These particular engines had low compession and they had this particular problem right from the factory. So with this said When I got mine which is used had the exact same issue. The problem is to cold a heat range on the spark plugs, mine came came installed with from the previous owner with champion r12yc spark pugs which is actually one heat range hotter then the r11yc recommended by the factory, I went to Oreillys and they sold me champion r14yc spark plugs which they assurred me were now the correct heat range. Shure enough the truck now performs flawlessly. I also after driving it for a few days pulled one of the plugs just to see if their were any heat related issues with the plug and the plug looked great. By the way this truck I'm discribing is a 1983 royal 150 has the 318 with 2 barrel carb with 77,000 miles very clean 2 wheel drive.