Carb problems heeeelp!

willyt

XS650 Enthusiast
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Hi guys I am new to the xs650 owners elite.
I have just got me an xs650 1978. I have taken it for one ride and prior to this I had a fiddle with the fuel shutoff valve under the tank just to familiarise myself before potentially running out of fuel.
Anyway when I got back fuel was leaking out of the carb (pouring out) and I have pulled the float chamber off and the float seems to be working ok, wasnt leaking when off the bike but put it back on and leaking again. I am assuming this cannot have anything to do with the shut off valve. Fuel is only leaking from left carb, looks to be coming out the pilot tube. they are Keihin CVK carbs.

Any ideas? think my next step will be to strip and clean carbs and reassemble and see what happens.


Also I have seen mikuni conversion kits, wondering if its a good investment and where the best deals are.

Any help would be appreciated
 
welcome willy.
Sounds like the float needle valve in the float chamber is not shutting off properly. if they are not used frequently the valves can become sticky with gas /petrol additive residues .
It occasionally happens to mine when it hasn't been run for a few weeks and usually a sharp blow to the fuel bowl usually does the trick in dislodging a stuck float needle .

The carbs probably could benefit from complete overhaul and clean but to be honest that could intoduce a whole host of new problems. If it persists you can remove the float needle and needle valve seat to clean or replace them without removing the carbs although it will be awkward obviously and you won't be able to set the float height without removing and inverting the carbs
 
It's both? The petcock should stop all fuel flow when the engine is off, but the vacuum style petcocks are a bit fussy and prone to the foibles of old age, dribbling whether you want them to or not! There is a petcock rebuild thread, but many aftermarket parts don't work correctly. I can usually get them to work right with new parts but I have had one or two put a up a pretty good fight. Can't help on the carb 'cause I haven't used a PWK. Does the bike have tygon fuel lines? is the tank shiny clean inside? Older black fuel lines can shed bits of rubber that get caught in the float valve.
 
An quick temporary solution to prevent fuel from flooding the crankcase when the bike is left unattended could be to fit these http://www.ebay.co.uk/itm/Petrol-Fu...917565?hash=item5ae29bcb3d:g:p6kAAOSw~OVWzHcT ;)
inline fuel tap.jpg
 
@willyt if you haven't already found it, this thread may help.
It seems I remember if you capped one of the vents instead of putting a tube on it they overflowed. . . .
A quick skim of a google search (EX500 Carbs overflowing) points to the most common problem (as used oem) is the nipple shears/cuts/slices a piece of the fuel line and that gets stuck under/between the float bowl needle and seat. Removing the needle and back flushing seems the most common remedy
 
Hi guys I am new to the xs650 owners elite.
I have just got me an xs650 1978. I have taken it for one ride and prior to this I had a fiddle with the fuel shutoff valve under the tank just to familiarise myself before potentially running out of fuel.
Anyway when I got back fuel was leaking out of the carb (pouring out) and I have pulled the float chamber off and the float seems to be working ok, wasnt leaking when off the bike but put it back on and leaking again. I am assuming this cannot have anything to do with the shut off valve. Fuel is only leaking from left carb, looks to be coming out the pilot tube. they are Keihin CVK carbs.
Any ideas? think my next step will be to strip and clean carbs and reassemble and see what happens.
Also I have seen mikuni conversion kits, wondering if its a good investment and where the best deals are.
Any help would be appreciated

Hi willyt and welcome,
Elite? Us? I'd have said we were the raff and scaff of old bike enthusiasts, being unable to afford a British vertical twin of that era.
Or worse, selling one's British twin back in the day for the price of a case of beer. Or part-exing it for a Honda.
It looks like you have two problems:-
1) The stock fuel taps are supposed to be vacuum-operated to automatically open when the engine starts and close when the engine stops.
That may have worked when they were new.
These days you'd do better transmogrifying them to manual operation.
Then the carbs would only leak on parking if you forgot to turn the taps off.
2) Most likely the engine vibration will shake the float needles into mostly doing their job so long as the engine is running
So it's only the parking fuel leaks that are likely to flood the crankcase.
Manual fuel taps will likely stop that from happening but WTF, you should fix the float needles anyway.
 
Thanks. I'm blown away, this has to be the first time in my many projects I have found a still functioning current forum with people keen to help!
Thanks
So I had another go on my break at work and pulled the floats out and potentially the little tab that presses on the needle was a tiny bit bent so I made it look straight like the other one. Was planning on putting it back on the bike when I got home. I left them at work and was itching do get stuck in so the bike no longer has an engine in the frame.
Rebuild time :)
 
As I will agree with everyone on here because they have more experienced than me. Here is what I have done in the past with the three XSs I have owned when this problem occurred. I tend to spend money when I don't need to, but that is just my nature and I try not to waste time rebuilding to find out the rebuild cured nothing.

1. Replace petcocks entirely w/ brand new ones. Vacuum petcocks have tended to be a pain on some models, so I just switched to ones offered on MikesXS.
2. Clean carbs thoroughly to make sure nothing is getting stuck due to old gas or crud.
3. Replace needle seats - buy from boats.net instead of MIKESXS. The ones on Mikes are terrible and never worked for my three bikes
4. Adjust float height per manual.
5. Do a float level test. - Detach 10mm plugs, run some clear line. Hold carb steady with a vice, run gas through carbs, make sure float height is spot on.
 
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