Atomik nitrous won't run right

[TYE]

So I bought an atomik nitrous second hand and made the mistake of not checking all the nuts. One nut on the carby was loose and the other was tight and after bouncing around the casing of the carby cracked. So I went to my local pit bike shop and picked up a new mikuni carby and uni filter (because the air intake was smaller than the old one). Me and my dad fitted it, kicked it over and it was running rough as guts and missing, dad reckoned it was getting to much fuel but there is no air/fuel mixture screw on the carby. So please any help is much appreciated.

 

[Phil67]

It has an air leak, is the manifold seated properly?

 

[zwebx]

What cc is your bike?
you could just need to jet it.. you cant just buy a carby and expect it to be tuned out of the box
the best way to jet it is to get it running (show a video i should be able to tell you to go leaner or ritcher) if the audio is okay

 

[zwebx]

It has an air leak, is the manifold seated properly?

Yes that also
or the jet could just be tiny or blocked

 

[8r3nd0]

Air intake smaller then the other one so I'm right in saying it's not the same size carb as the original? There is a air fuel mixture screw in the mikuni it will be under the carb throat where it bolts to the manifold. Check the jets are the same as the old carb if not change them over, it's amazing the bike ran at all if the carb was so loose! Did you put a new gasket on or are you using the old one?

 

[TYE]

It has an air leak, is the manifold seated properly?

Would this be the air leak?

 

[zwebx]

that looks like a big one, you need to straiten the manifolds
take em off and get a flat tile, or wood just has to be flat and then sand them flat on the flat surface
or put a couple gaskets in there to take up the room (i cut mine myself)

 

[8r3nd0]

yeah youve got no gaskets only a heat spacer, you need a gasket between the carb and black spacer on both sides. you can even do without the spacer and just run one gasket to limit the chance of a leak. also the shorter shaft there is the mixture screw screwing it in will lessen the fuel mixture, out will richen it, its known as a fuel screw if it was on the other side of the carb it would be an air screw.

 

[my67xr]

the china Mikuni copy carby's normally have a rubber o'ring seal on the manifold side mounting face, same with the plastic insulator plates.
they can still leak air into the fuel mix though.




in the pic of the carby, that little hole is blocked at the bottom centre, dont worry about that being a leak.


the easiest way of testing it is to start the bike and let it run
then spray some wd40/degreaser on all the joins in the carby/fuel bowl, carby/ spacer, spacer/manifold,
and if the idle changes in any way, then there is your leak.
try what the other have suggested, and face off the mounting surfaces with some 320 W&D paper on a flat block.
otherwise make up some thick paper gaskets and fit inbetween the carby/spacer, and spacer and manifold.




here is a pic of the fuel /mixture screw on the mikuni




and this pic shows the 2x Jets you may need to swap from your old carby into the new one, if they are bigger
Pilot jet is the longer jet towards the manifold side of the carby,
Main jet is the bigger one in the centre