www.zxrworld.co.uk

Hi there, new to this site so if possible give me some help. Have a 'Hot Start' problem with my race bike. Starts from cold fine but when pull in after race for tyre check etc it will not start.

H model with L engine and SP cam. Everything looks ok on dyno carbs and power good. Running mid range Spark Plugs NGK CR9EK.

Have heard this is a common problem when the SP cam is fitted and not much you can do about it!

Any ideas greatly appreciated.

It seems common on standard engines too, a few peeps here have had that problem, but it does seem few and far between.

I think the general solution was to let the bike cool for a few minutes and it starts fine.

zxr's 400s and 750s were known for hot starting problems, as robB says leave it to cool for a few minutes but i guess you don't have the time whilst racing?

Thanks guys, looking for something more tech like valve expansion and lack of compresion when hot etc!

Bike needs more than a few minutes and needs to cool down completely.

Thats about a techy as we get on this subject cos thats all we know

I think there was some ideas about it being something to do with the carbs. I guess hot carbs might have summit to do with it?

Could be, as thermostat and cooling fan removed. The bike runs at normal temp when racing but heats up v-quick on cool down lap. Possibly fuel boiling.

that was the problem, the engine gets hot and evaporates the fuel in the carbs, are you using ram air?

No, Sports Production rules does not allow Ram Air !

you need to direct more cold air towards the engine which was the original purpose of the hoover tubes, just too much may cause the opposite problem of carb icing, does your bike have the heater tubes running beneath the carbs?

No, found them to be restrictive on Dyno and more BHP without!

I would up my spark plugs to CR 10 ngk and also it has nothing to do with the cams its the way the engine has been tuned

Take a cooling fan to the race track that will sort that out and aim it at the rad

Good luck

Sloweracing click on link below

Try a bit choke, if it still has the choke cable running, about a third or a quarter, if it fires up a new set of carbs or a carb repair kit. Is it flatslides or is it an H1 with normal CV carbs?

Not losing any coolant are you?

Been down the Spark Plug avenue tried 8,9 & 10.
With 10s it is better but will not start from cold atall.

Stil running CV carbs!