Part way there to finding cause of missing. While changing the plugs, noticed soot on the outside of EVERY sparkplug. Also found one wire with damaged boot that was jumping to block. Took the plugs to who set up my carbs to let him read the plugs for the fuel mixture. First thing he said is "you have exhaust leak blowing on every plug".

Taking EMI exhaust manifolds off tomorrow and checking to see if manifolds are hitting the head bolts and not allowing the exhaust manifolds to mate properly. Anyone else with this experience? Grind the manifold for fit around head bolt?

Did you use the bolts that came with them? On my Imco exhaust the bolts were too long they would bottom out but manifold was slightly loose.I just put an extra washer on each and it was fine.

Who installed the manifolds? When the engine was first started with the EMIs, you would have heard loud popping if there was not a good seal. Were new gaskets used and were the old gaskets removed fully and the block surface cleaned well? Also did the EMIs come with new bolts and were they torque correctly?

Thanks

This could be the problem because the leak has caused such uniform soot on all 16 spark plugs. Engine builder said they don't use gaskets, but rather high temp RTV. He suggested bead of RTV on both sides of the gasket when reassembling. Going to buy 16 washers, can't hurt! Hope not in conflict with head bolts.

I installed new EMI with hardware and gaskets that came with exhaust on the clean surfaces from the engine builder. Torqued them too.New motors (rebuilt) did smoke slightly in engine compartment but no popping. I thought nothing of the slight haze in the engine compartment. Thought probably new paint baking off. Hindsight(25 hours run time later) haze was the exhaust leak.

The only reason I found it on install is when I tighten the bolts one of the washers would spin.Thats when I checked them all and added a washer to each,get a decent thickness one. Hope its that easy good luck

I found that the gasket that came with exhaust didn't quite match up (or distorted) and my bolts were a little more than hand tight! I only have one manifold off, but you can see in the two photos where there is poor coverage of the gasket and it has already failed in the corner blowing hot exhaust onto the plug cap that was arcing. I'm installing new fel-pro gaskets. Think I'm going to use lock-tite on the bolts when I reinstall the new gaskets.

got the port side manifold off of the starboard engine. Way worst. I think the gasket just failed.

To me, it looks like the cores may have shifted in their casting, especially the port manifold. Can you tell if the surface right next to the thin machined face is a cast surface, or if it was machined. From the picture, it looks like a cast surface with a lot of stock on one side, but very little (as evidenced by the very narrow machined face) on the other side. Manufacturing (casting) defect, possibly?

Seen this before...Note: The exhaust gaskets Eddie Marine sends will line up with bolt holes and not line up with exhaust ports resulting in exhaust leak if improperly installed on the exhaust manifolds.