New motor bogging down - not sure what to check with Edelbrock carb

[DesertCoupe5.O]

While my car was in the body shop I did new HCI on the motor with Trick Flow heads and a Comp XE266HR-12 cam. It idles and revs fine, but bogs under low RPM (1000-3000 or so) load when I give it gas. It seems to clean up at higher RPMs, but the power isn't there like it should be. I opened the carb and cleaned all the jets twice and blew air through everything. Vacuum at idle is ~15 inches. When I give it part throttle at 30mph or so it feels like I'm running on 7 cylinders. I've only driven about ten miles. #1 spark plug looks new. Could the new HCI cause my carb to need new calibration? Any help would be appreciated - this is really my first time trying to mess with a carb other than on small engines. It was running great 8 months ago with a stock HO 5.0 top end.

[Hwyman]

When you first open the throttle, especially at low rpm, you lose vacuum and the air doesn't suck fuel out of the carb. as well. The accelerator pump compensates for this by shooting fuel in to the carb. until rpm and vacuum increase. Check the accelerator pump to see if it is shooting gas in to the carb. when you open the throttle. You can also use another hole on the carb. to make the pump deliver more gas.

[09Frank65]

1. What is your vacuum in drive with brake applied? (Safely!)
2. With the car in drive with the brake applied check to see if your step-up pistons are in the down position. You can slide the cover around just enough to see if the piston is up or down. If the piston is up the metering rods will be in the narrow portion of the rods causing a rich condition.
3. What torque converter stall are you running? Depending on cam specs you may be losing some torque until your RPM gets up into the power band of your combo with a stock converter.

Just some thoughts from my own experiences. If I understand correctly this is not just an off-idle transition issue but sustained at low rpms. If it is just an off-idle stumble or hesitation the other poster may be right with adjusting the accelerator pump linkage.

One other thought on edit is timing. You may want to bump your initial timing up a bit as well and then reset your idle speed accordingly.

[DesertCoupe5.O]

Originally Posted by 09Frank65

1. What is your vacuum in drive with brake applied? (Safely!)
2. With the car in drive with the brake applied check to see if your step-up pistons are in the down position. You can slide the cover around just enough to see if the piston is up or down. If the piston is up the metering rods will be in the narrow portion of the rods causing a rich condition.
3. What torque converter stall are you running? Depending on cam specs you may be losing some torque until your RPM gets up into the power band of your combo with a stock converter.

Just some thoughts from my own experiences. If I understand correctly this is not just an off-idle transition issue but sustained at low rpms. If it is just an off-idle stumble or hesitation the other poster may be right with adjusting the accelerator pump linkage.

One other thought on edit is timing. You may want to bump your initial timing up a bit as well and then reset your idle speed accordingly.

I haven't measured vacuum in D, but I suppose I can have a look at the step-ups and see what they're doing. I'm running a 2500 stall - it's not that it's low torque, it sputters and feels like it's missing. The accelerator pump is working, and I've tried it in all three holes.

[2manyhobbies]

What are the specs on your cam? If its pretty radical it will feel weak until it actually gets into its powerband. Mine doesn't really wake up till about 2500rpm.

[evoasis]

Just a shot in the dark but how's your fuel pressure?

[DesertCoupe5.O]

Originally Posted by 2manyhobbies

What are the specs on your cam? If its pretty radical it will feel weak until it actually gets into its powerband. Mine doesn't really wake up till about 2500rpm.

It's mild - it's 216/224 at .050", and I'm using a 2500 stall converter.
35-514-8 - Xtreme Energy? Hydraulic Roller Camshafts, Computer compatible (E.F.I.) with O.E. hydraulic roller cams 1985-95
Again, it's not weak, it's sputtering and feels like it's missing a spark plug or two.
Fuel pressure sits at 6 psi, but I can't see the gauge when driving.

[Huskinhano]

Which model E carb do you have? The electric choke version is jetted quite a bit leaner. I have a E carb on my tired 302 and it was way too lean. Get yourself a tuning kit and fatten it up. The manual is great in explaining how the carb works and how to tune it.

[2manyhobbies]

It's possible the secondaries are opening too soon and can cause it to bog down but shouldn't cause a misfire unless its overpowering your ignition system. I wouldn't expect you to be running a points dizzy but at least some sort of electrical system with that we up right?

[GT350R Klone]

What is the initial timing and advance? Have you tried advancing it to see if it gets rid of the low end bog?

[DesertCoupe5.O]

Timing is right around 10*, when I rev it advances close to 30. Where should it advance to?

[GT350R Klone]

Initial is to the book, total may be low 4-6 degrees, but shouldn't be causing your issue. I would however try it at 12, 14 initial and see if there is any change. It may not be the answer, but it costs nothing to do.
I learned from an old timer mechanic to throw away the timing light. His thoughts were that once an engine is old or modified, that the initial timing marks are probably not reading right or not correct for the car. He showed me to hook a vacuum gauge to the manifold and change the timing at idle until max vacuum, then back off 1 1/2. It is the only way I have adjusted timing since and has worked for me.

[09Frank65]

Originally Posted by DesertCoupe5.O

Timing is right around 10*, when I rev it advances close to 30. Where should it advance to?

I am at 16 initial, 36 total with XE274H cam.

If you have a tach in the car, see at what RPM it stops sputtering. It'll be easier if you keep it in one gear, i.e. second or third, whichever covers the RPM range best.

Then, back in the garage, see what the advance is at that magical spot, raise the idle speed to that setting and check advance with your timing light (which obviously will require a timing light with an advance knob).

That should give you an idea where you stand and whether it is advance related.

OR you could just do what I did and keep bumping it up until it ran nice and make sure it is not detonating...

[DesertCoupe5.O]

Originally Posted by Huskinhano

Which model E carb do you have? The electric choke version is jetted quite a bit leaner. I have a E carb on my tired 302 and it was way too lean. Get yourself a tuning kit and fatten it up. The manual is great in explaining how the carb works and how to tune it.

It's a 1405 and it was tuned for emissions in phoenix (1500 ft) a couple years ago and now I'm at 400 ft. I have a tune kit coming for it.

[1969sag]

This is just a suggestion.
Check your trans kick down cable, or TV cable.
I had a similar problem with my MSD. The advance curve springs were to heavy, causing the car to bog, and hesitate. I swapped out different, lighter springs, then retuned the carb, and reset the timing. Never had the problem again.