Hi,
could be your poppet valves hanging open. These are in the throttle
plates on late HS4's and all HIF4's. They have little springs to keep
them closed, but to allow them to open on a heavy vacuum to keep some
fuel going into the engine for anti-backfire and emissions purposes.
As the valves age their springiness decreases, so they hang open when
they shouldn't, giving a lumpy idle and other badness.
This may not be your actual problem as you say the carbs were rebuilt.
If it turns out that it is the problem you have three solutions:
1) Fit new throttle plates with new valves.
2) Fit new throttle plates without valves
3) Solder the old valves shut.
Of course options 2 and 3 may not be legal in your vicinity.
Andy
--
'69 Roadster
______________________________ Reply Separator _________________________________
Subject: lumpy idle
Author: Alan Lott <lottala@mail.auburn.edu> at Internet
Date: 2/25/98 12:59
Hello all,
Finally got myself a dwell meter and tach combo and decided to do some
adjusting to attempt to fix my lumpy idle. Well, after all of the following...
carbs recently rebuilt by Jim Taylor
carbs equalized and adjusted
fuel pump- ok
new fuel filter
new points
new condenser
new rotor
new dist cap
new plugs
new coil
plug wires seem ok
checked the dwell per spec- ok
checked the timing per spec- ok
...the idle is still lumpy. It just will not stay in one place. The idle
probably fluctuates in a range of 150 RPMs. At higher RPM, there is a faint
miss that is not really rythmic, but more intermittent. At idle, the car runs
very rough with the miss being much more pronounced (but still intermittent).
At this point, any and all suggestions would be appreciated. Thanks in
advance :)
Regards,
Alan Lott
1971 MGB
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