Stumble under quick wot

[iamtherealJayy]

1978 Chevrolet K10 350/sm465. Today I replaced my distributor because the vacuum advance didn’t work and I was hoping this would solve my issue. So if I’m sitting at idle and just stomp it to the floor it kinda stumbles. Timing should be around 12-14° I can’t read the tab just counted the mountains. Carb is an edelbrock 1405. If you press the throttle at a regular speed it’ll rev to the moon but if you just instantly floor it it seems to fall on its face it doesn’t stall but really sounds like it wants to. Vac advance is at ported also. Mechanical advance works and vac advance seemed to work. Vacuum gauge reads 19/20 at idle. I’m looking to get better fuel mileage from this engine I’m only getting around 7 currently and I’d like to see 10. I have a quadrajet I can put back on(originally took it off because had no idea what I was doing and edelbrock was given to me) would changing back to the qjet maybe fix my wot stumble? And maybe get a couple more mpg. I know edelbrock comes slightly rich from the box. I can get new rods/jets to lean it up some if that’ll get me over 10mpg and fix my stumble.

 

[Shorty81]

Don't floor it, take off slowly. Your mileage will improve greatly..

 

[iamtherealJayy]

I don’t usually floor it I drive the truck fairly easy most of the time staying under 3k rpms. I just want the ability to take off if I need to instead of the stumble. Like prior if I’d lay into the throttle going up a hill it would barely maintain speed to get to the top. Fastest the truck would go is downhill with the wind pushing it. I’m not aiming for race truck with 20mpg. I’m looking for the most efficiency since it’s my work truck I put 25ish miles on it 5 days a week I just need it to fire up and drive easily to and from. I’m hoping once I get it running optimal to change the flywheel clutch throw out bearing etc to fix my shudder issue when taking off.

 

[Radiohead]

Is the accelerator pump over/under doing it when you mash a whole shot at once?

 

[Ricko1966]

Give it some more timing see what it does. Since you can't read your timing marks try.its not real scientific without being able to accurately check timing.but take off hard check top speed in 2nd gear,give it a little more timing check it again repeat until top starts drop speed or you get detonation then bring it back a little. I would tell go up and down in 2 degree increments but I guess we are going to have to be happy with up a little down a little.
Just reread your post in more detail,move your vacuum advance to manifold then readjust your carb to get the idle speed down.If you are idling on the transition circuit it will stumble.

 

[75gmck25]

More timing may help. The stock engine has really low compression, so it needs a little help.

Another possibility is to change the Edelbrock step-up springs, which control when the rods transition from cruise to power mode. Stock springs are probably 5” vacuum rating, and Edelbrock sells 6”, 7” and 8” springs. Using a higher rated spring means the carb goes to power /rich mode sooner as vacuum drops, which can help get rid of a bog.

 

[AuroraGirl]

A powerblast kit would probably help if only just for atomization. But the new distributor... whats the distributor brand, what kind of parts is it using? is the centrifugal advance generic, does it come with different springs?

 

[iamtherealJayy]

The accelerator pump is set at the original location I believe it can be moved once in either direction. The timing tan I have is the 12’ o clock one with the tube and up down notches. It’s set as far advanced as the tab shows. Should be around 12ish(lost my good timing light that was adjustable.) my only issue with advancing the timing is I don’t want to go so far that it starts causing issues such as the advanced slow crank or detonation or something? My advance is at ported and vacuum gauge is at manifold. I’m honestly thinking the secondaries are too rich because it’ll blow a little dark smoke with a quick rev to the moon. As for the distributor… I was hoping you wouldn’t ask. It’s like the #3 best seller on Amazon for distributors. It’s just an hei distrivutor was like $80. It did come with some other stuff in the box but I didn’t change anything I just needed the truck to run (fired right up like nothing happened) it does have mechanical advance which works I verified it before I hooked up the vac advance.

 

[iamtherealJayy]

You must be registered for see images attach

I got this photo online, my timing tan look like this and counting the notches is completely to the left So roughly 14°Ish?

 

[AuroraGirl]

The accelerator pump is set at the original location I believe it can be moved once in either direction. The timing tan I have is the 12’ o clock one with the tube and up down notches. It’s set as far advanced as the tab shows. Should be around 12ish(lost my good timing light that was adjustable.) my only issue with advancing the timing is I don’t want to go so far that it starts causing issues such as the advanced slow crank or detonation or something? My advance is at ported and vacuum gauge is at manifold. I’m honestly thinking the secondaries are too rich because it’ll blow a little dark smoke with a quick rev to the moon. As for the distributor… I was hoping you wouldn’t ask. It’s like the #3 best seller on Amazon for distributors. It’s just an hei distrivutor was like $80. It did come with some other stuff in the box but I didn’t change anything I just needed the truck to run (fired right up like nothing happened) it does have mechanical advance which works I verified it before I hooked up the vac advance.

can you show me a picture of the advance weights? I promise its not to nitpick rust or anything, I have read that Aftermarket distributors are absolute crapshoot as to whether the weights are even installed the correct direction

also your black cloud thing sounds like youre running rich. i would, if I were you, get your timing figured out and go find edelbrock 1405 tuning manual and dial in your carb. also ensure your choke is consistent and it didnt shift (as to allow the choke to not fully open)
A powerblast kit and following edelbrocks instructions will probably do a lot for the hesitation

 

[AuroraGirl]

You must be registered for see images attach

I got this photo online, my timing tan look like this and counting the notches is completely to the left So roughly 14°Ish?

i wouldnt be go off of the timing marks unless you know your balancer is good

 

[iamtherealJayy]

It’ll have to be this afternoon before I can get pics I’m about to drive the truck to work. Maybe I’ll be able to get on it a little in the straights. As for top speed in second, roughly 50mph at 3500ish. I’ve got small tires though, like a 255/55/15 or something.

 

[iamtherealJayy]

Truck started this morning and made the journey to work, going up hills it still doesn’t want to gain much speed but it maintains speed a little better. It takes off a little better in the straights, not like my tbi does, but better than before. Currently sitting at idle, warm, at 20-21 inHg vacuum. It’s not dead steady it keeps changing a little between the two. I took videos of starting revving and driving this morning I’ll put on here later.

 

[iamtherealJayy]

Truck started this morning and made the journey to work, going up hills it still doesn’t want to gain much speed but it maintains speed a little better. It takes off a little better in the straights, not like my tbi does, but better than before. Currently sitting at idle, warm, at 20-21 inHg vacuum. It’s not dead steady it keeps changing a little between the two. I took videos of starting revving and driving this morning I’ll put on here later.

 

[AuroraGirl]

Truck started this morning and made the journey to work, going up hills it still doesn’t want to gain much speed but it maintains speed a little better. It takes off a little better in the straights, not like my tbi does, but better than before. Currently sitting at idle, warm, at 20-21 inHg vacuum. It’s not dead steady it keeps changing a little between the two. I took videos of starting revving and driving this morning I’ll put on here later.

it changes? unless im mistaken that be due to a valve train thing