Got the 351 started, but running like crap

[thegreatjustino]

OK, so I got the electric fuel pump mounted and wired in, and it works great - feeds the carb, fills up the bowls quickly, and the Bronco starts up better than ever.

However the 351 that I swapped in now runs terribly. Setting the idle at anything under 1100 RPM causes it to stall out. If I have the idle set at 800 RPM or so and then feather the throttle at all as it is about to die, the RPMs will shoot up to 1500 or so and sit there for a few seconds before dropping back down to the 800 I have the idle set at.

With a vacuum gauge hooked up to the manifold, I have a steady 17 pounds of vacuum at 2,000 rpm, but at lower idle speeds I've got 5 or 6 and the needle is kind of erratic. I'm not sure if this indicates a vacuum leak or is just because of the RV cam.

For the heck of it, I took it for a drive around the block and it stumbles upon acceleration. At idle the throttle response is great. Under load, it's terrible. It seemed to want to stall out all the way around the block. Forget trying to take it on the freeway.

I have not gotten a can of carb cleaner to spray around the manifold and vacuum lines, but plan to. Just looking for any further suggestions on what to check for these symptoms.

 

[pcf_mark]

I would check the firing order. Ford did some neat stuff with changing the firing order. Also make sure you go around the cap in the direction the engine turns when setting the firing order. I got this wrong once and it idled if you set it fast but would not take a load when you put it in gear and drive like the accel pump was bad.

You may be on to the vacuum leak also but it would be a big one to cause the behavior your describing.

 

[dbevans2249]

Was this a running engine that you swaped in? Has anything internal been replaced such as the RV Cam? If it was running and just swaped in it should still run. It should be an external problem such as a vacuum leak or wiring as was mentioned. You may want to do a compression test. A compression test will help to rule out a cam timing issue.

 

[orangecrush4u]

What type of shape is the carb in.

 

[thegreatjustino]

Firing order is correct. When I was having issues getting it started, I checked the order a half a dozen times to make sure it was correct.

Engine is a fresh rebuild that had been sitting for 2-3 years. The rear passenger intake manifold bolt was so loose, I could tighten it with my fingers, so that's why I am suspecting a vacuum leak

Carb is a brand new Holley.

After thinking about this some more, I realized it has the same symptoms that I once had in the 289 in my '65 Mustang years ago. That was a loose nut on an exhaust rocker. So it looks like the valve covers are coming off for inspection.

 

[broncnaz]

probably a combonation of things big vacuum leak would explain the low vacuum and hesitation. loosen exhuast rocker probably wouldnt cause that low of vacuum unless more than one was loose. Try retorquing all the intake bolts I usually have good luck retorquing after running the engine a while.