Honda CB500F 1972 Carburetors


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Hey Guys,

So i just finished rebuilding the carburetors on my Cb500 and reinstalled them onto the bike. As soon as i turned on the fuel at the petcock fuel started pouring out of the overflow pipes, some even seems to be flowing through into my airbox and dropping out the overflow tube on that also.

My thoughts are that i have the floats set too high/low (depending on which way your looking at them) and that is causing the issue.

The fact that it keeps flowing out the overflows until i turn the fuel off at the petcock has me thinking there could be more to it?

Any help or suggestions with this will be much appreciated, as i am hoping to get another chance to attack this tomorrow.

Summer is coming down this end of the world and i want to get the bike back out on the road!

Float needles are stuck open due to schmutz and/or your floats are set too high.
...or one or more of your brass overflow tubes inside the carb body have hairline cracks.
I know it sounds silly but make sure the floats are installed right side up. I put one in upside down once and the fuel poured out.
Its running out of EACH over flow tube, so its a problem with all four of the carbs.

My thoughts are that i have set the floats too high. The 'Clymer' handbook doesn't state the right height for the floats on this model, but does for the 350cc version.

Would they be at the same or similar heights? 22mm sound right?
I've pulled the carbs apart and check the height of the floats. All 4 were bang on 22mm, or within a half mm of it at most.

Put them all back together, but have gone back to the original float valve instead of the new one to try that.\

Since i don't have a garage I've run out of natural light and will need to finish re-installing them tomorrow morning. Fingers crossed it was just the valve not seating right. I really want me baby working again!
Can anyone suggest where to buy a carb rebuild kit online? i bought the last ones off ebay and am seriously disappointed in their quality.
i get them from these guys
Clymer is full of bad info.

I try and only buy carb parts OEM from Honda.

Check each float bowl to make sure the drain tube isn't cracked. Just hold them level and fill them with fuel....see if they leak.

Make sure the floats are set and level, often guys only check one side.
Are the floats hitting the side of the bowl?
Do the floats even float? Check that in fuel too.
So i decided to attack the carburetors again tonight and try sort it out, thanks Surffly for the ideas!

Check each of the float bowls for leaks (all fine), and that the floats actually float (all fine), but noticed that the two carbs that were still giving me trouble had floats that were slightly uneven.

Straightened that out and gave it a tickle, bang it starts up and is back to life........ almost.

Only issue now is that the bike will not start or bogs down and stalls with the choke in the closed position, while if it is in the open position the bike runs fine as long as i am giving it some throttle, as soon as i try let it idle it stalls.

I am guessing this would be to do with the air adjustment screw.

I was running it without the airbox or filter on it for the sake of ease if it hadn't worked. Would this have an effect on the idling and need for throttle and no choke? I am thinking of putting on pod filters soon so should i be waiting until those arrive before doing anything else?

Thanks guys!
No point in adjusting a thing if the air box is off.
Pod filters are the worst idea ever, they suck and make things impossible to tune.
Hi guys,

I've got the bike totally reassembled, it is starting and idling.

Issue now is that it smokes heavily, and bogs down while revving under load. I am sure that the bogging issue is due to the carbs not being tuned correctly, but would this also cause smoking at all?

I've tried adjusting the air-screw while the bike is idling, but with the four carburettors i'm struggling to understand how to get this perfected.

Am i just out of my depth? Or am i just doing something wrong?

All help will be much appreciated.
Smoke color will indicate what the issue is.
You need the factory manual and go step by step through the tuning section.
There is an order to doing things.

If trying to run pods or zero filters you will need three or four complete sets of jets on hand. Trial and error.
Bit if something isn't stock the manual is less helpful, at that point you might be better off paying someone to do it.
Oh k, thanks Surffly, I will check the colour of the smoke when i finish work tonight.

I have it back on the original airbox and filter, not pods. Will have another read through the manual and see if i have missed anything.

Thanks again!
Hi Surffly,

The smoke only seems to start once the engine has started to warm up and looks to be white-grey in colour. Not blue or black anyway. What would you think this is? The bike is putting off quite a smell as well, i'm pretty sure its a petrol smell, not a burning oil smell.

I just moved house and can't find the shop manual, so until i find that i'm looking for an online version.

Without seeing it it's hard to tell.
Almost impossible to describe a color.

Start at the beginning with the manual. It will guide you through tuning a stock bike.
Worth while to check compression too. Don't us cheap tools...
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