Only burning nitro with less than 20% methanol will leave any nitric acid. And even then it disapates and burns off on its on. That is the reason the dragster racers have built in filters with acid neutralizer in their helmets. If the nitro percentage is high enough to have huge flames from the headers you probably have some nitric acid. Such as with the dragsters and funny cars. But the nitro motorcycles use much less nitro and have no flames. The nitric acid will be neutralized from the hydroxide (HO) left from the methanol exhaust.