Any help with a bad exhaust smell problem

[PatrickGMC70]

Hey guys. I'm pretty new to this truck, and older cars in general, so I was hoping to get some help here. I'm pretty frustrated with this truck at the moment, but I'm trying to keep my cool.

The symptom is that whenever I'm near this truck when it's running, even for a short time, I reek of exhaust. It gets in your hair, on your clothes, and even gets to your eyes after a bit. It's really intolerable.

I don't know exactly what the problem(s) is/are, but I suspect that my carb is way too rich. I paid to get it rebuilt, but I think they didn't do such a great job. More on that in a bit.

I think the second problem is that I may have an exhaust leak. I haven't seen any visible exhaust smoke, but there is carbon on the manifold. Here's a pic:



Even though there's a lot of carbon, I can't see any visible cracks.

I took it to a local exhaust shop (Meineke) and they told me that there is a crack in the manifold and heat riser. I said that I couldn't see a crack, and they said that the carbon indicates a leak somewhere. They said I have to replace the manifold and heat riser (plus gasket and studs). [I should add that while I am a bit suspicious of their explanation, I'm very reluctant to call anyone a liar, when I know so little myself. I should also say that they were very courteous to me.] They said I can bring in my own parts and they'll put them on for me, but it's 2.5-3 hours of labor per side, which equals about 5-600 bucks (plus parts).

I really don't want to mess with these manifolds because I don't know what I'm doing, and I definitely don't want to mess with a torch or worse, drilling out a broken stud. Actually, I really don't want to replace them at all, but I absolutely have to get rid of this smell because the truck is useless to me now.

As for the carb, I'm really lost. I suppose I can try replacing jets and rods, but well, I don't know what else. I feel like I'm just going to keep throwing money at this thing, but never solving the problem. I guess I'm just fed up and I'm really looking for some guidance here before I just run this thing over a cliff.


P.S. I tried not to make this post too long, but I certainly provide more detail if needed.

P.P.S. The truck is a 1970 GMC 350/3spd with a 1975 Quadrajet (from the casting #s anyway).