Spent several hours with the 250 this weekend and the good news is that it
fired right up after the extensive mods this winter (shaved head, GP3 cam,
resealed front sealing block, up-rated dual valve springs, SS header w/
Jet-Hot, 2 1/4" SS pipe to the rear). It sounds really nice and I can't
wait to get it on the road.
I worked on the timing per the suggestions on the list and found that 10
degrees BTDC is pretty good. Not too difficult to start and it idles OK at
900 RPM. It is even better with the vacuum retard hooked-up (at least it
was until the very hot header melted the plastic vacuum tube shut).
Retarding the timing at idle makes the car idle more smoothly, so I'm going
to keep this hooked-up. Car starts easier too.
I'm a bit unsure about the advance methods though. At idle with no retard,
I'm set at 10 degrees BTDC. With the vacuum advance disconnected, I
increased the engine speed to about 2500 RPM and the timing moved to about
20 degrees BTDC. With the vacuum advance connected and engine speed at
2500, I got the same 20 degrees BTDC. Shouldn't I get an additional amount
of advance with both the centrifugal and vacuum advance working? I had
hoped that with both the centrifugal and vacuum advances working, I'd get to
the magic 30 degrees BTDC.
Another interesting thing is that if I create a vacuum on the vacuum advance
at idle (by sucking on the hose), I get a pretty significant advance (maybe
10 degrees). I wonder if I'm getting any vacuum from the fitting on the
back of my front carb where the hose attaches (I had a machine shop add this
fitting last year). Any easy way to check this?
Finally, at idle I get small jump in the timing (about 4 degrees) every 3-4
secs (as seen by the timing light). Is this normal? , or something to hunt
down and fix?
OK, I lied, one more question. The distributor is sitting at a 10 o'clock/
4 o'clock position. The tach cable is very tight. Have folks who have
their timing set at 10 degrees or more found it necessary to move the lower
gear one tooth to compensate for the rotation of the distributor?
Thanks for all your help thus far.
Peter
'68 TR250 (almost on the road again)
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