mounting bars on the coils are not earths, according to all the diagrams they dont seem to form any part of the circuit? You were right K2, the earth for the ht side is the cyl head.

The clue was in the fact that the fuse only blew when the coils were clamped down, when they were free standing i could connect up all the wires without any problem. These replacement coils have spade connectors coming from the moulded body. On the left side coil (1 & 4) the spade connector gets slightly pressed up against the frame mounting when the coil is tightened up, but its got a protective plastic sheith so should be ok, but this one had a tiny split and was shorting out. 2nd problem was that the polarity of the wires was wrong, i wrongly assumed that the black wire was the positive feed but in fact it was the other way round. There is a crude + and - moulding in the coils thats not so easy to spot unless you have a good look.... I’m not sure that would have caused a problem anyway, i think it might have run but its the right way round now.

So after much frustration she now starts and runs on all four again... next job carb balancing. I’ve bitten the bullet and bought a set of £107 sealey gauges which i hope will work ok.
« Last Edit: July 22, 2018, 09:06:29 PM by Rob62 »

Offline Rob62

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Re: CB750K4 New project
« Reply #123 on: July 24, 2018, 10:30:28 PM »
Had a quick go at balancing the carbs yesterday.... was getting late so packed it in but was struggling to get her running evenly. Ended the day worrying that there may be a problem with the motor ie compression. So tonight i double checked all the valve clearances, which were ok, then I ran a compression test. Cold engine, left 3 plugs in the motor, throttle wide open, 5 seconds on the strater motor, 150 psi on each cylinder, so I was happy with that. Again it was getting late so i made some adjustments to the carbs and just fired her up for a few seconds, seemd to be running better but still not too smooth..  Will balance the carbs at the weekend and then i reckon she just needs a good run. Im going to send off my registration application tomorrow so i took a couple of photographs of her to support the application. She is now virtually complete, just needs the side panels lacquering and a few decals adding. Hopefully I’ll be riding her in a couple of weeks 😄





« Last Edit: July 26, 2018, 01:07:51 PM by Rob62 »

Offline Rob62

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Re: CB750K4 New project
« Reply #124 on: August 03, 2018, 07:32:23 PM »
Mine is all done now... just waiting for a reg number. I think its the first resto that i have actually completed before i started riding it. Usually i am finishing off loose ends weeks after first riding them.  Will have a few snags to fix after the first shakedown no doubt, cant wait

Offline Green1

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Re: CB750K4 New project
« Reply #125 on: August 03, 2018, 08:25:34 PM »
Looks great you've got a really good shine on that oddball colour  8)
Current bikes
Honda CB750k1 Valley Green Metallic
Honda CB750k1 Candy Gold
Honda CB550k Candy Jade Green
Honda CG125
Aprilia Pegaso 650
Moto guzzi 1200 sport
Kawasaki EX650R (Mine until dave pays for it)
Kawasaki ZXR400 J

Offline Rob62

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Re: CB750K4 New project
« Reply #126 on: August 03, 2018, 08:32:48 PM »
Haha cheers.... they always say you can’t polish a turd.... but you can roll it in glitter

Offline Green1

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Re: CB750K4 New project
« Reply #127 on: August 03, 2018, 08:43:10 PM »
Mine starts off as glitter
Current bikes
Honda CB750k1 Valley Green Metallic
Honda CB750k1 Candy Gold
Honda CB550k Candy Jade Green
Honda CG125
Aprilia Pegaso 650
Moto guzzi 1200 sport
Kawasaki EX650R (Mine until dave pays for it)
Kawasaki ZXR400 J

Offline JamesH

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Re: CB750K4 New project
« Reply #128 on: August 04, 2018, 10:36:51 AM »
Looks superb, well done Rob.

Offline adespin

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Re: CB750K4 New project
« Reply #129 on: August 04, 2018, 12:57:15 PM »
Haha cheers.... they always say you can’t polish a turd.... but you can roll it in glitter

I think Gary Glitter was already a turd,

Gotta say i don't normally like 4 into 1 pipes, but on yours it looks good, very nice job and unusual colour.
1971 cb750 K1

Offline Rob62

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Re: CB750K4 New project
« Reply #130 on: August 05, 2018, 08:56:48 AM »
Thanks guys....  :) The 4 into 1 sounds nice, i always prefer the clean sound compared to the 4 into 4. Plus at £280 new for a full stainless system they are a bit of a bargain.

Offline Laverda Dave

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Re: CB750K4 New project
« Reply #131 on: August 05, 2018, 09:26:32 AM »
Well done, it's a peach. The exhaust looks great.
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

Offline Spitfire

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Re: CB750K4 New project
« Reply #132 on: August 05, 2018, 06:00:16 PM »
Great looking bike, nice one

Cheers

Dennis
1976 CB750F

1977 CB750F2 In bits

1964 BSA A65R In bits

Offline Rob62

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Re: CB750K4 New project
« Reply #133 on: August 09, 2018, 05:21:19 PM »
Woooohoooooo !!!! I have a registration number, exactly 2 weeks after i sent off the application, its an M reg 😄

Many thanks to all those who gave advice on what to include in the registration application...... now for some number plates.

Offline Nurse Julie

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Re: CB750K4 New project
« Reply #134 on: August 09, 2018, 05:30:35 PM »
Great news, these things are easy when you send off everything they need to do the job !!!
LINK TO MY EBAY PAGE. As many of you know already, I give 10% discount and do post at cost to forum members if you PM me direct.
https://www.ebay.co.uk/sch/julies9731/m.html?item=165142672569&rt=nc&_trksid=p2047675.m3561.l2562

LINK TO MY CB400/4 ENGINE STRIP / ASSESSMENT AND REBUILD...NOW COMPLETE
http://www.sohc.co.uk/index.php/topic,14049.msg112691/topicseen.html#new

 

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