Carbs Install

[Oddjob]

What kind of tap is fitted Martin? The double outlet with the small bowl underneath?

[K2-K6]

"One other significant finding. The bike had just had an oil change. When I checked the oil, the level was fine and it was clean. I checked it again after my run and it is now half an inch over the upper line, with a slight emulsion and an odour not quite of pure oil. It seems thinner, but it was hot. There was dripping from the end of the valve cover breather pipe, which seemed almost clear, not really oily. Could this be fuel contaminating the oil? What could cause this? I did forget to turn the fuel tap off when I filled the tank and paid. Maybe 5mins at most."

Possible the fuel has diluted it, smell it to see and compare with fresh oil in can, smell wise. Unburnt petrol is easily picked up in aroma.

See also my post on idle jets, if run too rich there it'll soon wash some down the bores to give dilution too.

[K2-K6]

For oil level on the 750, you can check it running as that's the true system level. If it shifts significantly after being left off overnight that would confirm "sumping" and need attention to oil pump seals. Not difficult on these as it's just sump off to get to the pump.

Dry sump system are usually checked this way generally.

[Martin6]

What kind of tap is fitted Martin? The double outlet with the small bowl underneath?

Hi, It is a single outlet pipe. Looks original.

[Martin6]

K2-K6, thanks.

I will take the carbs off and try again. I think i was too lazy first time round, not dismantling the upper part of the carbs.  I've also bought David Silver's carb refurbish kits. I will compare with the current hardware in the carbs. I'd prefer to keep the original needles and jets, but after 46 years, I guess there's no guarantee they're original anyway. At 40,000 miles, if they are original, they're possibly due a change, but I won't rush into that if the existing parts look good.

After a day and a bit, there's no sign of the oil level dropping. May be too early to be certain. My Commando takes a couple of weeks. It smells oily. It seems thin, but I'm used to the Norton's 20W50! I'll check it against the 10W40 I bought today. I got a gasket set, so I can do the sump and look at the oil pump, if it starts to sump. I'll also now have a gasket for the cam chain tensioner, to check if that's actually moving.

Appreciate your input.
Martin

[Martin6]

On the first carb, I've removed the main jet and jet holder, but the needle jet is stuck in the carb body. How do you get the needle jet out?

[Skoti]

Needle jets need to be tapped out from the top with a pin punch the correct size.
Change the needles and needle jets with original Honda items and you'll cure the lumpy running below 1/3 throttle.

Good luck

Skoti.

[Nurse Julie]

Martin, you probably are doing it correctly but I thought I'd ask anyway, you are setting the float heights with the bank of carbs standing upright in the vertical position, like a flag pole?

Non 750 carbs I know but the theory is the same on all CB SOHC/4 carbs I'm my attached link below.

http://www.sohc.co.uk/index.php/topic,23233.0.html

[Martin6]

Needle jets need to be tapped out from the top with a pin punch the correct size.
Change the needles and needle jets with original Honda items and you'll cure the lumpy running below 1/3 throttle.

Good luck

Skoti.

Thanks.

[Martin6]

Martin, you probably are doing it correctly but I thought I'd ask anyway, you are setting the float heights with the bank of carbs standing upright in the vertical position, like a flag pole?

Non 750 carbs I know but the theory is the same on all CB SOHC/4 carbs I'm my attached link below.

http://www.sohc.co.uk/index.php/topic,23233.0.html

Thanks for this. I was setting mine with a Vernier, carbs angled so that the tang just touched the valve, but didn't move it down. So I think the same result, but I'll check with your method this time.

On my 750 K6 carbs, the bowl rim casting is a different shape to your photos. They have a lip for a strong compression of the rubber bowl seal, plus a small flange at the side within that. I set the vernier tip on that small flange, rather than the seal lip. No idea if that's right. Makes just under 1mm difference.

So far I'm only on no.1 carb. I've found:
- The air screw didn't have a spring on it. It hadn't moved though, so not likely that's my issue.
- This time I've taken the carbs off the gantry. No.1 slide is stiff after the first 1/2 of its movement. There was a small patch of corrosion inside the slide cylinder (of the carb body). I've gently polished that area with Autosol. That's improved it a little. Am I OK to give it a little more of a polish. I'm holding off, as I'm concerned I may interfere with the 'vacuum' seal if I over-polish it, but a little more may give a smoother movement to the end of its run. The slide movements of the other 3 carbs are fine.

Thanks.

[Nurse Julie]

Yes, on the 750 carbs the measurement is taken on the inner flange, not the outer lip.

[Martin6]

Thanks. 👍

You've all been very helpful. The manuals are OK, but it's great to get experienced input. I appreciate it, thank you.
Martin

[Martin6]

I've hit a problem on carb #4. I've been replacing the needles. On my version of the Keihins, this requires a 'stay plate' to be removed, so the plunger and top of the carb can be pulled out, revealing the needle. The stay plate is held in with two small x-head screws. One of these is seized. I have the right screwdrivers, but I now have very little grip on the head remaining. I soaked overnight with penetrating oil, but still no joy. I'm reluctant to clamp the slide in the vice, as this could distort it. There's no space to clamp the screw head. Out of ideas. Please, any suggestions?

The bike seems to be fighting me at the moment! 

[K2-K6]

Any chance of boring a hole into wood block such that you can stand the sllide down into that, then you can really lean on the screw to get traction.

[Oddjob]

Any of the screw sticking out of the bottom of the slide? I seem to recall they are slightly too long, if that's the case you could if all else fails drill the top off the screw and try and use a pair of pliers to turn the screw out from the bottom, the problem is probably the bottom of the screw has gone rusty, this won't allow the screw to go through the threads in the body, doing it from the bottom should mean the threads inside the body, which are usually clean will then just turn out of the body. Try and tighten the screw a little beforehand so any rusty threads are out of the body.

Other than that buy another slide.