4bbl running rich.

-
V

VeryValiantVellow

Active Member
Joined
Nov 13, 2017
Messages
34
Reaction score
12
Location
Casselberry Fl
Edelbrock 650. New on a 340 punched to 413. Not even on street yet. Running rich. Have reset floats. Put in recommended needle and seat. Better, but Still rich. Any thoughts on cause? Oh, and have worked timing a bunch. It will idle at 700 with a decent cam. Don't remember specs on it. Could look it up I guess.
 
What model edelbrock is it? You might need to change the springs in the top that hold the enrichment circuits closed. If its a larger cam with low vacuum the stock springs wont work. If I recall correctly, the springs hold the needle down (closed) and when vacuum drops they open up. The less vacuum you have the lighter spring you will need to use.
You would need to order the calibration kit for whatever model carb you have.

600.jpg
 
Last edited:
VeryValiantVellow said:
Edelbrock 650. New on a 340 punched to 413. Not even on street yet. Running rich. Have reset floats. Put in recommended needle and seat. Better, but Still rich. Any thoughts on cause? Oh, and have worked timing a bunch. It will idle at 700 with a decent cam. Don't remember specs on it. Could look it up I guess.
Click to expand...
What fuel pump? Fuel pressure? Those carbs like 4#.
 
I should note that it may idle just fine but as soon as you crack the butterflys your vac drops and the valves open too early. If this sounds like what is happening thats where I would start.
 
Thanks guys. I mistyped.. it is a 750 single pumper vacuum secondaries. Pump is electric holly. I cut pressure to about 5. Could drop to 4 and I have light springs in it now. I was thinking I might actually need heavier springs since it puffs slightly blue for a split second when I goose it. Also thought maybe 'economizer might be rich so I cut it back one slot. Any thing else come to mind?
 
Is it a Holley?
I have ran many edelbrocks with stock pumps so 5-7 psi shoudnt be a problem. If it were too much fuel pressure it wouldnt idle. If I read your post right you said it would idle fine.
 
MoparMike1974 said:
Is it a Holley?
I have ran many edelbrocks with stock pumps so 5-7 psi shoudnt be a problem. If it were too much fuel pressure it wouldnt idle. If I read your post right you said it would idle fine.
Click to expand...
Yes. Mike. It idles nice and starts easy. Took it around the block to see if it shifted ok and (4 spd) goosed it. Went sideways immediately. So it's getting fuel but don't know about top end. Never let it out yet. 416 w lots of tweaks like headers, cam, NEW everything. Moroso spark.
 
Give us more detail about the engine. First off, you cannot "punch" (bore) a 340 to 413. There has to be some stroke (longer throw crankshaft) involved, too. Details. KNOWN and MEASURED static compression ratio. Not JUST "oh it's got 10:1 pistons". Camshaft specs. Not just "decent cam I could look the specs up I guess". Solid or hydraulic? Roller or flat tappet? Type of ignition. How much initial and total timing? Intake manifold type? Cylinder heads? Ported or not? What exhaust? Headers? What size tubes? Manifolds? My GOD. You want help or not?
 
Part number and picture of the carburetor, too. That would help tremendously. That way we'll know what we're dealing with. If it's a base model 750 vacuum secondary, it does not have an adjustable idle circuit or adjustable air bleeds. Those are damn near mandatory with big camshafts and bigger cubes. It might be good "everywhere else" (doubtful) and be pig rich at idle.
 
Well Rusty. You are right. Was hoping for an easy fix like, "you need a lefthand monkey wrench". Ive never had much trouble with one of these carbs, have always been simple to tune but the mods are, as you say, extensive. I'll have to pull the stats and come back when I have more time to discuss.
 
VeryValiantVellow said:
Well Rusty. You are right. Was hoping for an easy fix like, "you need a lefthand monkey wrench". Ive never had much trouble with one of these carbs, have always been simple to tune but the mods are, as you say, extensive. I'll have to pull the stats and come back when I have more time to discuss.
Click to expand...
It's not hard to do. It's a little involved, yes. But as I said, we need to know what we're dealin with first and we can give you some accurate help.
 
VeryValiantVellow said:
Well Rusty. You are right. Was hoping for an easy fix like, "you need a lefthand monkey wrench". Ive never had much trouble with one of these carbs, have always been simple to tune but the mods are, as you say, extensive. I'll have to pull the stats and come back when I have more time to discuss.
Click to expand...
Here, read about these. Read ALL of it. There are some drop downs further down the page. I'm a BIG fan, one, because I have one of their 450s on my slant 6 and it runs GREAT and 2 they are a good bang for the buck. Read about all their adjustability. I'm not tryin to say run out and buy another carburetor. You may have constraints to work within. It's just a thought for now.
Quick Fuel SL-750-VS Slayer Series Carburetor 750CFM VS
 
I like those Quick-fuel series carbs. I think he's got an Edelbrock though.

20211019_194309.jpg
 
RustyRatRod said:
Give us more detail about the engine. First off, you cannot "punch" (bore) a 340 to 413. There has to be some stroke (longer throw crankshaft) involved, too. Details. KNOWN and MEASURED static compression ratio. Not JUST "oh it's got 10:1 pistons". Camshaft specs. Not just "decent cam I could look the specs up I guess". Solid or hydraulic? Roller or flat tappet? Type of ignition. How much initial and total timing? Intake manifold type? Cylinder heads? Ported or not? What exhaust? Headers? What size tubes? Manifolds? My GOD. You want help or not?
Click to expand...

Yep, this is what you need to do guys! If you give this forum the detailed info on your engine, drivetrain they can narrow down a solution. Trust me it's impressive to a guy with backyard mechanics skills needing diagnostic help. And they'll be right!! I've been helped several times.
 
RustyRatRod said:
Here, read about these. Read ALL of it. There are some drop downs further down the page. I'm a BIG fan, one, because I have one of their 450s on my slant 6 and it runs GREAT and 2 they are a good bang for the buck. Read about all their adjustability. I'm not tryin to say run out and buy another carburetor. You may have constraints to work within. It's just a thought for now.
Quick Fuel SL-750-VS Slayer Series Carburetor 750CFM VS
Click to expand...
I've been considering going with a Quickfuel VS carb myself over the 750 Ultra DP I currently have. I much prefer the vacuum secondary carbs. The carbs I've looked at are the 750 Slayer you mentioned as well as the 750 HR series. The only difference I see between them is the HR is a 4150 and the price tag shows it. Any thoughts about one being better than the other?
 
Try pump gas, 89.
Test drive it at 32 total timing/full advance and move 2 degree up till it pings..then go back 2 degrees and lock it down.
Stiffer spring on the secondary is what it sounds like.
'If holley vac secondary'. Go stiffer on the spring till it gets a flat spot into the secondaries wot...then go light till it just goes away..that's the spring you wanna use.
Intial timing can be dialed last as we were going to focus on the wot richness.
 
Last edited:
Vacuum holds the rods in the primary jets. Vacuum decreases and the spring lifts the piston and pulls the rod out, adding fuel. The pistons should be held down at idle.
 
I did not see where anyone mentioned this but I may have missed it but I would adjust my mixture screws following Edlebrock's procedure.. My 340 was running rich at one time and that is what I did... Worked out well for me..
 
Gator said:
I did not see where anyone mentioned this but I may have missed it but I would adjust my mixture screws following Edlebrock's procedure.. My 340 was running rich at one time and that is what I did... Worked out well for me..
Click to expand...
I agree, though he mentions blue puffs of smoke upon goosing the pedal..which could be too much pump shot. There a few positions on the pump arm of edelbrock/carter carbs that increases/decreases that. If this is occurring in neutral 'no load' I'd say that's where its originating from. Under load then the step ups.
While info is needed.. we dont need to know every last thing. CID vs cam size is important, compression sure.. but mostly if we are either dialing a timing curve or encountering a ping issue...otherwise it's mostly not helpful for a rich off idle issue or pump shot issue... but let's not chrystal ball too much... lol.. but basically I'm getting at that it's safe to assume a 413 sb is a 4" crank ...and they dont make any sub 8.8.1 pistons for them...though they could, but turbos and super chargers havent been mentioned... so in other words... we can cut out some lengthy once overs on everything in and around the engine.
 
You must log in or register to reply here.
-

Back
Top