the old race bike has been giving me the absolute shits. it hs been breaking down through croner to the point where i have to ride off the track once shut down it starts up and runs normally. about the bike standard engine cv carbs have tried main jets 115 120 130 wil test 130 in the morning float hieght 7mm running 98 ron fuel have tried derestricted cdi stock cdi with m deristrictor. new leads fitted coils meter out primary and sec windings pick ups meter out ok new battery running solid state fuel pump through secondary filter. have wasted three race meets now and desperate for sound advice and guidance.

leithncbr400 wrote:the old race bike has been giving me the absolute shits. it hs been breaking down through croner to the point where i have to ride off the track once shut down it starts up and runs normally. about the bike standard engine cv carbs have tried main jets 115 120 130 wil test 130 in the morning float hieght 7mm running 98 ron fuel have tried derestricted cdi stock cdi with m deristrictor. new leads fitted coils meter out primary and sec windings pick ups meter out ok new battery running solid state fuel pump through secondary filter. have wasted three race meets now and desperate for sound advice and guidance.

Sounds like the carbs are running out of fuel to me. Is the secondary filter standard? If not get rid of it. Are you sure the pump's running correctly? What pump is it and is it running as per the standard relay setup? Are you running the standard fuel tap? It's better to remove the internals and fit a dry break connector, they can stuff up.

Have you tested the electrical system (stator, reg/rec etc)? They're a known weakness.

If you go through and test all possibilities you should be able to diagnose the issue.

Did you ever get to the bottom of the problem?

Nick is obviously being slack with replying, so I'll let you know what ended up being the cause of all his issues. Last August we were racing at Broadford (just north of Melbourne) and he was struggling to get the damn thing running first thing Saturday morning. He worked out the standard fuel pump didn't want to cooperate and thankfully another mate had an electric pump he'd purchased with the idea of exploring a ram-air option on his NC30. Since he had it with him he gladly let Nick use it to get his bike running.

Finally got the bike out onto the track but as soon as he pinned it down the back straight one of the pistons decided to say hello, rather intimately, to one of the valves, ending Nicks weekend (the head looked like someone had used it for shotgun practice!). Once the engine was replaced the issue that was discribed in the OP reared its ugly head, denying him of several expensive race weekends...not a happy boy!

After a bit of experimentation he found that with the tank and airbox removed, fuel would start pouring out of one of the overflow tubes, or breathers (I can't exactly remember) everytime the bike was leaned over and the engine would stall. He ended up removing the fuel pump and just using a gravity feed system which solved the problem.

Upon further investgation it was found that the electric pump had a flow rate of 4.8l/m, when the standard pump is only about 600ml/m. Suffice to say the poor little engine was drowning (not 100% sure of the exact reason, Cammo would probably be able to explain it a lo better?). He's since installed a standard OEM pump and hasn't had any problems since...until he tries his greasy hands at some more mods

thanks for the response j. slack busy on the next project nc 29

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