Engine bogging.

[az1970k5]

I have a 1970 with a sbc 350, new, HEI, rebuilt quadrajet (electric choke) from National carburetors, new fuel pump all the way to new lines and gas tank. My truck starts on the first try even in the cold, it idles smoothly and drives perfect at first. When it gets hot or at operating temperature, it starts to bog down at stop and go traffic. Not all the time but most of the time. If I floor it I can keep it going, if not bogs down and wants to stall. It has never stalled, but sounds like it will. Also at higher rpm when kicking into the last gear it bogs down until it finally kicks in. Again, this is only when hot. It drives perfectly the first 10-15 miles or so. I have replaced everything. Could it be a bad carb or distributor? Both are either brand new or rebuilt.

['68OrangeSunshine]

Luis, How old is your HEI? Do you have the OEM External Voltage Regulator?
What brand and octane fuel are you using?

[az1970k5]

HEI has 400 miles on it, about 2 years old. I just filled up with 91 octane and it seems to be a little worse now with the better fuel. I was using the lower octane until yesterday when I decided to switch to the 91.Maybe it''s a coincidence? I got rid of the external regulator, I updated the wiring with the aaw and now use an internally regulated alternator.

Originally Posted by '68OrangeSunshine

Luis, How old is your HEI? Do you have the OEM External Voltage Regulator?
What brand and octane fuel are you using?

[az1970k5]

It kind of sounds like it is starving for fuel but only when running hot. It drives perfect when cold. Maybe the choke? I was told by National carbs I would not have to adjust anything, which I have not.

Originally Posted by az1970k5

HEI has 400 miles on it, about 2 years old. I just filled up with 91 octane and it seems to be a little worse now with the better fuel. I was using the lower octane until yesterday when I decided to switch to the 91.Maybe it''s a coincidence? I got rid of the external regulator, I updated the wiring with the aaw and now use an internally regulated alternator.

['68OrangeSunshine]

Originally Posted by az1970k5

HEI has 400 miles on it, about 2 years old. I just filled up with 91 octane and it seems to be a little worse now with the better fuel. I was using the lower octane until yesterday when I decided to switch to the 91.Maybe it''s a coincidence? I got rid of the external regulator, I updated the wiring with the aaw and now use an internally regulated alternator.

Funny, I have a similar gripe on my '71 GMC Jimmy w/350. Sometimes it runs better with high octane or Chevron regular. Let the 91 octane work into your system more -- you could've been still running old gas.
I heard an urban myth that External Voltage regulators would spike at high RPMs killing the module or cutting it out temporarily. Since you deleted the old reg, and still have the gripe, I wonder? Also HEI coils can overheat. I rebuilt my Mallory HEI with all new Blue Streak components last June. Still bogs but not as bad. It used to kill itself when accellerating.
Mine runs better when it's cold.

['68OrangeSunshine]

Originally Posted by az1970k5

It kind of sounds like it is starving for fuel but only when running hot. It drives perfect when cold. Maybe the choke? I was told by National carbs I would not have to adjust anything, which I have not.

What fuel pump?

[az1970k5]

Originally Posted by '68OrangeSunshine

What fuel pump?

Just the stock mechanical.

If we are both having the same issues maybe it's the gas, we live just around the corner from each other. When I filled up yesterday with better fuel at Conoco it started bogging down when the passino gear would kick in.

[RichardJ]

>> I was told by National carbs I would not have to adjust anything, which I have not.<<

You're kidding?

Carburetors ARE NOT plug-n-play. There are bench adjustments made when carburetors are rebuilt, BUT the idle speed screw and idle mixture screws MUST be adjusted ON the engine, hot and running.

Short of a vacuum leak, both of you guys problems sound like adjustment issues.

[az1970k5]

Originally Posted by RichardJ

>> I was told by National carbs I would not have to adjust anything, which I have not.<<

You're kidding?

Carburetors ARE NOT plug-n-play. There are bench adjustments made when carburetors are rebuilt, BUT the idle speed screw and idle mixture screws MUST be adjusted ON the engine, hot and running.

No I am not kidding. They told me it would not need any adjustment. I'll try adjusting it maybe it needs some adjusting.

['68OrangeSunshine]

Originally Posted by az1970k5

Just the stock mechanical.

If we are both having the same issues maybe it's the gas, we live just around the corner from each other. When I filled up yesterday with better fuel at Conoco it started bogging down when the passino gear would kick in.

Definately the local gas is cr@p. At least it's cheap.
I use Shell, Fry's and Chevron, mostly, Arco sometimes. Arco's not as good as Shell [and Fry's]. Chevron seems better but costs more, but they're both fed by tankers from Western Refining, so who knows?
As for the fuel pump, have you measured your fuel pressure? I don't know how it affects QJets, but AFBs and Edelbrocks are pressure-sensitive and will flood with more than 5.5 PSI. Some people put a fuel pressure regulator inline with the fuel pump and carb.

['68OrangeSunshine]

Originally Posted by RichardJ

>> I was told by National carbs I would not have to adjust anything, which I have not.<<

You're kidding?

Carburetors ARE NOT plug-n-play. There are bench adjustments made when carburetors are rebuilt, BUT the idle speed screw and idle mixture screws MUST be adjusted ON the engine, hot and running.

Short of a vacuum leak, both of you guys problems sound like adjustment issues.

Well I could check for vacuum leak, since I have a squarebore carb on a spreadbore intake [with an Offy SqB/SpB adaptor] but it's a leak prone area.
I only noticed the problem since last June, when I jetted way down to pass emissions.

[Steeveedee]

Sounds like it is leaning out after the choke is open. The choke can cover up a vacuum leak, so, as has been mentioned, check for leaks. That, or the idle jets are just wet too lean. Try hooking a vacuum gauge to manifold vacuum and adjusting the idle mixture screws for max vacuum. That likely isn't the only problem; I would check for vacuum leaks first.

[snipescastle2]

Take a spray can of carb and choke cleaner and while the engine is running,spray it around the intake, the base of the carb, etc... if you have a vacuum leak, the engine will try to die.you can also hold your hand over the top of the carb, if there is a. A vacuum leak, that may raise the rpms too.
Ben

['68OrangeSunshine]

Originally Posted by Steeveedee

Sounds like it is leaning out after the choke is open. The choke can cover up a vacuum leak, so, as has been mentioned, check for leaks. That, or the idle jets are just wet too lean. Try hooking a vacuum gauge to manifold vacuum and adjusting the idle mixture screws for max vacuum. That likely isn't the only problem; I would check for vacuum leaks first.

I have a manual choke, and hardly ever use it, unless it just won't start.

[az1970k5]

Originally Posted by snipescastle2

Take a spray can of carb and choke cleaner and while the engine is running,spray it around the intake, the base of the carb, etc... if you have a vacuum leak, the engine will try to die.you can also hold your hand over the top of the carb, if there is a. A vacuum leak, that may raise the rpms too.
Ben

Tried that and engine remained the same, so no vacuum leaks. Could it be running too rich?