4160 carb install and tune (for Mike)

Good morning Mike!
My name is Jim.... it's right there in my signature.

You have a Cobra and I have a Hard Working Truck.
Just turned 460,000 miles, full of northern rust and never without a half ton of carpentry tools in my two Knaack boxes.

Yep. I'm a carpenter by trade.
Started in high school going to apprentice classes at night, once I quit my night job.

Everyone has questions.
None of them are "dumb questions"
If it helps you, or someone else, understand how their truck works or how to fix it.
That's why we participate in this forum.

It's going to be OUR conversation about the DuraSpark II ignition system.
It's advantages and flaws.

What would you like to know about how it works?

I'm going to "read the mail" for the most part.  But we have the section of the factory shop manual on ignition systems on the page at Documentation/Electrical/Ignition.  And it has a decent overview of how the DS-II system works.

Mike - Jim pointed out that he has his name in his signature.  Would you mind doing the same?  That really helps me keep names straight.  Thanks!

Did someone change the bowls on that thing? 4160s don't usually have a fuel feed like that.

My 750 Angelo?

They don't usually have a quick change secondary or a Stub Stack either....

How else would you set it up if you wanted adjustable center hung floats and jets plates instead of metering blocks?

I'm obviously not as into this as you.
So I'm sure you could help me understand

ArdWrknTrk wrote

I have to get the engine to high idle while the choke is on and the fast idle cam in place.
When it starts I check the float levels are good and I try to set the throttle stop screw for about 1,600 rpm.

By setting it this way, I think you are going to find that the fast idle speed is going to be much too high when  temperatures get warmer again.  The fast idle adjustment works much better when it is set at full operating temperature.  That is how Ford set them when they were new.  

1600 RPM is when the choke should come OFF.  You wouldn't want it that high on a stone cold engine that has just been started in the middle of December. That speed is a bit too high under those conditions, and it will climb even higher as the engine builds up heat.  And then you have to blip the throttle much too soon to get the idle to come down.  And that kind of defeats the purpose.  

If you set the fast idle speed to 1600 RPM when the engine is fully warmed up, it will never need to be re-adjusted.  When outside temperatures are coldest - like in December - the fast idle cam will initially hold the throttle at about 1200 RPM. (Just like on most modern fuel-injected vehicles.) If you sit there and let it idle, you will find that fast idle speed will start to increase as the engine begins to warm up.  When the fast idle speed climbs to 1600 RPM, that tells you the choke is ready to come down to the next step on the fast idle cam - which is usually about 1200 RPM in cold conditions.

But, you do not have to sit there and let it "warm up."  1200 RPM is enough to keep the engine running smoothly and you can drive away on the choke, if you like.  As the engine warms up from driving, the choke will automatically come off gradually.  This practice is actually *better* for the engine.  A cold engine will warm up faster in mile of [conservative] driving than it does sitting at idle for 10 minutes.

When the outside temperatures are warmer - like in July - the fast idle cam will initially hold the throttle a bit closer to 1600 RPM.  That's because a warm engine needs very little choke and for a much shorter time period.  Fast idle speed will rise to 1600 RPM much faster, and the fast idle cam will completely drop off when you blip the throttle.

I have found that chokes can work very well when they are set correctly.  In the end, there should be very little difference between driving a cold carbureted vehicle compared to a cold fuel-injected vehicle.

Good point Rick!

But if you see the photo, the choke is wide open.

Cam adjustment is by bending the tab on this carb. (there's no screw)

I successfully got my truck starting with one pump cold (not bitter cold) and it's driving well.

I think it needs a bit more pump shot, but I'm not going to do any more tuning until conditions improve.

You guys are way ahead of me, but Im following this conversation closely.

What kind of carburetor do you have on your truck Sam?

Honestly, since this Holley 750 was working well for me a decade ago.
I thought I could drop it on.
Obviously my engine is getting tired, but it does show me that the Thunder 650 was restrictive on top.

I definitely need to do some fine tuning.

Thank you Lariat85 for you input on the fast idle setting, I've currently have a fairly fast idle that just continues to climb, and find myself having to tap the throttle to calm the beast.
More over before I make that adjustment I need to figure out why she's got what seems to be either a miss, or really rough idle on a cold start up. I almost have to babysit her initially just before the fast idle kicks in and the rpms come up so it won't stall. After rpm's come up to and the fast idle speed she seems to runs smooth.

26ftcobraBBF wrote

Thank you Lariat85 for you input on the fast idle setting, I've currently have a fairly fast idle that just continues to climb, and find myself having to tap the throttle to calm the beast.

In colder conditions, the fast idle speed should start lower and climb much slower.  That's because the engine needs to be choked more to build up heat and run on the leaner mixture that was set at full operating temperature.  When the engine is very cold, the choke shouldn't come off by depressing the throttle.  If it is only a bit cold, depressing the throttle will sometimes drop the fast idle cam down to the second step, which reduces the idle speed.  

The trick is, you want the choke just tight enough and the fast idle speed just fast enough to keep the engine running and to allow you to be able to drive away immediately without losing the choke and stalling out. To achieve this balance, the tension on the choke cap should be set when the engine is cold, but the fast idle speed should be set when the engine is at full operating temperature.

26ftcobraBBF wrote

More over before I make that adjustment I need to figure out why she's got what seems to be either a miss, or really rough idle on a cold start up. I almost have to babysit her initially just before the fast idle kicks in and the rpms come up so it won't stall. After rpm's come up to and the fast idle speed she seems to runs smooth.

On a cold engine, fast idle should start immediately.  You should not have to "babysit" the engine to keep it running smooth.  

Before starting your cold engine, step on the gas to set the choke - but do not start the engine yet.  Remove the air cleaner lid and verify that the choke plate is completely closed.  In the cold month of December, it should close with an audible *snap."  In other words, there should be a fair amount of tension holding the choke plate tight against the air horn.  If there isn't - or it is only loosely closed - rotate the choke cap a bit richer by loosening the choke cap screws.  

I had a chance to swing by the Cobra Headquarters yesterday. I did as you instructed and did infact hear an audible snap. Pulled the air cleaner and took a look.

 The flap was closed tighter than a left hand thread bolt. However I felt the spring could use some more tension, so i made an adjustment.
After making the adjustment I fired it up, it didn't run any better on initial cold startup but the fast idle was kept in check by having more choke. It still has a fairly rough idle or miss for about 30 second to a minute.  It kind of seems like when the rough idle is present on initial start up the engine is chugging , low idle, sounds like it wants to die, and struggles to gain high idle RPM. The fan clutch is engaged the motor is idling rough and as the RPMs slowly but steadily pick up. It gets really loud from the fan turbulence, then all at once maybe 30 seconds or so the fan disengages the fast idle kicks off , RPMs come down, and then it's a nice smooth steady idle, it's very quiet at this point sometimes second guess myself that it's still running... I did find what appears to be a lever on the carb under the fast idle cam thst looks bent . Let me know what you think about that.
Thanks in advance for  reading and your consideration of my issues.
Mike

possibly

Top of the Morning Jim , as mentioned I have some pictures for you to look at. To answer your question
Next is there are no spider air tubes. This vehicle isn't equip with them, all ports are plugged
EGR is still in place acting as a temp block off plate till I can change the intake.
Lastly the A.I.R bypass valve/ tube..left in place, capped with high temp thread sealant.
It's a work in progress.

'Mornin, Mike.  

I keep doing a double take, because your pictures are from an unfamiliar perspective.

I see you don't have the coolant pipe bolted to the front of the passenger head, that I would expect (with A.I.R. pumps.)

I'm using the L&L bracket in place of that big casting.
If you look at the front of the heads you'll see a Welch plug .666" diameter (the mark of the devil!  )

Most people with this engine in a truck can't ever get to the little Y shaped retainers that hold that thermactor crossover to the back of the engine.
But you could easily -and inexpensively- eliminate it.
NAPA sells those plugs in a bag of 5, I believe...

What intake do you intend to go with?
Edelbrock's 2166?
Consider you'll need to modify your throttle cable bracket when you do.

I can kinda see the tab in your first pic... on my phone.

I'm going to suggest you set your choke a little open, on the vacuum pull-off.
The engine won't chug if it can get some air.

But,you can play with it from inside the RV!
Reach over with a finger and touch the choke blade.
You'll see how that initial choke setting has an effect before it starts to open up and set on the fast idle cam.

The plugs are NAPA #SEP 3812188

https://www.napaonline.com/en/search?text=3812188&referer=semantic&se=1

$1.49 each.

26ftcobraBBF wrote

Can you post a picture of that sticker on your valve cover?

Jim,
I think cracking the chole plate open a bit is going to fix the issue it makes perfect sense.
You mentioned a welsh plug in the front of the head, which is not a concern for me right? But you reference it size because it's the same size I'll need for the therm. crossover?
I open for recommends for an intake. My research suggest a duel plane. What are your thoughts?
It was tough trying to get a snapshot of what appears to be bent linkage possibly.

I mentioned them and gave you a part number, because the thermactor crossover fits into the exact same holes on the back of the heads...

If you want to get rid of that plumbing cap, and the pipe it's attached to, spend the $2.90 and buy two of those plugs.

I would use the Edelbrock manifold that I mentioned ^^^ up there.
Performers are ideal for a rig like yours.

My opinion, of course.

JIm
I had a chance to dive into this yesterday. I did some research. What I have is O'Riley's Spectra premium Distributor. They didn't have a spec sheet  to tell me exactly what was inside so I had him pull the part number for the "74 Elite with the 460 4 valve" as recommended in the link you sent me.  Come to find out the part number were the same. So I'm not sure if if what I have is optimal, but it's close I suppose.

It's hard to say what slot is used, what springs are in it, or how much preload is on the vacuum advance.

I've never taken a deep dive into Spectra's specs, because I've always tuned it myself.

I would hope it's good for your motor home, but as I said keep an ear out for the rattle of detonation under 'cruise'