302 Idles Fine in P but Runs Rough and Stalls When in Gear

[Mikey]

OK....74 with 302, Holley 4160, List 6919 (idle mixture air control needles), 600cfm, new distro for factory Druaspark, Blaster coil, new ignition module, 83-85 Mustang GT aluminum intake with Edelbrock solid aluminum EGR block off spacer plate and heat shield, new PCV valve, rebuilt C4 with low miles, new vacuum modulator, Trans Go shift kit per tech article, chebby power disk conversion, timing at around 12 deg, idle set at about 600rpm, vacuum at idle is around 15-16 inches, 5.0HO timing chain, heads marked as 1978 vintage, Hooker comp headers with dual exhaust 2.25".

It idles really nice but runs terrible and stalls some when I put it into gear. Once I give it a little gas while in gear, it will run better but still just a bit rough. C4 shifting not feeling quite right either. Did the usual vacuum checks with carb spray, unhooked the brake power booster and line to the trans vacuum regulator no effects. I don't know what cam is in it but the heads seem to be changed to 1978 with no holes for the air injection. I didn't rebuild the engine so don't know. I even swapped in a good condition rebuilt Holley both were List 6919...the old one had loose throttle shaft, "new" one is tight, swapped in the Truck Avenger vent. The driver's side idle mixture has no effect even though I shot carb spray into hole shooting a small geyser up through bleed. If I push in electric choke manually when warm, vacuum goes up to nearly 20 inches.

Am I missing something? Really acts like a vacuum leak. Before I pull intake off and replace gaskets or even swap in an old cast iron 4V intake I have laying around, I plan to change the fuel filter, check the volts to the coil and check the fuel pressure. Iv'e worked on Holleys, Ford 302s and 5.0Ls since I was 15...53 now and this one is stumping me.

Thoughts? Ideas? Please share experiences!
Thanks!
Mike

 

[Mikey]

By the way, anyone run an anti-stall dash pot on their Holleys with a C4 trans?

 

[Slowleak]

Is your vacuum advance hooked up to ported vacuum? Hooking it to full manifold vacuum can cause stumbling and stalling when shifting a C4 into gear. My vacuum advance module had a hole in the diaphragm. It caused all kinds of grief. Ran rough, stumbled, didn't shift right.....

 

[Mikey]

Yes, ported. The distro is new and came with a new vacuum can. How did you troubleshoot to your vacuum can?

 

[Slowleak]

Yes, ported. The distro is new and came with a new vacuum can. How did you troubleshoot to your vacuum can?

I just stumbled into it after owning the Bronco for 2 years. When checking my timing, I applied vacuum to the hose to see how much vacuum advance I was getting. I got nothing. Replaced the can and my 1-2 shift got much smoother. The vacuum leak apparently was affecting the vacuum module on the transmission among other things.

 

[NC-Fordguy]

Shift Modulator hooked up with no vacuum leaks?

 

[DJs74]

Sounds like a vacuum leak. Could be an internal leak with the intake manifold - port to port that wouldn't show up when spraying carb cleaner around the perimeter of the intake or valves adjusted to tight and not seating.


DJs74

 

[Mikey]

Yeah, I unhooked the line to the modulator and it had no effect on the vacuum reading.

I've never adjusted the valves and I believe the heads of this year used positive stop studs, right? It ran OK a few years ago so something changed so I'm thinking the port to port internal intake leak just might be it.

 

[broncnaz]

78 heads should be pedestal rockers no adjustment. You might try checking the torque on your intake bolts. Some times a few heat cycles with cause the gaskets to shrink and leak. I think your idle speed needs to be set higher probably needs to be around 800 in park 650 in drive.

 

[DJs74]

I've never adjusted the valves and I believe the heads of this year used positive stop studs, right? It ran OK a few years ago so something changed so I'm thinking the port to port internal intake leak just might be it.

I wasn't sure what valvetrain you have but if they are positive stop rockers, it's probably not a valve adjustment problem.
You might try re-torqueing the intake manifold

http://www.gtsparkplugs.com/SBF-Intake-Torque-Sequence.html


DJs74

 

[Mikey]

I did retorque the intake bolts earlier. Just don't recall what gaskets I used. I think even 74 heads are non-adjustable. I can try bumping up the idle but think that won't solve it but, who knows, right? Just wondering if the later model intake with the early heads might just have things a little off. Doesn't help that I don't know the pedigree of the engine. When I was in California, I was at high elevations so dropping down to near sea level in Virginia may have aggravated the problem. Sighhhhhh!

Ordered some FelPro intake gaskets in anticipation of pulling the intake but sure would like to avoid it if possible.

 

[jckkys]

The fact that the driver side idle mixture screw has no effect, is something that has to be addressed and fixed. If one 6919 was good except for a loose throttle shaft just swap the base plates. Another thought is the way the idle mixture and speed are adjusted. Specs are based on the C4 being in gear. So you want 650 RPM in drive with a smooth idle "in drive". What it does in park or neutral is irrelevant. As I said before the OE cast iron 289-302 intake is surely the most trouble free and reliable there is. The only disadvantage is 20 extra pounds over aluminum. To the Bronco 20 lbs. is nothing.

 

[Mikey]

I thought of swapping just the base plate but had another 6919 in near new condition but goofed up the primary metering block when I did a full rebuild so it has the same metering block. I did shoot cleaner through the mixture needle hole until I had cleaner shooting through the small bleed hole. Still the needle has no effect. Do I need to take off the front bowl then? I was wondering if the bank opposite the needle is where the vacuum leak is in the intake since it's a dual plane intake? This weekend, I'll recheck the idle per your recommendation. Thanks for all your help!

 

[Rustytruck]

I would check that all the plugs are firing properly. Get your idle speed back up where it belongs. I would also check your power valve in the carb. If its leaking down it will cause Idle mixture problems. I gave up on Holley's long ago because I didn't run them hard enough to frequently open up flow to the secondary's. After bouncing around some, the secondary side would over flow and dump raw fuel down the carb in the most in opportune times. They use to work pretty well in my Mustang that was used much harder but in my Bronco not so well.

 

[Mikey]

New power valve and the vent is now the Truck Avenger type. I put a lighter spring in the secondaries. I'll check that idle again. I had it too high and the vacuum advance wouldn't return and the needles had to affect so was exposing too much transfer slot. I will add firing order to my list

 

[jckkys]

The Truck Avenger bowl vent will work on most any Holley 4150, 4160, or 4180 4bbl. I never believed it helps either. The emission Holleys have extra holes in the main body/metering block gasket surface. They are close together and the gasket will fail to seal if there is any warpage from over tightening of the float bowl screws. Check it with a strait edge and also make sure no holes are blocked by an incorrect gasket. A warped gasket surface on the main body would have to be filed flat. The emission carbs have idle air bleeds in the venturi walls in addition to the ones at the top, next to the base of the booster venturi leg. Both have to be unobstructed. Use any modular assembly ie main body, base plate, metering block etc that works from either carb to make one carb that works correctly. They are both List 6919s so the parts are interchangeable. Tuning of the vacuum secondary springs, power valve, jets, and accelerator pump system can wait till the malfunctions are resolved. Changing multiple components at one time makes tuning difficult to impossible.

 

[Mikey]

Thanks .... Forgot it's a holiday weekend. Hope to get to it.