The Stovebolt Site Forums The Shop Area Engine Shop Erratic Engine Idle

I've seen some of the YF models with .008" warpage gap between the 4 screws. That's pretty severe when you total up the area from all 4 sides. It is like having another (and unregulated) jet feeding fuel into your manifold all the time and it definitely will allow your fuel bowl to drain into your manifold when your engine is off. Please look also at the gasket between your float bowl and your throttle body (image attached). If you're suffering from the warped bonnet problem, it is likely you'll see that gasket looking wet pretty much all the time. In worst cases I've seen fuel run down the side of the throttle body and onto the heat spacer (as you can see it did in this case). The bonnet gets warped when somebody overtightens it and I've even seen one YF which appeared to have only been used a brief while...basically brand new. It suffered a manufacturing defect that was not caught by the assembler. There was a casting lump on the bottom of the bonnet which prevented it from sealing and had caused the rest of the bonnet to be warped when it was assembled. Good luck.