NC35 jetting issue

[Mark-091]

Hi, need some advice on jetting my NC35 again. Bike was previously running with 112.5 jets all round with a full Tyga system, the induction side is all standard with genuine air filter, the springs and washers also standard. The bike ran well with no flatspots but I decided to try 115 mains just to see how it would perform.

So gt the jets in 2day and was amazed how much better it pulled over 7k rpm however with the extra pull up top comes a slight hesitation at 5k rpm which is quite annoying as the rest of the rev range is great. Note the flat spot only appears after the bike is fully warmed up after 10mins of riding. I tried raising the needle with extra washers bt this made it worse and so I removed them again, then I tried the HRC springs which also didn't work.
Now knowing that I have a rich midrange I removed the standard washers from under the needles bt this made the bike run badly it wouldn't even pull fully to the redline as if the needles where restricting fuel flow. So the needles are nw shimmed back to standard and I have run out of ideas :)

Would appreciate any advice on trying to remove this Flatspot as I really feel the 115s provide the best power.

Could you use washers that aren't as thick as standard e.g 0.3 to try and lower the needle without restricting the fuel completely, or perhaps ther is sim other way of leaning out the midrange ??

Thanks

[kevprojex]

I cans see why the bike pulled ok with the 115 mains and the shim under the needles but wouldnt pull with the shim removed ? it should have done . i think you may have trapped a diaphram rubber or something when testing with the shim removed, the shim isnt thick enough to alter the fuelling that mutch it wouldnt pull up to the red line, you are right in thinking you are runnung rich in the mid range so removing the shim should have improved this. my nc35 with the twin stack tyga system is the same so i removed the shim as well, i still have a slight rich stumble at about 6-7k but the bike is only used for track days so its no drama.

[Mark-091]

Cheers m8 for the fast response I will retry with the shim removed 2moro to see if it helps. Thanks again.

[NC 35 owners]

mark how do you set the carb..?mind to teach me as I'm new

[mo haggs]

I cans see why the bike pulled ok with the 115 mains and the shim under the needles but wouldnt pull with the shim removed ? it should have done . i think you may have trapped a diaphram rubber or something when testing with the shim removed, the shim isnt thick enough to alter the fuelling that mutch it wouldnt pull up to the red line, you are right in thinking you are runnung rich in the mid range so removing the shim should have improved this. my nc35 with the twin stack tyga system is the same so i removed the shim as well, i still have a slight rich stumble at about 6-7k but the bike is only used for track days so its no drama.

kev, in a previous post you mentioned it may be an advantage to use a stronger spring. how difficult would it be to get a suitable spring with a grater resistance? and could/would this be something that you/rick oliver could offer as a set? (ie. like ricks hrc spec springs)

[Drunkn Munky]

Whats the benefit of a stiffer spring? The HRC ones are softer than stock aint they?

[mo haggs]

both the 30 and 35 have a flat spot in the midrange, caused by a lean midrange in the 30 and a rich midrange in the 35.

hrc springs on their own will make the 35's worse (as they will richen further) - to get the benefit you need to do other mods.
so in theory a std rvf with nothing other than a stiffer slide spring would lean of the midrange giving a reduction or an elimination of the flat spot in the midrange.

with the 30 the same thing is acheived with shims and drilling slides - only richening the midrange instead.

[kevprojex]

The nc30 spring rate seems ok once the damper holes have been drilled, drilling the damper holes makes the slides lift faster, hence lifting the needle faster as well, adding the shim to the needle just lifts the needle slightly to add a little more fuel.
On the 35 the fueling and throttle responce are ok apart from the 6-7k area , idealy when the slide is at this point the needle needs to be leaner(thicker), Now if rick has the dimentions of a stock 35 needle he may be able to select a leaner needle for better mid range fuelling if they are available.
I have seen non adjustable needles(needles without circlip grooves) that have had the top washer machined thinner( from the underside ) to lower the needle, i was going to try this on the 35 but if i f@@K em up i would be in the shit so i didnt bother lol.

[mo haggs]

So rather than a heavier spring a thicker needle is better.
Ok.

Sorry for the thread highjack.

[kevprojex]

So rather than a heavier spring a thicker needle is better.
Ok.

Sorry for the thread highjack.

Like any carb set up it will be trial and error just fit it and test it, i dont know what will work best as i havnt done it, basicly we need a slightly thicker part of the needle in the emulsion tube at that point in the slide lift, it could be achived by lowering the needlle,different needle or a stronger spring.If i had a spare set of standard needles i would make a holding jig for the lathe and machine the underside of the top washer to lower the needle and see what happened.