78SC engine problem - new info

[RazorRacer]

Newly purchased 78SC with 67,000 miles

Starts up every time (hot or cold).
Runs great if accelerating, coasting or idle.
Runs great until constant speed for a while (~2 miles) and it acts like it's out of gas.
It will continue to act like it's out of gas unless idle, revving with no load or above 6000 rpm with load.
Continues to act this way until idle or off for about 10 minutes.
Then runs great again.


New dist. cap, wires, and plugs.
Valves adjusted 6000 miles ago.
Have replace fuel pump, fuel check valve, and fuel filter.
Have checked cat. converter.
Have checked for rust in gas tank and lines.
Thought it might be exhaust gases leaking into engine compartment, but putting more fresh air into engine comp. didn't solve problem.
Thought it might be a clogged tank vent valve, but running the engine without the gas cap has not solved the problem

Any guesses as to what might be wrong?

[joseph]

Check your catalytic converter sounds like the guts may have come apart and clogged your exhaust. This causes to much back pressure to build up under a load.

[RazorRacer]

Joseph,

That's what I thought, too. Attached is a photo of the cat. conv. that recently passed emissions.

So after it came out I drove the car to the nearest freeway (without the cat. conv. or muffler), but experienced the same symptoms. Also, got many questionable expressions from nearby drivers.

So was the cat. conv. tested right? It's back in the car now.

[smestas]

RazorRacer,

I've had a similar experience with my 78sc. It seemed that after the motor was warmed up it started to stutter and act like it wasn’t getting any fuel. After replacing all suspicious fuel parts and still having the same problem someone suggested checking my WUR (warm up regulator). There was the culprit! My WUR had finally given in. In the intermediate time while a new WUR was on the way I just unplugged the vacuum line from the WUR to the air box and the car ran fine.

Hope this helps.

[pkfrdh]

I'll jump in so I can find out what the problem was. Was it the WUR?

JGL

[mperkins]

How much did the WUR cost you?

[RazorRacer]

Simon,

You have my interest. I'll start playing around with the WUR tonight. I'd like to know more about the vacuum line to the air box. Which line in this diagram do you mean? What did you do with the disconnected line (leave open, block, etc.)?

Thanks.

[smestas]

RazorRacer,

All I did was dissconnect the vacume line from the WUR going to the air box. I put a plug on the open airbox hole and left the hose from the WUR open. I ran my car for about 3 months like this.

[RazorRacer]

Taking the vacuum line off the WUR didn't solve the problem.

Simon, I enjoyed your suggestion. In the process of finding this problem, I may get to know everything about this car. I'm getting frustrated because I would like to take her for a long sweet drive.

What would cause the engine to act like it's out of gas when it's hot and driven at constant speed, and then let the engine come alive when it gets over 6000 rpm?

[MotoSook]

Saw a link to this discussion from a more current discussion.

Razor, did you fix your problem?

Souk

[MotoSook]

OOPS loss my right brain for a second there..I'll return to the othe discussion..slap me someone!