Low Idle and Hesitation Problems (SC)

[old_skul]

Okay, a little off the beaten path for me:

A friend (really!) has a 1978 SC Coupe. This was the first year for the 3.0l I believe. Lately he's been having problems with hesitation and idle reliability. Basically, the engine will not stay running unless he's giving it some gas.

The problem has gotten worse and worse over the summer and several track events.

I have noticed that when he starts his car it idles higher than my Carerra. It idles at 2000 rpm, and once it warms up the idle speed drops to normal, and then won't stay running unless it's given gas. He also indicates hesitation on acceleration until 3000rpm or so.

What's wrong?

[john walker's workshop]

perhaps it leans out so much that it won't idle. that would also account for the low rpm hesitation. he needs to set the CO on a gas analyzer @ 1000 rpm. 3.5% works on most of them.

[Superman]

Yes, do it. I think the '78s don't have catalytic converters to worry about. 3.5% is higher than spec, but they run much better when they're not so terribly lean as specs call for.

[RazorRacer]

Don't know for sure, but I would play around with the timing and the vacuum advance. Try plugging the vacuum advance at the distributor and see if that stops the hesitation.

Currently my 78SC has the vacuum advance plugged and the timing set to 10 degrees BTDC. It still needs some tweeking, but that's where I am now.

[MotoSook]

Right on razor...I couldn't get my vacuum advance steady enough to alleviate my giddy up stumbling off idle, so I just plugged mine too. I'll have to wait 'til the dist rebuild I guess.

old skul...if this happend without any adjustment to the mixture screw, but the idle is higher then before on start-up and then the mixture is lean when warm...could be an intake leak (or vacuum) too. Not to contradict JW, but I would probably try to find the problem before I cover it up by compensating with a richer screw setting.

Good luck

[john walker's workshop]

the mixture setting is not a coverup, just one of the things that need to be checked.

[pbs911]

I think the '78s don't have catalytic converters to worry about. 3.5% is higher than spec, but they run much better when they're not so terribly lean as specs call for.

Well sort of. my 78 came with a cat from the facotry but was removed before I bought it. If it had come with the car it would be on the sehlf in my garage with the rest of my 78 exhaust system and smog pump.

I have probelms with the motor dying when warm-hot. I hooked it up to gastester and found the CO level climbed to over 16%, and was still going! I set it to about 1.5 (without air pump and pre-74 exhaust) for emissions testing and it had no guts. After the test pulled the air pump and set it just slightly above 3.5. The car now runs strong and does not die or flutuate at idle. The CO level is the first thing you shoudl check. It has to be done so do it first. You may be surprised.

[RazorRacer]

During my emissions testing its failed without the smog pump:
15 mph 3.70%
25 mph 3.70%

It passed with the smog pump:
15 mph 0.80%
25 mph 1.30%

Is my air mixture adjusted properly? Is it close enough?

If not, should I turn the hex bolt clockwise or counter-clockwise?

How will it effect performance turning clockwise?

How will it effect performance turning counter-clockwise?

Thanks in advance.

[Joe Bob]

Setting the CO without an analyzer is like teaching a pig to sing.....waste of time and annoys the pig....

Most P-car shops will warm up the analyzer, test it for for you and do an adjustment for the minimum rate.

Guessing doesn't work, use the right tool.....

JC Whitless sells a CO analyzer BTW.....

[stuttgart]

Mark,
Are we talking about Carston's SC... Yep.... I know the thing is having a spot of trouble stayin runnin right now. I thihk abit of the trouble is that he cracked the exhaust, which may have it running rich.. plus he snapped a fan belt at the track on Sat, and
got her VERY HOT!!!!! then the trouble strted to a bit more of a problem if you know what i mean. Please guys if anyone has any more helpful ideas please post them. i have run out of ideas as we were trying to figure it out at the track. I could only think of the exhaust crack causing a bit of the problem.

Eric mckenna
78SC

[Doug Zielke]

Have the injector O-rings and shells been replaced (since 1978)?
They go hard and leak air, leading to very lean mixtures.
Spray a little carb cleaner (with the motor running) around the injectors and intake runners to check.