STILL having ignition issues on my 5.0

hi all i have been battling this for a long time. I've narrowed it down to a single problem, all others are fixed.

I've been having a pretty pronounced stumble when i step on it to the floor at slow speeds, namely around 1500 in first gear (1985 302 roller with a t5). so bad that it jerks the whole car pretty violently then it picks up like normal. and when I'm cruising at 2000rpm in 4th gear and i hit the gas it'll stumbles a little bit and picks up again.

this is when it is set up at 22 initial timing (proform hei with medium springs hooked to manifold vacuum). went down to 20 and nothing changed. so i decided to try the old fashioned way and i used a vacuum gauge. unplugged the dizzy can and went to max vacuum and then down 2 inches giving me 12 inches of vacuum at idle (cam is edelbrock rollin thunder). i checked to see where it went with the light and its at 30 degrees initial?? that seems way too much.

but i drove it and the stumble is gone, but it seems to have lost out on torque. and it still stumbles at 2000rpm in 4th.

I've been screwing with fuel a lot (670cfm Holley with an edelbrock mechanical pump and a Holley red electric pump) but to no avail.

other specs:
weiland street warrior intake, e7 heads, longtube headers to glass packs, bored .30 over

its gotta be a dizzy issue right? because the dizzy is what is changing how the car reacts and how it stumbles it seems. I've been battling this for a pretty long while and I'm pretty sure its almost fixed but I'm just stumped at this point. if any of you can give some ideas its very well appreciated, you guys have helped me immensely in the past. hope i gave enough info and thank you ahead of time!

 

My bet it's carb issue, a 670 is quite a bit of carb for a stock headed 5.0...

Still there is a great video on YouTube by Summit racing that gives details of tuning 4150/4160 carbs...

https://video.search.yahoo.com/vide...c=3&sigr=11amalpgu&sigt=12iooolqd&age=0&&tt=b

 

Yeah I've been trying to get this carb to work.. I'm hoping I did considering the issue changes with the dizzy.... But it's still very possible.

 

Running too lean accelerator pump. If it stumbles when you accelerate, and you are not seeing black smoke out the tailpipe, too lean. If it was too rich, which most people automatically assume, you would see a puff of smoke.

I just finished fixing the same issue on my carb. Ended up with the largest accelerator pump cam out of the kit on the rear, next largest on the front.

 

30 degrees initial? Where are you at total advance?

 

It goes off what my balancer will read for total. And I thought it was lean too. When I got on it it even kinda smelled lean

 

......

 

lol okay let me rephrase that. when i get on it it makes a smell that doesn't smell like gas or burning oil. and when my squirts were clogged up on my edelbrock it made the exact same smell. i don't know if its actually a lean smell but i assumed it was lol

 

Yes if you nose is sensitive enough and you're in tune(pun intended) to the smell, a rich vs lean condition is different in odor... No I can't tell you what the differences are but I know it's true...

 

I thought so too lol... I am leaning toward a lean condition as well. I can't believe it because I thought I'd have rich issues because it's a big carb for a 302 but I get the same 'lean' smell at start up and full throttle

 

UPDATE:
i was messing with the idle system today and i got it as good as i can (played wight he secondary blades so i don't need so much of the transfer slots exposed) and used a vac gauge for tuning the mix screws and it hardly stumbles when i step on it anymore. can still feel it some so its not perfect but it did help. so it does look to me that its a carb issue not so much ignition... I'm gonna keep playing with the carb, gonna order some pump cams and the secondary blade adjustor that i can adjust with the carb on the car. hopefully the end is near for this gremlin I've been having...

 

That can't be good. Got a good timing light? I don't think you want any more than 36 - 38 degrees total. Dial back timing lights are great for measuring the advance curve... You should make sure the timing is where you want it before messing with the carb.

 

Okay that's a good idea. The light I have is of questionable quality anyways

 

The balancer only goes up to 30 and then the marks are gone.

 

an over sized carb will be more prone to run lean than rich. the way a carb works it that it needs air velocity to draw the fuel out. a big carb has big holes and big holes dont accelerate the small amount of air that a small motor uses compared to a big motor. so while lots of air can get into the motor with a big carb, it wont mean that a lot of fuel will be dumped into the motor.