NC24 1987 BAD RATTLING FROM REAR CYLINDER HEAD

[CMSMJ1]

Rumbly is normally the big ends isn't it? Not good..

[pagan1001]

No did them with feel gauges. The noise is coming from cylinder 3 and I have rechecked the timing it is not that. Could the valves be bent or damaged on the head I put on as that is where the noise is and that is the valves I had bother with in doing the clearances. If I go to the other side of the bike and listen it sounds great but walk round to the right hand side and the noise is from that set of valves only. Tomorrow I am putting my old head back on to try and eliminate causes. If not that then I will buy a second engine to get me around and strip the shit out of this one and rebuild it as new. cheers

[pagan1001]

Got it!!! the copper and rubber gasket for the rear exhaust was really badly worn so have them replaced and fired her up a little while ago and she is running and sounding great. Its a lot of work for a little thing like that. But its great can get out on her tomorrow cheers guys.

[pagan1001]

Hi again lads. Hope some of you have encountered this problem and can solve it for me. When I hit 115 or 120 it is like she cant go any faster but there is plenty power left so I reckon there must be a restrictor. I have checked the carbs and nothing but when I opened up the speedo there is a thin metal disk that is attached to the speed wheel/disk and it goes in between two metal bars/blocks. So when you hit that speed it must lock the speedo thus stopping the bike from going faster. Can I just remove this thin strip of metal or even just put insulating tape around these metal bars/blocks to stop them magnetically sticking to the disk????????????????????????????????????? All I can find is some guy in Hong Kong selling after market black boxes (CDI) for £75 but he says this will do away with the restriction and also give better timing and a more powerful spark as well as more BHP and revs. But my bike is fine and I dont want to spend that much money on some thing that may be an easy fix. So if you can help me out on this I would be most grateful Iain

[Old Painless]

Hey fella, i have that same disc in the clocks on mine, i have taken it out of the clocks and reconnected it, i have been told it is only to bring on the 80 KPH warning light on the dash. I haven't done a high speed run yet so i dont know the exact truth of the matter.

[Neosophist]

Hi again lads. Hope some of you have encountered this problem and can solve it for me. When I hit 115 or 120 it is like she cant go any faster but there is plenty power left so I reckon there must be a restrictor. I have checked the carbs and nothing but when I opened up the speedo there is a thin metal disk that is attached to the speed wheel/disk and it goes in between two metal bars/blocks. So when you hit that speed it must lock the speedo thus stopping the bike from going faster. Can I just remove this thin strip of metal or even just put insulating tape around these metal bars/blocks to stop them magnetically sticking to the disk????????????????????????????????????? All I can find is some guy in Hong Kong selling after market black boxes (CDI) for £75 but he says this will do away with the restriction and also give better timing and a more powerful spark as well as more BHP and revs. But my bike is fine and I dont want to spend that much money on some thing that may be an easy fix. So if you can help me out on this I would be most grateful Iain

The NC24 was 100% NEVER restricted on Speed. The law was later changed so that later bikes like the NC30's / ZXR400's were limited to 180km/h

That disc in the NC24 puts the 'speed' warning light on when you reach 80km/h.. this was the maximum permissible speed a motorcycle could legally travel at during Japan at the time these bikes were manufactured. (this has since changed)

I don't think theres any implications of removing it but all of my 24's still have it connected.. there all unbutchered, unmolsted fresh jap imports.. bar 1 of them that had been pissed about with silly by uk people, but i've since put it back to stock.

Standard loom / gearing (15/45), Stock carbs / jets (115's all around) / Stock airbox filter / plugs / wiring loom.

All of mine top out at 135ish.. but I'm just under 10 stone.

The only things that spring to mind are.

They'll top out at 115 - 120 with a heavy (+12 stone) rider on them.

Is your gearing standard?

Has anyone in the UK put carb restirctors (33bhp) in it?

Carb / Air problem.

It should pull to the red line in 6th (as all of mine do) which equates to roughly 135mph

Watch this video one of my friends made.

http://www.youtube.com/watch?v=8ODFsHigOXU#t=1m14s

It starts with the bike 180km/h.. then shows you it rev to the rev line in 6th :-)

[pagan1001]

Maybe the carbs do need balancing am just waiting on a special screw driver coming so I can reach them so will check that out. I have been through the carbs looking for these restrictions but they are fine. I just find it weird why this disk and metal bars/blocks are there if it is just to flash a light when you hit 80 there are simpler ways to do that without resistors, metal disks and bars/blocks. Cause when I hit 115/120 there is plenty power left in her she could go to 130 I reckon but something stops her going that extra bit. Some guy on ebay is selling cdi boxes that do bypass the restrictor so if it does not have one why would they be getting made for the nc24????. Or is this a con??? It is very confusing as some people on different sites say they are restricted then on here they are not. But I have to say I do trust your word as you do know your stuff when it comes to the nc24. Or could it be that your nc24's already had them bypassed???. I have looked for this light when you hit 80 but I do not have it. My bike is running as good as ever and does hit the red line in every gear but in 6th it does not it stops short at 11 or 12. But you can feel she wants to keep going. Thats the only way I can describe it. I am going to buy one of these new cdi boxes and give it a try as the guy said if you dont notice an improvement I can send it back. Or could it just be the box that is on my bike anyway as I have heard they are prone to faults and not very reliable at all????. But I will take your word on that as you have had many nc24's but I will let you know if this cdi box does make any difference at all. Cheers for the info on that. Iain

[pagan1001]

Alright guys! I just found this on the web infact there are a load of these flying about but I dont know if it works as I cant even budge my bars/blocks so they cant be moved unless I was to desolder them and remove them from the circuit board. I am so bloody confused by this are they or arent they restricted????????????????????????

In standard trim an NC24 was restricted to around 111 mph or 180 klicks :-
The restriction is controlled by a sensor in the speedo, which can be circumvented fairly easily.

* First remove the speedo assembly - two bolts, speedo cable and the two connector blocks.
* Remove the cover from the speedo - Lots of black posidrive screws plus the odometer knob. This is held in place by a tiny posidrive screw in the end, which is normal ......
* Remove the speedo unit - undo 4 silver posidrive screws at the rear of the assembly.
* You should now be able to see the sensor. It is a cam shaped disc attached to the speedo drive, which makes contact with a metal strip (you will see its connected to one of the two wires that come in through the back of the speedo) at the magic 180 klick mark. All one needs to do is bend the strip out a tad so it doesnt make contact with the disc and snap ..... the bike is derestricted.

You will also see that the two wires entering the speedo are connected together by a resistor. This is just to tell the bikes electrics if the sensor has been disconnected, and if it is not in the circuit causes the bike to misfire above 5500 rpm.

Disclaimer: This work if tried is entirely at your risk

[CMSMJ1]

Those CDIs are just shite..don't bother.

I'd agree with Neo that these should not be limited,m but if they are, in the same way as NC30s etc thenm you need a resistor in the wiring to fool the CDI into thinking the speedo is not registering any high speeds.

Have a quick search for resistor mod, or PM Leopard Pagan - she makes kits...and sells them on ebay if you must!!

£75 wasted if you buy that CDI...

[pagan1001]

Cheers for that will check out this resistor kit! Here is another I found on the web there are loads of people on about this. But this resistor kit sounds like the best advise yet am going to look for this just now cheers for that.

Ian Daly
Son of Arthur

Join Date: 27-09-02
Location: On t'hill in Kingston
Posts: 3,748
Hi.

It depends on the type of restriction, the one that limits power to 12kW (33bhp) is a restricting washer sat in the rubbers that connect the carbs onto the inlet throats, take off carbs, take out washers, replace carbs to find bike de-restricted.

These bike however, can be restrictred by a speed limiter (for the Japanese market, to roughtly 118mph), this involes some contact in the speedo unit. Once it reaches the limit speed the needle or whatever gives a connection and the two rear cylinders have their spark cut. There are a couple of way to stop this, but let me know whether it's the restriction or speed-limiter that you're having difficultly with.