NC29 Running problems

[Paul&Jax]

Hi all again,

Have been doing up an NC29 for a while now and just finishing it, it starts well and sounds great on tick over and also when riding at low to medium revs but when i open it up it runs very spluttery have had the carbs apart and cleaned, have got new plugs as the old one were stopping it starting, it does poing to a possible fueling problem but where?

[greggo]

Check:

Fuel flow at the fuel tap, should be pissing out, not dribbling out.
Fuel flow past the fuel filter, should have a stead stream.
You could also check your fuel pump is pumping a good flow of fuel too.
(lots of fun, garage will smell like petrol for weeks!)
Carb breather hoses are not blocked, that will prevent the carbs filling properly.
Check your carbs are sealing properly on the engine rubbers and haven't pinched or folded them letting air in.

Check your battery and charging circuit are all okay. Spark might be getting weak if it can't generate sufficient power to run the engine (bit unlikely unless you have a duff battery AND charging circuit but you never know).

If the bike has been sitting a while the tank and fuel filter will catch a lot of dust and cr@p, that would be one of the first places i'd look.

[Paul&Jax]

hi greggo,

Thanks for the reply, fuel is supply seems ok, have fitted a new fuel filter so eliminates that one every time i've have the carbs off the float chambers have been full, so getting into there ok, have new iridium spark plugs and starts on the button,
here's one i thought of, it seems to go flat above 6000rpm on average could this be some sort of restriction, have checked the inlets and no restriction washers there and the carbs look standard but is there any other type of restriction placed on them?

Paul

[leopard_pagan]

"it seems to go flat above 6000rpm on average could this be some sort of restriction"

you have hit the nail on the head there m8.
check the main fuse box for the fuse to the dash, is it blown?
have you left a plug off behind the speedo/dash? if so plug it back in to the speedo.
when i get home i can tell you which wires you need to check the condition of at the ECU/CDI unit, if they are cut/broken it will also cause this.

was there a small black box fitted behind the speedo or at the ECU?
there is a kit you can get to sort this out, a DIY version or full kit with parts.
link below explains the restriction...
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... 0256673308" onclick="window.open(this.href);return false;

[Paul&Jax]

can't see any black boxes, but its not a speed restriction, its seems to be a rev restirction, i.e. after 5000rpm theres nothing! could it be the ECU? or are there rev limiter devices? what does the 33bhp restriction do?

[leopard_pagan]

did you read the link?

it IS a speed restriction thats put in your speedo in Japan.. at 112mph there is a signal sent to the ECU/CDI unit to cut 1/2 the spark plugs.....

*IF* the power is disrupted feeding the sensor in the speedo and IS the result in your current problems. the CDI unit is NOT receiving a signal that all is ok and automatically cuts 1/2 the spark plugs as soon as you get to 5,000RPM.

[Paul&Jax]

i have just measured the out put of the restrictor circuit inside the speedo(there was a bit of water damage on the PCB which i cleaned) and reference earth i am getting just over 11V moving the speedo needle so the disk goes through the opto coupler has no effect on this voltage, i am assuming that as i have a voltage on the output of the 'restrictor' pcb that this is correct????

[Paul&Jax]

Bypassed the restrictor circuit by putting a resistor accross the outut of the circuit and IGN live, and stiil have problems! low down the rev range great but after 5-6000rpm shit! don't want to spend a fortune on an ECU if its not faulty, any ideas anyone????

[leopard_pagan]

ok as it sounds like you know what bits of a PCB to poke.... i will PM (think i can attach a file) you with the DIY instructions for by-passing the speed limiter.

[Paul&Jax]

have just tried a different ECU but this has had no dramatic change in the bikes performance, it seems to be getting to slightly higher revs now but still struggling when past 6000ish. Anyone with an NC29 local to me in Farnborough hants? Am running out of ideas now could use devine inspiration