Bike slower when up to temperature, faster when cold.

[racefactory]

Hey guys,

It's not a problem as such, but I have noticed that when my NC30 is up to temperature (85 onwards) it is slower at the low rpms. It just does not have that punch and the front end doesn't quite feel so light under full power. Sounds slightly different too, maybe a tad more 'boggy'. I'm not sure about the difference over 10K rpm though, think it's fine then.

This is not to say that I full throttle it whilst completely cold but once it is at 70 degrees (gettting warm) it definately has more punch and power at the lower rpm ranges. It's no problem as such, but it's enough so that when its in the 70's... it really makes me smile under full power, not so much when up to temp.

This bike has had ER10EH plugs instead of ER9EH plugs. Last owner said it's better for high speeds/high revs. That's all I can think of mechanically.

It is the 92 model so bigger jetting from the 89 model.

Any idea what I can do?

Sounds like jetting/carb thing... but I won't say any more. Air filter? Shit I don't know...

[CookMySock]

This engine is EFI ? If it is, then will will be richened right up when its cold, and leaned out as safe as possible towards stoich when its warm, for cleanliness and economy. So yeah you are probably right - maybe its a little lean.

IF this this the problem, you can put a variable resistor on the water jacket temperature sensor and 'fool' the computer into thinking it's colder than it really is, and it will keep it slightly richer for you. Of course you could fuck the engine completely playing with this stuff too, so YMMV.

My ol' skyline was the same - bags of omph while she was warming up and a little laggy while warm. It had a worn throttle body - was leaking air in around the spindle, so maybe you have a similar leak. It also had a big dead spot when warm.

Alternatively there might be a simple fault elsewhere.


DB

[Tank]

This engine is EFI ? If it is, then will will be richened right up when its cold, and leaned out as safe as possible towards stoich when its warm, for cleanliness and economy. So yeah you are probably right - maybe its a little lean.

ummm - if its being 'leaned out towards stoich' then its still rich - you have to have a mixture that is GREATER then stoich for it to be lean.

Dangerous mechanic...

[racefactory]

Lol. No don't think it's lean. Boggy acceleration is not a sympton of lean mixture as far as i know.

No it's not fuel injection it's an NC30.

Thanks.

Another thing to note- when it's up to temp, when you slam on the throttle full blast it is worse, engine note changes to a more burbling, boggy kind of sound. If you roll on the throttle, it seems to be better, still not the best but bit better. So basically you just can't make the revs climb too fast otherwise it will go rich.

I think i've pretty much answered my own question in terms of what's wrong? But it's just a stock bike, what could be causing this?

I've never looked at the air filter, and they are harder than most bikes to get to (like every simple maintenance task on these bikes) so that's why. Don't know if that could cause this though as when it's getting warmish it goes liek hell.

[mowgli]

Another thing to note- when it's up to temp, when you slam on the throttle full blast it is worse, engine note changes to a more burbling, boggy kind of sound. If you roll on the throttle, it seems to be better, still not the best but bit better. So basically you just can't make the revs climb too fast otherwise it will go rich.

Sounds like an ignition timing issue to me. When you open the throttle rapidly the timing should advance. I expect the NC30 has electronic ignition so check the wiring around the carbs and inlet manifold. You might find the plug to the vacuum sensor or throttle position sensor is loose.

[riffer]

Sounds like you've got worn jet needles.

[racefactory]

ok took the air filter out and had a look... doesnt look that dirty to my eyes but it's the first time i've seen one anyhow. Don't understand how the machine can actually suck any air through that series of sponges though. Don't know how much oil is supposed to be on the sponge either. Shall I try running it with only the little sub air filter element in place? Shall I just put some pantyhose or something over the main air filter gauze and run it as opposed to having that thick sponge blocking the air and see if that makes it better?

I don't understand how it's electronic issue as it goes like a raped ape in cold weather/ warming up engine temperatures.

needles- yes well the problem is at low rpms, suggesting the needles but then again... it runs like a raped ape when it's cold and wouldn't a worn needle jets be shitty when in colder temperatures too?

Surely it's to do with air flow since air is less dense when warm?

One thing to remember here is that it's not exactly a problem in a 'problem' sense lol, it's just something i've noticed... it still goes like mad when it's warming up. It's just I only get, say 10 mins of real good fun before it gets slower and less punch.

apparently fuel tank breather can affect mixture, is that true? What if i run it without that?

[mowgli]

I don't understand how it's electronic issue as it goes like a raped ape in cold weather/ warming up engine temperatures.

Resistance increases with temperature. If a plug is only making partial contact then there might be little effect at colder temps but as the engine warms up the resistance across the partial contact might override the resistance in the sensor.

[racefactory]

Shall I try running it with only the little sub air filter element in place? Shall I just put some pantyhose or something over the main air filter gauze and run it as opposed to having that thick sponge blocking the air and see if that makes it better?

apparently fuel tank breather can affect mixture, is that true? What if i run it without that?

Please! Have no idea if it's that bad to do that or not..

I've also learnt that there is absolutely no way for cold air to get into this air box on these! There are no tubes or any passageways to feed fresh cold air in. The intake for air filter is in a little enclosure where i presume it's just going to to be sucking in all the really hot air that these bikes produce in the frame.

I've seen a lot of bikes have pipes from the front or some sort of ram air system. Surely i'm not the only NC30 owner who's seen this performance drop then?

[hayd3n]

clean your plugs give it a oil and air filter change

[lostinflyz]

two things. those #10 plugs will foul out in about 30 seconds. there absolute cunts. ive gone through about 4 sets on my race bikes and there crap. use the 9's when u replace them.

sounds like the carbies are outta synch a bit. my old nc30 used to struggle like a mad bastard when u cracked the throttle fast. either that or you may have a slide thats sticky or not working properly.

best advice is check/clean/change the plugs and see how she goes. if that fails a big ol carby clean and synch session is in order.

another thing. why do you have 2 air filters???

anyway cant see a fuel breather effecting mixture outside possibly causing fuel stavation but thats not a mixture problem.

the stock airbox is pretty crappy but playing with it can be alot more pain than its worth. HRC did a scoop that collected air from forward of the top radiator but its not really ram air. just remeber that these vacuum carbies are a weee bit picky about air flow and all the like. but anyway drifting off topic.

[racefactory]

two things. those #10 plugs will foul out in about 30 seconds. there absolute cunts. ive gone through about 4 sets on my race bikes and there crap. use the 9's when u replace them.

sounds like the carbies are outta synch a bit. my old nc30 used to struggle like a mad bastard when u cracked the throttle fast. either that or you may have a slide thats sticky or not working properly.

best advice is check/clean/change the plugs and see how she goes. if that fails a big ol carby clean and synch session is in order.

another thing. why do you have 2 air filters???

anyway cant see a fuel breather effecting mixture outside possibly causing fuel stavation but thats not a mixture problem.

the stock airbox is pretty crappy but playing with it can be alot more pain than its worth. HRC did a scoop that collected air from forward of the top radiator but its not really ram air. just remeber that these vacuum carbies are a weee bit picky about air flow and all the like. but anyway drifting off topic.

This is the kind of answer I'm looking for- thanks.

Thing is, my idle is very smooth, the engine sounds smooth and solid... I've heard that when carbs are out of sync the bike looses that. The bike feels nice and solid still... just not as powerful.

For how much it costs to sync the carbs, I don't think it's worth it if the cause is not confirmed... i got quoted for absolutely hundreds of dollars...

Maybe i should squirt some of the ''carb cleaner'' down the air intake holes??

Anooying me more day by day! Keep it coming guys... cheers.

Also... what do you mean exactly by 'foul out'? I don't have any miss fires or any trickery with them as far as i can tell.

I don't have a fucking tool to get the spar plugs out which is very annoying... my standard spark plug socket does not work on these tiny fuckers. Anyone know what size socket i'm going to have to fork out for?

[quickbuck]

Getting a carb balance is always worth it.
Will cost a little bit, but at least all 4 cylinders will be doing the same thing once it's done.

Not sure of your plug size,, sorry, but as said, get rid of the 10's asap. They are way too cold.
It could be even a case of one fowling after a period of time that is causing it to be sluggish when warm....

[lostinflyz]

you can synch the carbs urself if your patient (or cheap)

those 10 plugs are a nightmare,they work for a while but they certainly dont last.

that carby cleaner shit is pretty useless. you really gotta pull the carbs and properly clean everything.

cant rem the spanner size (maybe 3/4"). theres a nc30 tool kit online cheap thatd prob be worth it.

[racefactory]

oh shit forgot about the tool kit i've even got it!

yes carb sync,.. i was talking to a guy who said that may well be it. I tried at honda and they said something fucking rediculous like 800 bucks...

where shall i go to get them synced?? Can anyone here do it for me (paid of course) ?

Yes thanks for the advice i shall have to get some 9's...