Hello, All:
I'm hoping the wisdom of this list may help me with questions on the TR6
engine in my '76 TVR 2500M I've on occasion thought that I had this British
car thing figured out, but while I may have figured out some things, I
certainly don't have it all figured out.
For all you engine tuning gurus out there, I'd appreciate your considerations
of the following:
Condition--
1. TR6 engine, late commission number, all original car and engine with only
12K total miles on entire package. Overall condition is nearly as-new.
2. The original owner (I'm the second) fit six-into-one headers into a TR6
Ansa exhaust system and removed original filter box for Hellings and
Schillings air filter set up. I've left the headers on, but I've removed the
ill-fitting Ansa bits and replaced them with a 2.5" straight pipe and a
SuperTrapp. I've also fit K&N filters in place of the H&S things. These are
the only modifications from stock that I've identified.
3. All emissions gear still fitted, and working properly (maybe this is
paradox). It was never fitted with an air pump, however.
4. Well maintained throughout its low-mileage history.
5. Ignition system. Fresh ignition consumables--plugs, points, condenser,
wires, rotor, rotor cap. All ignition bits working and nearly in as-new
condition. Coil is original, and the TVR used an external ballast resistor
rather than a resistor wire. I keep the mechanical advance and distributor
shaft properly lubricated. I had to replace the vacuum retard capsule. No
tricks here like altered advance springs.
6. Valves adjusted.
7. Dwell and timing adjusted.
8. ZS carbs rebuilt meticulously (ridiculously meticulously, really, but
taking care pays off in numerous ways) a few years ago by me. I have good
understanding of these devices, with the exception of one important area that
I'll mention below.
9. Starting. The car always starts beautifully. I mean really. It fairly
bursts into life, hot or cold, almost as fast as current gets to the starter.
Symptoms/behaviors--
1. Idle not always smooth. The idle can hunt a bit.
2. Engine doesn't return to idle properly. When letting the engine return to
idle, it will often nearly stall, or stall. If the throttle is tapped, it
will usually return to normal idle.
The mysteries--
1. Setting mixture. I think I understand the ZS carbs, but I may simply be
ignorant of my ignorance. What I do know is that I've not had a lot of
confidence that I've been setting the mixtures correctly, and a misadjusted
mixture could explain the noisome behavior. I intellectually understand the
lift-the-dampers test, but often have a hard time interpreting the resulting
engine behavior. I've got a Gunson's ColorTune, but can't seem to got the
optimum color from it with this engine. I've also got a Gunson's GasTester,
but I'm not sure how to use with a double-carb set up, so I don't. The spark
plug color looks okay. They display a lightish tan color. If anything, the
color may be a bit light, but the color doesn't indicated a very lean
condition. The plugs are also very close in color from one another. Oh, I've
also read all the very helpful literature on tuning SU and ZS carbs from the
Internet.
2. Setting timing. This is something that confounds me. Dwell? No problem.
A bit fiddly, but no problem. But the static or dynamic time is confounding.
Whenever I set the static timing given in the Haynes or Triumph Emissions
Tuning (which actually almost describes how to use gas tester with double
carbs) manuals, the engine runs horribly. It's hard to start and performs
poorly, though the idle can be okay. The same when I set the dynamic timing
to book spec. How do I set the timing? Well, someone, a long time ago,
scribed a neat mark across the distributor and it's hold-down. Aligning these
marks gives pretty good results. As far are increasing advance until pinking
or pinging occurs, I've not been very handy with this method. I understand
how this method should work, but not sure of how it looks in practice.
So, after all this, my questions are--
1. Could this type of idling behavior be a result improperly adjusted
mixture?
2. Can anyone help me with some insights into setting ignition timing?
3. And to get entirely ahead of myself, I'm looking for another, say, 30hp
and a few more ft/lbs of torque from this engine. What're the easiest ways to
do this, if there are either easy or even ways to do this. I'd just like to
know if some more meaningful hp can be had with the stock long block set up.
Is anyone out there familiar with the tuning stages of this engine?
Thank you most kindly for your help,
- Steven Jackson
'67 Lotus Elan S3 dhc
'76 TVR 2500M
'85 TVR 280i (unfortunately, I have to sell this one)
'96 Dodge ACR Neon coupe
|