I have a 68 AMX 390 that has been in storage for a couple years. Tried starting and it turns over, fires up briefly and runs for about 30 seconds and rapidly shuts off. After a couple times, it now just turns over and won't fire. It ran just fine before being put into storage. It does have a Mallory HEI distributor that I think is the issue. It has a brand new carburetor and fresh gas. Any ideas?