Fuel System FAQ

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banner001
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Fuel System FAQ

Post by banner001 » Wed Apr 16, 2014 11:55 am

Note: Ill be adding to this, and tidying it up as i go, for now this is just somewhere to dump information for the FAQ, if anybody want to add something post it up and ill add it and edit it later.

1. For general CVK-D32 Carbs
A. Needle sizes
H1: N36Y
H2: N77C
L1: N77R (Austria and Germany)
L1-8: N77S
L3: N77Q (Japanese import only)
L7-9: N77W
J1 or J2 F3 kit: N70A (adjustable)
J1 or J2: N78B

B. Pilot jets
All models: 35

C. Emulsion tubes
H model has a slightly different side-hole drilling pattern to the L model, different L-model needles use different emulsion tubes (difference unknown)
N77W = 13280-1063
N77S = 13091-1783 or 13091-1800
N77R = 13091-1634
N77Q = 13091-1827


D. Main jets
L1-9: 95 (standard), 90/92/98/100 (options)

E. Main air jet and Pilot air jet
It is possible to remove these (they are a press-fit) and tap a hole to allow you to adjust the size of the air jet...but in practice the gains are minimal and if you are doing this a set of fully-adjustable FCR's is likely the best way to go.

2. What fuel should i use?
The zxr400 is rated for 92RON fuel, the minimum RON for fuel in the UK is 95 so any that you use will be fine, and wont cause knocking, 95RON can be used up to a static compression ratio of 14:1. Some people swear by one brand over another...feel free to try them all out, but understand that its YOUR personal preference.

3. How big is the fuel tank? Is there a reserve?
The fuel tank is a single tank with a dual level tube to allow for "main" and "reserve". The fuel tank has a capacity of 16L, this allows for 12L of fuel to be drained from the tank with the fuel petcock set to ON, and an additional 4L to be drained once the fuel petcock is switched to RES.

4. What mpg will i get?
This is all dependent on how your bike is setup, what speed you are riding at, weather conditions, pillion etc... But as a general rule of thumb, estimate 50-60mpg on the motorway, 40-45mpg doing A-B roads, and 35mpg stop-starting in towns. If you are constantly in the top part of the rev range you could be as low as 25mpg (~90 miles until empty from a full tank).

5. My bike bogs down with full throttle, what is wrong?
Its likely that your bike is running lean, you can test this by seeing if opening the choke at the same time as going full throttle cures the problem. If the bike increases its rev rate then you are lean, buy 1-2 size bigger jets (i.e. if you have 95's buy some 98's or 100's), and repeat the test. If the bike becomes significantly worse/cuts out then you are probably rich on the main jets, buy 1-2 sizes lower and repeat the test.

6. My bike bogs down at mid throttle, whats wrong?
Its likely that you are lean on the needle, test this by opening hte choke as the bike starts to bog, if the revs drop significantly you are too rich and need a leaner needle or a change of clip position (hopefully more on this to come), if your revs increase keep reading. There are 3 options in order of most likely, a) you have standard needles, buy some small M3 washers and slip between 1 and 3 underneath the needle jet so it raises the needle away from the carb body and allows more fuel into the carb. b) you can buy a Dynojet Stage 1 kit with thinner more tapered needles that allow more fuel through, these come with their own fitting instructions. c) you have kit needles that are adjustable, in this case you raise the clip towards the large fat end of the needle to make the midrange leaner, or you move the clip towards the pointed end to make the midrange richer.

7. My bike bogs down at mid throttle AND full throttle, whats wrong?
Refer to the two steps above, you likely have a problem with both.

8. Petrol is leaking from my carbs from one of both of the two pipes either side of where the fuel goes in.
You have one of 2 possible issues (or both). You have a damaged fuel float needle (its the small bit attached to the carb float) that is not sealing and thus is allowing too much fuel to build up in the carb bowl AND/OR you have got a leaking o-ring so that your individual carb fuel filters are not sealing...both of these things can lead to issues. Its also possible that if you have your floats set massively rich that fuel can escape from the overflows, although this is a sign that something is very off with your carb. If your o-ring is damaged it is possible to temporarily seal it with some instant gasket, although its better to buy a replacement. If your fuel float needle is damaged you will need to buy a new one (usually as part of a carb overhaul package).

9. Should i drill my slide holes?
Probably not if you are on the road, unless you are running a low/mild stage of tune and are using a kit that recommends it. Drilling the slide hole wont give you any more bhp, it can increase the responsivness of the carb by shortening the time necessary for the vacuum in the venturi to affect the pressure in the diaphragm and start to raise the needle. If you drill it too much you can start to get slide flutter where the slide moves due to very small differences in the pressure in the venturi. Dynojet supply a 3.1mm drill bit where as the original hole is ~2.5mm (~54% larger area).
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003

ManxMan
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Re: Fuel System FAQ

Post by ManxMan » Wed Apr 16, 2014 12:54 pm

why does germany and austria have different needles

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Re: Fuel System FAQ

Post by banner001 » Wed Apr 16, 2014 2:09 pm

different countries have different exhaust emission and noise regs, in california most motorcycles have to have fuel-vapour catchment tanks, its like the mph restriction on japanese imports.
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003

tamd86
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Re: Fuel System FAQ

Post by tamd86 » Wed Apr 16, 2014 10:02 pm

what is the standard main jet for h1 model?

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Re: Fuel System FAQ

Post by Rasta-ninja » Tue Jul 01, 2014 9:23 pm

I know how to balance carbs but im not 100% certain on exactly what im changing or affecting which got me thinking. If you were to balance your carbs, and then adjust the fuel screws(mixture screws whatever you want to call the), would you need to balance the carbs again...? My original thoughts were as long as you adjusted each screw the same amount it shouldn't matter

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Re: Fuel System FAQ

Post by ManxMan » Tue Jul 08, 2014 10:51 am

Rasta-ninja wrote:I know how to balance carbs but im not 100% certain on exactly what im changing or affecting which got me thinking. If you were to balance your carbs, and then adjust the fuel screws(mixture screws whatever you want to call the), would you need to balance the carbs again...? My original thoughts were as long as you adjusted each screw the same amount it shouldn't matter

I was wondering about that too. what does the little screw thing you turn to make the balance right do does it change mixture

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Re: Fuel System FAQ

Post by banner001 » Tue Jul 08, 2014 3:29 pm

The balance screws turn the carb butterfly's individually. So they open or close them individually in order to adjust the pressure in the carb Venturi.

It doesn't change the mixture composition, but it does change the volume of fuel/air sucked into the cylinder.
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003

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Re: Fuel System FAQ

Post by Rasta-ninja » Tue Jul 08, 2014 9:51 pm

So are you saying every time you adjust the fuel(mixture) screws you would need to balance your carbs, since the mixture going through is a different density so therefore a different pressure? or would the changes not be significant?

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Re: Fuel System FAQ

Post by banner001 » Tue Jul 08, 2014 11:16 pm

Rasta-ninja wrote:So are you saying every time you adjust the fuel(mixture) screws you would need to balance your carbs, since the mixture going through is a different density so therefore a different pressure? or would the changes not be significant?
If you are moving the screw more than 1/2 a turn, or if you are adjusting say screws 1 and 4 only, then I would balance the carbs again.

Only takes 5 minutes.
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003

lozza
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Re: Fuel System FAQ

Post by lozza » Wed Jul 09, 2014 12:25 pm

I think i might be rich on the needles, mine are N77C, I have the N36Y as spare but this is clearly richer, anyone know which needles are leaner than the N77C? thanks

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Re: Fuel System FAQ

Post by Rasta-ninja » Wed Sep 02, 2015 7:12 pm

For everyones sake thought i'd just post a message about main jets. If you are going to buy some and don't want to pay the price for genuine keihins (about £7 each) most companies supply an aftermarket brand called Keyster(about £3 each) which are also made in japan so i'm guessing decent quality. I've been using them for a week and had no real problems..... APART from a certain company had sworn they sent me the right sized jets that were coded 228100. Something was wrong with the thread on the jet and it didn't really fit properly(tightened up before it seated). The company said, and i quote, "Some jets will do that, as you say they tighten but will leave thread showing." to which i replied no they shouldn't do that. Anyway the long and short is i got stuck with these jets (no refund), i purchased some off ebay after being assured they were genuines, which turned out to also be the 228100's but i managed to get refunded. Then i asked wemoto if they supplied genuine keihins to which they replied yes, i bought some and surprise surprise they were keysters :smt011 After having a paddy i realized they were slightly different, these ones were coded 228600 and fitted just fine biggrin

So if you need some aftermarket jets for your CVK-D32 carbs make sure you get the 228600's if you're getting keysters. My bike was an L model so i'm not sure if its the same for the H but it should be since they are both CVK-D32's.

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Re: Fuel System FAQ

Post by fstarocka » Fri May 13, 2016 3:10 pm

tamd86 wrote:what is the standard main jet for h1 model?


98 -

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Re: Fuel System FAQ

Post by fstarocka » Wed Sep 07, 2016 5:30 pm

I have a 1990 H2 zxr400 - pressed out my emulsion tubes today and almost ruined one of them, my needles look good and I have what appears to be 177 stamped on the needles -

anyway, ive been thru just about everything and conclude my tubes MUST be worn, even tho its SOO hard to see - i can see a little bit of weaar in at least 2, but ever so tiny.


bike just runs bloody rich no matter what, despite float heights, mix settings, removing filter, redoing coils, just rich, new plugs fouled up today after running for 45 seconds revving at 2-4k rpm.. so im in the market for a replacement set - can anyone tell me where to go get a cheap set? :)

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Re: Fuel System FAQ

Post by Pietvis » Tue Aug 20, 2019 2:20 pm

Hi, I'm new to the group and from sunny South Africa. Got a h2 with the same problem. Overfueling at low rpm. Pilot screws at 1.25 turns

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