Occasional, slight burning smell and misfire on Stage II

[bluegecko]

I just had my car upgraded to a Stage II over the summer. Since I've got it back, it's generally great, but I've noticed an intermittent faint burning smell coming from the exhaust at times. It's not strong, it's intermittent, and it doesn't (in my opinion) really smell like what I'd normally think of as burning oil. More just…a faint whiff of something a bit burnt. The engine runs smooth, albeit it's usually quite rough with visible shimmy for a minute or two after cold start, and I think I'm hearing some minor misfires (and maybe a backfire, although it's a very quiet backfire if that's what it is) when I sustain past 3000 RPM. I feel like something off, but I'm not even quite sure where to start on this one; any thoughts?

I attached a recording, if that's useful; the volume can be misleading, but I think it's possible to hear what I'm hearing at least. I don't live anywhere near DMC Orlando (where I had the work done), so I'm really not keen on shipping it back there to figure out what's up if this seems like something I can take care of myself.

[David T]

The smell could just be from the work and new parts and should become less and less noticeable. If it gets worse or does not diminish, then you should inspect further. As for the misfire, on another Stage II that I worked on, one of the adjusters of one of the tappets was not locked tight enough and worked itself loose enough to fall out of the rocker and lay in the rocker cover. That *could* be what is happening here but it is only a wild guess. It could be a LOT of other things. Typically a miss at high speed is going to be a problem in the secondary ignition circuit, a bad spark plug, ignition wire, coil, cap, rotor, etc. You should call DMCFL and discuss this with them, they know what they touched and didn't touch and can at least point you in the right direction.

[kenny]

I’d agree on the slight smell, give it a while to settle.
I have a stage 2, the cats gave off a funny smell but I had the old mild steel exhaust.
The engine does idle a bit rougher than stock, fairly sure this is common and is due to the cams.

The missing at higher speeds isn’t normal and could be a lot of things, can’t help you much there I’m afraid

[Michael]

If this was done last summer and you have done any driving at all, any contaminants or residue from the manufacturing process should have burnt off long ago. Secondly, if you have a dead cylinder upon start, you may have either a bad plug wire or plug(hard to imagine since I can only assume they replaced both with the stage II package) or you have an injector failing (I am assuming they only test injectors but do not replace them unless necessary?) It's also possible your timing is off due to a broke or loose vacuum line at the distributer.

After a drive, put a infrared temp reader on each of the header pipes close to the head, see if there are any big changes in the temps which may zero you in on the culprit.