Subject: Re: TR6 mileage
Date: Fri, 19 Jul 96 18:59:00 EDT
From: "Randell Jesup" <jesup@mailhost.scala.com>
Vadim Akselrod writes:
>I have not had mine long enough to know exactly what the problems could
>be (only went through 3 tanks of gas so far). It just passed smog - it
>was set somewhat lean. I checked the SUs. Okay, the leaks are no good,
>so the out leaks out, but I don't think that should be a big deal. Other
>than that, they look clean. Air filter is okay. Retuned the carbs so
>that when manually letting in more air, it gains RPM rather than losing
>it (about 2 turns more rich).
SU's? On a TR6? The stock carbs are Strombergs, not SU's. I
wonder what wierd conversion the DPO managed to do.... Not that I dislike
SU's; I love them. But if the conversion wasn't done right (in particular
selection of needles), the performance would be poor, and quite possibly
the mileage as well. It's probably way over-rich. Strombergs don't have
a nice easy mixture nut to adjust (and some years of TR6 have NO mixture
adjustment at all).
>Timing is set to 4 degrees past. Have not checked the valves yet.
4ATDC is the dynamic spec, I think. if your RPM is too high at
idle, or (VERY LIKELY TRUE) the retard hose isn't hooked up or is hooked
to the advance port on the SU's, then the timing will be totally FUBAR.
I advise disconnecting the retard, starting with static timing and then
adjusting it for best acceleration (rolling-start time between two markers
or time to speed). I think the static spec is ~10 degrees BTDC
>Other symptom - sometimes it misses even after warmed up and at freeway
>speeds. I can floor it and still slowly creep past 65, topping out at
>70. Other times though, it runs fine. Hmmm. The bad running seems to
>be after it's been parked overnight. But it has definitely warmed up (10
>miles, 15 minutes from start, still running rough) - and it's in
>California, so weather is not an issue.
Fouled plugs, perhaps. Another symptom of over-rich mixture.
>I cannot see any liquid on the driveway, so I don't think it's leaking
>gas. Oil pressure is fine.
It could be evaporating, too.
Marc Siry writes:
>This reminds me of a problem I had on my motorcycle, Vadim-- one plug (out
>of two) was fouled and firing intermittently. My mileage dropped
>precipitously since I was burning twice as much gas to maintain the same
>speed, and my maximimum was 10-15 mph below what I thought it should be. I
>replaced the wire and the plug and the symptoms vanished.
Make sure gas is _getting_ to both carbs. I've seen SU's with a
blocked connector between the carbs - the rear carb got 0 fuel.
Also, make sure that the floats of both carbs work. If one is
sticking, then those 3 cylinders will get LOTS of fuel, and perhaps even so
much that they won't fire (which would explain the total lack of power at
times, and why it tends to happen after sitting overnight).
>The upshot is, before you mess with the valve train check the easy stuff
>(plugs for fouling, check the spark, points, etc.) Your symptoms sound like
>a misfiring plug.
Agreed.
--
Randell Jesup, Scala US R&D, Ex-Commodore-Amiga Engineer class of '94
Randell.Jesup@scala.com
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