Hit a milestone on Saturday. Fired the ol 428 up after being rebuilt 12 years ago in my 76 F-250. Fired right off so huge relief to know all my wiring was correct. Ran really good and good oil pressure. I’m having trouble keeping it idling tho. I’m suspect of a vacuum leak but can’t find anything externally. Running a brand new Holley 670 avenger carb.

vacuum port on carb is giving 20+ revved up to 3000 rpm. Getting 5-10 on port on the actual intake manifold. I did not plug the vacuum advance hose off dizzy when I was timing it if that matters. It seemed to smooth out by holding a rag over top of carb to kill the air. I’m not super sure my timing is optimal either. I think it’s a little too much. Around 18 degrees

forgive my ignorance because I’m a super newbie when it comes to these kind of things. I think I’m close just not perfect on it

shooting for 800 idle, correct me if I’m wrong. Has auto tranny.


Anyone point me in the right direction on troubleshooting? I haven’t had a whole lot of time because of farming but I piddle with it at night. Thing sounds like a beast. All the gauges are even working. What more could a guy want!😝

 

Is it running long enough to get warmed up and getting off the choke?

 

Yes have ran it for over 20 min. Even unplugged electric choke to see what it’d do

 

Unplugging the choke only makes it stay closed longer. it opens due to the voltage.

If covering the carb makes it run a little better you're either way lean or you have a vacuum leak or a messed up carb. . what happens when you cover it a lot ?

 

I can kill the engine by completely covering it. I think it’s way lean. Sprayed it all down with brake cleaner and got no engine change looking for vacuum leaks. A friend of mine has 2 670 Holleys and he thought sounded like possible power valve on carb

 

Is the choke plate fully open when it is warm?

Did you mess with the mixture screws at all or is it set straight out of the box?

I'd start with 10 or 12 degrees of initial advance and work from there.

Are you using a mechanical fuel pump?

What reading are you getting with a vacuum gauge?

You could spray a squirt of starter fluid in different spots around the intake and listen for a change in rpms or propane from a torch.

 

Does the exhaust smell rich? Try pulling a plug and tell us what it looks like or better yet attach a pic.

 

yes mechanical factory style fuel pump. I did adjust mixture screws per the directions. I’m not sure on choke plate being completely open. Vacuum gauge is giving me 20-25 at 3000 rpm straight off carb. I was going to try propane tomorrow

ok I’ll pull a plug as well. Doesn’t smell rich to me but hard to tell with a lot of fresh burnt paint smell off headers

 

If you can kill it with a rag you don't have a bad vacuum leak. I'd look elsewhere.

If you can swap carbs to rule that out. generally power valves make you run too rich . you should be able to rich up your idle with the screws if you can't something is messed up. personally I don't like the avenger series, even worse the Truck Avenger series. they're just weird.

Are you sure your timing mark is correct ? I'd play with the timing a little .

 

Yes I’d like to play with timing some more. It just seems so touchy. Barely move it and it sure changes the engine. I was also wanting to find another carb to throw on it just to see what happens to rule out carb

 

Is your vac advance hooked to ported or manifold vacuum ?

 

hooked to ported per Holley instructions. The one specified for distributor

 

You can run quite a bit of initial then. as long as your mechanical all in isn't over 36 or so at 2500 the more initial the better.

 

can you explain total timing and how to figure that. I was reading other forums talking about that but don’t understand it I guess

 

The simplest way to explain it is this. unhook your vac advance , rev up the engine to around 2500 RPM, set your total mechanical advance to 34 BTDC with your dial back light. hook the vac advance back up and check it again. it should be in the 50's . you can check your initial again if you want but as long as it starts and idles good it's irrelevant.

Then drive it and see how it runs out, if you hear no pinging under load you may be able to take a little more advance. if you do hear pinging back it off a little at a time until you don't. detonation will destroy your engine, retarded timing will harm it as well.

You'll have to pick the fuel you're going to run for this too, otherwise you'll have to do it again.