Red Hot Exhaust Manifold

  • Thread starter Thread starter Mike Wilson
  • Start date Start date
Yeah. It doesn't take much spark to keep a car going at highway
speed. And you don't have much in the way of hills out there either.
So 12% advance is enough to keep the engine running at fairly
low rpms, say 2000-2500 at 80kph in high gear. But I bet your
acceleration really sucks.

And even though the engine is running, there's a LOT of unburned
HC's going out the exhaust and heating up your manifold.
You still might want to try blocking off the secondary air hose before
you fix this problem just to see if the glowing stops.

The return springs in the distributor are probably broken or
streched out (just like that throttle return spring), so the dist
is stuck at full mechanical advance and you've compensated for
it. But you also have vacuum advance when the throttle is open,
and that plus the 12% keeps things running, sort of, on the highway.
If the mechanical advance actually worked, your engine would be
knocking (pinging) like crazy on regular gas.

A brand new distributor assembly is $340 from Hyundai, or a lot
less used from a junkyard. Part number is 27100-21430 for a
manual, and 27100-21440 for an automatic tranny. Any dist from
a carburated Excel from 86 and later will work if it has the same
tranny as yours. (Timing advance curves differ slightly between
the two.) It's a shame, but there was a guy on Ebay trying to
get rid of a couple of these Excel distributors a few months ago
for next to nothing. I checked, but there's nothing out there right
now or in the last 30 days (just a couple of different auctions for
a 91 Scoupe dist, not compatible).

I wouldn't bother with the EGR passage right now. Find a
used distributor first.

Bob
 
Lots of hills here Bob, My girlfriend is a valley girl : )
Saskatchewan is hilly (most of it) there is a ski hill down the road from
us.
Now, Manitoba is flat, watch your dog run away for a week. : )

Actually the car has good acceleration all the way up to 130Kph
I'll try blocking the secondary air control valve, never thought to try
that.
I'm not sure I agree that the car would be pinging with the distributor set
to 12% BTDC as most cars are set to 10% BTDC, I don't trust the Haynes
manual, nor the emissions sticker (4% BTDC) on the underside of the hood,
however I do agree that I might have a distributor problem. I'll check that
out tomorrow. One thing to note: I tried 4% BTDC and the car was backfiring,
asuming (crankshaft is at it's respective timing mark) so the distributor
could be the problem.

One thing I tried tonight was, have the GF revv the car to 2,500 RPM and
observ the ERG valve, it opens up all the way when the car is stone cold.
The Haynes manual says that the ERG shouldn't open (up to 2,500RPM cold
engine) when the engine is cold, if, it does, then the thermo valve has to
be replaced. The ERG vacuum is controled by the thermo valve, engine heats
up and the thermo valve applies vacuum to the ERG if the temp is hot enough
(185degrees), and engine is revved past 2,500 RPM. The ERG does open up all
the way when the engine is warm/hot. Also the manual says that the ERG valve
shouldn't open at full throttle if the engine is hot. The ERG opens up fully
when I revv the engine to full throttle (hot or cold), but not at idle. I'm
thinking that the problem may be the ERG opening at the wrong times.

Another thing I tried tonight was, drive the car down the highway really
fast, checked the exhaust manifold, red hot, drove back home in over drive,
at low RPM (2,500RPM) around 80Kph for about 20 min. Checked the
manifold,,,,wahoooo!!! it doesn't look like a bright red cherry tomato. LOL
So, the problem is only occuring at 3/4 and full throttle.
I'll double check the routing of the vacume hoses, if no go, then check the
distributor and or find a used one, if no go, order a thermo valve.
Unfortunately, the dammmm Haynes manual only shows the ERG diagram for a 88
and up, I'll have to go by that diagram.

Thanks for the help, at least I have a troubleshooting path to follow now.
I'll try your suggestions tomorrow and get back to you. At least I don't
feel like driving the car off of a cliff now!
 
Before you go out and get a distributor, please check out the
1988 Excel service manual online at www.hmaservice.com/webtech .
Select your car (1988, not 86) and click on "Shop". Under
"Engine Electrical System" read the specs on page 2, then read
about the distributor on page 30.

I was surprised to read that the mechanical advance for this dist
is only 5° at 2500 rpm, and tops out at 16° at 6000 rpm. This
probably explains why things don't glow when you drive at 2500 rpms
(there's enough advance) but do at higher speeds (not enough).
Vacuum advance ranges from 0° to 23° tops.

When you tested the advance, you probably didn't rev the engine
much past 3000, which sounds pretty fast at in neutral. 5° is
not a lot of movement when looking with a standard timing light.

Don't concern yourself too much with the EGR opening when cold.
It's not serious, and will only cause hesitation and poor performance
until the engine warms up. And don't worry about the EGR being
open at full throttle. EGR works off of ported vacuum, which is
highest at about 1/2 throttle, dropping to zero when fully closed or
fully open. It's difficult to see what fully open is like when the car
is in neutral, because it revs too fast too quickly.

I'd concentrate on the distributor first. Recheck the mechanical
advance with the vacuum hoses removed & plugged. Then reconnect
the hoses and there should be a lot more advance than before.
If not, make sure there's vacuum at the hoses when you open
the throttle. Follow the hoses back to their source, which may be
the same defective thermal switch that's also running the EGR.
Or, you may have mixed up the hoses where they attach to that
switch. I haven't checked, but the online manual probably has
vacuum routing diagrams too.

Good luck.

Bob
 
Update:
Took the distributor apart, the governor weights were stuck, they moved but
barely. So I cleaned the governor weights, spindle and greased them up. The
weights move more freely now, which was part of my problem. The breaker
plate was also sticking a little, cleaned it up and greased it, adjusted the
igniter (.030 ")
I think that I might have to replace the vacuum advance module as it doesn't
seem to move to much. With a vacuum line attached to the bottom nipple,
sucking (with my mouth as a don't have a hand pump) on the line to build up
pressure, the igniter advances, but not very much, maybe 2 or 3 mm. The top
nipple doesn't hold any vacuum at all. The car is definitely working better
now. I set the ignition timing to 4 degrees BTDC, now there is no back
firing. With the engine warmed up, timing light attached, revved the engine,
observed the timing advancing properly. Before I fixed the distributor the
timing was actually going to ATDC 1 or 2 degrees and then advancing BTDC 5
to 10 degrees, as I revved the engine. Took the car for a drive down the
road, brought it up to 130 Kph for 15 min, stopped and the exhaust manifold
is still red hot. Drove back home in over drive at 100Kph, the exhaust
manifold isn't red hot. I'm still baffled, any suggestions?
 
My gut feeling is that it's still the lack of advance on the distributor
at high speeds resulting in too much unburned HCs. The vacuum
advance is available from Hyundai as a separate part for an
unknown price (their parts website is down right now). There are
2 parts numbers, one for an automatic tranny, the other for manual.
Or once again you can check out a local junkyard for a lot less.

After writing the above, I went to http://www.hmaservice.com/webtech/
and selected a 1988 Excel and looked at the TSB's.

Under Fuel System there's a great article (V1-30-002) explaining how
feedback
carbs from 1986 and later work, along with lots of diagrams.
For the 2 nipples on the distributor, one is for normal vacuum
advance, the other is for additional advance when the engine
is cold or at high altitudes. I can't tell from your description which
one of the two is broken, but you can:

When the engine is warm, there should be no suction at either of
the two hoses connected to the advance at idle. If you rev up the
engine, there should be vacuum at one hose but not the other.
This one is the normal advance hose, the other is therefore the
cold advance hose and will only have vacuum when the car is
cold, even at idle. If the cold advance nipple is the one that
doesn't hold vacuum, then you'll only have cold driveability
problems. If the normal advance nipple is the one that's shot,
you're not getting enough advance at highway speeds. If this
is the case, I'd try switching the two hoses temporarily to see
if it eliminates the red-hot manifold problem.

Once you've got that fixed, I'd check out the O2 sensor next. If
you've never changed it, it's probably burnt out after all these
years. You can test it by using a digital voltmeter (not an analog!)
to see if it produces voltage at the connector when the car is
fully warmed up. No voltage = dead sensor, and the computer
thinks the mixture is too rich and tries to lean it out. I'm not sure
how it's done on your carburated engine. Aftermarket O2 sensors
are fine, but you need an impact wrench and a lot of penetrating
oil (or a torch) to get the old one out of the exhaust manifold
without breaking it off.

And finally you can always try finishing cleaning out the EGR
passage in the intake manifold.

But do try fixing up the distributor first.

Bob
 
Ok we'll do that
I'm pretty sure both chambers should hold vacuum, it's the top chamber that
doesn't hold any vacuum at all. I'll try the local wrecker, but the last
time I was there they had 4 Excels but all were missing the engines, just my
luck. I'll call them on Monday. I tried to reverse the vacuum lines (sorry I
forgot to mention that) it didn't solve the problem. The 86 model doesn't
have a O2 sensor. I'll try the wrecker, or buy a new part for the car. Again
the problem does disappear if I drive slow (100 Kph) on the highway.

Mike
 
Just for my own curiosity, I did a google search on Red Hot Exhaust
Manifold, and was sort of surprised to see this thread near the top.
But further down, there's a variety of opinions as to the cause. The
most common ones are: mixture too lean, timing retarded, burnt or
leaky exhaust valves, mixture too rich.

You're currently working on the 2nd one, but I was wondering when
you replaced the head gasket (properly) if the valve clearance was
set properly when you put things back together? If it's too tight, the
valves may start to burn, and they might start to float (not seat for
long enough) at high rpms? You should check the clearances, 4
valves at a time at TDC and then the other 4 after turning the engine
over to the next TDC. The engine should be fully warmed up but
not overheated. It's better for the gap to be slightly looser than too
tight. Also, I assume all the valve springs were in decent shape,
none shorter than the others. I ask this because I made this mistake
on a Datsun about 15 years ago. It ran perfectly for 10 miles on the
highway until it just died, no warning. Started right up a few hours
later after it had cooled down completely. Seems that I had set the
cold clearance properly, but should have simply warmed it up in
the driveway for 10 minutes, not taken it out on the road before
setting the hot clearance.

Bob
 
Ya I also did a Google search for my problem and found various reason why
this is happening. More often then not, the problem was timing. But what's
got me concerned is the fact that, the problem doesn't happen when I drive
around 100Kph, Surely it could be that I do have a defective vacuum advance
module, but why at full throttle? Today I'll be checking out a local wrecker
for another distributor or engine. I wish the problem was burnt or leaky
valves because the car would perform quite badly and the solution is
obvious. When I installed the new head gasket, I looked at the valves, there
was quite a bit left on the valve margins, so I assumed that the valves were
ok. Again the mixture cannot be too rich as the spark plugs are a tan
colour. As far as the valve clearances go, I originally set them loose,
because I thought that the valves weren't closing. After I determined that
wasn't the problem, I set them when the engine was cold, I just added
another thousand to the measurement to compensate for the engine being cold.
Not sure of the condition of the valve springs. If I don't have any luck
with the distributor, I'll try setting the valves to the hot clearances, if
no go, I'm going to bring the car to a friend's heated garage so I can tear
the whole thing down. I did mention that the car is running better now? LOL

Mike
 
Here's a test for you:

You said that the manifold glows at 130Kph, but not at 100Kph.
I feel it's because you have enough advance with a defective dist
at whatever the rpm's are at 100Kph, but not enough when the
engine is running faster at 130Kph (the faster the engine turns,
the more advance is required because the burn speed of the gas
remains constant).

So, what happens when you run the car at 100Kph in a lower gear?
The rpms should be the same or higher as when you're at 130Kph,
but the load on the engine is less. If it's indeed the timing, your
manifold should glow in the lower gear at the lower speed simply
because of lack of advance is dumping unburned HC's into the
manifold, where they continue to burn.

Try it and let me know.

One other q: Are you truly at wide open throttle (pedal to the floor)
at 130Kph once you hit that speed (not just when you're accelerating)?
If you are, you're asking too much from your engine. One of those
google posts (regarding the motor home going uphill at WOT) mentioned
that a glowing manifold is often the result of running at WOT for
extended periods of time. Most carbs have a power circuit that
enriches the mixture at WOT (as a result of manifold vacuum dropping
to near zero) for better acceleration. But the rich mixture results in
the glow after a period of time, but how often does one actually
floor it for more than a minute or two, even? Hardly ever (you're
supposed to downshift instead).

Bob
 
Never stopped by the wrecker today as, I had to bring the wife to her
prenatal doc today. I did call the wrecker and they suggested that I call on
Saturday to make sure they have a Excel with a engine in it.
Yeah! I was thinking about doing a test like that also, I never got around
to trying such a test. I'll try it tomorrow and get back to you about it.

I have to clear one thing up, on my last post I said that the exhaust
manifold didn't glow red when I drove 100 Kph, that is true, except for some
very very dark red colour (just on part of the manifold). You can't see this
very dark red colour during daylight hours, only at night. SORRY I forgot to
mention this yesterday.

What I meant by wide open throttle is: almost to the floor. If I don't get
anymore acceleration from pressing down on the gas pedal, I'll back off the
foot feed a little. If I try and squeeze every ounce of speed out of the
engine, I can get her going close to 150Kph. It's a good theory you have,
because there is a point when accelerating in over drive, that, pressing
down the foot feed, actually stops the car from accelerating, thus I have to
back her off a bit.
One thing is for certain, that I wouldn't be driving the car as fast, as
possible all of the time, however I would like to drive at 100 plus from
time to time without the worry of something catching on fire.

I'll get back to you tomorrow

Mike AKA Deefer Dog
"Never pet a burning dog!"
 
Hey Bob
Drove the car for 20 min, in 4th, at 100 Kph, the exhaust manifold isn't red
at all, not even "very, very dark red" as I mentioned on my previous post. I
guess the problem can't be cause by vacuum advance as the engine speed is
higher in 4th then in over drive. One thing I'll try is driving faster,
let's say 120Kph, in 4th, and see what the result is.

What I'm thinking it that the problem only happens when the car is under
load. This would suggest a valve problem, however the car drives fine, good
acceleration, doesn't spit and sputter. Maybe the problem has to do with the
fact that I'm in over drive, vacuum switch thing. The transmission does
require vacuum for it to switch into over drive, the vacuum canister maybe
leaking slightly, however the car does switch into over drive without any
problems. Are you as confused about this problem as I am? LOL

Mike
 
Update:
Drove the car at 130Kph, 4,000rpm, in 4th for about 10 min, took a look at
the manifold, it's red hot. I thought for sure it wouldn't be red, seems
like the problem starts to happen around 3,000rpm and up.
 
I was going to say that I didn't expect this either, but in a way I
did, because if it's dist-advance-related, the rpms are the key.
Try one more test:

Set the base timing back to 12° BTDC, or whatever it will take
without knocking or misfiring. On most cars with a properly
working distributor, this would cause a *lot* of pinging under
load, but since your vacuum advance is questionable at best,
this extra base advance may just compensate to give you better
results at high rpms. It won't solve your problem, but it should
at least a) reduce the slight red glow at 100Kph to no red glow,
and b) reduce the bright red at 130Kph to something less.
IOW, there should be some noticeable improvement, even if
it doesn't solve the problem completely (because the vacuum
advance provides an extra 16° of advance, and you're only
providing an extra 8° using this method).

BTW, is this a manual or automatic (I'm still not clear)?

Bob
 
Hey Bob
The car is a manual Transmission
That'a good test to try. I'll let you know what the result is.

Mike
 
Hey Bob
Haven't tried that test yet, been busy with family stuff. Tomorrow I'm going
into town to wrecker to see if I can get a used distribution for the car.
I'll let you know how it goes. Thanks for all of your help so far.

Mike
 
Hi Bob
Got the new distributor, the new vacuum advance module works fine IE holds
vacuum unlike the old one. The car run a shit load better now, still the
same problem with the exhaust manifold except for one small difference: this
time I have to really drive the piss out of the car 130Kph for the for the
problem to occur, before the manifold would start to turn dark red around
100 Kph, now if I drive at 100 the manifold isn't red at all. tomorrow I'm
thinking about changing the distributor all together and setting the valve
lash to the hot setting as I set the valve lash with the engine clold
(added a thousand of an inch for the engine being cold) will let you know
how that turns out
Cheers!!!!!!!!!!
Mike
 
Hi Bob
Not sure if your still with me on this problem, I'm 90% sure I got the
problem nailed. The new distributor made the car work better, along with
adjusting the valve lash when the car is hot (remember I added a thousand of
an inch to the specs on a cold engine) Drove the car at 130Kph for 20 min,
the exhaust manifold is dark, dark, red, any lower speed and the problem
doesn't occur. So for now I'll just have to take it easy on the car, until I
can find out what is causing the slight problem at 130 Kph. I was thinking
that, the carb might not be set up properly, something I overlooked. Anyhoo
I just wanted to let you know that I got most of the problem figured out.
Cheers
Mike
 
Thanks for the update. I've never driven my brother's 91 Fuel Inj
Excel at that high a speed for an extended period, but I did notice
that the exhaust manifold heat shield that I replaced a couple of
years ago looks pretty beat up for such a relatively young part,
which may mean that this may just be a design flaw with this
engine.

As I've said before, if you're pushing the engine to keep it going
at 130Kph, you may not be supplying it with enough ported
vacuum to keep the dist at its maximum advance. If you have a
vacuum gauge, try putting it inline using a tee with the hose going
to the dist advance, and see what the readings are at 100 vs 130.

You can always advance the base timing from 12 to, say, 14 BTDC
as long as the engine doesn't knock and performance doesn't
suffer.

I doubt there's a carb problem, but if it was running too rich at full
throttle, it should backfire a bit when you let up sharply on the gas.
Other than a weak power valve spring or slightly clogged secondary
air bleeds, there's not a whole lot to adjust on a carb.

And once again, check out the air injection hose to the exhaust
manifold. Block it off, plug it, whatever, to stop any air from entering
the manifold.

And for what it's worth, I won't have a 91 Excel to work on anymore.
My brother managed to effectively total his on a slippery interstate
last week during that New England storm. Fishtailing and bouncing
from an adjacent car to a jersey barrier and back, even at a really
low speed, will tend to do that. And damn, I just got it to pass a
state emissions test for the first time in 6 years thanks to a new
catalytic converter I installed over Thanksgiving. The new part just
messed up the car's karma, and it was doomed.

Bob
 
I agree it could be a design flaw, however Hyundai would have taken care of
the problem by now (1986-91)
I'll research the problem, check to see if the dis has enough vacuum as you
are suggesting.
BTW, the dis timing is around 6% BTDC, I left the dis timing like this
becacause I knew it to be correct. When I said that I changed the dis timing
to 12% BTDC, and got a posiative result, I changed it back to the
recommended specs 4 BTDC +-1
I found 4 degrees to be a little sluggish and 6 degrees to be right on the
money.
With the setup the way I have it right now, releasing my foot from the gas
pedal sharply doesn't produce any back fire, however I think you ment if I
had the engine set to 12 degrees BTDC. That is a good theory that you have,
I'll give it a shot. One thing I forgot to mention in my last post...I has
some white deposits on #1 and #2 spark plugs, after readjusting the valve
lash with the engine hot, the plugs are fine, funny...when I lived in
Ottawa, I worked as an auto mechanic for 7 years and have known lots of
mechnics to add a couple of thou to the specs so the can adjust valves (over
head cam) on a cold engine. This methiod has always worked great, I gess in
my case I have valve margins that are warn unevenly producing a little bit
of a gap. I'll definatly plug the air injection system and see if that makes
a difference, however it may be a few days before I get back to you as I
have to reinstall Windows XP having a internet problem and did everything
that is humanly possiable to fix the problem and no go, so gots to reinstall
the OS. BTW if you have any computer, hardware, software, networking
problems, I'm the man. My specility is operating system trouble shooting. I
worked for Compaq for 4+ years in the commercial divsion and have 10 years
of combined trouble shooting experience.
Anyhoo I'll do a few tests on the car and let ya know.

Mike

Bob Bailin said:
Thanks for the update. I've never driven my brother's 91 Fuel Inj
Excel at that high a speed for an extended period, but I did notice
that the exhaust manifold heat shield that I replaced a couple of
years ago looks pretty beat up for such a relatively young part,
which may mean that this may just be a design flaw with this
engine.

As I've said before, if you're pushing the engine to keep it going
at 130Kph, you may not be supplying it with enough ported
vacuum to keep the dist at its maximum advance. If you have a
vacuum gauge, try putting it inline using a tee with the hose going
to the dist advance, and see what the readings are at 100 vs 130.

You can always advance the base timing from 12 to, say, 14 BTDC
as long as the engine doesn't knock and performance doesn't
suffer.

I doubt there's a carb problem, but if it was running too rich at full
throttle, it should backfire a bit when you let up sharply on the gas.
Other than a weak power valve spring or slightly clogged secondary
air bleeds, there's not a whole lot to adjust on a carb.

And once again, check out the air injection hose to the exhaust
manifold. Block it off, plug it, whatever, to stop any air from entering
the manifold.

And for what it's worth, I won't have a 91 Excel to work on anymore.
My brother managed to effectively total his on a slippery interstate
last week during that New England storm. Fishtailing and bouncing
from an adjacent car to a jersey barrier and back, even at a really
low speed, will tend to do that. And damn, I just got it to pass a
state emissions test for the first time in 6 years thanks to a new
catalytic converter I installed over Thanksgiving. The new part just
messed up the car's karma, and it was doomed.

Bob

Mike Wilson said:
Hi Bob
Not sure if your still with me on this problem, I'm 90% sure I got the
problem nailed. The new distributor made the car work better, along with
adjusting the valve lash when the car is hot (remember I added a
Click to expand...
thousand
of
an inch to the specs on a cold engine) Drove the car at 130Kph for 20 min,
the exhaust manifold is dark, dark, red, any lower speed and the problem
doesn't occur. So for now I'll just have to take it easy on the car,
Click to expand...
until
I
can find out what is causing the slight problem at 130 Kph. I was thinking
that, the carb might not be set up properly, something I overlooked. Anyhoo
I just wanted to let you know that I got most of the problem figured out.
Cheers
Mike

difference:
this the
car.
Click to expand...
way
I
Click to expand...
took
a car
Click to expand...
has
to to
you
Click to expand...
floor.
If car
as the
gas to
the at
WOT circuit
that checking
out
Click to expand...
looked
at assumed
that originally
set
Click to expand...
After
I
Click to expand...
cold,
I the
hot to
the warmed
Click to expand...
right
up
Click to expand...
that
I warmed
it problem.
The Kph)
on HCs.
The for when
the suction If
you not
the is
the
Click to expand...
lot
of
penetrating
oil (or a torch) to get the old one out of the exhaust
manifold
without breaking it off.

And finally you can always try finishing
Click to expand...
cleaning
out
Click to expand...
Click to expand...
 
Well, my day job is as a systems administrator, also solving O/S
problems, so I won't have to trouble you with that sort of problem.
Personally, I'd do anything to avoid having to reinstall XP, unless
there's little or nothing in the way of software to save or reinstall.
If you do, try to start with the SP1 version right off the bat as a
fresh install if things are really that bad off.

But this is known as thread drift...

Bob

Mike Wilson said:
I agree it could be a design flaw, however Hyundai would have taken care of
the problem by now (1986-91)
I'll research the problem, check to see if the dis has enough vacuum as you
are suggesting.
BTW, the dis timing is around 6% BTDC, I left the dis timing like this
becacause I knew it to be correct. When I said that I changed the dis timing
to 12% BTDC, and got a posiative result, I changed it back to the
recommended specs 4 BTDC +-1
I found 4 degrees to be a little sluggish and 6 degrees to be right on the
money.
With the setup the way I have it right now, releasing my foot from the gas
pedal sharply doesn't produce any back fire, however I think you ment if I
had the engine set to 12 degrees BTDC. That is a good theory that you have,
I'll give it a shot. One thing I forgot to mention in my last post...I has
some white deposits on #1 and #2 spark plugs, after readjusting the valve
lash with the engine hot, the plugs are fine, funny...when I lived in
Ottawa, I worked as an auto mechanic for 7 years and have known lots of
mechnics to add a couple of thou to the specs so the can adjust valves (over
head cam) on a cold engine. This methiod has always worked great, I gess in
my case I have valve margins that are warn unevenly producing a little bit
of a gap. I'll definatly plug the air injection system and see if that makes
a difference, however it may be a few days before I get back to you as I
have to reinstall Windows XP having a internet problem and did everything
that is humanly possiable to fix the problem and no go, so gots to reinstall
the OS. BTW if you have any computer, hardware, software, networking
problems, I'm the man. My specility is operating system trouble shooting. I
worked for Compaq for 4+ years in the commercial divsion and have 10 years
of combined trouble shooting experience.
Anyhoo I'll do a few tests on the car and let ya know.

Mike

Bob Bailin said:
Thanks for the update. I've never driven my brother's 91 Fuel Inj
Excel at that high a speed for an extended period, but I did notice
that the exhaust manifold heat shield that I replaced a couple of
years ago looks pretty beat up for such a relatively young part,
which may mean that this may just be a design flaw with this
engine.

As I've said before, if you're pushing the engine to keep it going
at 130Kph, you may not be supplying it with enough ported
vacuum to keep the dist at its maximum advance. If you have a
vacuum gauge, try putting it inline using a tee with the hose going
to the dist advance, and see what the readings are at 100 vs 130.

You can always advance the base timing from 12 to, say, 14 BTDC
as long as the engine doesn't knock and performance doesn't
suffer.

I doubt there's a carb problem, but if it was running too rich at full
throttle, it should backfire a bit when you let up sharply on the gas.
Other than a weak power valve spring or slightly clogged secondary
air bleeds, there's not a whole lot to adjust on a carb.

And once again, check out the air injection hose to the exhaust
manifold. Block it off, plug it, whatever, to stop any air from entering
the manifold.

And for what it's worth, I won't have a 91 Excel to work on anymore.
My brother managed to effectively total his on a slippery interstate
last week during that New England storm. Fishtailing and bouncing
from an adjacent car to a jersey barrier and back, even at a really
low speed, will tend to do that. And damn, I just got it to pass a
state emissions test for the first time in 6 years thanks to a new
catalytic converter I installed over Thanksgiving. The new part just
messed up the car's karma, and it was doomed.

Bob

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