1980 Spider 2000 sounds like lawnmower or go-kart

[mckeig]

My Spider all of a sudden sounds like a lawnmower. It starts right up, but kinda hobbles on idle. When I gas it, it's like a little go-kart; not a lot of power and not a smooth sound, much like a lawnmower. Upon inspection below I noticed the welds are broken at the rear of the rear-most apparatus on the exhaust. (muffler or cat? It's a California car.) It also seems to have been that way for a long while, and the lawnmower started this week. From the time I last drove it to the time I fired up the lawnmower was about two months. I don't drive it often, but I make sure to cycle through a tank of gas every few months. It is fuel injected, as I believe all the 2000s from this year are.

What should I check? I'm thinking plugs, wires. Could it be misfiring? What about distributor? I'm mechanically inclined, but I'm not familiar with electrical systems so much. Any tips on where to start would help. Perhaps I can shoot a short video of the sound and put on YouTube if it would help?

Thanks,
Chad

[So Cal Mark]

the muffler is on the very end of the exhaust and a broken inlet will cause it to be louder. If the engine is misfiring it should be idling very rough. If you leave it sit for a few months at a time, you may have a stuck fuel injector. The fuel these days tends to varnish pretty quickly. If the engine is running rough, I'd try to isolate which cylinder isn't firing by removing the wires from the dist cap one at a time

[mckeig]

It is rough compared to normal, which is why I didn't suspect the muffler alone. I'll try to isolate the cylinder.

[kmead]

Could be a clogged catalytic converter. If its been running rich it could have overheated the catalyst causing it to melt and clog.

A clogged cat will usually allow it to easily idle but will not flow enough exhaust at higher rpms. It will sound very odd, actually getting a deeper note (bbrrrooowww) and the engine will bog down. If it is this problem you will need to replace the cat.

[mckeig]

Thanks for the tips. I finally had a moment to check it out. The number 3 cylinder (from the front counting backwards) seems to be the culprit. If I unplug the wire from the distributor there is no change in idle, whereas removing any other wire drops it markedly. If I hold the end of the wire near the metal body I see an arc, so I suspect the wire is ok. That leaves spark plug and fuel as possible causes? I thought if I replace the spark plug and there is no change, it must be the injector, correct? Can I just start it with the spark plug out (but connected to the wire) to see if it's working? If it is the injector, could it just be clogged? I replaced the fuel injectors on my Jeep a few years ago (4.0 inline six cyl.) and it was not difficult, but I remember them being a chunk of change each. Trying to avoid costly measures since I'm low on cash.

[mckeig]

Changed the spark plug for a new one today, no change. I suspected the injector, so I tried the cheap solution first: injector cleaner. I put it in with a fresh tank of gas and took it out for an evening highway drive up the valley. Within two or three miles it was running smooth again. I guess sitting for months at a time must have clogged up the injector. Seems like it's good to go, for now. I'll post if there's any change. Thanks for the replies.