Author Topic: CB750 Barn find project - First Timer  (Read 32299 times)

Offline Underdog1

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Re: CB750 Barn find project - First Timer
« Reply #570 on: September 09, 2018, 09:04:43 AM »
Finally going to have some fettling time today so going to sort the petcock and carbs.

Running on the rich side so need to raise the needle clip either 1 or 2 notches. How long do I need to run the bike for before looking at plug colour again to see if I need to move needle position again? And do I need to clean up the plugs if they’re already a bit blackened from rich running or does this get burnt off?
« Last Edit: September 09, 2018, 07:50:17 PM by Underdog1 »

Offline Underdog1

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Re: CB750 Barn find project - First Timer
« Reply #571 on: September 09, 2018, 08:10:32 PM »
Okay so pulled the carbs off and raised the needle clips one notch to lean out the mix a bit, I’m at one clip from the top so still got some further adjustment if needed. Checked the floats and they are all bang on 26mm and operate smoothly. I’ve replaced the float valves with the original ones incase the cruzin image ones aren’t sealing properly. The aftermarket ones go into a point whilst the original ones are blunted off at the tip. I also noticed that the air mixture screws were no longer at the 1 turn out, on was at about 3 turns out.. no idea how these have worked themselves out but put them back to 1 turn.

Got them back on the bike and synced with a carbtune pro which was pretty easy but then noticed I had a significant leak around the front sprocket cover. Whipped the sprocket off and seen this



The drive seal wasn’t sitting flat as it should and was leaking at the bottom where it protruded out slightly. Unsure whether it wasn’t lined up correctly when I closed the cases or not but it’s not leaked for the first 50 miles until now. I even put a smear of hondabond on it as recommended in hondamans book so perhaps this held back the oil until now.

Rightly or wrongly I carefully tapped it back in flush and it doesn’t seem to leak any more. Am unable to ride as the seats with the upholsterer but fingers crossed it’s fine

Still getting a bit out the overflows so don’t think swapping the float valves has done anything. I’ve not got any sort of washer beneath the float valve seat and carb body, none was supplied in the rebuild kit and none were on it when I stripped them.. have seen in some pictures that some sort of washer is present - did this appear on certain years only or am I missing them possibly?
« Last Edit: September 09, 2018, 08:15:07 PM by Underdog1 »

Offline Laverda120

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Re: CB750 Barn find project - First Timer
« Reply #572 on: September 09, 2018, 08:19:25 PM »
I feel your pain underdog :(. I suffered a similar fate with my CB250RSA drive oil seal. It was fine for 10 miles and then just let go in the same way dumping oil all over the road. I had to split the cases to replace the seal. Hopefully yours will be OK, good luck.

Offline Trigger

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Re: CB750 Barn find project - First Timer
« Reply #573 on: September 09, 2018, 08:24:28 PM »
Do your air screws have springs ? They should not move ;)

Offline Underdog1

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Re: CB750 Barn find project - First Timer
« Reply #574 on: September 09, 2018, 08:41:45 PM »
I feel your pain underdog :(. I suffered a similar fate with my CB250RSA drive oil seal. It was fine for 10 miles and then just let go in the same way dumping oil all over the road. I had to split the cases to replace the seal. Hopefully yours will be OK, good luck.
Yeah time will tell, it’s a new seal so no idea why it’s happened.

Do your air screws have springs ? They should not move ;)

Yeah they do, it’s possible I had a brain fart at some point but I’ll keep an eye on them to see if they move at all in the future

Offline Underdog1

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Re: CB750 Barn find project - First Timer
« Reply #575 on: September 14, 2018, 08:45:33 AM »
Seats got covered, upholsterer text me yesterday but not managed to pick it up yet




Offline Nurse Julie

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Re: CB750 Barn find project - First Timer
« Reply #576 on: September 14, 2018, 09:14:26 AM »
Very nice.
Im a Nurse, trust me, this won't hurt.....much !!!

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

Offline Underdog1

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Re: CB750 Barn find project - First Timer
« Reply #577 on: September 15, 2018, 06:33:26 PM »
Seats fitted and took the bike out for a spin. Have also had a fiddle with and synced the carbs



I think it looks great and is just what I wanted. Bikes running alright still a little stumble at 3.5k but I’ve got another needle clip position to try in the future. The front sprocket oil seal is now doing its job since tapping it into place but will keep an eye on it, just getting some drips from one of thof oil hoses which I’ll look at getting repaired when I change the oil.

Since replacing the washers on the fuel tap with dowty style ones as recommended by Bryan I’m not getting any more leakage through the petcock, I am however still getting overflowing carb bowls when the fuel tap is left on, just dribbles out. Have tested the brass overflow pipes for cracks and they’re all good, have swapped the replacement float valves with oem ones but still no joy. Pushing the floats up by hand stops the flow of fuel when the bowls are off

Offline Nurse Julie

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Re: CB750 Barn find project - First Timer
« Reply #578 on: September 15, 2018, 07:18:26 PM »
Well done you, it looks great and its a real credit to you. I know you have had plenty of agro and dramas along the way and I'm sure there will still be little problem that pop up and need sorting but that's old bikes for you. Enjoy.
Oh and make sure its totally legal and safe, Mr Plod just loves to pick on something a bit different !!!
« Last Edit: September 15, 2018, 07:20:35 PM by Nurse Julie »
Im a Nurse, trust me, this won't hurt.....much !!!

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

Offline Underdog1

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Re: CB750 Barn find project - First Timer
« Reply #579 on: September 15, 2018, 08:34:23 PM »
Well done you, it looks great and its a real credit to you. I know you have had plenty of agro and dramas along the way and I'm sure there will still be little problem that pop up and need sorting but that's old bikes for you. Enjoy.
Oh and make sure its totally legal and safe, Mr Plod just loves to pick on something a bit different !!!
Thanks Julie! Been a steep learning curve as I’ts my first time dabbling with engines and before I started this thread I don’t think I even owned a set of sockets.. I’ve now got a pretty well equipped workshop.

Big thanks to you, Graham, Bryan and all the others who’ve given me help along the way, few last bits of tinkering and that should be his thread closed. Only took 2 years  ;D

Offline Wenman

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Re: CB750 Barn find project - First Timer
« Reply #580 on: September 15, 2018, 08:54:29 PM »
Love it well done bud! Let me know if ur ever riding it down south! I’ve not long completed my 550 brat/cafe which looks very similar!

Alan
If at first you don't succeed.. hit it with something!

Offline Underdog1

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Re: CB750 Barn find project - First Timer
« Reply #581 on: September 15, 2018, 09:12:09 PM »
Love it well done bud! Let me know if ur ever riding it down south! I’ve not long completed my 550 brat/cafe which looks very similar!

Alan

I’m in the south west between taunton an Axminster, where abouts are you?

Offline Wenman

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Re: CB750 Barn find project - First Timer
« Reply #582 on: September 15, 2018, 11:57:49 PM »
Torquay bud!!!

Don’t suppose you are par taking in the gentlemen’s ride out from Exeter on the 30th are you!

Small world eh!

Be great to meet for some rides!!

Al
If at first you don't succeed.. hit it with something!

Online K2-K6

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Re: CB750 Barn find project - First Timer
« Reply #583 on: September 16, 2018, 08:47:22 AM »
Nice work, looks good out in the wild  :)

Riding these bikes when contemporary it was kind of habitual to shut the fuel off just before end of journey to avoid chance of carbs leaking.  Generally they didn't but it was just good practice at the time so not too unusual.

Something that may help though, I think It was Kevski that described lapping in gently the brass needle valves to get a good seal with the carb.  I've forgotten what he's suggested so if reading this may get it explained more thoroughly for you.

Hope you enjoy riding it after all your hard work.

Offline philward

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Re: CB750 Barn find project - First Timer
« Reply #584 on: September 16, 2018, 12:34:54 PM »
Seats fitted and took the bike out for a spin. Have also had a fiddle with and synced the carbs



I think it looks great and is just what I wanted. Bikes running alright still a little stumble at 3.5k but I’ve got another needle clip position to try in the future. The front sprocket oil seal is now doing its job since tapping it into place but will keep an eye on it, just getting some drips from one of thof oil hoses which I’ll look at getting repaired when I change the oil.

Since replacing the washers on the fuel tap with dowty style ones as recommended by Bryan I’m not getting any more leakage through the petcock, I am however still getting overflowing carb bowls when the fuel tap is left on, just dribbles out. Have tested the brass overflow pipes for cracks and they’re all good, have swapped the replacement float valves with oem ones but still no joy. Pushing the floats up by hand stops the flow of fuel when the bowls are off
Nice job - all your hard work has paid off
Current Bikes:-
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Honda CB750K2
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Honda CB750K6 Cafe Racer Project