MOTOR LOSES POWER AT 8K all fresh WHY??

OK, got a 1428cc 14:1 comp dragbike .460 and .480 cams, HD valve springs. Bike was run last week and 60ft 1.24 steady w a 1/4 et at 9.05. this week put a 36 rear sproket on instead of last wks 38. ran fine the first couple passes. Then I belive he overrevved it but am not sure. Now it 60ft 1.30 and 1/4 et is 9.50. So, It still pulls hard to 8K or so and then noses over like its losing power. Checked the compression and its strong- no bent valve. Next checked the timing and the static timing and they are on. So what happened to this thing that is causing it to lose power?

If I was to take a total guess, I'd say it was either fuel starving or maybe weak valve springs letting the valves float at high revs.

are you running a fuel filter, it may be slightly obstructed, also check the vent on the tank

what are you running for ignition?does it have a chip built into it for rev limiter like msd?;)does it piss and pop above 8 grand or does the power just start tapering off gradually?

did you check valve clearances? i would still check for a valve problem. did you do a leakdown check or puff?

well any updates or more info for us?

Its got an Dyna 4000 ignition with a built in limiter. Also, it doesn't piss and pop it just loses power at 8k. there is not fuel filter on it, its got a back bone fuel tank thats feeding the lectron carbs. I can't see any obstructions in the fuel lines. Tha fuel cap has never given a problem before and neither has the petcock which is a pingel dual feed drag model. checked the comp and they all have it so, No bent Valve? and the springs never gave any problems before unless they were damaged when he overreved it?

what is the limiter set at,im wondering if that gear change didnt push you into the rev limiter without your knowing it?ive got a dyna 2000 somewhere still in a box ,ill see if i can dig it up

The limiter is set at 11000 but who knows what it truly is with that ignition. Also, I have my personal set with one at 10500K and a second at 12K. I've seen these things turn 12 and run fine if there built strong. the bike owner bought the ignition used so I can't be sure of anything on it although i've only ever had trouble with Dyna S ignitions. i would imagine this thing def. bounced of the limiter if it worled otherwise it surpassed it by god only knows what. any Ideas what got tweaked when it was overreved to cause the power loss at 8k?

those roller bearing cranks dont like spinning much over 10,000 but 1/4 at a time aint much of a problem i guess.anyway see it will pull an harder than 8000 with the bike in neutral with a fan blowing on motor of course with no load on it,then check where the ignition/rev limiter is set at.if it still holds back throw a dyna s on there just to see if there is any differance.electronics are really tempermental creatures in my experiance :S

Thanks for the info plummen we're going to test and tune wed. so im going to play with it tomorrow and hopefully wed. I'll let you know what I find. :woohoo:

HERE'S AN UPDAT :ohmy: What happened; the bike was definately overreved and the previous mechanic didn't tighten the cam gear bolts enough hence, the cams twisted and through off the centerline. When I checked the centerline it was dead nuts off at 125 on the intake and 88 on the exhaust So I redegreed and made sure I tightend the bolts the bike should be ready to rock, didn't get to race yesterday as we had bad weather hear so we'll try again friday night. I'm still going to test that 4000 ignition b/c I don;t think it limited. Thanks, for the help guys!