Hi List,
Does anyone have suggestions regarding this problem with my 1600 stroker (2.0L
Pushrod)?
I rebuilt my engine about 2 years ago.
0.040" oversize flat top pistons, new
Deves Rings, new
Butt gaps were within specs according to literature in Deves box
Piston bore in block was at high limit for ID, meas'd by me.
New Mikuni dual 40mm carbs
Over many months found that the jets that worked best were:
Main fuel jet 120 (tried 110 to 130, not much affect)
Main air jet 180 (never changed)
Pilot jet 62.5 (tried from 50 to 65, major affects)
Starter jet 120 (never changed)
Large Venturi 33 (stamped on them, hard to read, maybe 32)
Timing set to 20 degree btdc at idle
Distributor is pre-smog (7.5).
Vacuum advance not hooked up (doesn't seem to make a difference anyway)
Mileage is about 18 miles/gallon
Engine now has about 24K miles on it now.
>From the first day, I had popping noise during deceleration, and this was
>especially annoying when going downhill, using engine compression to slow the
>car -- which is the situation for about 1/5 of my daily 20 mile drive to and
>from work.
The only way to fix the popping was to richen the idle screws which made it run
fairly rich for "throttle off" coasting.
So I may have had rich mixture wash the cylinders and maybe cause uneven wear
on cylinder walls and hence the rings may not have seated... based on various
inputs.
Today:
Too much smoke coming out of exhaust pipe when going downhill with throttle
off. Most I think was black from being too rich. Some might be oil. So to fix
the black rich smoke, I leaned back the idle screws to where they should be.
Also, I may be (or have already) damaging the ring/cylinder interface.
Now get the popping sound again and it is too much to live with, especially
when I drive to work at 5:30am (to others who can hear this).
Compression check: 155 psi +-1 psi dry
206 psi +-2 psi wet with 6cc of engine oil used
6cc of oil by itself raises pressure to ~198psi
Compression Ratio ~9.2
Will start to monitor oil usage, but since there are some small leaks, may be
hard to tell.
Questions:
1) How to determine if my rings have not seated, or the cylinder walls are not
round? There is some kind of "pump down test" where you put piston at TDC and
pressurize throught plug hole.... anyone know about this? Does it give a more
accurate "view" of ring situation vs compression test (which looks quite good)?
2) Is it possible that the popping sound is from oil being sucked into the
cylinders (during deceleration, going downhill, throttle off, high vacuum) and
detonating??? Or does everyones roadster engine do this?? Before the rebuild
mine didn't.
Thanks for any suggestions.
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