NC30 - How should it run?

[JDPercival]

So, I've had the NC30 for about 1 year now. I bought it from a chap who seemed to know his stuff and actually handed me a pack with lots of information. Some of which from this forum. So I assumed the bike was running correctly.

The bike has an NC35 exhaust (From what he has said). The bike has always been loud and quite boomy, sometimes it struggles through the rev range but just presumed this was normal for a carbbed old bike. I've never ridden another NC30 so if something is slightly off I would struggle to notice it.

I filled up at a petrol station yesterday and when I was turned the bike back on an pulled away I noticed it was a lot quieter and felt much smoother. Didn't need as much throttle pulling away from lights etc... after about 2 minutes the boomy exhaust came back and it felt much rougher.

I can't see why petrol would have made any difference? Normally I fill up with VPower, This time I filled up with BPs Momentum or whatever the premium stuff is. Should I be filling the bike with cheaper fuel since its an older bike? would this make a difference?

I spent the rest of the day craving the smoothness I had when I left the station.
I currently keep the bike in my parents garage and don't have much room to work on it.

What should my first checks be when I get some space to work on it? Exhaust? Spark Plugs? Fuel? Compression?

Appreciate any help.

[CMSMJ1]

Welcome :)

The bike, when setup nicely, will run as smooth as a waxed eel - they are a lovely thing. It sounds like your bike has perhaps been "modded" and is not running a standard setup.

So, I would start with checking your airbox is all there and the flaps that live under the carbs are in place - you can see these with tank off.

Missing induction/airbox stuff will make it run poorly.

Stick a pic up - some of us old timers may well remember the bike and owner and there is probably some threads where they did some of the fiddling on the bike.

[JDPercival]

Welcome :)

The bike, when setup nicely, will run as smooth as a waxed eel - they are a lovely thing. It sounds like your bike has perhaps been "modded" and is not running a standard setup.

So, I would start with checking your airbox is all there and the flaps that live under the carbs are in place - you can see these with tank off.

Missing induction/airbox stuff will make it run poorly.

Stick a pic up - some of us old timers may well remember the bike and owner and there is probably some threads where they did some of the fiddling on the bike.

I've attached a picture of the bike itself. I did change the air filter when I serviced it along with the oil and oil filter. I didn't check spark plugs as they seemed a bit awkward to get at the time. I've done some research and will check them when I get chance.

Do you think the problem I am having could be caused by the exhaust such as an exhaust leak? I remember I found the rear part of the exhaust header was loose and 2/3 bolts had shaken off. Since I have put 3 new nuts and washers on to keep it sealed but I didn't replace any gaskets etc.

I'll make an effort to get the tank of tomorrow after work. do I need the airbox off to inspect the carbs?

Previous owner has told me that he changed the exhaust for an NC35 and the rear wheel size he changed as well as dogbone link.
He also gave me a Aprillia RS250 rear shock that he said he ran for track days.

Thanks for the welcome :) and the help

Cheers,
Josh

[CMSMJ1]

Could well be a loose system - but they normally make more of a ticking than a booming noise!

Checking airbox has the front snorkel and the flap beneath the airbox is in place is the first step. If you can pull the airbox/carbs up as a unit and it moves at all - then you might have loose carb rubbers - where they connect to the motor - might need to re-seat them and nip them up. You'll need a long screwdriver for this - think it is a pozidrive x2 head - someone will correct me!

[JDPercival]

I will get the tank off tomorrow evening. and take a look.

Thanks for the quick response and help

Cheers, Josh

[magg]

Are you sure it is running on four cylinders.

[JDPercival]

Are you sure it is running on four cylinders.

I'm not 100% but I can rev it all the way out, Its pretty linear and doesn't really struggle to get there. I assume that means all 4 cylinders are firing?

When it was running smooth, Low down power came easier. Pulling away etc. So maybe its not running on all 4 cylinders until I get over a certain rev range?

[gavins]

Start it from cold, let it idle and check that all 4 exhaust headers get hot at around the same rate, that should tell you if you've an underperforming cylinder. Certainly sounds like it could be running on 3 most of the time.

[JDPercival]

Start it from cold, let it idle and check that all 4 exhaust headers get hot at around the same rate, that should tell you if you've an underperforming cylinder. Certainly sounds like it could be running on 3 most of the time.

I'll give that a shot tonight. thanks for the advice

Cheers,
Josh

[JDPercival]

Start it from cold, let it idle and check that all 4 exhaust headers get hot at around the same rate, that should tell you if you've an underperforming cylinder. Certainly sounds like it could be running on 3 most of the time.

So I started it from cold and kept feeling the headers, or what I could feel of them, All of them heated up pretty quickly.

So I suspect they're not the issue?