Think he went with lt4 cam ,the ht383 cam might be a tad better ,but haven't seen a 4 bolt vortec block yet , even in the pcm motors . If this guy gets it right , a 300 hp 17 foot boat should be quite a sleeper.sounds like he's missing some flywheel weight .

dont know about all the 4.3's as some have balance shafts, some do not. the ones with the balance shaft I know are externally balanced. right now you need to pull the engine and get a balancer and flywheel for a 350. I would bet that fixes it.

Agree with last 2 replies and he had the crank out at the machine shop so he needs to try to balance it all. The 4.3 balance shaft came into play around 1993 model years before that Merc used fluid motor mounts to help. He needs to at least change the flywheel and hopefully he has the correct harmonic balancer. At least he is trying. Hopefully he doesn't mind pulling the engine again.

I think 4.3 v6 flywheel can be use on 5.7 motor,if I not right .Would you give me parts number flywheel for v8,it wont take too long to full the engine out .

i have a 4.3 flexplate sitting here and it has a huge weight added from the factory. also the balancer has twice the thickness on one of the three spokes so i would say neither of them would work on a 350. put a post in the wanted section and i would bet someone has the ones you need.

ok, just did some surfing in s10 forums and came across novak conversions which was talking about putting 4.3 in jeeps. in 86, when they offset cut the rod journals so it was an even-fire engine even though it was a 90 degree v6, they went to an externally balanced flywheel. that is ALL one piece seal 4.3's. the flywheel IS the culprit. but get rid of the balancer too. I have about 5 to 10 small block balancers that'll work with a boat. but the lower pulley will most likely bolt right on the 350 balancer that came with the truck. go to JEGS or Summit and order a 350 flywheel. only about 80 bucks. you wanna do ebay, find the right part number for a 1 piece neutral balance flywheel so you don't get sold the wrong one. what starter bolt pattern? A; one about as far forward from the other as they are wide apart and the both bolts same length? or B:both bolts next to each other with outer bolt shorter? if A it is 168 tooth flywheel. if B it is 153 tooth flywheel. you can use either flywheel, but you need the starter to match. some early mercruisers used a flywheel cover that won't fit over a big flywheel, but I think they were before the 4.3 existed. the one 4.3 boat I had was mid eighties and had big one piece flywheel. I just looked for that flywheel in garage but couldn't find it to check for the counterweight, but I think I remember it being there.