CfieldVette

Ok, I have been fooling around with tuning this engine for the past 2 weeks and I feel like I'm throwing darts in the dark ... as well as throwing a full tank of gas down the engine! I'll start off by listing my engine stats:

L48 modified
Same block - 4.00" bore
Same pistons - dished about (-13)
Same crank
Same con rods: 3.48 stroke
(rebuilt 2006 w/ new bearings, rings, oil pump, fuel pump, water pump)

Brodix IK180 64cc Alum. Heads (180cc intake runners)
2.02 intake ports
1.6 exhaust
(springs: max valve lift 1.525, outside diameter 1.25 This is not the lift I have, see cam below)

Cam: Lunati VooDoo 60101LK (Hydraulic - not roller)
1,000 - 5,500 RPM
213 in / 219 ex @ 0.050 lift
Lift: 0.454 in / 0.468 ex

Intake Manifold: Edelbrock Performer dual plane
Edelbrock 1406 Carburetor - 600 cfm, electric choke, not endurashine
All emissions equipment removed (no egr, no pcv, no cat. converters, no exhaust manifolds)
Full Length Headers
Proform 1.5 Full Roller Rockers

Est Compression - around 9.5:1
PSI - just above 150 (i think... compression guage broke!)
Running Premium 93 octane


Now, my first problem was backfire through the carb, but I fixed that with correct timing (needed more advance). I just made sure the TDC mark on the balancer lined up with 0 on the timing tab yesterday. I set initial without vacuum adv at 12 and centrifugal at 36, which came in around 2500-3000 (loosest springs in dist). I hooked up vac adv and got around 52 total advance at around 3300. Ok test run - ran perfectly unless I mashed on the pedal. Then she'd bog down and would not accelerate well at all.

Ok time for the carb kit for the edl 1406. As recommended by Greg Suyenaga from Edelbrock, I went with 73x42 rods and the pink step up spring to keep the rods open longer. Stock setup was: 75x47 primaries. I also installed bigger accelerator pump nozzles and adjusted the accelerator linkage to pump more gas. Next test run - much, much better! Now I can get 0-60 in somewhere around 6 - getting better. BUT now there is the problem of WOT. If I keep the pedal in for more than 5 seconds or so, the car bogs down again..... as if it was being flooded ....... or maybe running out of fuel???? Ok maybe too much gas so I changed accel linkage to pump much less gas and even tried leaner rods w/ stock springs. Still, she is bogging at WOT if I hold in the pedal for a while. Keep in mind she accelerates just fine. After that first big accel or 2, I let off the gas and I hear slight popping from the mufflers. Then she bogs when I touch the pedal and cuts off.

I disconnected vacuum advance to no avail. Yes it was on direct manifold vacuum (out of carb - not ported). I checked 2 plugs and the insulation was half yellowish/tan half white, some carbon buildup, looked fine tho. I could keep playing with settings here and there but if someone has a recommendation for timing, carb settings or anything else, please let me know! Thanks for any help!

TedH

Nice setup. I hope Lars chimes in soon... He may be able to help you dial that carb in. He rebuilt both rochesters on my '80 and '69 and the distributor on the '69. They both run extremely well as a result.

blunblk68

i think your carb is a little small for that engine? How far out are your air fuel mixture screws 2 or 3 full turns??
I think if it were me i would be running a 700-750 cfm carb on that motor!!
it dosent hurt to have to much carb as you can always thin it out by turning the a/f screws in but if you dont have enough carb it can lean your engine out and cause damage!!

CfieldVette

Screws are out about 2 turns or so, I have adjusted them so much it's not funny but I laugh anyway. ha. It's hard for me to tell if she needs more gas or not getting enough. It seems though, with my limited experience of flooded engines, that this is the case since I have to let the car sit for a minute or 2 before starting up again. Maybe I should've tried pumping the pedal a few though. Might be running out of gas. I believe the stock float level is fine but who knows. I tried leaning out, but yea maybe I should try pouring in the fuel.

BigBlockk

I don't think Lars will do any work on the Edelbrock carburetors.

Before you do anything else you need to hook the PCV system back up. This will help keep moisture out of the engine oil.

As far as the tuning goes, you really should unhook the secondaries until you can get the primaries to function under all driving conditions. It sounds like the primaries may be pretty close but the engine is leaning out when the secondaries open up.

Don't rely on seat of the pants to do your tuning. You need to make timed runs to gauge your progress. Time the car between 40 and 60 MPH in second gear on the same stretch of road. This way when you make an improvement you will be able to see it. This is for main jet tuning at WOT. Once the main jet is set you can then tune the cruise by changing rods and springs.

When the primaries are running well reconnect the secondaries and tune them.

BigBlockk

Later.....

CfieldVette

That makes sense. I will disconnect the secondaries to make one less variable in the big tuning equation. So your theory is that during WOT my engine is leaning out and not being flooded with fuel. I can experiment with this and change the 2ndary jets if necessary.

I understand about keeping the oil and lower end free from water, I just want to make sure this won't hurt my performance and air:fuel ratio. To my understanding, the carb will pull air from pcv just like from the air cleaner, then mix this total air with fuel - so it should be ok.

Any other help or ideas are much appreciated!

Thanks

Tim H

AS I always say and do, unhook the vacuum to the dist, get a dial back timing light, set dial on 36, rev motor to 2500 RPMs ,if timing mark goes back to zero you, are set at 36@2500.
Don't worry about idle timing unless its hard to start.
carb: turn one at a time, idle screws in until the car almost dies then back out until it smooths out, then go about a 1/4 turn more.
Or get a vacuum gauge and turn out idle screws until you get the highest reading.

CfieldVette

Thanks for the timing info. I've got it pretty much set at 36 at around 2500 to 3000 without vacuum. Then I hooked the vacuum adv back up. I am almost positive it is not timing because I have tried about a million different timing settings. The only problem I have is at WOT and after I go WOT for several seconds. Then the engine afterfires in the exhaust with popping and bogs when I press the accelerator again because it gets flooded with fuel. I am going to try to change the accelerator nozzles to smaller nozzles. I tried disconnecting the secondaries with different settings several times and the same thing still happens. I am almost positive this is a flooding because when I press the accelerator in, the car bogs down again. Then I have to let it sit and run without touching the accel to get back to normal. It will only bog like this after I go WOT. Thanks for your help!

CfieldVette

Actually the car runs like a dream except after the 1st WOT. I can even accelerate perfectly smooth and fast with good times that 1st run. After that, she bogs and pops because of flooding. I can't touch the accelerator at all until I wait until the fuel clears out. It could be the rich period when I release the accelerator after stomping the accelerator - there is a lot of afterfire and popping during this time. I need to figure out a way to prevent the flooding condition after WOT. The solver of this problem wins a high five. Thanks

1976-L82

Sounds to me like it is running out of fuel instead of flooding. If it were flooding, it would die when you let off of the accelerator, too much fuel not enough air. After WOT there is enough fuel in the idle circuit but not in the main jet circuit, when you open the butterfly air rushes in and leans it out. Sounds like fuel lines, fuel pump, fuel filter or maybe trash in the float valve or even improperly set float level. Had this on a 78 Chevy truck turned out to be the fuel pump would keep up until WOT. Hope this helps

tracdogg2

You are definiitely running out of fuel, not flooding. Weak fuel pump, collapsed sock in tank, and/or kinked hose at the fuel pump.
Mike

BigBlockk

Everything you are telling us (spark plug color, backfiring, popping in the exhaust, hesitation on acceleration, surging) are lean conditions. Why do you think the engine is flooding?

BigBlockk

Later.....

CfieldVette

Ok I'll check the fuel pump pressure, fuel lines for kinks, filter, float level, and everything else I can to make sure fuel delivery is good. The reason why I thought it was flooding is because I had to wait to restart the engine after it died (after going WOT). When I would even tap the throttle it would die again. I guess I'm just not good at telling rich from lean conditions yet. However, I will work on this until I get it right. I can't really do timed runs until I can get the engine to run without dying. Slowly but surely. Thanks for all the help it is much appreciated!

CfieldVette

This again confuses me:

Quote from internet sources-
AfterFire
Afterfiring, sometimes called afterburning, often results when the fuel/air mixture is too rich. Overly rich mixtures are also slow burning. Therefore, charges of unburned fuel are present in the exhausted gases. Air from outside the exhaust stacks mixes with this unburned fuel which ignites. This causes an explosion in the exhaust system. Afterfiring is perhaps more common where long exhaust ducting retains greater amounts of unburned charges.
Afterfiring can also be caused by cylinders which are not firing because of faulty spark plugs, defective fuel injector nozzles, or incorrect valve clearance.

If my engine is leaning out, then how could I have afterfire??

CfieldVette

Let me be clear - I'm talking about afterfire (through the exhaust) and not backfire (through the carb). It only afterfires after I let off the accel. after WOT. Then there is the afterfire and the car will shut off sometimes. I thought afterfire in the exhaust was due to a rich condition. Pumping more fuel seems to do more harm than good. Does this change the analysis?

tracdogg2

This is why I feel you are running out of fuel. You have to wait until the float bowl fills back up to touch the gas again. If you were flooded you couldn't restart the engine without holding it to the floor.
Mike

CfieldVette

Ok maybe I'll run it again and hit this same scenario and manually check to see how the float level is doing and where the gas is (if there at all). I'll let you know what I find. Thanks

CfieldVette

Ok. Test results for today: it turns out that when I thought it was flooding, it was when I was messing around with the carb screws and rods .... ..... anyway this was actually a two-fold problem. I fixed the rich mixture and set everything the way it should be. I took a drive in 2nd gear and hit 4000+ rpm. indeed she sounded like she was running out of fuel so when I got home, I decided that it would be a great idea to hook up a fuel pressure guage. Interestingly, it read 3, went to 5psi for a moment, then back down to 3. Bingo I found the problem. I just bought this pump brand new last year, too. (It could be in the fuel lines or filter - I'll double check this.) Oh well I might get a new high flow pump and might as well get a braided fuel line. Any recommendations on a good fuel pump (mechanical)? I have a return fuel line, too. Do I really need this? Thanks

CfieldVette

Could anyone recommend a fuel pump and psi/gph I should buy for my car? What are the psi/gph that some of you guys have with your fuel pumps? - mechanical
Thanks

TimAT

Watch the braided fuel line. Most of them are just a rubber hose with braid covering- let's NOT have a BBQ!!