1989 NC30 track bike few issues

[Haydn]

Ok,

The airbox baseplate is removed and there is definitely no rubber flap installed near the support strut. I've also rechecked the old ER09 plugs and they are indeed sooted up so It was running rich before I bought the bike.

I've printed off and read the Carb jetting guide and all makes sense so Saturday ill be taking the carbs off. Thanks Cammo - great guide. In the meantime I have more questions to try and extract all the knowledge you lot have.

1. Should the choke cable be in the position it is? See pic below.
2. Do I need to run the rubber flap? If so Where can I get one?
3. I used some foam on top of the frame to stop the tank rattling around, see pic. Could this be stopping the airflow to the airbox?
4. There are two smaller pipes off the back of the carbs, look a bit short to me. See pic. Where should they go?

Thanks again
Haydn

[Cammo]

1. Should the choke cable be in the position it is? See pic below.

No, it should run between the V of the cylinders under the carbs and run into the choke mechanism from the right.

2. Do I need to run the rubber flap? If so Where can I get one?

Without it can cause a midrange running/fuelling issue. Not really essential for a track bike but if you feel you must have one then stick a wanted ad in the classifieds.

3. I used some foam on top of the frame to stop the tank rattling around, see pic. Could this be stopping the airflow to the airbox?

No, most of the air comes from under the headstock, above the top radiator.

4. There are two smaller pipes off the back of the carbs, look a bit short to me. See pic. Where should they go?

This is the carb overflow pipes, that's how they're intended to be.

I'm pretty sure your problems will be cause by your carbs. Take them each apart, write down what you find for each (main jet size, pilot jet size, needle code, and idle screw setting) and get back to us.

[Haydn]

Ok today I've taken the carbs off and this is what i've found. Please be patient this could be an extensive write up.

FRONT LEFT

Main Jet = 115
Idle Jet = 35
Emulsion Tube = 4 Holes
Pilot Screw = 2.25 Turns out
Carb Needle = (J51A) 1x0.5mm washer


FRONT RIGHT

Main Jet = 115
Idle Jet = 35
Emulsion Tube = 4 Holes
Pilot Screw = UnKnown as I altered it thinking it was the drain screw
Carb Needle = (J51A) 1x0.5mm washer


REAR LEFT

Main Jet = 118
Idle Jet = 35
Emulsion Tube = 5 Holes
Pilot Screw = 3 Turns out
Carb Needle = (J51A) 1x0.5mm washer


REAR RIGHT

Main Jet = 118
Idle Jet = 35
Emulsion Tube = 5 Holes
Pilot Screw = 3.5 Turns out
Carb Needle = (J51B) 1x0.5mm washer

Carb ID just says "VD", no other numbers which doesn't line up with the Haynes manual.

Please correct me if i'm wrong but reading through the guide and looking at the Haynes manual there seems to be a few issues.

1. Only one of the float bowl drain screws were on the outside, the other 3 on the inside so it seems they have been mixed up at some point with carbs off another bike. Does this matter?
2. 2 of the Idle jets were completely blocked.
3. Pilot screws were set wrong.
4. Both front carbs have the wrong needles, and the rear right has the wrong needle.

The bike is a 1989 "K", so its one of the early grey imports. The frame and engine numbers confirm this. So as standard should have 110 main jets all round, however this is deemed as too lean?

The Plan

1. Put needles in correct carbs with 1mm RO washers (Will need another J51B needle).
2. Drill slider holes to 2.5mm.
3. Set pilot screw to 2.25 turns out (DONE).
4. Set float heights in accordance with the Haynes manual.
5. Install new jets from RO. This is where I need advice on size.
6. Replace float bowl gaskets and drain screw o rings.
7. Balance Carbs.

The bike was missing the rubber flap, but will now be running standard air filter, snorkel and rubber flap. It has a loud Gibson end can which is pretty black on exit at the moment.

I would really appreciate your advice.

Thanks
Haydn

[Haydn]

"Cammo Cammo where are you?!"

[Cammo]

As per the guide mate, 118 front and 120 rear main jets will be fine with your setup.

Probably best to stick wanted ad up for the correct needle also.

Let us know how it all goes.

[Haydn]

Ok thanks.

So what do you think is causing the richness? The wrong needles, idle screws? Bigger jets will make it run richer that's all I'm thinking.

Cheers
Haydn

[Neosophist]

Ok thanks.

So what do you think is causing the richness? The wrong needles, idle screws? Bigger jets will make it run richer that's all I'm thinking.

Cheers
Haydn

Did you get it on the dyno before you started messing?

You could have had a leaking flaot bowl or something else causing overfuelling. It's literlaly impossible to say for sure what would have caused your richness without having examined the setup and carbs personally.

It is proven though that 118/120 jets are FINE on properly working carbs with end can.

You can also stick with the 115/118 and try that, either setup should be a great starting point... some dyno time might help and is recommended after you get a good feeling bike to fine tune.

I always found 2.0 turns is fine for the pilot screws. Any more and when the bike is really warm the idle can become sloppy due to slight richness, again for track bike it wont make any difference I doubt.

If the needles are messed up the carbs have been made out of some bits.

The carbs themselves could be buggard, warn passageways or something. Not common but ive seen it before.

Most often ex race-bikes, they are put back to stock and the carbs are thrown back to somewhat original spec.

A friend bought a bike once that was supposed to be a one owner straight jobby, carbs were all bitsa inside and there was scruitineering paint all over the engine... hmm.

Anyhow.

Get the carbs sorted out and see how you go from there.

If you dont want to up the jets just yet then stick with what you have now and get it dynod, but you shouldnt have a problem with either size providing your carbs are working properly and your airbox isnt blocked up.

[Cammo]

It certainly would have had a rich idle with those pilot screw settings - if the bike was idling for even a few seconds before you inspected the plug then idle mixture is all you will see.

You'd need to do a plug chop at high rpm to check the main jet fuelling, not always practical (or safe, even on the track). Easier though is to just stick with known main jet sizes that work, with a standard induction setup you won't go far wrong with 118/120.

More likely that it was lean up top with the standard jet sizes, no rubber flap and blocked pilot jets (which supply fuel through whole rev range).

Sorting out the carbs should help it a heap.

[Haydn]

Thanks a lot for the help. The black exhaust could well just be from idle so ill take your advise and go 118/120. Hopefully get all this back together in the next week. (As long as i can get a B needle).

Has anyone had one of cylinder coolant drain bolts shear on them? Mine went like chocolate today, it went tight on the way out so I used loads of spray and slowly worked it back in but eventually it snapped on me. Hopefully it won't leak but as its a steel m6 bolt and ally cast then do bing a weld over it is out of the question. No access at all for easy outs. Sounds terrible but maybe a smear of high temp silicone or liquid metal might do the trick. It's obviously pretty tight in there now.

[Haydn]

Thanks a lot for the help. The black exhaust could well just be from idle so ill take your advise and go 118/120. Hopefully get all this back together in the next week. (As long as i can get a B needle).

Has anyone had one of cylinder coolant drain bolts shear on them? Mine went like chocolate today, it went tight on the way out so I used loads of spray and slowly worked it back in but eventually it snapped on me. Hopefully it won't leak but as its a steel m6 bolt and ally cast then do bing a weld over it is out of the question. No access at all for easy outs. Sounds terrible but maybe a smear of high temp silicone or liquid metal might do the trick. It's obviously pretty tight in there now.