cuprabob

Hi any ideas welcome this is just a new cosworth i bought it has a msd chip with there wasted spark all new 3 months ago the multi plug has been cut out and soldered the engine and the ignition have been earthed still the same what happens is it works fine untill the car starts to boost up and the counter stays the same or drops back come off the power and it jumps back but if you rev it slowly it works fine and some times when you start it you have to bump the dash to get it to lift i have still st strip the speedo out and check for loose plugs but any one seen this before please let me know