Hard stalling after REBUILD

[jgf100]

I recently did a top end rebuild (heads rebuilt, edelbrock rpm performer intake) 600cfm holley carb that was installed before I bought the truck, and after assembly and setting timing, I am having hard time getting to accelerate on gear without bogging and stalling. Messed with carb, I was able to get it to run pretty good, but not great, took it to mechanic, said more than likely my carb needs rebuild and tune with mixture screws. Didnt want to mess with it, so I bought a new one, same model. Installed and still having the stalling issue in gear. Have not found any vacuum leaks, at least to the best of my knowledge.
Stuck and very frustrated. Any ideas on what my next steps are in diagnosing and/or fixing? Sorry for long post.

Thanks
1970 F100 302

[yellercat]

That sounds like a timing issue to me, with all those changes.
Have you researched how it should be set?
I would start there.

[jgf100]

That sounds like a timing issue to me, with all those changes.
Have you researched how it should be set?
I would start there.

I first timed it myself, set it at 13 btc using timing light. Drove it to a mechanic, he checked timing as well and said it looked good. He also said he didnt "see or hear" any vacuum leaks. I can rev it just fine in park or neutral.

[Johnnewc]

Another place to check for a vacuum leak is by the shift modulator. There is probably a short rubber hose that connects the steel vacuum tube to the vacuum modulator. This is only if you have an automatic transmission. You should see it on the passenger side near the rear of the transmission. Just another place to look.

[jgf100]

Another place to check for a vacuum leak is by the shift modulator. There is probably a short rubber hose that connects the steel vacuum tube to the vacuum modulator. This is only if you have an automatic transmission. You should see it on the passenger side near the rear of the transmission. Just another place to look.

Thanks for advice. I'll check that tommorow.

[sparky72]

What is your manifold vacuum reading at idle? Are you using vacuum advance, and if so how is it connected?

Is the everything below the heads factory? i.e. any changes to the cam, pistons, etc as far as you know?

Also, are you running points ignition?

[My427stang]

Sparky is asking good questions

In a case like this, hearing the engine would be good, but a couple things I'd ask

1 - Have you verified that your timing marks are correct?
2 - Did you set timing with a timing light, and was the vacuum advance disconnected?
3 - Have you checked firing order (even as an FE builder, every so often I will cross one, I always double, triple check)
4 - Which intake gaskets did you use?
5 - How did you determine bolt length for your intake?

[jgf100]

Sparky is asking good questions

In a case like this, hearing the engine would be good, but a couple things I'd ask

1 - Have you verified that your timing marks are correct?
2 - Did you set timing with a timing light, and was the vacuum advance disconnected?
3 - Have you checked firing order (even as an FE builder, every so often I will cross one, I always double, triple check)
4 - Which intake gaskets did you use?
5 - How did you determine bolt length for your intake?

Good questions.
1. I verified timing marks by doing the "finger in #1 spark plug hole", rotating engine and checking for the compression stroke. Marks lined up pretty good.
2. I advanced timing with timing light and yes, the vacuum advanced was disconnected.
3. Verified firing order, 1, 5, 4, 2, 6, 3, 7, 8. All plugs are correctly connected. Distributor is using electronic Pertronix ignition.
4. I used the fel pro intake gaskets. https://www.summitracing.com/parts/fel-ms90145
5. I used ARP-154-2001 intake bolts for the manifold. https://www.summitracing.com/parts/arp-154-2001

I tried some adjusting the idle speed along with the air/fuel mixtures today, wasn't successful. Attached are some pics of what I am working with.
My vacuum reading is steady about 19.
Using my timing light (dont know how accurate it is), i tried getting close to 850rpm at park, with 15 degree advanced.
As for my distributor, i plugged the retard connection and have the advanced is connected to the ported on the carb, again I plugged all those when checking vacuum.

So that is where i stand. It idles on park and neutral, but stalls on acceleration in gear. As far as I know, the cam and pistons are stock. Any ideas??
Thanks for the help.

[sargentrs]

Personally, I like to time my engine to max timing at 2500 rpm. Leave everything connected and idle her up to 2500 rpm. Then rotate the distributor until you achieve 38* and tighten down the dustributor. Back the idle down to 700-750 and let the initial timing fall where it may. Tried setting my 302 initial timing from 8* all the way up to 15* but she still ran like crap at acceleration. Set it to max timing and she ran great. Initial fell in at 22*! Don't know if the harmonic balancer slipped, timing light was off or what but she loved it there.

[jgf100]

Personally, I like to time my engine to max timing at 2500 rpm. Leave everything connected and idle her up to 2500 rpm. Then rotate the distributor until you achieve 38* and tighten down the dustributor. Back the idle down to 700-750 and let the initial timing fall where it may. Tried setting my 302 initial timing from 8* all the way up to 15* but she still ran like crap at acceleration. Set it to max timing and she ran great. Initial fell in at 22*! Don't know if the harmonic balancer slipped, timing light was off or what but she loved it there.

Hi,So I decided to try your method. Got the distributor dialed in to 38 at 2500 rpm which set initial to 18. Test drove down the street in my neighborhood, and although it wasn't perfect, was able to drive it which gave me hope. Turned it off for about 5 min. Decided to drive it to parts store down the street. Well, wasn't able to drive it because it was stalling so bad on acceleration. I don't get how 5 min could've caused it to get worse. Thoughts?

[My427stang]

So first, with a stock distributor, be careful at 2500 RPM because it probably doesn't get full advance by then. This means that when you do get it dialed in,when you run it hard, you will be over-advancing it

Now, warning aside. LOL

1 - Initial carb setup

- Once it warms up, choke fully open, check the vacuum port on the front metering block near the choke, and see if it is alive. If it is, your primaries are too far open and you are deep into the transition circuit, which isn't helping. If it is, we will address later but gives a good idea of what is happening.

- Shut her down, and look at the accelerator pump shot, it should start immediately and be nice streams of fuel, no sputtering, no delay. If it does either, I would start with a new pump diaphragm and ensure it was adjusted correctly. The way to adjust it correctly is to go to WOT, often handy is to take a carb spring and hold it there (not running LOL) then bottom the little accel pump arm with a screwdriver as a prybar, and measure the clearance between the adjuster and the arm. You want .015 clearance, which ensures the MOST travel, without collapsing the diaphragm

- Next, adjust the carb a/f adjusters to 1 1/8 turns out, just a starting point, but real close

- After that, fire the engine, warm it up and adjust float level, warm. It should just trickle out of the sight plugs, but it has to come out on it's own. If you are shaking the fender to get it to do it, it's a little low. When low, all circuits start a little slower. Not saying that IS the problem, but basic initial setup

- Now back to the vacuum port, if it is alive still, you need to pull the carb, and open the secondary idle a little using a set screw on the passenger side rear. Give it a couple turns, and while upside down, close your primary until the vertical slot (transition slot) is just peeking through by the throttle blade (choke open). Put it back on and fire it. If it idles too high, take some secondary out, if too low, you can go maybe a turn on the primary, but likely have to add more secondary. At this point, the vacuum on that port should be dead.

- Adjust idle a/f for best idle, shouldn't be too far off your initial 1 1/8 and when you turn in, it should kill the engine.

2 - Verifying timing

- Check your timing again, no vacuum lines connected, both plugged if using both. If you want to power time, keep climbing until it stops advancing, likely will be closer to 3000-3500. Set at 36-38, then drop it to idle, and note initial so you don't have to do that anymore, you now know mechanical advance value (38-new initial)

- Do not connect the vacuum port closest to the distributor body, but do connect the one closest to the fan, run it to the vacuum source you checked on the side of the carb.

3 - Road test

Last comment - If a carb runs well cold, and gets goofy with heat, it could be a percolation problem, carbs cannot meter boiling fuel, so if it is somewhat good, two things. 1 - make sure you are not running a drop base air cleaner (it acts like a heat umbrella) and 2 - if possible run a phenolic spacer, 1 inch 4 hole is likely better if a flat base air cleaner will still fit (it should, I ran an RPM with a flat base and a 4 inch air cleaner for years before I converted to EFI)

Let us know what happens, to me, sounds like a carb setup problem, combined with a percolation problem

[sargentrs]

Great write up My427Stang! Saving that for later reference. Thanks!

[jgf100]

My427stang ,
1. Checked the vacuum port on the front metering block and verified that there is no vacuum on idle. Also, I am not sure on how to adjust accelerator pump. It does seem like there is a bit of play, but when adjusting it seems that acceleration gets worst. Am i supposed to adjust accelerator pump with choke opened or closed?

2.Verified timing. When adjusting timing, should I do that on park, neutral or gear? Also when connection vacuum gauge to adjust a/f, I can continue to turn out screws without much change in the vacuum. Is that normal? Only time it makes a difference is if I turn them in too much.

3. I am starting to wonder if it is a percolation issue. Just for reference, after getting the engine pretty hot, i turned it off, went to check in the spray nozzle, and as soon as I opened throttle, fuel seemed to steam up pretty quick. Is that normal after running and everything getting hot?

Thanks for suggestions.

[My427stang]

My427stang ,
1. Checked the vacuum port on the front metering block and verified that there is no vacuum on idle. Also, I am not sure on how to adjust accelerator pump. It does seem like there is a bit of play, but when adjusting it seems that acceleration gets worst. Am i supposed to adjust accelerator pump with choke opened or closed?

The free play at idle is irrelevant really, but could indicate it is adjusted wrong.

1 - Engine off, open the throttle all the way to wide open and hold it there. It helps if you disconnect the return spring and reattach it somewhere where it will hold it open for you.

2 - Take a small screwdriver and use it as a prybar to gently push down the little bitty 1 inch or so arm that the linkage pushes, mounted to the accel pump. You want to gently bottom it.

3 - Measure the distance between the linkage foot (where the nut and spring is) and adjust the nut and spring to give you .015 with a feeler gauge.

Generally, when you go back to idle position, you have zero play after that, the spring should work as a shock absorber as you work the pedal. Stomp the pedal, the spring compresses slightly so you don't rupture a diaphragm. Some guys misinterpret the adjustment to be .015 when sitting at rest, that is incorrect and won't give you a full pump shot

However, you need to look at your accel pump now and see how it's working, it could be a bad pump too.

2.Verified timing. When adjusting timing, should I do that on park, neutral or gear? Also when connection vacuum gauge to adjust a/f, I can continue to turn out screws without much change in the vacuum. Is that normal? Only time it makes a difference is if I turn them in too much.

Park or neutral is close enough for what you are trying to solve, but remember, we talked about power timing, you sure aren't going to do that in gear, and I think park with the emergency brake is your friend!

If you think power timing is too tough, just set it at 12, at idle, with all vacuum disconnected and plugged, that is close enough for trouble shooting.

As far as the a/f adjustment changes, it won't change a lot. If you start at 1 1/8 from bottom, there should be minimal changes 1/4 turn in or out, and very little changes further out, a good ear will hear it, but at some point you stop metering because the passage is wide open, but if you go way in, the motor should stumble, maybe even stall. If it doesn't let me know, we need to look at something else. Be sure you are starting at 1 1/8 from bottoming though. (turn in, then back out 1 1/8 turns)

3. I am starting to wonder if it is a percolation issue. Just for reference, after getting the engine pretty hot, i turned it off, went to check in the spray nozzle, and as soon as I opened throttle, fuel seemed to steam up pretty quick. Is that normal after running and everything getting hot?
Thanks for suggestions.

It's not abnormal, but when checking your accel pump spray, do it cold. and do it slowly, you are looking to see if a poorly performing pump works at small throttle movements, stomping it won't tell you much

I do think it sounds like a percolation issue too, and that is very common. However, the base setup is important before you get it hot and see what it does