Engine tuning - where to begin . . . - Team Camaro Tech
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post #1 of 23 (permalink) Old Aug 27th, 18, 01:39 PM Thread Starter
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Gregg
 
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Question Engine tuning - where to begin . . .

Good afternoon all,

This is probably a fairly basic topic, but thought it would be worth asking.
I have a 68 convertible with a 350 engine. I purchased this car about a year ago and had it shipped cross country - yes, i bought it sight unseen . . . . lesson learned.

I recently flushed the coolant, changed the oil, installed new plugs, new wires, air filter, PCV valve and a new Edelbrock Perfomer 1406 carb. The engine runs - starts up easy, but idles rough. I have no other information about the engine - cam type, cylinder bore, compression, etc.

So, given that information (or lack of), I am trying to figure out what adjustments I should make and, maybe more importantly, what order I should make the adjustments in:

1.) Initial Timing - assuming this comes first. Not knowing much about the engine, where is a safe spot to set it.
2.) Advanced/Total Timing - Assuming the vacuum advance is working properly, what range should this fall in at 3,500 RPM if my initial timing is set ?
3.) Air/Fuel mixture screw adjustment - assuming this comes after timing is set. I've read about using RPM's to adjust these.
4.) Idle adjustment - Assuming this comes last. What is a normal range for idle RPM's to be at?


Thanks in advance for any input.
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post #2 of 23 (permalink) Old Aug 27th, 18, 01:52 PM
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Re: Engine tuning - where to begin . . .

Timing start with 12 initial VA disconnected and plugged total mechanical at 3500 36-38 (total is not a big deal if youíre looking to get smoother idle)

Adjust idle screw to achieve highest vacuum.

What rpm is it idling at now? If you increase rpm does it smooth out?
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post #3 of 23 (permalink) Old Aug 27th, 18, 01:58 PM
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Re: Engine tuning - where to begin . . .

Gregg do you have really have a problem? Before you try to fix it you need to see what is under the hood. And what is the cause of your rough idle (It could be a carb with bad gas in it from sitting for a year).

A Top Fueler idles at 2,600 RPM because of the blower and cam while your wife's van idles at 500 RPM with a stock cam and a computer monitoring and adjusting timing and air fuel on the fly. Your Camaro lies somewhere in between. But without the specs on the cam we have no way of knowing what is a normal idle for your motor.

I recommend buying a big (size wise so it is easy to read) vacuum gauge, and if you have points a dwell meter. You can use a vacuum gauge to set idle air fuel ratio, but it is much easier with a air fuel meter. It is impossible to tune the carb as to air fuel mixing on the main jets unless you also know how to read spark plugs, so an air fuel meter is very handy for that part of the tune up as well.

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post #4 of 23 (permalink) Old Aug 27th, 18, 03:27 PM
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Re: Engine tuning - where to begin . . .

Replace dizzy cap, rotor and change points or convert to pointless electronic ignition
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post #5 of 23 (permalink) Old Aug 28th, 18, 07:41 AM Thread Starter
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Re: Engine tuning - where to begin . . .

Thanks all - All of your replies kind of confirmed what i was thinking. Set the timing and fuel mix to the basics and then find out what is actually under the hood.

To answer the reply questions:
It idles now around 1,100 when warmed up. If i increase to 2,500, it does run much smoother.

Should I be concerned that Big Dave knows my wife drives a van???
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post #6 of 23 (permalink) Old Aug 28th, 18, 07:23 PM
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Re: Engine tuning - where to begin . . .

Unless you've got a radical cam in that motor, 1100 rpm idle seems way high and 2500 rpm is probably a good 1000 rpm above what some might consider a reasonable high speed idle as activated by the choke.

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post #7 of 23 (permalink) Old Aug 29th, 18, 05:36 AM Thread Starter
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Re: Engine tuning - where to begin . . .

Thanks Chris - I thought 1,100 was high too . If I set the idle below 1,000 it gets really rough. I'm bringing it over to a rebuild shop this week to do some diagnostics and see what they can tell me. My guess is they will suggest a complete rebuild . . .😁
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post #8 of 23 (permalink) Old Aug 29th, 18, 08:16 AM
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Re: Engine tuning - where to begin . . .

Have you checked for a vacuum leak?

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post #9 of 23 (permalink) Old Aug 29th, 18, 02:02 PM
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Re: Engine tuning - where to begin . . .

What is this "air fuel meter" never heard of one,,Ebay has just gauges you put in a car with a sensor?

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post #10 of 23 (permalink) Old Aug 29th, 18, 03:02 PM
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Re: Engine tuning - where to begin . . .

Quote:
Originally Posted by Niblet View Post
What is this "air fuel meter" never heard of one,,Ebay has just gauges you put in a car with a sensor?
https://www.jegs.com/i/Innovate-Moto.../3795/10002/-1

I use Autometer's but this works and it is a third the price.

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post #11 of 23 (permalink) Old Aug 29th, 18, 03:35 PM
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Re: Engine tuning - where to begin . . .

Thanks for that, where do I plug it in to a stock 67 ss 350? I honestly never heard of these

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post #12 of 23 (permalink) Old Aug 29th, 18, 03:38 PM
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Re: Engine tuning - where to begin . . .

Quote:
Originally Posted by Niblet View Post
Thanks for that, where do I plug it in to a stock 67 ss 350? I honestly never heard of these
You have to install an O2 bung in the exhaust pipe. The O2 sensor screwed into the bung.

They can be welded in or Summit sells a bung that clamps to the exhaust pipe.

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post #13 of 23 (permalink) Old Aug 29th, 18, 06:34 PM
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Re: Engine tuning - where to begin . . .

interesting, how far back from the manifold? and when your finished you just put a plug in the bung? or is this a perm instrument?

so you can adjust lean/rich mixture with this?

Thanks for the info

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post #14 of 23 (permalink) Old Aug 29th, 18, 09:01 PM
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Re: Engine tuning - where to begin . . .

Itís just a gauge with a wideband that reads AFR. You still have to tune conventional.

The gauge can be installed for monitoring or just for tuning and plug the bung when not in use.

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post #15 of 23 (permalink) Old Aug 30th, 18, 08:50 AM
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Re: Engine tuning - where to begin . . .

I installed mine under the hood for tuning, since I don't care what it is doing going down the road (I have a fuel pressure gauge and a vacuum gauge in the car to monitor the motor when driving). As long as it has gas and is sounding normal I'm happy. I don't drive in the rain so it doesn't get wet (I have a hard enough time keeping it going straight on a dry road).

This kit has a wide band oxygen sensor, so it has a heater wire to get it to light off faster. The older oxygen sensors that only showed rich or lean condition (not a number) required it to be as close to the top of the exhaust pipe as possible to be heated by the exhaust gasses. I put mine in the collector with a welded bung (clamps can loosen up while driving from heat cycling, and vibration when clamped to metal). Hose clamps work best on hoses.

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