Float Height and carb woes

[FANDANGO]

Hi,

Could I please get a check on what the float height is for standard carbs and also the float height for carbs with DynoJet/Factory Pro, etc jets.

I have it my head as being 9mm for standard and 14mm for Dynojet/etc

I'm not a pro by any means but I've read so much stuff I've started to doubt myself so want to double check.

Bikes stuttering, and popping on a constant throttle at anything below half throttle, hard acceleration is really good, smooth and pulls strong, you do though get a hesitation when rolling off and then back on again.

I've had the carbs off, stripped and cleaned - looks to be a Dynojet kit fitted as needle and tubes are silver not brass (from posts on here they appear to be fairly new). Pilot jet was at 3 turns out and the needle was on the 2nd or 3rd clip ( I stupidly didn't record the setting), float heights where both at 9mm and the TPS is set correctly.

I've raised the height to 14mm (that should give a greater reserve of fuel so should help the roll off/roll on stutter) and gone to 2.5 turns out on the pilot. Thought being its to lean so winding it in with richen it up and assist with the constant throttle, lower throttle opening position.

No luck its still stuttering and popping. Bikes been stood a while due to a back injury and so I've serviced it, had to put a new loom on as the old one had ben hacked into, coils are apparently from an aprillia (cant be them breaking down under load as it accelerates well??) and I serviced the fuel tap as it was shot.

I had back surgery this time last year and as part of my rehab I had to set a goal, mine was to get back on a bike and do a lap of the TT course aging (touring not racing)...I've two weeks to sort this.

Any pointers are gratefully received.

[Con Rod]

Float height should be 5mm measured as per the workshop manual

2.5 turns out on the fuel screw and start with the middle clip on the needles and go from there

A search will show up a wealth of information on the forum

[FANDANGO]

Hi,

To get the float height I had the carbs upside down on the bench and measured the height from the face of the carb to the peak of the float.

I've seen the manual states 5mm, but I don't have the tool to do the measuring - I found 14mm and 9mm and the method I've described on several posts on the forum. Have I ballsed up the float heights?

[Con Rod]

unfortunately with the down draft carbs on the TRX, not have the float bowl in the conventional position at the bottom you wont be able to set the height that way

All you need is some clear 5mm tubing. You can get some in Bunnings or any hardware usually in the gardening section. $5 will get you about 10metres of it. Also handy for bleeding brakes

Have a look at the picture below, you are measuring against that mark on the carb body

[FANDANGO]

Ahhh! That makes more sense. I'm checking the needles tonight to confirm the clip position so will reset and give it a go.

Fingers crossed.

[FANDANGO]

Moved the needle up one clip to richen it up, float heights set using the advised method (they were well out!), three turns out on pilot jet and bingo. Only odd thing is I've had to put the standard cans on or there is still a hint of a stutter. Opened up the carbon cans and the packing was missing from near the bottom of the can. Repacked using rope type deadening and then used fibre deadening to fill the remaining void. Getting some db killers tomorrow and then see how the bike runs.

[Abikebloke]

I'm new here.
A lady friend brought her TRX to my shed and asked me to help.
I thought I'd clean out and set up the carbys ready for balancing.

I notice a range of conflicting advice and confusion regarding float height and fuel height.
A forum search brings even more confusion.

Conrod points the way.
Fuel height is the final arbiter.

The trick is how to get there.
These are nice carbys, but require delicacy and understanding.

The float serves to close the fuel inlet with the needle valve.
The needle valve has at one end, the valve seat to stop fuel coming in.
At the other end it has a plunger with a spring internal to the needle valve.

If you hold the carby so the float hangs AWAY from the body and slowly rotate the body to allow the float to swing towards it, the tang on the float first contacts the end of the plunger.
As you continue to rotate the body, the float sort of "rests" there a moment, then commences to compress the plunger spring and the plunger disappears inside the needle valve.
This is critical to observe.

You have about 20 degrees of carby body rotation in which it "rests".
Either side of this is useless,as the float is either hanging loose, or compressing the plunger.
This "rest" point is the correct orientation at which float height is measured.
Practice this and get familiar with the sequence before and and every measurement.

The floats are assymetric, meaning they have different shapes on either side of the main jet.
Because the carbs are bolted together, the outer on the left is a different shape to the outer on the right.
It's pretty much impossible to measure the float height of the inner two (i.e. RH of LH carby and LH or RH carby)
Despite the different overall shape of each side of the float, they have the same shape upper outer corner and they are at the same level.
When that corner is 14mm above the float bowl sealing surface, that's the float height setting.

To adjust the float height:-
Bend the tang with a tiny flat blade jewellers screwdriver or the like. Gently. Very gently.
Its easy to reduce the height with the float in place.
Its easier and less risk of damage to remove the float to increase height, but be careful replacing the needle valve in its seat and ensure it's hanging freely from the tang.
Give it all a few gentle shakes, rotate the body back and forth, gently tap the float, to make sure it AND the needle valve have settled into final positions before measuring again.

You'll need a clean bench, excellent lighting, a vernier caliper or the like, patience and a willingness to keep work clean and achieve accuracy.

Float height is 14mm from float bowl surface to peak of float with needle valve seated, plunger fully extended.
This will achieve a fuel level of 5mm below the Mikuni body mark as shown in the post by Conrod.

The carbs on this bike were way out (2mm below and 12mm below)
I now have a table of float heights and corresponding fuel heights and a whore would be proud of the number of carby insertions into the rubbers.
I found it useful to use a wide white marker to put a line below the Mikuni body mark, then use a black fine sharpie to mark on that, a line at exactly 5mm below the mark.
The Mikuni mark is in a bugger of a spot to see easily due to frame members and TPS and arranging the sight-glass hoses needs cunning.
Look at Conrod's photo.

ABB
BlueMts NSW

[Mav617]

Great post, thanks muchly.

[cobbadiggabuddyblooo]

So if you had fitted yzf 750 dogbones to lift the rear 30mm and dropped the forks down on the front (even R6-R1 forks which are shorter) how much would this come into play with your float height do you think????

[Abikebloke]

bugger all

What's critical is that both fuel heights are set the same,in spec, idle air screw set the same, in spec, carbs accurately balanced after valve clearances set/checked.

After that, if it's hunting on steady throttle, or small throttle changes seem inaccurate (you'd notice it more in the wet) and fuel consumption is up, its probably got worn needle jets.
If so, a following rider can usually smell the excess fuel when accelerating off the lights.

They're an excellent carby, but with lots of use, the steel needle hanging from the slide wears the brass of the needle valve from round into a pear shape and mid-range fuel metering literally goes pear shaped.
Dynojet needles aren't drawn needles, they're machined and the surface is very slightly rough, like a very fine file, so they chop out the jet heaps quicker.
The shape of the needle ensures an accurate donut shape for the air/fuel mix metering at changing slide lift.
It can't be sorted by fiddling with needle height.

[Rubes]

So if I'm using Conrods natty little fuel height tip and the fuel level is too low I have to gently bend the metal tang down a smidge to raise the fuel level?

BTW I see some talk on other forums of the fuel height affecting the mixture ratio to a degree eg fuel height higher = slighly richer mixture. Is this a factor for the stock carbs?

[Con Rod]

So if I'm using Conrods natty little fuel height tip and the fuel level is too low I have to gently bend the metal tang down a smidge to raise the fuel level?

BTW I see some talk on other forums of the fuel height affecting the mixture ratio to a degree eg fuel height higher = slighly richer mixture. Is this a factor for the stock carbs?

Yes, bending that tang will raise/lower the fuel height. It is a bit of a painstaking task to get it right given you need to check it, take it apart, adjust it, put is back together, re check it, and so on but once it is right it is right, it wont change.

This is helpful

http://www.factorypro.com/tech_tuning_p ... gines.html

and this

http://www.iwt.com.au/mikunicarb.htm

[Rubes]

Thanks Conrod

Yes real PITA. Think I have it sorted now. Found it surprising difficult to get the levels right. Much easier with a makeshift longer fuel line.