[Roadsters] U20 - Rough low idle - Chain slop

[nmleeds at mindspring.com]

All,

How much do people's U20 chains slop around at low idle? Here are my symptoms: at 700 rpm's, even with a warm engine, the idle is swinging from 660 to 740 and there's a chain noise caused by the chain slopping around against the housing. (At 1000 and higher there's no problem, no backfiring on slowdown, or anything else timing related -- at 80 mph drivers, and local law enforcement, have complained about a little lead foot disorder but that fades on the other side of 100 mph) 

The first thing we did was looked for vacume leaks -- the carb is freshly rebuilt and bushing are in good shape -- a quarter can of carb cleaner and no leaks were found.

Still confused, we pulled the valve cover off and ran the engine with the valve cover off -- messy, but a useful diagnostic. When we looked in, it looked like the timing chain was slopping all around and the tensioners weren't doing such a good job.

The engine is freshly rebuilt. The tensioners have plenty of material left on their feet. All of the oil passages were freshly cleaned when we did the rebuild.  We've got three theories:

1) The tensioner springs are shot, if so, does anyone have the specs for new ones?

2) Because the engine is so new there's just not enough oil pressure to push out the tensioners are low idle.

3) We put on really loose exhaust (big pipe, fancy muffler, straight shot bent under, not over, the back axle) and the lack of back pressure is compromising the engine's overall tuning.

Any ideas?

Nathaniel