Float Height Setting/Float Valve(CV carbs)

Correctly servicing the Carburettors on these bikes is paramount to good running and fuel economy so any work done will pay back in better mileage :)
Forum rules
To use Search function add Asterisks around the words like *fork oil*

No Racism.Slanging Matches(unless witty and funny :)
No spamming.Anonymous posting disabled.

Float Height Setting/Float Valve(CV carbs)

Postby Gman » Tue Aug 26, 2008 2:54 pm


Before doing any work on the carbs always check for Carb Boot leaks.
From the right hand side of the bike with the engine idling spray some Carb/Brake cleaner or Hairspray or WD40 type stuff around the carb boots on the Air intake and engine side of the boots and also shoot through to the left hand side inner boot areas.If the engine speed changes even the slightest in either direction there is a leak.

Repeat from the Left hand side of the bike.This is to make sure you get all round all possible areas where there can be an air-leak.These leaks can be really sneaky :shock:

Repeat check after re-fitting the carbs ! :evil:



Note:The Float Needle Valves are,"Spring Loaded" with a very tiny little spring inside.They cannot be stripped for service but the springs can become corroded/stuck and cause overflow problems.Soak with WD40/Penetrating fluid and make sure they pop up-and-down ok.


Quite often people have problems with the CX/GLs not firing correctly on one cylinder,Fuel leaking from the overflow pipes,fuel in the Airbox.Normally this would point to an Ignition problem and on these bikes usually a corroded Plug cap including in the US a Faulty and worn and not needed Suppression resistor in the Plug cap(See Electrical Section for removal and replacement) or Failed HT(High Tension) Thick wire to the plugs from the coil or a break in the LT(Low Tension)wire from the harness that supplies the coils or indeed a failing/failed coil.

However another cause of this with the CV(Constant Velocity) carbs is an incorrect float height and related a float needle valve that the floats lift not being correct and or the float needle valves not seating correctly.This can cause flooding of the cylinder and then incorrect/none firing of that cylinder.

Tilt the carbs so the floats press onto small Float Needle Valve lightly.The distance from the edge of carb body to outer part of the float MUST be 15.5mm as per below,

Image

Note:I normally use a Steel Ruler to be more accurate,the tape was only as an example.

In this picture they are down 0.5mm ish so need to be gently bent both at the same time to make them 15.5mm.They both need to be level and not twisted as this will cause problems as well.

Another common problem with these carbs is that after taking them off and cleaning(See other Stickies for great information on correctly cleaning them) is that they overflow fuel.Once you know the float heights are correct this is usually caused by the Float Needle Valve not seating correctly because of curd/grit in the seat or on the Valve or the valve itself or the valve seat in the body damaged.If the Seat is too badly damaged the only fix is another set of carbs.

However in most cases you can service the FNV as in the picture below by putting some fine metal polish or Toothpase on it's tip and then inserting it into the hole and twisting it a few time gently(Like grinding in valves but much less harsh).Then totally clean the valve and the hole by blowing Carb/Brake cleaner on and through them so they are spotless.

Image

This recommendation comes from my Haynes Workshop manual and I have used it several times with Success.

Note:If at any time you feel grit or dirt on your hands whilst working on the carbs go and wash you hands.You need to make sure 100% that no F.O.D(Foreign Object Damage) can get into any part of the carbs.To this end I always recommend fitting a small cheap in-line fuel filter so that any of the good work you do it not undone if something gets dis-lodged or through from the tank etc.

Also it's quite common after moving the carbs and on re-fit that there's a fuel overflow.Is this happens try tapping the float bowl of the offending side with a small hammer lightly as sometimes it takes a short while for the FNVs to bed in and also go for a ride and get really get some fuel through the system.If it continues you may have to try again until you get it right.

Tip:I have fitted Allen Screws in both my carbs into the inner hard-to-get-to screw so that I can easily take off my float bowls without taking off the carbs.OK I cannot really reset the float heights properly but I can clean the bowls and clean the FNV and it holes doing this.


Warning:If you take the float bowls off the right hand side with the carbs in the bike and you remove the Inspection Breather to gain access please put some Masking tape or similar over the exposed hole.The last thing you want is to drop a screw into the engine!!!!


Tip:Place a container underneath your Carb overflow pipes on the ground at the back wheel then undo the Screw in the side of the left hand float bowl a little way out.The fuel should empty from both Float bowls now.This will make it less messy taking the carbs off and also once you have put them back on if you are getting an overflow problem sometimes doing this to drain the bowls can cure it once the bowls fill up again :)

Note:The full plastic types of floats are not supposed to be adjustable.This is not true.If their height against the body when the carbs are tilted so that the FNV has just closed is less than 15.5mm you can bend them away from the carb body evenly and hold them under tension for around 15 seconds and then re-check.They should spring back close.
If the floats are greater than 15.5mm you can see the picture below using the thin shaft of a small screwdriver or in my case the shaft of a fine file or take the floats off and use a pair of Pliers to hold them and manipulate them but the floats MUST be warm so heat with a hairdryer.
Remove the FNV.Replace float.Press evenly on the floats til they touch the carb body and hold under tension for around 15 seconds.Replace FNV and check.If the floats are uneven you may have to twist them a little.
Do this in a warm environment and also you may want to drop the floats into a warm pan of water or use a Hairdryer to make the old plastic a little more flexible.

Be prepared to get another set of floats/carbs as the full plastic ones are NOT as good as the Metal and Plastic float types.


Image


It may take several attempts with either of the above to get them right but Float height setting is so important that you must get them as close to 15.5mm as possible otherwise all other carb cleaning may be to waste.Incorrect float heights can cause bad starting,single cylinder none firing/Rough running and bad mileage.
User avatar
Gman
Site Admin
 
Posts: 1141
Joined: Thu Jul 24, 2008 8:11 pm
Location: Hull.Yorkshire.UK.2x1980 CX500ZABs:Citroen ZX TD(250,000 miles)

Re: Correct Float Height Setting/Float Valve(CV carbs)

Postby DanInOregon » Sat Oct 18, 2008 6:50 pm

Is it safe to assume that 5/8" is close enough to 15.5mm in this case?
78 CX500 basket case going to many new homes...
83 CX650C waiting to tear up this town!
DanInOregon
 
Posts: 4
Joined: Fri Aug 22, 2008 10:31 am
Location: Cornelius, Oregon, USA

Re: Correct Float Height Setting/Float Valve(CV carbs)

Postby Gman » Sat Oct 18, 2008 8:05 pm

So long as the conversion from metric to imperial is exact. :)
User avatar
Gman
Site Admin
 
Posts: 1141
Joined: Thu Jul 24, 2008 8:11 pm
Location: Hull.Yorkshire.UK.2x1980 CX500ZABs:Citroen ZX TD(250,000 miles)

Re: Correct Float Height Setting/Float Valve(CV carbs)

Postby cxmaniac » Fri Jan 02, 2009 7:11 pm

Just wondering,are the 2 different types of float interchangeable :?: Regards Sean.............
Black 1980 CX500A
DONT GO OUT ON THE MOOR!!!
cxmaniac
 
Posts: 54
Joined: Thu Sep 25, 2008 10:29 pm
Location: Cornwall Nr England

Re: Correct Float Height Setting/Float Valve(CV carbs)

Postby Gman » Sat Jan 03, 2009 9:29 pm

cxmaniac wrote:Just wondering,are the 2 different types of float interchangeable :?: Regards Sean.............


I know they can be on the UK/European CX500s so long as you use the float needle that matches the floats but..........

The Metal and Plastic Float's Float Needle Valves are longer as is their brass insert in the carbs.You may have problems getting a good idle which may dip too slow on opening the throttle from standing start and vice versa you may get carb flooding with the Full plastic floats in the wrong body.If at all possible us the matching floats to the carbs.
User avatar
Gman
Site Admin
 
Posts: 1141
Joined: Thu Jul 24, 2008 8:11 pm
Location: Hull.Yorkshire.UK.2x1980 CX500ZABs:Citroen ZX TD(250,000 miles)

Re: Correct Float Height Setting/Float Valve(CV carbs)

Postby baugh55grfmj » Sun Aug 09, 2009 11:50 pm

When you take the initial measurement, are the little plungers in the FNV compressed or up?
User avatar
baugh55grfmj
 
Posts: 17
Joined: Sun Aug 09, 2009 11:31 am
Location: Stanley, WI

Re: Correct Float Height Setting/Float Valve(CV carbs)

Postby Gman » Mon Aug 10, 2009 1:02 am

Neither as such.You turn the carbs so the floats just start to rest on them.So at a kind of angle,or flat.= if you like.I prefer to have them just touching on the FNVs.
User avatar
Gman
Site Admin
 
Posts: 1141
Joined: Thu Jul 24, 2008 8:11 pm
Location: Hull.Yorkshire.UK.2x1980 CX500ZABs:Citroen ZX TD(250,000 miles)

Re: Float Height Setting/Float Valve(CV carbs)

Postby Gman » Sat Mar 10, 2012 12:33 am

Note:something often overlooked when doing the Floats and Float needle valve is that the small Float Needle is actually,"Spring Loaded" and this can be corroded and seized.It should be drenched with Rust release/WD40 and operated so that the small plunger actually works.
If it does not move in and out freely it should be replaced same as if the tip is worn or scored.
User avatar
Gman
Site Admin
 
Posts: 1141
Joined: Thu Jul 24, 2008 8:11 pm
Location: Hull.Yorkshire.UK.2x1980 CX500ZABs:Citroen ZX TD(250,000 miles)


Return to CV(Constant Velocity) Carbs

Who is online

Users browsing this forum: No registered users and 1 guest

Help keep this forum ad-free - please Donate


This free, ad-free forum is hosted by ForumLaunch