92 GSXR11 CV float heights

[Rocket]

I'm gunna pull my carbs and try to find out why it's running really doggy down low.
On a light throttle (steady cruise and after gear changes) it runs rough and doesn't clean up until i get a bit of throttle into it. Then it seems to pull okay.
It won't idle properly either and my exhaust is very black.
I'm pretty sure it's fouled the plugs up too so will also give them a clean.

I'm thinking it's my float height. Can anyone tell me what they should be ? I'll have the carbs off and upside down on the bench.
i believe I'm supposed to measure from the gasket surface to the top of the float. But is this with the float tang just touching or actually closing the float valve ?

At first I thought I might try dropping the needle but I think the needle doean't come into play until higher up.
Advice please...I'm a bit of a noob at this stuff but am determined not to let a lack of competence get in my way of fucking this right up!
Not helping the fact is that it's running a pressurised fuel system because of the turbo. Although I think normal tuning rules do still apply.

[cutcat]

Hey Rocket, my uneducated diagnosis is...that your float levels will be fine as long as they are all even. What you are suffering from is that your bike is drawing too much fuel thru the carbs because of the restricted inlet passage the turbo has given your motor. Once boost develops everything becomes fine and is balanced out by your pressurised carb set-up. So to stop sucking too much fuel when the turbo not boosting you will need to add an air priority valve or jet down your idle circuit.

[Rocket]

thanks Cutcat, while i've got them out, i'd still like to measure them.
anyone got the float heights ?
If not, I'll just go with the advice and make sure they're even.

[Hillsy]

Hey Rocket, this is a bit in-depth, but it might help:

http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

[Rocket]

cheers Hillsy, i found this info pasted on a thread last night but didn't spot the link to the actual float setting tips.
Should help.

[cutcat]

Rocket, you may need to run your float levels a whisker higher(ie smaller measurement when upside-down) than stock because of the higher fuel demand of your turbo motor, so don't drop your float height thinking it will clean up your low-down. Remember running rich is your safety net.
Good luck.

[Ed74mnd]

or if that fails...
check for worn emulsion tubes.

Cheers

Ed

[Rocket]

For anyone interested, the factory float height is 14.7mm +/- 1mm.
I took Cutcats advice and didn't lower the fuel level in the bowls, but i also decided not to go higher because fuel is supplied by a fuel pump and not poxy old gravity.

Also, I am borrowing a set of stock carb tops (my ones are now fully sealed) and will see if we can balance the carbs using a vacuum guage set. I'm assuming that while the turbo isn't producing boost when it's at idle and or low throttle settings, there will be some vacuum there. We eyed off the butterflies and got them closeish.
The needles are a little worn but I'll leave them in and see how it goes.
Should be back in one piece in a couple of days when my new throttle cable turns up and will let youse know the result.

Interestingly, looking at the plugs, I have 1 and 4 burning black and 2 and 3 burning nice.
I'm wondering whether i might also have a coil issue as 1 and 4 run off the same coil.

[Hillsy]

quote:Originally posted by Rocket


Interestingly, looking at the plugs, I have 1 and 4 burning black and 2 and 3 burning nice.
I'm wondering whether i might also have a coil issue as 1 and 4 run off the same coil.


Inner cylinders run hotter = you need them a bit richer than 1 and 4. (in your case, you'd need to run 1 and 4 a bit leaner).
Most 4 cyl bikes will have 1 size larger mains for 2 and 3 as standard.


Oh - that's assuming you've got same size jetting for all 4??

[Rocket]

Good point. Will check that.
We only unscrewed one jet and I just assumed they'd all be the same.
learning every day here !!