Author Topic: CB750 Barn find project - First Timer  (Read 34161 times)

Offline Rob62

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Re: CB750 Barn find project - First Timer
« Reply #585 on: September 16, 2018, 02:16:25 PM »
Great job UD!.... all your hard work and problem solving paid off in the end.... enjoy the indian summer  :)

Offline Underdog1

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Re: CB750 Barn find project - First Timer
« Reply #586 on: September 29, 2018, 06:49:07 PM »
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?

I raised the needle clip one position and didn’t really see a difference. Today I changed the main jets from #120 down to #110 leaving the needle position the same, was hoping to see a difference either good or bad but literally feels exactly the same with the flat spot at 3.5-4krpm. As I’ve said before I appreciate with pods it will never run as well as with an air box but I thought I would at least feel the difference of a significant change in jetting?

Offline K2-K6

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Re: CB750 Barn find project - First Timer
« Reply #587 on: September 29, 2018, 08:35:51 PM »
It's more or less the transition point (under light throttle opening)  of the idle circuit going fully to main jet running. Because the mods make the vacuum gradient go a bit chunky then it's this bit that is hard to define regarding jetting and making decisions about it.  It will be hard to decipher so needs alot of trial and error to get improvements.

Could start as it is by trying it with the idle screws turned in 1/2 turn to see what it does. Then do the opposite, 1/2 turn out and try it to see what you can feel when riding. That's both from the original idle screw start point, 1 turn out? Ish?

Make sure the plug gaps are very concise on their minimum gap, which plug's are you running?

Offline Laverda120

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Re: CB750 Barn find project - First Timer
« Reply #588 on: September 29, 2018, 10:31:37 PM »
Great Job and nice looking shortie exhaust. Now you've completed your first bike you've probably been bitten by the bug  :). I agree with Nigel, always turn the fuel off before you finish your ride to stop the incontinent carbs dribbling!
1976 Honda 400/4
1977 Honda 400/4
1981 Honda CB250RSA
1977 Rickman Honda CR750
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Offline MarkCR750

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Re: CB750 Barn find project - First Timer
« Reply #589 on: September 30, 2018, 05:00:51 PM »
Great looking machine UD, well done, pound to a penny it’s the pods causing the stumble, stick some velocity stacks on it.
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Offline Mag1

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Re: CB750 Barn find project - First Timer
« Reply #590 on: January 01, 2019, 04:50:52 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

That is a great looking bike you should be proud of, been away a lot myself and need to complete mine, been on the back burner now for nearly 2 years, just the wiring, fuel system to redo, poss a new tank as mine as the pin hole syndrome and needs re-stripped. This has given me the jump start again to do mine. Thanks for sharing your build.
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Offline gp_st3

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Re: CB750 Barn find project - First Timer
« Reply #591 on: January 01, 2019, 05:02:50 PM »
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

Well, from looking at the picture I would say that either your drive seal is fitted backwards (inside/out) or mine is... I have no leak but perhaps I've just been lucky!