rvf carbs - emulsion tubes

[G-MAN]

If HRC say it should stay 35 then there is a reason for that because it works for them and I see no reason why it wont for anybody else and carb tips are there to use so why not cut and paste there is more info in that to be used for better under standing . HRC have three needles with different hight settings suppose they made that for nothing to . They easy way out is often not the right way out

[Cammo]

First thing to do is get your main jets right, your sizes will be too lean and will affect midrange to some extent.

[zymon]

stickshift,

you reckon i should try i bigger main jet than the sizes i currently use??

[zymon]

i keep reading the bit about the weber emulsion tube, it says u need the holes at the top ( which the hrc ones are - they do away with the holes at the bottom ) and thats what is fitted to my carbs...

also it says it affects the low area rpm's - well my problem is at the high end of the scale 8.5-9k . in order to make positve changes and not just swap settings willy nilly you need to get an idea whats going on? When i think its a weak area / flat spot i tried raising the needles and when at the top highest setting i even tried a washer under the needles but it just bogged.

Would it be worth trying just to see if its that area ;

- change back to the original emulsion tubes with the extra 2 holes at the bottom ( maybe go up a jet size too if the holes weaken top end ?? )

- try bigger pilot jets as suggested here by someone? jets again alter

Has anyone here on a higher state of engine tune ever played and adjusted fuel level heights??

Thanks all so far for input- it has helped and given me more of an understanding

[Neosophist]

i keep reading the bit about the weber emulsion tube, it says u need the holes at the top ( which the hrc ones are - they do away with the holes at the bottom ) and thats what is fitted to my carbs...

also it says it affects the low area rpm's - well my problem is at the high end of the scale 8.5-9k . in order to make positve changes and not just swap settings willy nilly you need to get an idea whats going on? When i think its a weak area / flat spot i tried raising the needles and when at the top highest setting i even tried a washer under the needles but it just bogged.

Would it be worth trying just to see if its that area ;

- change back to the original emulsion tubes with the extra 2 holes at the bottom ( maybe go up a jet size too if the holes weaken top end ?? )

- try bigger pilot jets as suggested here by someone? jets again alter

Has anyone here on a higher state of engine tune ever played and adjusted fuel level heights??

Thanks all so far for input- it has helped and given me more of an understanding

You really do need to goto a dyno who will be able to anaylise fuel air mixture for you.

Not meant in a bad way but you dont' really seem to know what you are doing properly and while it's admiral that your having a go at it, carb tuning is a specialist art. You will probably need to adjust the fuel level when tuning as it is part of the process..

Unless you tune in order and do it properly your wasting a lot of time / money and petrol >.< it's a slow and iterative process that can take ages with some exotic set-ups. Probably why most people seem to find carb tuning a mystic art. You can't cut corners and really need either a dyno or gas analysier to evaulate your state of tune. A dyno shop will most likely have lots of jets available to try to find the correct one, otherwise you'll be buying many jets until you get the right ones.

Adjusting the needle position is a bit like trying to polish a turd if your main jets are not right.

Adjusting the needle position with the correct mainjet however will get rid of any flatspots between 5-8k.

Basic Tuning guide:

First off make sure you have the correct main jet, this is where to start. this is the jet that causes the bike to pull the hardest at full throttle from 8000rpm -> redline. The bike must be warm and at temperature when testing. If your bike is pulling better until warmed up you need to drop a few sizes and try aggin.

Only when you have the best main jet size can you start adjusting the position of the needles, start from the middle and either richen it up (raise the needles) or lean it out to suit.

Now after all the kerfuffle of sorting out your midrange / full throttle we can tune the low rpm out, this is done by float height. You want to adjust the level of the fuel so that you can gas the bike fairly hard at low rpm (3k) without it bogging down too much.

You shouldn't need to variate more than 2-3mm from factory settings. If you do check for excessive jet and needle wear, float height works backwards too, 7mm-6mm will richen up the mixture.

Finally sort the pilot screw out for smooth idle and part throttle (1/10th) cruise.

[Cammo]

once above the spot it hoons, using 150 and 152 mains atm, used smaller jets down to 132/135's and initially started off with the hrc start point, b needles ,142 jets ( i think ) but even then it felt asthmatic a bit top end.

My thoughts are that your 150/152 jets will be nearest the mark, but you might need to fine tune on a dyno.

I imagine the flatspot would be to do with your airbox, you'll probably be getting some sort of charged air in there (e.g. ram air effect, higher than atmospheric pressure) which will be playing havoc with your normal fuelling settings. The hrc setup doesn't take into account any ram air effects, and won't work with charged air.

I get around this flat spot on my hrc carbs (nc30 though) by using #40 pilot jets. It gets rid of it entirely.

Superlite is on the right track to tune this out.

Your nc35 carbs aren't handling the fuelling transition between needles and main jets, and are running lean. No amount of needle tuning will get rid of this. Restricting the air jets (and then installing significantly smaller main jets) and increasing the pilot jet size would be a step in the right direction, but this is a lot of fussing to find a state of tune that not many racers or others use.

Your best bet to get rid of this flatspot entirely is to mod the carbs for a ram air type setup. This will involve some carb plumbing mods, and by the sound of the serious nature of your bike's tune it might be perhaps best done by a pro. I'm sure peeps on here can recommend the man for the job...

Personally I think that's the easiest way to sort it. You could put in all sorts of dyno time with your current setup but I doubt that you'll be able to tune the flatspot out entirely without some big changes to your setup.

[doodleface]

Just to bump this...
This guys issue is exactly, down to a god damn tee, my problem, i get a terrible spot in the same area. I just posted on my HRC carb thread that perhaps I should up my idle jets... i'm running 150's mains all round... no airbox, ram air is really a misnomer cause it will cause more problems then it will alleviate... will get some and report back.

[kevprojex]

Has anyone ever rode a factory HRC set up bike ? , it may have run like a bag of shite untill you screamed the tits off it, the little 400cc race bikes were set up to make the most power high up in the rev range and they didnt give a toss how it rode in the mid or low rpm becauce they never dropped the revs that low. Ive only had one nc30 on the dyno with a HRC carb kit and airbox(or lack of it) and it ran like a turd untill about 9k then took off like a raped ape making peak at around 13.5k. It made about 2.5bhp more with the HRC kit fitted but the dyno curve was terrible compared the the bike when it had the airbox fitted. Give me an airbox anyday over the open airbox setup.

[doodleface]

I haven't no, on the track occassionally you end up at 8 k rolling on because to be the next gear down you are top of redline and can't roll on properly. Still I'm no where near 60hp i don't think at. Just funny this guy sounds like his problem was identical to mine, sucks I can't see a HRC setup in the flesh.

[Cammo]

My race bike with full hrc nc30 carbs ran like a dream and pulled like a train throughout the rev range. The power and delivery proved time and again to be superior to most bikes running a standard type airbox setup.

Most 'hrc' carb setups I come across on track bikes are either incomplete (don't use all the correct parts) or are setup horribly wrong.

I've never ridden a bike with rvf hrc carbs, different kettle of fish!