7aull

iTrader: (2)

Well crap -
spring resurrection of beloved 80 12a SA a big disappointment this time. Recorded as a Utube vid:

http://www.youtube.com/watch?v=z1YbnWBF7j8

As it shows, she is not performing on accelleration.

Symptoms:
-starts OK (starter actually drags a bit, which is new too)
-idles fine
-drives normally under light engine load to about 3000 rpm
-over that it starts hesitating, does NOT build power - note (in vid) engine "rumbles" as rpm climbs
-hard accelleration it has little power, note pitch of rumble turns more "metallic" above 4000 rpm
BUT:
revs fine with no engine load

Status of car:
75,000mi original 12a; dead stock NO mods; stock emissions
-right out of 7 mo correct (as best I know) storage
-full fuel tank (for 7 mo), treated with fuel stabilizer
-13,000mi on plugs and dizzy cap
-changed fuel filter - no diff in problem
-checked vac hoses for leaks, all seem OK
Needless to say, "Ran Fine When Parked"

Maddening because she has always come out of hibernation ready to go...!
Thoughts??

Stu Aull
80GS
Alaska

Rogue_Wulff

Start with the basics. Check fuel flow. Filter could be partially clogged, or one of the lines. Check for restriction in the exhaust.

7aull

iTrader: (2)

Rogue-
yeah, I'm thinking fuel - or lack thereof would account for power loss - but YIKE! what is with that gawd-awful sound??
Only "flow" thing I know to check is if the carb diaphram is pumping as it should - do that tomorrow. Archive search has some power-loss ideas -but the SOUND!?!?
Stu Aull
80GS
Alaska

yetterben

check for spark on the leading side!

Rogue_Wulff

Stu- Remove the fuel line at the carb, and place a jug under it. Turn the key on, and time how long it takes to fill the jug. FSM lists ~1L/min as the standard flow rate.
Also, if the carb has accumulated some trash in the area of the jets, it could be restricting fuel flow thru one or of the jets. If this is the case, and it's got a restriction in a secondary jet, one rotor will be running fine, while the other is not. That could account for the roughness and sound.
A restriction in the exhaust could also be the culprit. The sound could be simple as an exhaust leak that only shows up under hard acceleration.

7aull

iTrader: (2)

Thanks guys -
PLUGS, and their ability to spark, are now my first check, tho how does one check if they are firing properly under LOAD?? Obvious (??) they are firing correctly when NO load, so what would make the diff there?? will swap in a new set- IIRC the 1980 Sa is set up so the...trailing? plugs only fire at certain rpms... Could this be coils or an ignitor problem?

AIR FILTER: K&N just cleaned and re-oiled last summer - but can pull it and take a run ...

FUEL: ok Rogue - will pull line off carb and see how the pump performs.
Q: does the pump feed MORE under load? or just steady pressure, with the fuel regulation set at the carb.

EXHAUST:
NO CAT! Its a reactor exhaust - which I realize still doesn't mean it can't collapse inside. Tho, with only 75K miles?? These are pretty overbuilt units. Maybe finally time to swap in my RB exhaust....
If it was a leak Rogue, that shouldn't affect the power output should it?
Could the sound (re: YouTube vid) be coming from an Emissions valve of some sort?

KEEP THE IDEAS COMING GUYS!! Appreciate all input
Stu Aull
80GS
Alaska

Rogue_Wulff

Stu- The fuel pump only puts out 2.5-3.5 PSI. It relys soley upon volume, rather than pressure. There is a check valve located in the return line (silver do-dad about 6" from carb) that helps to regulate the fuel pressure at the carb, the rest is handled by the needle/seat assemblies.
The noise could be related to an emmission valve of some sort, but I'm leaning more towards one rotor misfiring under high load. This could be from a fuel issue, or spark issue. My money is more on the fuel side of the equation.
New plugs will not hurt, since 15-20K is about all the life that can be got (reliably) from a set of plugs.
I do not remember if the 80 had the trailing ignition cutoff under certain conditions, but I know the 79 did. I *think* the 80 also does this, to assist the TR in cleaning up emmissions. Trailing ignition has almost no effect on power, it is mainly used for reducing emmissions.
75K is a little early for TR failure, but it is certainly possible. If there is a restriction somewhere in the exhaust, any slight leak will be intensified, as the pressure inside the exhaust builds up, normally under higher loads. Under little load, the leak may not be detectable.

IanS

iTrader: (4)

If you still have vac secondaries, check to make sure they are not stuck as them not opening will cause that sound. It happened to me, and it made a similar sound.

Edit: Shoudl also add that my engine made a similar noise when the fuel filter was clogged real bad.

7aull

iTrader: (2)

Thanks Rogue, Ian-
adding secondaries to the list BUT:
How does one check secondary ops?
If they need vac, don't you need a LOAD on the motor (ie, driving it) to get them to respond? Any way to do this sitting at the driveway?? Anyone? Carl?
Re: fuel filter - first thing I did was replace it - no joy-
Keep those ideas coming - will report here as I run thru the to-try list-
Thanks ALL!

Stu Aull
80GS
Alaska

tallbozo

iTrader: (5)

make sure your plug wires are in the right order...i had this issue once and once i checked, i found that i switched the leadings and trailings...idiot me...

j9fd3s

iTrader: (3)

that noise sounds like detonation

two things that pop to mind are a plugged exhaust, or weak fuel pump. my first choice would be the fuel pump. i actually did have a car with a weak pump once upon a time, similar symptoms, although mine would do that in 3rd gear.

possible the ignition isnt right, but i think it just wouldnt work at all, and the plug wires could be wrong, but i doubt they moved themselves.

engine should be fine, if it was bad it wouldnt idle.

clogged carb jet? possible. ive rebuilt a few of these carbs and it never been the problem, its just a "car doesnt run right, it must be the carb" thing. but anyways its pretty easy to pull the top off the carb.

cdrad51

It's time for the open-hood-while-car-is-in-motion-and-look-into-the-engine-bay-trick!

Or find a dyno.

But start by actuating the secondaries by hand and thus making sure they are not stuck or otherwise not moving as freely as they should be.

7aull

iTrader: (2)

FIXED!!
New plugs-
New Dizzy Cap-
New Rotor-
NEW CAR!
Guys, I am embarrassed, relieved, puzzled;
-Embarrassed it was so easy and just didn't do it first!
-Relieved because, well, it was so easy
-Puzzled because I would NOT think a "minor tune-up" requirement like this one would be so "ON" or "OFF" - there was some 13,000mi on these parts (how does that compare to everyone else??) and, as I said, it ran just fine when I put it away in the fall-
I always assumed these parts wore out, ie degraded, over time - NOT just stop working correctly!?
OR:
timing is everything and the "problem" is still there, masked by the new parts....

THANK YOU EVERYONE!! Hope my little "adventure" offered some tidbit for someone else in the same boat. For me, I think I will now religiously change plugs/cap/rotor every 10K and be done with it!

Stu Aull
80GS
Alaska

stranger

ahh the essentials. i would still double check the carb and make sure everything it working right, secondaries opening and that it is not flooding under load to be safe.

j9fd3s

iTrader: (3)

except for the plugs, 13k is way low.... wires maybe if they are really old

7aull

iTrader: (2)

j9- 13,000mi is LOW? Really?... so how long do most of you all hang onto caps/plugs & rotors?
My wires are RB's R100 Magnecores - expect they might out live the car
Stu Aull
80GS
Alaska

Jeff20B

iTrader: (13)

I have a set of plugs from 1995. Probably low mileage but high age.