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
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