Technical Edeldbrock carb tune for lumpy camshaft

I have and Edelbrock 600 cfm carb(1405) on my souped-up 5.0 SBF. Got good heads....RPM manifold.....headers.....T-5 tranny.....snotty camshaft with 230-236 duration @050 on a 108LSA.
Runs pretty dog-gone good/idles @750 RPM fine But........while driving under 20mph in 1st or 2nd gear it wants to start "motorboat'in"(that's how I describe it!) give it a little more gas and it calms down. I can kick-in-the-clutch and clean it out a little and that helps but ...if I don't accelerate it does it again.
I THINK....if I go to a stronger metering rod spring that might smooth it out some. What's your thought?
Also don't Eddie carbs usually come jetted pretty rich?............Maybe I need to lean it down some, I just want to lean it so much 'I burn stuff'!
Thanks for all your input
6sally6
PS........Don't need any" you-need-a-Holley" comments because THIS is what I got.

 

Need pics.

 

Of?

 

Matters not to me....Just pics.

 

change the position of your accelerator pump lever. There are three different holes you can try. May not be your problem but it costs nothing and is pretty easy to try.

 

Usually surging/bucking is a lean condition, running fat will feel sluggish and bog. I’d try a smaller metering rod first before changing the spring. But too much vac advance can cause similar stumble feeling at light throttle too. Before messing with the carb, Disconnect your advance canister and see if it improves. Most ford distributors I have encountered have adjustment of vac advance by using an Allen key in the vac connection port.

also download the edelbrock carb manual, lots of detailed info on the individual circuits, tuning for certain conditions, and charts to help choose jets and rods.

 

^^^^ What he said about downloading the manual and get the tune kit.

 

Your idle circuit is probably a little lean. This is where a wideband setup works pretty well, because at this point, you're probably fine on the mains, fine at curb idle, and lean at slow cruise, especially if it drives well everywhere else. There are several ways to richen up the idle circuit on Edelbrocks...I usually "shrink" the idle air bleed on top of the primary venturi cluster. To do this, I measure the bleed with a pin drill, find a small ball bearing, tap on the bleed until is "closes up" a bit, and clean out the bleed with a smaller pin drill. I usually start by closing the hole 4 thousandths.

One way I've found to verify this is by counting how many turns out the idle screws have to be to get a smooth idle. If you're up around three turns out, the idle circuit is probably lean.

I've included a picture from another website that talks about it a little. Of course, I'd probably try a few other things before I started this. Is your timing too advanced/retarded. Are you running vacuum advance?

Regarding some things you mentioned: a stronger spring won't hurt to try, but usually you get a bog when you stomp the gas if it's wrong. Good luck...

 

I do have 'light' advance springs in the distrib. Also have a bushing to LIMIT the total timing to 36*. I really enjoy the quick revving of the engine with the initial advance where it's at now. Total advance(36) happens by 2000 rpm. I took out some of the initial advance with no improvement so thought I would look at the metering springs and rods.
I understand with 'too weak' springs it allows the metering rods to pop up and down (correct?!) at low speed/
low vacuum.
I have a tune-up kit but was wondering.....do I need to richen or lean the carb ? Don't the Edelbrock carbs come "outta-the-box" pretty rich? So I've heard! Comments
thanx
6sally6

 

My experience, I have had to lean them down a bit.

 

With a big cam and low idle vacuum you need to go with a weaker spring to keep the metering rods in the jets at an idle

 

What is your fuel pressure?

Just watched a YT video yesterday by Thunderhead289 where he made a strong recommendation to use a fuel regulator adjusted to 5-5.5 lbs pressure when using an Edelbrock carb. I'm to understand this helps ensure that the carb can work optimally and that tuning tweaks will have the desired effect. If the fuel pressure is too much, the Eddy's circuits won't behave properly...

Gotta56forme/Scott

 

Above advice to use weaker springs is on point. Larger cams with tight LSA's have less vac at low speeds and cause metering rods to rise when they shouldn't. I'd try weaker springs first.

 

Get the fuel pressure under control as recommended by Edelbrock. Then proceed with tuning.

Phil

 

I'm with Aaron65, you are too lean in the idle ckts. When puttin along at 20-25mph the engine is getting fuel mostly thru the idle ckt, when it surges you crack the throttle and give it some gas. I'd be drilling the idle restrictor, he showed it to you, to about .034 to give it more fuel (it should be about .031 now, but check it to be sure).
You can actually see what its doing, look in the carb with it idling and you shouldn't see any fuel coming from the boosters, its flowing in below the throttle blades, when you raise your rpm to above 1200ish you will see the boosters start to flow fuel - your rpm, when it is surging, is below 1200 and quits only when you open the throttle blades. With the motor idling you can also take the cover off the pop up spring and watch it working as you roll into the throttle.
There is one other thing I have seen happen on the Edelbrock idle ckt, there is a plug just above and off to the side of the idle screw, this plugs is at the junction of where the idle fuel flows from the idle feed and where it goes to the idle screw, I have seen them use the wrong size plug and it'll block the passage. It is so common that I test every edelbrock that I rebuild (a considerable amount) to be sure this passage is clear, how you can tell is if you have just a minimum amount of idle scrw adjustment or the customer coimplains the idle screw doesn't do anything, you can run it all the way in.

 

Try loosen the screw on the cover over the metering rod piston and turn it enough to let you see the piston and tighten the screw enough to hold cover in place. Now start the car let it idle look and the piston should be all the way down if it is not the spring is to strong. If you blip the throttle and you should see the piston jump up.

 

6sally6, you said that it starts to "motorboat", then you push in the clutch to clean it out. To me, that sounds like it's running a tad rich. Maybe check the fuel pressure and float level first to make sure everything is good. Then do what you have to to lean it out. If its loading up or blubbering, it's running rich.

 

Sunbeam........that sounds like a good idea! (It looks like I went the worng direction on the spring strength) I went with a stiffer spring by mistake.

oj..........thanks for your info but............I'm really not comfortable sticking a ball bearing in the idle circuit and then drilling a hole. Call me a wiener but drilling in the circuit where one bum move will trash the whole carb!!! Makes my sphincter draw up! (you ain't seen some of my drilling jobs) although the way you explained it makes a lotta sense.

So far I have leaned it out with a jet change and meter rod change (and the wrong spring)Maybe its wishful thinking but.........it seems like its not bucking quite as much.
Might turn back some on the initial advance to see if that has a positive effect.

I've lived with it for a couple years soooo it ain't THAT bad, I guess
Thanks
6sally6

 

how old is carb? fuel filters clean? how old is distributor?

 

I think idle speed is a little low.

 

Reversion

 

Seems not many have worked with Carter/Weber/Edelbrock (Holley !) carburetors much here..!

LEAVE the IDLE circuits ALONE...at least until you try other things. Messing with the idle circuits is JUST fine tuning the main jet and to some extent, the idle circuit. You are a LONG way from that point right now.

The FIRST thing to do (like chicken said), put lighter springs under the metering rod pistons. If you have a lot of duration and or overlap, the manifold vacuum will be low. Most likely not enough to properly pull the pistons down into the proper idle position. The engine will run terrible with the metering rods at the full "up" position..!

With the little covers off of the pistons, start the engine (full warm !). Make sure that the pistons/rods go all the way into their wells. Try different springs. Find a set of springs that allow the piston to go all the way down at warm idle...BUT will snap them to the top of the travel as soon as the throttle is opened quickly.

Next - you "may" have to richen the accelerator pump. This will show up, similar to other things, as a "bog" when you hit the throttle hard.

Next - make sure that you have the mechanical/initial timing set high enough. Low vacuum (high overlap, high duration), normally means low cylinder pressure, which requires a bit more initial ignition advance for the engine to run its best.

Next - raise the float level slightly (try .06" first). Again, low vacuum/air speed will cause the system to be very lazy in pulling fuel thru the booster venturis. You need to have the fuel flowing quickly like any other time.

Next - don't mess with the jetting (jets/metering rods) OR air bleeds (at ALL) until you see what the spark plugs look like. The actual "jetting" like everything here, will take some experimentation. Look closely at the spark plugs. New plugs are required when it gets to this point to be able to get good readings. Look into how to read spark plugs with todays gas if you don't know how. It's a bit different than it used to be with leaded gas.

Next - The idle screw adjustment will most likely need another 1/2 a turn, maybe a little more. This will help the "system" get fuel flowing quicker into the booster venturis to help get the engine to run smooth, a "little" more fuel at low rpm will be critical.

There's a bit of experimentation to do, the above will get you going to a reasonably good spot, but then continued experimentation of all adjustments will be required to get the engine to run its best.

Go slow, change ONE thing at a time.

Mike

P.s. - If you start screwing with the air bleeds, and mess up...that's it, you'll need to go find a set out of another carburetor. I don't think the booster is sold separately..!

 

Did you try disconnecting vac advance (assuming you’re using it) first before tearing into the carb? Takes 2 secs to rule that out.

 

Its easier than you think, its just the restrictor, look at the illustration that aaron65 posted of the primary cluster, do you see the arrows pointing to the 'idle jet', that is the restrictor, where it necks down at the end of the tube, the arrow is pointing right at it. You just drill it a few thousandths bigger and you're done (you have to do each side, both clusters). You aren't making an irreversable change, the idle ckt is still controlled via idle screws, you are just increasing the range.

 

One of the guys in my Ford Group had about the same issue as yours with his SBF I suggested he replace the metering rods in his 1405 with metering rods from the 1406 (the jets are the same) it was a huge improvement the Edelbrock part # is 1459 your local O'Reillys should have them. You might want to check out this too. https://www.hotrod.com/articles/rebuilding-tuning-edelbrock-carburetor/ The spring kit is part # 1464 might want to grab that also.

 

I agree with Jeff for street driven cars the 1406 tune works better but the primary are smaller in the 1406 .100 vs .095

 

Well I swapped the jets to .100 and the metering rods to 14.48 (1405 tune but one step leaner) tried 3 different sets of springs....more advance and less advance....one step richer on the accel. pump still
sux big time.
Only found slight improvement with one set of step up springs.
Not sure if I told y'all but, I installed light advance springs in my duraspark distributor(limited to 36* total advance) I have full advance a@ 2000 RPM.
Can't believe this is the problem because I did this modification YEARS ago!?!
Comments
6sally6

 

Every Eddy carb I have ever touched is RICH out of the box . They don’t impress me much . But , that’s me , don’t hang me ! I’m a QJet guy on GMs and a Holley on Ford’s . I think as suggested your air bleeds need to be opened up or drill a SMALL hole in each primary throttle plate to allow the plate to close farther , making use of the idle air slot in the carb body

 

would drilling a small hole in the throttle plate accomplish the same thing??
I always thought the transition slots were not the problem. The idle RPM is 750 or even a little lower!
what about holes in the secondary plates?
6sally6

 

Put a vacuum gauge on the ported vacuum port and see if you have any at idle.