Chev 4.3 vibrations (John Scott??)

[Guest zthang43]

I'm wondering if the vibration that my 4.3 makes is just something all the older (non balance shaft) 4.3's do, or if I have some sort of problem. It has sort of a weird vibration at about 1700-1800 rpm. It really smooths out above that, and below that isn't bad either. I'm wondering if it's just something to do with the firing order and the harmonics of the engine, or what. John Scott, did your 4.3 do this?

Mine is from an 89 S10, I'm using a Quadrajet and HEI from an Astro van. Hah ha that little puking guy is cool.

[John Scott]

The 4.3 isn't noted for being silky smooth. As long as you haven't changed any of the stock reciprocating pieces, using the stock flexplate/balancer...Probably why they added the balance shaft in the later years. They claim the oddfire crank is smoother at really high rpms than the even. Why? My mount system used the stock 240Z motor mounts which were soft, pretty good at absorbing the bad vibes, but it was buzzy at low rpm, like you mention. I noticed a little improvement after my third round when I had it balanced, added a fluid damper. Tied my Procharger bracket into the strut tower after reading a supercharged mustang tip. Big mistake. Felt like I turned on a blender! Did you ever get your carb. figured out?

JS

[Guest zthang43]

yeah, the carb is working great. Thanks for the metering rods, those were what it needed.

I could probably get rid of a lot of the vibration by using original GM mounts, which are supposedly softer than the aftermarket replacements I am using. JTR warned about this and like a dummy, I ignored them. When I rev the motor, the mounts don't flex at all; the whole car moves instead.

It just seemed a little more than stiff mounts, that's why I was wondering if it was a 4.3 thing.

I'll be sure not to tie my blower (when I get one) onto the strut tower. thanks for the warning.