bike carbs.

[pyromaniac_yeti]

okay, so ive got a pretty much standard 1.2 carbed nova.

i've overhauled the ignition system recently...new coil, plugs, leads, dizzy cap, rotor arm

its got a "performance" (i.e very loud and badly fitting) backbox on it, and a foam "mushroom" style air filter on it.

i've come across a set of kawasaki GPZ 400 carbs (four of) on ebay for peanuts, planning on making up my own manifold for them. looking at bogg bros guide to fitting bike carbs, im going to need to modify the jets on the carbs to get the fuel mix right...they say 1.8mm for a 1.8 engine, 1.65 for a 1.6 engine...(this is on a set of r1 carbs) so would i be right in saying that i'd have to drill the jets out to 1.35mm to get em to work right? would the standard mechanical fuel pump be up to the job? i mean after all its a carb fuel pump, and im fitting a set of small indiviudual carbs, rather than one large carb.

the other thing i could see being an issue would be the vaccum feed to the brake servo. would it work fine if i just tapped four threads into each inlet tract on the manifold, and linked them up via a series of T pieces to even it out over all four cylinders?

budget powers the name of the game on this one, hence the unusual choice of carbs...and the spec of the engine so far. i figure that i can do a manifold, get the carbs, filters and gaskets for roundabout £50-60. then all ive gotta do is keep a lookout on ebay for a 1.3SR cam/kent/whatever and i should have myself a fairly fun little engine. nice low mile engine tbh...old lady owner for 43,000 miles, college student had it for a year after that racking up a further 5,000 then i've had it scince...only payed £400 for the car, so its something i dont mind playing around with a bit y'know.

anyway enough of my rambling...any thoughts/suggestions??

[NOVA-KID-93]

im gonna keep a close eye on this thread and steel any advice that comes up if its ok :)

ive already got a set of carbs and mines a 1.2(spi tho :() with a 4 branch manifold and straight through system fitted, just need help on fitting the carbs!!!

[mk1nova_rich]

the standard mechanical pump will be fine, but you will need to fit some sort of fuel regulator to bring the pressure down to around 3psi, which is what the bike carbs require.

keep the standard cam for now, the money would be better spent on a secondhand exhaust 4 branch manifold and decent exhaust system.

You will only need to tap into one inlet tract for the servo vacuum hose, as per the standard setup.

The carbs you have should be ok but when it comes to setting the carbs up, you may counter other problems than just the jet sizes. I had a go at fitting CBR900 carbs and found the floats will need playing with to run properly as they were overfilling and petrol was pouring out of the back of the carbs.

The manifolds can be made very easily, i found the best way to mount the carbs was to use short lengths of silicone hose and jubilee clips but some people use the original mounting rubbers and make their manifold to suit.

Hope this helps

[mowgli]

my initial thoughts are to go & buy a 1.3 bottom end instead. it will cost way less on insurance & make it go a lot quicker

[mk1nova_rich]

my initial thoughts are to go & buy a 1.3 bottom end instead. it will cost way less on insurance & make it go a lot quicker

or use the 1.3 and 1.2 bottom ends to make that high compression 1.4 and stick bike carbs on that lol

[mowgli]

ok, but learn to walk, then run......

bike carbs on 1.2 novas are not going to do much, apart from make noise & cost you money, and we have women for that......

[pyromaniac_yeti]

"make noise & cost you money, and we have women for that......"

lol, too true...

well the carbs were only £18 for the full set of four with the rubbers...ive got acess to a great deal of scrap metal to make up a manifold with. so anyway, the conversions going ahead.

so when i go pick em up next weekend i can start making up the manifold...ill have to see if i can get a pressure regulator of some description and see how it goes :thumb:

[mowgli]

"make noise & cost you money, and we have women for that......"

lol, too true...

well the carbs were only £18 for the full set of four with the rubbers...ive got acess to a great deal of scrap metal to make up a manifold with. so anyway, the conversions going ahead.

so when i go pick em up next weekend i can start making up the manifold...ill have to see if i can get a pressure regulator of some description and see how it goes :thumb:

don't bike carbs have a bowl on them???

there is no need for a regulator, maybe use a filter king with an overflow, but you can spit quicker than a gm mechanical fuel pump

[mk1nova_rich]

don't bike carbs have a bowl on them???

there is no need for a regulator, maybe use a filter king with an overflow, but you can spit quicker than a gm mechanical fuel pump

yes they do have bowls, but if they overfill you run into the problems that im having with mine. somehow need to adjust the float levels

[pyromaniac_yeti]

hmm. might as well just stick em on there and then if it needs a regulator, then put one on.

one other question i had, was if i fitted a 90 degree bend on the end carb, fitted T pieces on the rest, linked them all up with bits of tubing...then ran that to a K&n cone filter on the T piece at the end, would that work fine for getting air into all four inlets?

just thought of that as a possible option instead of the bike airbox if that doesnt fit up against the bulkhead.

[mowgli]

the restriction caused would negate any gains.. make a plenum instead

[grasser26]

Hi-you'll need something like a bicycle cable for the throttle too,if you use a fuel regulator try it at a low setting first-I have cbr600 carbs and at 3psi the fuel overflows.Don't forget that the needles in the carbs should be lifted too-jet drills are cheap on ebay-try going up a size at a time.Don't forget you'll have to re route your heater hose outlet from the head too.

[pyromaniac_yeti]

right, got the carbs and stripped them...theyre keihin CVK's.

ive got the main jets out of all four, and the needles. (this is assuming im not being particularily thick by assuming the main jet is the one that the needle goes into?)

anyway. looking at the needles theres no clip to adjust how high the needles sit, so do i just put a small washer or something under each needle? if so roughly how big do i want the washer to be?

the main jets have to be drilled out...im going to try 1.3mm at first as its a pretty much standard engine and go from there....but there appears to be another jet in the float bowl aswell. does this need to be drilled? if so, how much bigger/smaller does this need to be compared to the main?

just trying to get the carbs and manifold done to the point where it should be a case of bolt on and make a few adjustments to get them on...fit em and set em up in a day as this is my only means of transport at the moment.

any advice anyone could give at this stage would be greatly appreciated

cheers

[grasser26]

Hi-I had the same issue with needles on my carbs-I used washers-about 4mm thickness in total.I think the other jet you refer to is an idle jet-on mine I left it alone and it seems ok-a lot of this stuff is down to tuning and setting up.If you have access to an air fuel meter or gauge it would be the best way to accurately set up your carbs-or on a rolling road.Try only make small jet changes at a time-no point in going too big.Another thing you may need is to have the choke-if fitted-connected up.