Hi All, after testing with an a/f sensor ive established my carbs are all running rich throughout the rev range. Its a 90/91 NC30 with same carbs and should have 118's & 115's main jets, but has 110's and 35 idle jets all round. Even after turning the pilots in to 1&1/2 turns out and raising float heights to 8mm, its still rich.

I've checked the needle jet openings and they all look a bit worn and oval, could this be causing this richness throughout?

Is Durban high up? It is on the coast isn't it?

Is your airfilter any good? old and manky? non standard?

Is the end can sooty?

can you take the washers out the needle hlders - lower the needles and see how that goes..it will lean up the fuelling and you'll find out if they actually work...

Are your air-jets standard.. you might need a bigger one to lean it up if it is rich everywhere.

Yup Durbans sea level, so plenty air, and my air filters new but standard flow. Ive taken the washers out and still appears rich lower down the rev range. the cans are sooty and the plugs black so this corresponds to a/f readings, also the bike stalls when slowing down to idle once properly hot, so absolutely sure its very rich.

Air jets? didnt know there were? what do they look like?

yes that would be classic rich symptoms (stalling when pulling up)

Erm... the air jets are pressed into the carbs.. not realy adjustable.

Take the air-filter out.. this will lean it up, see how it rides without one.

High flow (foam) filter would be my next thought.. these are the cheapest and easiest ways of leaning the bike up.

MexicanGringo wrote:i bought some pilot jets off you a couple months back..

Finally got round to welding nuts to the downpipes for an air/fuel sensor. Its telling me the mixtures rich right the way through and leaner(but still rich) on engine braking, this with the smaller pilots.

The setup now is 110's & 35's all round, not sure where the 110's came from because there should be 115 & 118's according to haynes for the year. Its also def the same carbs for that year based on serial.

On fitting those smaller jets a flat spot around 2-3k developed, which is strange considering the rich setup... Im gona try raising floats again to see if leans it enough.

(Apologies for posting your PM up, but it might help others to fully understand the issue here.)

I don't understand that you've gone from 40 (rich) pilot jets to 35's (standard) and the bike is too rich. Alarm bells should be ringing here, that is not right!

Some questions:

- Are you sure it's running rich?
- What sort of a/f ratios are you getting and at what revs?
- What instrument are you using to measure?
- Aside from a/f readings how does the bike run through the revs?
- Where did you mount the a/f sensor?


Before going any further I think returning the carbs to stock would be a good start. Might take a little more time but you'll never sort them out if you keep trying alternative tunes.

There is NEVER a need to adjust the float height to any other spec, they should be set at 6.8mm. This will cause running issues if not at spec.

Regarding stalling at idle, this will be to do with your pilot screw settings (2 turns out would also be a good place to start) and maybe also a combination of float heights out of adjustment.

MexicanGringo wrote:I've checked the needle jet openings and they all look a bit worn and oval, could this be causing this richness throughout?

Normally it's the needles that wear on the surface, you can see it quite easily as a scratching of the surface hardening. If the guides are worn then yes, it will create rich running issues. The old setup 40 pilot jets would have been very rich if the needles are badly worn.


By working through the issues you should be able to sort it.

Firstly when trying to set up fuelling on carbs you need to start at the beginning, you will never get it fuelling right no matter what you do if the main's aren't set right, are you sure the main jets in there are really 110's? it's not uncommon for dyno centres to re drill old jets when out of stock usually when you do this you would grind off the number on the jet to indicate it's been drilled but not every one dose this,

What's the spec of the bike? best thing to do is put the carbs back to standard spec and work down from the top, have a read of this set up guide its by far the best explanation of how carburetors work and how to set them up properly

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

Let us know how you get on
Simon

Cheers for the replies.

All main jets are def 110's, the one number is slightly scuffed but not indicating its been filed.

Im using a digital multimeter attached to a bosch universal lambda, each downpipe has its own nut to attach to. these are around 30cm from the ports, but the sensor has a heating element so min 300' operating temp not a problem.

Even with 8mm floats, all washers out and pilots 1*1/2 to 2 turns out, this reads 800-900mV from idle - 14k. It looked to run lean on hard acceleration in the upper rev range just now though...

But steady accel is running rich. The acceleration is fairly strong, but when slowing to idle the revs drop and it stalls sometimes with blipping the throttle.

Theres a noticeable hesitation around 3-4k, which only came about after putting 35's to replace the 40's, this is odd given what the sensor tells me...

Thanks for the advice, i'l try different settings till i come right, gona investigate new needle jets as well.

It'll run lean on hard accelleration if you've lowered the fuel level as it'll drop even more when running at WOT.

If you need more than 1mm from stock on the float height you need pilot jet changes.

I agree with Cammo on this one, get them back to stock and see how it runs.

You might find you have a leaky carb.. I had a float valve that wasn't sealing properly was leaking fuel into the engine.

Are all the plugs the same colour?

Are any of your chokes sticking on?

Did you try it without the air-filter.. did it make it better or worse?

Those cheap universal lambdas are no good for getting a proper A/F there way too inaccurate.. bin that and go by feel of the bike.

You need a high senstive wideband lambda plus fancy computer control software to avoid burning it out (the heater elements have funny controls to them) to build a home-brew A/F meter.. expensive too but kits are available.

Neosophist wrote: Those cheap universal lambdas are no good for getting a proper A/F there way too inaccurate.. bin that and go by feel of the bike.

I agree. Don't get too caught up in the numbers you see, go off how the bike performs.

If you have the main jets pretty much right the chances of causing engine damage are very low (unless you're racing in the suzuka 8 hr ).

It is a wideband sensor that you're using right? Forget anything else it will just be giving you more headaches than what it's worth.