Flatslide Jetting?

[Sorelegs11]

I hope that this one has not been covered before but after 2 hrs of looking I cant find anything.
I was running a flatslide carb on my yam490 last year at the nepean charity meet and the engine nipped up after about 5 laps at the end of the straight.
Totalled the piston, the bike was crisp and smooth with the carb so I am keen to give it anothr go.
I have an idea that the standard fuel tap was not up to the job, have fitted the YZ item and did a flow comparison and got abuot 30% more fuel flow.

I was running a 60 int and 400 main and have got my hands on 3 new needles, the needle jet is the same as stock.
Does anyone have any idea on a jetting set up with the mikuni flatslide for a 490  that won't cost me another piston?
Thanks Sax

[GD66]

  I have an idea that the standard fuel tap was not up to the job, have fitted the YZ item and did a flow comparison and got about 30% more fuel flow. 

Good idea, but your fuel tap only has to have more flow capacity than your mainjet so it's unlikely to be the culprit, more likely to be the jetting as you suspect, but in reality on an mxer you don't spend much time on the mainjet compared to a roadracer, so your much-overlooked needle and needle valve are very important to get right as well.

[Brian Watson]

I wouldn't be suprised if the engine doesn't have an air leak..... goes OK until the 5th lap, when , the engine is probably at it's hottest.... bingo....starts sucking air..making it too lean ..and... the piston is suddenly too big for the bore...!! I would also do a leak test...

[Sorelegs11]

The bike iis being used for dirt track and is running flat out a lot of the time.
As far as a leak goes its been 6 months since a top end rebuild and i have done quite a few laps since then without any problems using the round slide carby, I am just looking for that little bit extra.
Thanks for the suggestions.

[Lozza]

You have a jetting issue,or if it happen recently the engine could not get rid of the heat generated and detonation set in, a common thing with air cooled, they always seize at the end of the straight.

[oldyzman]

A fellow i know had a similar problem recently, after pulling his hair out for weeks he realised that the new carb which hed had purchased was setup for a snow mobile which uses a fuel pump and although all of the jetting was the same the needle and seat was much smaller and once he got half way down the straight at nepean it was starving for fuelhad. he put in the old needle and seat and all sorted. By the way the carb was purchased from an aust mikuni distributor.
Brett