essexmale2k

new piper cam bein fitted to my xr3i mfi cab, wiv sprigs and follower, cam run brill untill i hit 5,000rpm and it starts missing and then if u let off it runs on 3 cylinders for a moment. The timing is fully set up, new dizzy, new fuel filter, all norm things have been done, bottom end is soild and fuel pick up filter now bein cleaned. any ideas any 1. thank you

adduk

did you run the cam in properly.? My own experiences with the piper cams are that if you dont they last hours rather than years,

essexmale2k

well i got told it was ran at 2,500rpm for 20mins, i was thinking maby to sum how uprate the injectors mite be the prob now

Icurus

I'd do a compression test to see if a valve is not bent, as you may have the timing out slightly

dave81xr3i

I had the same problem its the valve springs what you need is to measure the length of the valve spring when valve is fully open the take out spring put it in a spring compression tester and wind it down to exact hight as in car then take note of the pressure thats needed to compress that far it should be around 180 psi if not you need to shim the spring seat to increase the pressure i had to use .60 inch whats happening is your getting valve float !!!!!!!!!!

tabetha

I'd be more tempted to check for coil binding first.
I've used piper and Kent for years, the kent do run in easier due to the phosphate coating they have, as it retains oil better, but after 20 mins should be fine, if it is allowed to idle for any length of time before this it can wipe the nose off the lobes.
That is why I always try to use regrind rather than new, as it is already work hardened metal.
tabetha

Paul Eggleton

Aside from your horrendous internet wording, have you double checked the dizzy? It MAY BE new but it's very easy to put a nick in the wires. I did this on a brand new CVH build many years ago.