Tune up advice

Turboomni

Turboomni

Old Man with a Hat
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Sorted out timing and vacuum advance with my points on my 440. She has never run better.
It is now in the mid 80's and I am getting a bit of detonation at part throttle but not all the time. Dwell is 29. The base timing is at 12 to 13 * btdc. I am running a Edelbrock 1406 with stock jets and metering rods I believe. Should I backoff timing first or should I try richer metering rods by one step first, or something else? . I know the 1406 tends to be lean. Plugs look good.
Hate to back off timing as she idles and runs great in cooler weather and when hotter too except for the slight pinging.. But I realize you got to do what you got to do if necessary. Any thoughts would be great to point me in the correct direction.

thanks
 
How I tune for detonation:
Advance it as far as possible while keeping it easy to start and then keep backing off until the knock stops using premium gas.

There will now follow posts from a cupla guys with 1,000 line replies on what ends up being exactly what I said.

It's the solution 90% of the time for street use.
 
Turboomni said:
Sorted out timing and vacuum advance with my points on my 440. She has never run better.
It is now in the mid 80's and I am getting a bit of detonation at part throttle but not all the time. Dwell is 29. The base timing is at 12 to 13 * btdc. I am running a Edelbrock 1406 with stock jets and metering rods I believe. Should I backoff timing first or should I try richer metering rods by one step first, or something else? . I know the 1406 tends to be lean. Plugs look good.
Hate to back off timing as she idles and runs great in cooler weather and when hotter too except for the slight pinging.. But I realize you got to do what you got to do if necessary. Any thoughts would be great to point me in the correct direction.

thanks
Click to expand...

I would leave the secondary metering rods alone. if necessary, try going one size larger on the primary metering jets. You can also back off one or two degrees of timing without much loss of performance. Another old school thing you can try is timing the car with a vacuum gauge. Hook the gauge to manifold vacuum and note the reading. Since you are getting some pinging, back off the timing until the manifold vacuum drops, now advance the timing in small increments until the manifold vacuum stops increasing and road test the car.

Dave
 
I'd forget the jetting issues, from my experiences. I've not seen that that part of things matter that much, if it's just in a particular rpm range and load. Besides, that requires some disassembly and tampering with a mixture curve that seems to be working pretty good.

Commando1's orientation is good, as it addresses the basic issue relatively easily. I'd try some of the next-higher octane fuel and see if that quietens it down. Otherwise, I'd look at taking a little vacuum advance "out" by seeing if the vac advance can is adjustable. Insert an Allen wrench that just fits into the nipple, see if it will engage with an adjustment nut inside the can, turn it about 1/4 turn clockwise to tighten the spring in the can, to make the advance happen at a slightly higher vacuum level (i.e., slow it down). It shouldn't take much if it's trace rattle, I suspect.

AND, if you've got the time, put some quality carb cleaner in the tank and don't stop until the tank is at 1/4 full. Steady-state highway cruise of 70mph is good to clean things up anyway. Another dose of cleaner and full of gas. Return to base.

Enjoy!
CBODY67

(17 lines used and within the "square")
 
KISS baby KISS. Tweak the timing before messin with the Carb, unless you know for sure that you need to dive into it to change something out. Maybe fatten the idle mix too maybe? Good Luck
 
If you do want to get into the carb, I would suggest going to a local engine shop that deals with edelbrock carbs/parts and seek their advice regarding changes. Has to do with sea level elevation and something else. There is a chart and they may also have personal experience.
 
I have the correct Edelbrock kit to modify my 1406 in every direction according to the chart they provide. That is not a problem and diving into the carb is not a problem either. Commando said back off timing till gone and that is absolutely correct and will do the job. Mr Lux's advice seems good too with backing off timing till vacuum just start to drop off and then advance it in small increments . What fascinates me most is the adjustment of the vacuum advance canister CBODY67 mentioned. There is an adjustment on many vacuum advances that make the vacuum advance behave as you would like.
Many have a stamp on the arm of it's behavior with vacuum without adjustments available and many do not have a stamp but are adjustable. I could back off basic timing but maybe my problem is the vacuum advance is just tooo sensitive and advancing a bit too much at part throttle on ported vacuum during part throttle acceleration. Interestingly I could have a knock sensor readout and a wide band O2 sensor readout but they would not tell me specifically what was wrong on my old Plymouth,,,only readout a symptom and point to something that was really out of whack like extremely lean/rich etc. So we are back to experience,,and feel....I love it
 
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The number stamped on the vac advance arm is usually the degrees of advance allowed by the "stops" on the arm. The wide spot that contacts the vac advance body on the backside. That can be filed down for more advance, if desired. I believe that would be in "distributor degrees" rather than "crankshaft degrees:?

A quick way to see if it's a lean spot in the fuel curve, you can put the next-stiffer power valve springs in the carb. That would need more vacuum to pull the rod/piston down, so it might richen the mixture in that one area (as they are two-step rods; AVS had three-stage rods). That might be the easiest way to investigate a lean window situation. Usually, I believe that a lean spot would be more evidenced by a slight unresponsive spot in the throttle travel, rather than pinging or trace rattle.

Another possibility, depending on what's already in the car, might be to use a spark plug that's one or two heat ranges colder than what's in there now. This might be another tool in the arsenal.

Please keep us posted on what you do and how it turns out.

CBODY67
 
There are 3 types of advance.

1. Your initial setting.
2. Mechanical advance (centrifugal).
3. Vacuum advance.

IMO, #2 may well be your problem but of course, the RKIA solves all on this board.
 
CBODY67 said:
look at taking a little vacuum advance "out" by seeing if the vac advance can is adjustable. Insert an Allen wrench that just fits into the nipple, see if it will engage with an adjustment nut inside the can, turn it about 1/4 turn clockwise to tighten the spring in the can, to make the advance happen at a slightly higher vacuum level (i.e., slow it down). It shouldn't take much if it's trace rattle, I suspect.
Click to expand...
This^^^^^^^

Computer controlled timing, keeping it just right, and combustion chamber shape keep new cars from pinging at 10:1 on mid grade.
My experience is they have almost no spring tension on any new V.A. can I've every put on.
3/32nd Allen wrench if I remember correctly.
 
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I am looking at the vac advance as my problem but another idea from Cbody67 is the use of a colder plug which I do on my Omniglhs.
 
Turboomni said:
I am looking at the vac advance as my problem but another idea from Cbody67 is the use of a colder plug which I do on my Omniglhs.
Click to expand...
Probably will not hurt especially in warm weather but at lower rpm I do not think it will make a difference with the big dead area in combustion chamber of 906 heads on your car. Cheap thing to try though.
 
First things first. Needed an inspection sticker. She passed but I have a worn inner tierod on the right front ....sigh...


IMG_20180618_111425.jpg
 
Carmine said:
Thank God we don't have them on anything!

View attachment 192519
Click to expand...
Yeah, yeah rub it in. Thanks

Inspection states help keep car companies and finance companies afloat. $1500 repair bill on $1000 car seems like a good time to trade it in and buy a new or newer one. Lot of good vehicles have met their demise at the hands of mechanics that can't resist cutting their own throat.
 
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70bigblockdodge said:
Yeah, yeah rub it in. Thanks

Inspection states help keep car companies and finance companies afloat. $1500 repair bill on $1000 car seems like a good time to trade it in and buy a new or newer one. Lot of good vehicles have met their demise at the hands of mechanics that can't resist cutting their own throat.
Click to expand...

People here complain about seeing some piece of crap on the road, but I've never heard a "inspection state has x% fewer accidents"... and I'm sure if that stat existed, some lobby group would be jamming it down our throat to save the children, whales, slugs, etc.
 
Carmine said:
People here complain about seeing some piece of crap on the road, but I've never heard a "inspection state has x% fewer accidents"... and I'm sure if that stat existed, some lobby group would be jamming it down our throat to save the children, whales, slugs, etc.
Click to expand...
Does nothing, people smash perfectly good cars into stuff and each other everyday all the time. It's mechanic welfare system that we pay for and benefits someone who can't keep a job because they are good, they just they have a piece of paper.
 
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