Carbed 302 running poorly. Need suggestions

The '95 mustang v8 swap into my '93 Ranger has been moving slowly. We recently decided to go carb and are still struggling. The truck is at my buddy's shop away from me and I'm trying to help him with troubleshooting ideas. The carb is a brand new Holley 570. The engine compression was 135-150 on all cylinders. Here's his description:

Right now the throttle response is pretty good everywhere except immediately off idle. I've tried adjusting the accelerator pump to adjust that but it doesn't seem to be the problem. After the engine get of idle, if your under a heavy load, the engine will spit through the carburetor. Past about 2500 RPMs everything seems fine except the motor really should be making more power and did when it was fuel injected and running poor. It seems to be rich everywhere. It definitely needs smaller jets, but I honestly don't think they are ridiculously oversized for the application.

Thanks for suggestions!

Whats base timing?

Is the firing order right? Seen that a lot on Ford 302s, because Ford numbers their engines odd and the 302 and 302HO had different firing orders.

Base timing is 10 degrees and the firing order is 13726548

sounds like timing advance issues to me. What is running the advance? (are you using a mechanical/vacuum distributor, or some sort of computer timing?)

Robbie wrote: sounds like timing advance issues to me. What is running the advance? (are you using a mechanical/vacuum distributor, or some sort of computer timing?)

It's an HEI with a mechanical and vacuum advance.

Robbie wrote: sounds like timing advance issues to me. What is running the advance? (are you using a mechanical/vacuum distributor, or some sort of computer timing?)

This is where I'd start as well.

To just close the loop on the firing order question; the firing order is dictated by the camshaft and since all of the Windsor family cams are interchangeable you do need to make sure you're using the correct one for the cam that's installed. However, It would run worse than described if you had it wrong.

Verify your mechanical advance and vacuum advance can are working, mech advance could probably use some fresh lube regardless. After that try different vacuum ports on the carb for the advance, some engines/distributors like manifold vacuum, some like "venturi/ported" vacuum.

Lof8 wrote:

Robbie wrote: sounds like timing advance issues to me. What is running the advance? (are you using a mechanical/vacuum distributor, or some sort of computer timing?)

It's an HEI with a mechanical and vacuum advance.

Base timing was set with spout out? Sounds like its a bit retarded down low and the advance comes in enough to clear it up but not far enough to make the power.

In reply to dropstep:

I thought the spout was only for EFI? Shouldn't matter if a distributor is handling the advance right?

Robbie wrote: In reply to dropstep: I thought the spout was only for EFI? Shouldn't matter if a distributor is handling the advance right?

Yep dumb move on my part. Spout out is for the efi distributor. Ive replaced so many distributors because people try to time them spout in that my mind automatically goes too that style.

Put an adjustable timing light on it and rev it to 3000 with the vacuum off. Timing should be all in by 3000 and dead steady.

Ported vacuum or manifold? Depending on your setup, it should most likely be manifold if it isn't already. Then you need to make sure the canister is adjusted properly for the vacuum source. Manifold vacuum uses much higher spring tensions in teh canister.

Dumb question since I'm not familiar with the build: junkyard longblock, or rebuilt? Pull the fuel pump and check timing chain slop. EFI with CMS and CKS covers a wide variety of sins.

An old timer taught me this and it hasnt failed me yet. Hook up a vacuum gauge to manifold vacuum. Advance timing until the vacuum stops increasing, then back it off just a hair. Do the same thing when adjusting the idle mixture. Im sure that there is still some to be gained with tweaking things out after that, but that always got things running good and put timing and fuel into a pretty happy place.

gearheadmb wrote: An old timer taught me this and it hasnt failed me yet. Hook up a vacuum gauge to manifold vacuum. Advance timing until the vacuum stops increasing, then back it off just a hair.

While that may work great for idle, it could put you dangerously high at higher RPM. Base idle is a result, not the starting point. Set your max advance first, then if the idle advance isn't satisfactory you'll have to start working on the mechanical advance inside the distributor. Some of the Ford Duraspark distributor's add a ton of mechanical advance; so when you set your max advance where you want it, the idle advance ends up far too low.

ross2004 wrote:

gearheadmb wrote: An old timer taught me this and it hasnt failed me yet. Hook up a vacuum gauge to manifold vacuum. Advance timing until the vacuum stops increasing, then back it off just a hair.

While that may work great for idle, it could put you dangerously high at higher RPM. Base idle is a result, not the starting point. Set your max advance first, then if the idle advance isn't satisfactory you'll have to start working on the mechanical advance inside the distributor. Some of the Ford Duraspark distributor's add a ton of mechanical advance; so when you set your max advance where you want it, the idle advance ends up far too low.

I agree with you fully, but the 'old-timer' procedure should actually work great to get you really close if you have manifold vacuum advance and you leave it connected during the procedure.

Vacuum is high at idle so you get a lot of vac advance, and because of that you won't set base too high. Vac falls as you open the throttle, so vac advance falls away as mechanical kicks in.

It is still a good idea to check full advance at 3000 rpm or so to make sure it isn't too high (revving in neutral should be very low load so high vac signal).

I've found that the accelerator pump & discharge nozzles are fairly finicky on Holley carbs. I realize it's a new carb but maybe pull off the primary squirter nozzle and make sure that the little needle below isn't sticking, or the nozzle isn't all plugged up. Sometimes teflon tape or just a little casting burr or something works there way in there and causes all kinds of problems. The fuel spray out of that nozzle should come out in a strong stream with just a quick push of that accelerator pump. I would also verify float level if you haven't as well as adjust the idle mixture screws via the vacuum gauge method described earlier. Turn them until you achieve maximum vacuum at idle.

I've done so much research on analog timing trying to get my car to do what I wanted, before installing a carb-replacement EFI system that let me set the curve however I saw fit.

First, you probably need more initial timing. My 302 ran best with 14° (set with the vacuum hose removed and plugged), even with the vacuum advance running on manifold vacuum (which is where you want it. Ported vacuum is for emissions).

Second, you want the mechanical advance to add timing quickly, and no more than 22° (for a total of 36°) for most decent small block Ford applications. Older stuff with crappy heads needed more.

Third, the vacuum advance can add 15° or more, which isn't the end of the world, because in high vacuum situations, the cylinder density is low, and the burn is very slow.

Final tuning involves driving it, and making sure that it doesn't sparknock.

Also, try this. http://www.thompsonperformance.com/shop_products.html

dropstep wrote:

Robbie wrote: In reply to dropstep: I thought the spout was only for EFI? Shouldn't matter if a distributor is handling the advance right?

Yep dumb move on my part. Spout out is for the efi distributor. Ive replaced so many distributors because people try to time them spout in that my mind automatically goes too that style.

What is this "Spout" you speak of? Do you mean the vacuum advance?

The "SPOUT" is a jumper plugged into the harness on a computer-controlled Ford that tells the EEC IV (with TFI distributor) that it's okay for the computer to run the timing, which it does to help control idle speed as well as at all other RPM and load settings. Removing the SPOUT sets the timing advance to 0° and doesn't let the computer control it, so you can set the baseline.

The effect is the same as if you take the vacuum line off the vacuum advance, and don't rev up the engine.

more initial timing: try 15 degrees or so, and make sure the vacuum advance is hooked up to a manifold vacuum source so it is doing it's thing at idle and under light load... once you get the idle and cruising timing set, then you can work on limiting the total timing to whatever the engine wants.. since it's an HEI, it is pretty easy to limit the total timing by pulling it apart and welding up the slot and grinding it to where it needs to be to properly limit the advance.. also, you want to run probably one really light advance spring and one moderately heavy spring: buy an advance kit and just use the springs out of it.

a good investment for a GM HEI style distributor is a Crane vacuum advance can since the one that came with your distributor will likely freeze up within a year. the Crane kit is easily adjustable for rate and comes with limiting plates to dial in how much vacuum advance you want.

once you get your timing all dialed in and put the carb back to exactly how it was when you took it out of the box, you are just a few minutes with a vacuum gauge and a screwdriver from getting the carb dialed in so that it acts like a finely tuned efi setup..

Initial timing is really inconsequential provided the rest of the curve is correct. I had a 454 that had 32 degrees initial, locked out mechanical, and used ported vacuum. (low compression + cam too big)

Lof8, can you post compression and cam specs? I should be able to give you a timing curve to suit your needs.

Let us know how you make out.

He said it was out of a 95 GT, so something like 8.8:1 compression (off the top of my head) and a broomstick for a camshaft. .42 or so inches of lift at the valve. It's a 90's truck motor.

Thanks for the insight fellas. The truck is up at my buddy's shop in Clearwater. He's currently scrambling to prep his Miata for the Sandblast rally, so my truck is on the back burner until next week. I'll direct him here to see your suggestions and give some feedback when he's back to working on the truck. Thanks again!

Get the carb specs. Go through the carb to see if it set up to spec. My broad experience with oem carbs that they are just thrown together.

Even Holleys.