For some reason, my other post is invalid. If it begins to work, I will delete it.

I have searched this forum using these phrases "engine sputtering" "engine missing" and "bad ignition" etc. to no avail. I think the PBB search function is still action up.

Every time I search, I get a host of threads that don't relate to engines at all.:confused:

Here is what I have: A 78 Bronco with a 70 429 with D0VE heads, a mild cam, a Holley 750 with mechanical secondaries, a C6, mid 80's Ford TFI distributor, MSD coil, and a Ford Duraspark ignition module.

Here are the symptoms. It starts and revs great throughout the rpm band when in Park. As soon as it gets into gear and accelerates, it sputters and hesitates. When back into Park, it revs just fine. Two weeks ago, it performed great. After sitting for this period, it has developed this problem.

Here is what I have done. I detached the fuel line at the tank and carb and cycled some fresh fuel through the line. Then I blew air through it. I have changed the fuel filter. I have not dropped the tank.

The carb was rather old; so I rebuilt it this past weekend. I installed new needle and seat assemblies, power valve, brass floats, and cleaned the jets. I can't remember what jet #'s are installed, but I reused the old ones. The engine still runs exactly the way it did prior to this rebuild.

As of yet, I have not checked the timing with my light. I plan to do so this evening.

The coil is throwing a strong spark. The distributor cap and rotor do not appear to be in poor condition. There wasn't any carbon tracing or cracks on them. Also, the magnetic pickup didn't have any carbon or dusting around it.

Any suggestions as to what I'm missing? I know the problems with Ford Duraspark and TFI ignitions. I have replaced several TFI modules in the past, but usually they fail as a result of excessively hot engine temps. But, I will see about installing some new modules to test this notion.

But, I can't figure out why it ran fine, sat for two weeks, and now runs poorly.:confused:

Vacuum? I'm not familaiar with the mid '80's TFI distributor, but from your
post, describing running good in PARK, then sputtering when in gear, I think
I'd check for vacuum leak. Spray a little carb cleaner around the carb's base gasket,
booster hose, intake, ect. If the rpm's pick up in any particular area, could be
the source of the leak. Sorry, not much help here.

might need a bigger squirter or a 50cc accelator pump you might not be getting enough fuel when a load is applied.

might need a bigger squirter or a 50cc accelator pump you might not be getting enough fuel when a load is applied.


Thanks for the replies.:D


I will definately check the vacuum pressure on the advance unit on the distributor as well as look for new vac. leaks.


Regarding fuel starvation, I will look into it. I replaced the original diaphram on the primary accelerator pump with a new one exactly like it. It was "taller" (I guess 50cc) than the secondary accelerator's diaphram.

bump

vacuum(hoses, carb baseplate, intake)
idle circuit
timing

thats what I would check

might need a bigger squirter or a 50cc accelator pump you might not be getting enough fuel when a load is applied.

A box 750 is Plenty for a mild429/460.


Check 4 leaks, and timing...........

:jester:

you may already know this one, but here's a good way to check for vacuum leaks. with the motor idling, run an unlit (gas on, of course) propane torch along the vacuum lines. any spot where are is leaking in will suck in propane, and cause the engine to rev up slightly.

you may already know this one, but here's a good way to check for vacuum leaks. with the motor idling, run an unlit (gas on, of course) propane torch along the vacuum lines. any spot where are is leaking in will suck in propane, and cause the engine to rev up slightly.


Yes, I've heard of that trick before, but I didn't think to use it in this application. Thanks for reminding me though.:D


I checked the timing and it was slightly advanced, but I haven't adjusted it in 3 or so years. Like I said, the engine ran fine a couple of weeks ago. As of now, it still sputters in gear. So, I'm thinking the problem will most likely be a vacuum line. Maybe the near 25ºF outside temperatures finally cracked one of rubber hoses?

In any event, I certainly appreciate everyones' replies. Thanks.:D

Sputtering can come from a lean condition in the cylinders or an over-rich condition in the cylinders. It could also stem from too little initial advance which would cause very low power and bogging.

Thanks for all the replies.


I beleive the problem was a cracked vacuum line on the tree at the back of the manifold. I replaced all the vacuum hoses attached to that tree and the sputter went away. So, it appears the engine was running to lean under load.

I will replace all the other vacuum hoses for cheap insurance....


Thanks again...:D

Re time it After you replace da hoses/lines.

:jester:

Another good way to check for vacuum leaks is to warm your engine up to operating temp, and then turn your two idle mixture screws all the way in, one at a time. The engine that has proper vacuum and all should almost die if it doesn't die completely when the screws are turned in.