Starting problems and petcock leaking cb400 SF project big 1

[Superjack44]

Things are looking up.
Keep us posted, CB 400 superfour's are brilliant bikes.

[mykel49]

Ok guys so I have another issue whilst waiting for the petcock to be delivered I'm just doing some maintenance ie checked oil as I'm going to be changing oil and filter and I noticed a smell of fuel from the oil. I noticed someone in another post quoted :

"I'm not 100% sure of the issue, but I suspect the risk is that the needle and seat in the carburettor may not be happy and that the carbs / float chambers overfill, the fuel then may overflow into the cylinders... this can get fuel in the oil (after seeping past the rings) which is obviously a bad thing."

So I'm wondering if this could be the reason my oil is smelling of fuel ie with bike lying for so long uncared for, that the float chamber overfilled and passed through cylinders into oil chamber, and should I forget about the oil change just now, and remove, strip down and clean carbs before routine oil and filter change ?

[Superjack44]

Certainly change the oil and filter, but do not remove the carbs , deal with the fuel leak first once that is dealt with try and start it, with a spark and fuel in the carbs it should fire.
However if its obvious there is no sign of it running such as the odd pop in the exhaust do not keep spinning the motor on the starter as all you will do is flatten the battery.
If you have to remove the carbs the airbox must be loosened first and pulled back as far as it will go in order to give some wriggle room for the carbs, be careful where you put the lever to prise them out of the mounting rubbers move them only a little at a time until you feel them give in the rubbers.
Once they start to move (come free in the rubbers) its a case of wriggling them free and out of the right hand side of the bike you will have to remove the choke cable and then remove the throttle cables.
Once out remove the carb bowls and jets clean them one at a time and then replace them one carb at a time .
DO NOT SPILT THE BANK OF FOUR CARBS INTO SINGLE UNITS.
DO NOT MIX ANY OF THE COMPONENTS UP WITH A DIFFERENT CARB BODY, you will notice that there are two different shaped carb bowls, in theory they should interchange as the jets are the same number don't do it.
Compressed air is handy to blow through the carb body but make sure you do not damage any of the diaphragms.
Remount the carbs and try again.

Re oil smelling of fuel take notice of how much oil comes out or even dip it first to see where it comes up to on the dipstick to try and gauge any excess.
When you dip it remember to get the true level unscrew the dipstick clean it off and the correct method of getting the correct level is to place the dipstick into the hole without screwing it home this gives the correct level, otherwise reading it from screwed in gives an additional half inch on the stick which may make you think it could be polluted with fuel.

[mykel49]

Hi again, so I got my petcock today from China which was amazingly quick and is superb. I can't believe I only paid £22 incl delivery. Fitted to bike today after work and is operating correctly with no leaks - one problem solved!! so I fitted new plugs and filled tank with fresh fuel, and turned her over, but nothing, nowhere near starting. So I cracked open drain screws on bottom of carbs and fuel only came out of one chamber ( no1 or 4 not sure, but it was the one on right, when sitting on bike, opposite side from petcock. I reckon that the other three chambers are blocked with gunge so will need to remove and clean, I don't have access to compressed air though. What do you think? I think this is the only reason left as isolated all other potential problems! What do you think?

[Mansie]

Glad to hear you sorted the petcock leak. Now your bike is less of a fire hazard

When you say that the fuel is not getting out of the float bowls when you undo the screw at the bottom, it could still be the lines that supply the carbs. Most likely though the carbs are gunked up and need an overhaul.

The guys at SCR Classic Motorcycles, who restored my bike, told me that they would always give the carbs an overhaul on any bike that has stood for a while as a matter of precaution. Badly polluted carbs give all sorts of problems later down the line and they simply don't want to run the risk that the restored bike would start or run poorly. It cost more to sort out such problems with the bike fully assembled because then they have to take the carbs off again to clean them.

Anyway, carbs are full of fiddly bits. I bought once a CB400 SF carbs bank to practice dismantling it and found the bolts holding the float chamber had seized and the bolts were soft metal too . Anyway, I had a look around to see how bits fitted together and decided it was too complicated to dismantle and put together at the required level. Others can disagree. There are also lots of rubber rings and perhaps after 20-odd years these could do with replacement. I see a CB400 SuperFour gasket set for sale on ebay for £70 which sounds about right. Also there could be trouble with one of the diaphragms, like a tear in the rubber.

If I were you I would send the carbs off to professionals who can restore the carbs to a high standard. Do a google search and you will find links to the websites of various outfits that offer this service.

[Superjack44]

Sound advice from Mansie.
Just remember what has been said about removing the carbs, also the fuel supply pipes fit onto a plastic T piece under the carbs be very careful not to break it as I believe they are difficult to find.

[dobbslc]

I would say after reading through this thread that those carbs will be very manky inside, after fuel goes like that it dries in the carbs leaving behind a right mess.
If there is fuel in the oil that means both the tap and at least one carb is letting fuel through.
As above be careful getting the carbs off, check the rubber manifolds for cracks and strip the carbs into 4 separate aerosol caps very carefully.
Getting the large jets and carb body drillings clean is easy it's the tiny ones that need a lot of time and sometimes an ultrasonic cleaner to sort properly.
The O rings need to be checked too as they degrade over time especially with the shit ethanol fuel we now have.
Take your time and you can sort it out.
PS carbs and cylinders go 1234 left to right as you're sitting on the bike.

[bureklton]

Good to hear about the petcock, burning down your house once is one too many times. Although cleaning your carbs won't be as easy as changing your oil, I would have to disagree with mansie and say that it is very doable. My CB400 SF, like yours was sitting for a while and became gunked up, had fuel leaking from carb 3, and had rips in two diaphragms. It was my first set of carb to dismantle and with a bit of research and examination I found it very enjoyable. There are loads of videos on YouTube explaining the works and how everything fits together.

I gave mine a complete overhaul replaced:

All the float needles (£20):
http://www.speedmotoco.com/product-p/029-329.htm

Two diaphragms(These are loose and are fitted to your existing carb slides, pretty easy do) (£40) :
http://www.nrp-carbs.co.uk/shop/index.p ... uct_id=682

All the seals(£27):
http://litetek.co/Carb_Kit_Honda_CB400_NC31.html

I found that compressed air was essential for cleaning the idle and air bypass ports, as you don't have a compressor id recommend a can of air:

http://www.amazon.co.uk/Star-Duster-Com ... 928&sr=1-1

Like mansie mention the screws for the float bowls are soft and can be hard to get with a screw driver but if you do ruin them a vice grips does a lovely job and they are less than a pound to replace:

http://www.cmsnl.com/trx450s-fourtrax-1 ... RFc6_msXLQ

[mykel49]

Ok everyone, had a day off work today an removed, stripped and cleaned Carbs. What a nightmare getting them out, took me about 2hours!! Anyway stripped down and cleaned all jets etc with pin and lots of carb cleaner. One of the floats was jammed and wouldn't move, and there was a lot of hardened shit on the bottom of float bowls. The inside was green just like the fuel that came out, see previous picture. Put all back together, although I had a couple of problems :

1st - a small rubber o ring on bottom of one of the jets had snapped, but put back together and doesn't seem to be any problems ( see in the Russian parts list it is on page 54 number 22)

2nd I cracked the air filter housing trying to lever back into place after refitting carbs, after air filter but before carbs, so will need to repair with maybe rubberised silicon to stop unclear air getting to carbs.

But apart from that she started and going well, however I'm sure I have incorrectly fitted the choke cable as even after running for half an hour when I turn choke down halfway she cuts out, any ideas?? does the metal end on plastic cable butt up against the clamp end or does it fit inside a clamp down. I put it inside the clamp and clamped down !!

[mykel49]

Forgot to mention I have another little issue the fuel sender does not appear to be working as amount of fuel not registering on gauge, any ideas on what to look for. I will also be tackling the fork seals and dust rings (not sure their called that but you know what I mean), whats the best way to do this job?