Problem With Just #3 & #5 Cylinders, No Fuel ONLY in idle circuit. HELP!

[dirwin]

I'm pulling my hair out here with this IDA 48 set up.

Carbs are sync'd nearly perfect.
Verified floats are all set between 5.25-5.5mm
Idle jets are 65 in 120 holders
Fuel pressure is 2.5 pounds consistent.

At idle my header temps are all around 230-250 degrees 2 inches from the header flange EXCEPT #3 which is running 90-95 degrees and #5 which sits around 125-130.

If I hold open the throttle and bring the RPM up to 3-3500 RPM, into the main circuit, and stay there for 45 seconds or so, my header temps will all equal out at about around 340-350 all the way around, including #3 and #5.

What I'm fighting is that I'm very rich, it will run you out of the shop in no time, even with the doors open. All of the plugs are Motorcraft 32 heat range and all are very black.

I know that I'm getting fire to the #3 and #5. I'm running a mechanical advance MSD with 16 degrees initial and 37 total timing.

At idle, when the engine is warmed up, turning the A/F mixtures on #3 & #5 have no effect on the idle at all.

The engine is a new Ford Racing crate 302, 10:1 compression, Z304 heads with the Z303 cam. Cam specs are .552/.552 lift, 228/228 duration at .050 lift with a 112 lobe separation.

What I've done so far:

verified correct float levels
removed idle mixture screws on #3 & #5 and blown them out (lightly) (no effect)
swapped the idle jet holders and jets from #3 to #4 (no effect)
swapped the idle mixture screw from #3 to #4 (no effect)
verified that the accelerator pump shooters are working on all carbs, including #3 and #5

I'm really struggling with this so any suggestions would be very much appreciated.

Dave

[Jerry Clayton]

switch the location of the carbs to verify that the condition travels with the carbs

[carmine]

Check that your .65 idle jet is actually sized correctly
God knows how many jets I've seen that have holes in them that don't match there markings
On cylinders 3 and 5 the idle jets may be actually larger than .65 mm dia hole
And that could cause an over rich condition on those 2 cylinders
That could explain the over rich smell and the cooler exhaust temps on 3 and 5

[Rick Parker]

dirwin:
I think you will find that the throttle plates on the suspect cylinders are not uncovering the idle ports in the throttle bores, causing no fuel to be pulled. To verify this, disconnnect the interconnecting links and the center pull. Each carb will then be independent, none will be connected to another (this is important). Then slowly twist the idle SPEED screw on the suspect carbs. When the throttle plate uncovers (creates a vacuum) over the port, fuel will be pulled and the cylinder will begin to fire.
If these are used carbs (symptoms indicate this) you will need to verify (correct as necesssary) the throttle plates are exactly the same in relation to the idle port when viewed from the bottom. Use a magnifying glass for this. You may also need to very slightly twist the throttle shaft to accomplish this.
The same syptoms can exist if you have bad valves on the suspect cylinders, but if the engine is relatively new, then the above is your issue. Go slow......
Report back

[Jerry Clayton]

the simplest primary move to make in an situation as this is to just change the mounting position of the carbs and see if the symnophs follow----------don't ever start doing any tuning changes on multicarbs with isolated intake runners without identifying that issue isn't real--------

He says he has no idle fuel, but also talks about rich smell and black plugs indicating an way over rich condition on all cylinders-------------also the temps he states are way low as very rich----they should at idle be up several hundred degrees

[dirwin]

Thanks for the replies. Very helpful group.

I figured it out though. What appeard to be no fuel was EXTREMELY rich. The way cool exhaust temps were what kept throwing me off. The solution was really pretty simple and I'm frustrated that I didn't see it earlier.

I decided before I swapped carbs around I'd change to a hotter range plug. Boy did that wake things up, I was so rich that I had some serious header temps once the plugs were capable of burning the fuel, glowing red on the #3 after 2-3 minutes at 2000 RPM. Dropped down to 60 idle jets all the way around (still with 120 holders). Started with the A/F mixture screws at 7/8 a turn out, ended up with all of them between 1- 1 1/8th out. Noticible difference when you try and lean it out just 1/8th turn, starts to spit at you and exhaust pops.

Finally got it out and drove it some, the main circuit was nearly as goofy. It was set up with 120 correctors, F7 tubes and 135 jets. The result seemed to be a rich stumble in transition and pretty fat on the main. Ended up playing around and now have 190 correction jets and 145 mains sticking with the F7 tubes and it seems to like that a lot better.

Bottom line is I'm still a little fuelie on the idle circuit but it is managable for now.

One more question though. After I shut the engine off, maybe 2 minutes and most of the carbs have fuel sitting on the butterflies. Is this like a Holley and an indication that the float levels are still too high?

[lemans24]

my timing is set @ 38 deg full advance. like most, i run the car for a few with the fuel pump off when i shut it down. ethanol boils at a lower temp than old style gas heat is probably radiating up the carb bodies and the fuel is boiling out on to the butterflys. the timing thing was solved on mine by Jim Inglese

[carmine]

dirwin

What type and part # of plug did you end up using

[dirwin]

Ended up with a Motorcraft AGSP-52-PP and that did the trick. Started out with the 32 range plug that Ford Racing recommends for the engine.

I'm going to have to put a switch on my fuel pump I guess. I sure don't like the idea of fuel just sitting there.

[jonalley]

Glad you found a solution direction. I don't feel so bad about redirecting/continuing this last part of the thread. I hear a lot about shutting off the fuel pump before a stop BUT what can you do about a mechanical pump. Any suggestions? Regards, Jon

[dirwin]

There is really no way, shy of installing an electric valve in the line between the pump and the regulator, to shut off a mechanical pump, and I don't know if that would be feasible.

I built mine originally as a Factory Five Challenge Car, so it I was already set up for fuel injection and it had the in 70 pound electric in-tank pump. I used a fuel inertia switch for safety and just wired the pump to the ignition. When i quit racing the car and went with a 392, 4 barrel setup, I installed a bypass regulator that got my pressure down to a solid 7 pounds, then added a Holley 1-4 pound regulator at the first carb for the Webers.

Sounds like the fuel leaking back into the carbs may be part of the Webers though. I may start another thread about what guys do to stop it.

Again, thanks for the replies, very helpful.

Dave