Pontiac 400 tuning plug question
 

Running 1977 pontiac 400 with # 62 heads 4speed and summit 2801 cam I have the initial timing set at 14 degrees w no Vacum advance what should my total be set at car seems to sound a little weird on one side of the exhaust ? I will set total tomorrow. What plug and gap should I run I be running. 1969 spec plugs or 77 spec plugs ? .

Sounding strange on one bank is not a good thing , can I assume with that statement that your talking about how the motor sounds at idle?

Anyway here’s one thing to try.

Get the motor fully warmed up and then kill the spark.

Next crank the motor over a number of times and listen closely to hear any change in the cranking speed as each cylinder rolls pasted TDC.

If no difference is heard then it’s safe to assume that you don’t have a valve adjusted too tight or a valve hanging open.

Plug wise I would start with the equivalent of a AC Delco 43.

The only way to tell if your heat range is good is by full throttle testing and then checking the plug with no idle time.

You should go on line and look at the info called Plug reading 101 by Mike Canter.

Plugs have s total 600 degree range where they will work well.

This 600 degree range means 300 degrees above and below what the motor tells you it needs as ideal, and 300 degrees is a lot!

What do you have now for total timing?

If you make a mark on the balancer that’s 2 1/8” from 0 then that’s darn close to being 36 degrees total.
We can’t tell you what plug gap to run for certain because you did not tell us what you have for a Distributor.

The 62 heads (and all pre 72 heads) require gasket seat plugs. I use the NGK XR5, which is a gasket seat plug pretty close to the Delco R43S that Steve recommended.

My 400 with 62 heads and 2802 cam likes 32-33* by 3300 RPM and 93 octane fuel. With more timing I get pepper on the plugs.

Do you have stock rocker studs torqued to 20 ft/lbs or did you convert to adjustable studs and polylocks? What rocker arms?

Chiphead
I used the stock rocker arms and if I remember I just tightened them down. Car run high 13”s then I blew a head gasket and just replaced head gaskets and now trying to get it back to its proper tune but it wants to run like **** under acceleration and a little under idle I suppose I should probably test each cylinder again just to make sure but I don’t have more than 100 miles on it

Do you have the firing order correct?

Got it running last night ran pretty good stumble was gone however the idle is still ****. It seems like When I go to stop it dies . other times it idles at 1500 rpm

When the motor die’s will it start right back up)

If so then your not running too rich low rpm or at idle, but your lean and or your Distributor is at fault.

Most likely cause then of a high none stable idle speed and the motor dying at idle is a vacuum leak or the throttle is not going all the way back to idle or your mechanical advance is hanging up and not dropping all the way back to your base timing setting.

What carb?

Any idea what your SCR is?

What head gaskets did you use when you replaced them, 1016s?

What intake gaskets?

What rear gears?

Steve25 & chiphead are pretty on target with line of thinking, colder plugs, 32 degrees TOTAL timing, rocker adjustment/setup, vacuum leak.

If your SCR is up there, a 2802 might be a better choice.

I was just commenting on another thread about NGK XR plugs, and NGKs in general, the temp jumps are in like 1.5 step each time, so they don't cross like one would think. I literally ran into this myself, and realized I was running a hotter plug than I thought.

There's also folks complaining many plugs these days are knock-offs, counterfeit, and may not be getting what you think.

Pics always help, post some.


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Steve25 yes it dies actually right before it gets to the stop sign but then starts right up again.
Is there a way to richer that up ?

With A/T idle rpm´s and mixture screws needs to be adjusted in "D".

What carb and how many turns out from lightly seated are the idle mixture screws?

Is the carb idle/lowspeed circuit adjusted/modified for todays fuels?

HTH

So the carb is the stock 1977 quadrajet 4-speed carb. I’ve always adjusted by closing air mixture starting engine then then turning the mix screws with a vacuum gauge hooked up once I hit the peak vacumm. Stop then repeat on.The other side I believe it should be about 17lbs ? From the Egr Vacum

Does your motor have headers?

Even if not with the 2801 cam that carb at least on the primary side is going to need some tweaking.

How is the play in the primary throttle shaft, and especially on the drivers side?

Many Carbs from the 70s with over 75k miles on them need to have throttle shaft bushings put in to stop vacuum leaks .

When the choke is on it tends to mask the issue .

To test for a lean condition which it sounds like you have get the motor fully warmed up and the once at idle close the choke off slowly to see if the motor idles better.

I used to close mix screws, adjust one until it's right, tighten it back down w engine off, counting how many turns, then cut it in half and apply to both screws. Then trim form there on both equally.

But this is from age-ol' memory banks, so grain of salt...

Yes to what Kenth mentions, shifter should be in drive, and wheels chocked, today's fuels, not out of the book.

Also to mention, sometimes the air filter assembly makes enough of a diff to compensate for.


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HYWSTR455

I tried looking for the thread you mentioned commenting on about NGK XR4 plugs and how NGK plugs in general change thier heat ranges in 1.5 increments but couldn’t find it.

Can you please let me know which thread your comments are on?

Thanks
Mike

It was kind of insinuated, but if you look at cross reference charts you will be able to see it.

This is the thread I made similar comments on:

https://forums.maxperformanceinc.com...=885230&page=2

So an XR5 plug roughly translates to an AC R45S, and an XR4 roughly translates to a AC R43S. The AC R44S falls in the middle.

https://ngksparkplugs.com/wp-content...rence_2019.pdf

When you say '2-steps colder' it has a different meaning in one brand than some others. That's the point I was trying to make.


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Thanks,
I thought the XR4 was eq to the ac R45 and the XR5 eq to AC 43/44. at least that’s what I’ve been reading.

Thanks for replying

Mike

Yeah, I had it backwards.

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