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fresh build idle problem
https://slantsix.org/forum/viewtopic.php?t=37342		 Page 1 of 2
Author:  zorg [ Thu Oct 01, 2009 10:29 pm ]
Post subject:  fresh build idle problem
I finally got my rebuilt engine in and hooked up. Fired it off for the first time, and have some questions...

First the details:
'76 225
Super six
bored .030
.060 off the block
Engnbldr valves, 340 springs, etc
roughly 8.5:1 compression
Reground cam, 280/270 I think?

The manifolds/carburetor stack was removed as a unit, and reinstalled untouched. Same goes for the distributor, alternator, fuel pump.

It starts and runs nicely... above 1,200rpm. Timing appears to be roughly 30-40 BTDC. Advanced farther and it dies. Can't retard it, I'm out of room on the dist. slot. Moving it a tooth doesn't really do anything but spin the rotor, no? It seems to run nicely from ~1,200rpm on up, but the bottom falls out below that. Idle mixture screws are out 1.5 turns. Curb idle screw is cranked way in to keep the car running. Valves are a little loose, but it's hard to set the lash at 1,200rpm! That's all the info I can think of off the top of my head. Ask away, and I'll answer what I know.

Thanks!

p.s. Not running a vacuum advance pod or any of that tangle of vacuum lines.
Author:  Reed [ Thu Oct 01, 2009 10:55 pm ]
Post subject:  Re: fresh build idle problem
Quote:
Timing appears to be roughly 30-40 BTDC...p.s. Not running a vacuum advance pod or any of that tangle of vacuum lines.

You should set your base idle timing between 0 and 12 BTDC, depending on your timing curve. You should also use the vacuum advance pod. It is only one hose.

Total spark advance should be 32-36 BTDC, but that is with all initial and mechanical added in together.

If you are running 30-40 BTDC base curb idle timing, you need to retard the rotor at least one tooth, possibly two, and loosen the bolt on the bottom of the distributor.

Check to make sure that you have slack in the throttle cable as well.
Author:  Aggressive Ted [ Thu Oct 01, 2009 11:00 pm ]
Post subject: 
Is the engine fully broken in? for 20 minutes at 2,000 to 2,500 rpm?
If so, it sounds like a manifold gasket leak.

What brand manifold gasket did you use and what are the manifolds torqued to? Remflex only suggests 5 pounds with their gaskets......

If you hold a straight edge across the manifold ports was it straight?
and clean?
Sanded or milled so the surface was fresh and clean?

I always install the exhaust first then add the intake to eliminate the potential for leaks.
Doc suggested making a sanding board out of 16 ply 3/4" with a 80 grit sanding belt screwed or stapled to it to dress the port surface.
Take a look at the pictures on the red link below my name. You will see the manifold face super clean.
Author:  zorg [ Thu Oct 01, 2009 11:52 pm ]
Post subject:  Re: fresh build idle problem
Quote:
You should set your base idle timing between 0 and 12 BTDC ... Total spark advance should be 32-36 BTDC, but that is with all initial and mechanical added in together.
Right, that's where I'm trying to get. However, if I move the distributor just one tooth (either way...) the car simply won't start.

Quote:
Check to make sure that you have slack in the throttle cable as well.
I've noticed that come up a bit lately, so was watching for that already. Thanks though!

Quote:
Is the engine fully broken in? for 20 minutes at 2,000 to 2,500 rpm?
15 minutes, yes.

Quote:
What brand manifold gasket did you use and what are the manifolds torqued to?
FelPro was all I could get my hands on. It's not their nice thick one like I used to run, either. I do have another cheap FelPro, if doubling might help? Oh, and ~10 lbs.

Quote:
If you hold a straight edge across the manifold ports was it straight?
No job is complete without forgetting something... I did however sand them nice and smooth. So I know at least neighboring ports aren't way off.
Author:  DusterIdiot [ Fri Oct 02, 2009 5:54 am ]
Post subject:  What cam?
What cam do you have in there?...a 280/270 with an overlap of 106-108 is going to make a 8.5:1 compression not a happy camper... big cams like a lot of rpm and compression. With the engine set at 1200 rpm is there vaccuum at the distributor port on the carb?

-D.Idiot
Author:  SlantSixDan [ Fri Oct 02, 2009 6:27 am ]
Post subject: 
It does sound like a lot of camshaft; it's possible it's not making enough vacuum to pull a signal on the carb's idle circuit. But you might tell us about the carb in detail…
Author:  Reed [ Fri Oct 02, 2009 8:43 am ]
Post subject: 
If the closest you can get is 30-40 BTDC, then you will need to do what I suggested- retard the rotor one tooth and use both bolts to adjust the distributor.

Or you could try shifting all the plug wires clockwise one tower on the distributor. That should retard the timing 60 degrees, and you should be able to adjust the timing back to around 0-12 BTDC using the slots.

Can you give us a vacuum reading with the throttle completely closed?
Author:  zorg [ Fri Oct 02, 2009 9:35 am ]
Post subject:  Re: What cam?
Quote:
What cam do you have in there?
I had the stock cam reground, the specs were similar to Doc's RV15?

Quote:
With the engine set at 1200 rpm is there vacuum at the distributor port on the carb?
Good question. Do I need a gage, or is sticking my thumb over the hole scientific enough?

Quote:
But you might tell us about the carb in detail…
'76? Carter BBD. I had the throttle shaft re-bushed, and then rebuilt it myself ~2years/7,000miles ago. I'll be the first to say I don't know what I'm doing dialing in a carburetor, but it seemed to run nicely on the tired motor.

Quote:
retard the rotor one tooth and use both bolts to adjust the distributor.
One tooth either way and the car will crank all day, but not start. As to both distributor bolts, I'm familiar with the hold down bolt adjustment, but do tell where the other adjustment bolt is.


I'm going to be out of town for a week. I'll keep checking in here, but won't be able to try anything until next Monday. Thanks for the help guys.
Author:  Reed [ Fri Oct 02, 2009 10:19 am ]
Post subject:  Re: What cam?
Quote:
Quote:
retard the rotor one tooth and use both bolts to adjust the distributor.
One tooth either way and the car will crank all day, but not start. As to both distributor bolts, I'm familiar with the hold down bolt adjustment, but do tell where the other adjustment bolt is.
Image

I had a similar problem with my brother's 74 Duster when we first got it. I had to adjust the bolt on the bottom of the distributor to get it timed right. It is probably easier to pull the distributor to adjust it then trying to do it with the distributor installed.
Author:  SlantSixDan [ Fri Oct 02, 2009 11:00 am ]
Post subject: 
I really like my Slant-6 distributor wrench for adjusting the timing via the underside bolt without having to pull the distributor.

I really don't like how I always seem to know where it is except when I actually need it. :cry:
Author:  zorg [ Fri Oct 02, 2009 11:34 am ]
Post subject: 
Reed, you rock, and I just learned something new! Thanks for the picture.
Quote:
I really don't like how I always seem to know where it is except when I actually need it.
Story of my life these last few weeks. Grease gun, tank drain pump, feeler gages, transmission inspection cover(!)... And it's not like I have a big shop for things to hide in either!
Author:  Aggressive Ted [ Fri Oct 02, 2009 12:18 pm ]
Post subject: 
Zorg,

If everything is set correctly and you still don't have enough throw to get the timing you want, don't be afraid to file both hold down slots for a little more throw. I was able to get up to 20 degrees initial timing out of mine. That was with some super stiff springs on the mechanical and no pod.
Author:  Reed [ Fri Oct 02, 2009 12:31 pm ]
Post subject: 
The difficulty in getting to this bolt is almost an A and F body only problem. Vehicles with larger engine bays (B/C/E, trucks, vans) usually have enough room to snake a 7/16 box end up there.

Of course, the best solution is to swap to a later non-slotted hold-down clamp that allows for full 360 degree movement (if you remove the vac advance pod that is). Making that swap is one of the first things I do.
Author:  Aggressive Ted [ Fri Oct 02, 2009 1:50 pm ]
Post subject: 
Reed,

Got a picture of that mod for the SL6?
Author:  Reed [ Fri Oct 02, 2009 2:15 pm ]
Post subject: 
Just for you, Ted! :wink:

Here are the two styles side-by-side:

Image

Here are the component parts of the later (more preferable) style:

Image

Here is how they fit together assembled on the motor (use your imagination for the engine block):

Image

Please note that I am missing the o-ring that goes under the plate on the distributor. If you leave this off you get a BIG oil leak.

The metal u shaped thing clamps the ring bolted to the bottom of the distributor to the engine block holding it steady.

I don't know the exact date of the switch in hold-down styles, but I believe it was in the late 70s. Note that the distributor showing the later style is a lean-burn distributor. The ring is a slant only piece (I think, maybe a v-8 would work), but could probably be easily fabricated from flat stock of metal. The clamp from a v-8 *might* work, but try and find a slant six one first.
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