Argh, my girlfriends nc30 is giving me too much stress!

Been having a few running issues for a while, but recently its gotten unbearable and with a french trip coming up its time to get it sorted right!

Ran ok lower down, but around 10/11/12k rpm was very hesitant in all gears.

Now I had a play with the jetting last time and moved from 112f and 118rear to 118 front and 120 rear. Seemed to clear it up a bit originally but its gone poor again. (bike has got a full race system fitted)

Thinking of what could get worse with mileage, bar the usual air filter etc (has had new filter and plugs) was valve clearences.. Soo set about sorting them, about 5 were too tight, one had no gap at all! I had them grinded down (tightarse) to the correct sizes, fitted them, checked the gap and all was good!

So, put the bike back together and go for a ride.

1st gear, hits a brick wall at 11k
2nd, 10k
3rd, 9k then refuses to go past 8 in the lest three gears.

If I back the throttle right off it will pull past it but any more than 1/3rd and it refuses to rev

Have removed the airfilter, no change, removed the inlet trumpet from the airbox, revs a bit higher and will pull through on 1/2 throttle just about. I was wondering if it had suddenly started running rich after the valves were set at the right gappage?

Plugs are quite dark too...

I'm thinking of going back to std jetting but am worried about running lean with the exhaust system.

Could it be an ignition problem, I did try disconnecting the speedo cable just in case but that made no difference.

Thinking maybe leads? They are the original items.. could be dead by now I suppose?

Any other ideas, very gratefully recieved!

Paul

114 front and rear mains, seems good now! not sure if its lean but will look into it more

Judging by your symptoms, and how it is affected by the load on the engine (gears), your problem is probably related to induction and airflow. The main jets will be adequate, and won't be responsible for any symptoms you're seeing.

Sometimes the best way to sort these sorts of problems is to return the induction system exactly to standard, and start from there.

Make sure you're using a a factory (paper) filter, airbox is standard, airbox snorkel is in place, and front flap is present in front of the airbox. As many peeps will know, changing just one of these things can have a dramatic effect on the way the bike runs.

Also check that the reg/rec output is adequate (should be over 13V at 5000 revs). Check that the fuel vacuum line is working properly also.

How is that flap supposed to sit really? I have forgotten...

I mean the thing that attaches to the metal cross bar and has two rubber flaps.

I fiddled around with my flap today... referred to some pics in the haynes manual where you can see it in the background so im not sure if its right, but it seems pretty good...

The round clips go onto the crossbar around the back and over the top so that the solid plastic bit goes forward towards the front of the bike... this should hook over the top radiator and the ridge in the middle of it should be reasonably close to the underside of the headstock! Therefore any air in the front will either go into the rads or up this scoop thing! This hard plastic thing also has 2 rubber seals on the sides which should go against the tubes of the main frame as they separate out from the headstock. The larger rubber flap from the bottom goes down and rests over the top of the front cam cover so that it heads towards the inside 'V' of the engine with all the HT leads and wires etc underneath it. The smaller rubber flap it held onto the top of the hard plastic bit and also goes towards the back of the bike in the same direction as the larger rubber flap and simply rests on top of it... therefore some of the air will flow between these rubber flaps and go through to the V and cool the bottom of the carbs, and the rest of it will go up into the headstock, round the rubber on the front of the panel on top of the carbs, and into the snorkel of the air filter housing intake!!! Phew

I think thats right... please feel free to correct if anyone knows any better, but as i say i got that from some vague pictures, and bit of intuition and a big helping of guesswork :D

Matt