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E4ME settings, timing, what else????

LannyL81

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Oro Valley, AZ USA
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81 White/Cinnabar, 96 CE LT4 sil/blk
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Slightly modified engine, 355, zero decked block, 2 valve relief pistons, about 9.1 static CR, 882 chevy heads with 2.02/1.60 valves, milled to about 74cc, 1.6 ratio roller tip rockers, Comp Cams 268H, headers with side exhaust, stock intake, E4ME carb:

Idle Air Bleed Valve: with engine all nice and warm, dwell varying, I adjust the Idle Air Bleed valve screw but have to blip the throttle before I see a change in dwell. Then after I do, I make adjustments so that I get an average reading of 30. I turned off the engine for about 20 minutes....re-started it, and was checking the timing...and after 10 minutes or so I looked at the dwell reading....it was off again...it was between 10 and 50, but not averaging 30 anymore.

Is something wrong here?

I still feel like this engine just does not have the power it should.

Checked the timing and it was at 38 at about 2200RPMs, which I believe is correct...but still....:W

I have rebuilt this carb, and checked and rechecked things....float level is good, idle mixture solenoid has correct travel....???

What else should I be checking???????????????????????????????????
 

Peer81

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What is het vacuum signal at idle?
Could be your ECM is thinking the car is in higher rpm and needs more fuel. In other words to much fuel into your carb. :)

Other thing, is the O2 sensor hot or cold. When the sensor cools down the ECM will go into open loop again (like warming up)
But I could as well be wrong :D

Greetings Peter
 

LannyL81

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Oro Valley, AZ USA
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81 White/Cinnabar, 96 CE LT4 sil/blk
I will have to check the vacuum at idle once again...it has been too long since I checked it.

But the stock L81 had 195hp.
With the mods I did which include zero decking the block to bring compression up to 9.2...I estimated it delivers about 230hp now. Not exactly ground shaking is it!!

So I am probably getting all it has to give....but perhaps a bit of tweaking on the timming and carb hopefully will yield better throttle response.

Oh and this is a 4 sp.
 

Sensei

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Jacksonville, Fl
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'81 dark blue
As Peter said, your car could be slipping into open loop at idle as you check dwell. Mine does that because the O2 sensor is farther away from the head than stock. But that should not make a "seat of the pants" difference in performance.

What have you done to the carb besides adjustments? You should modify the air valve, tune the linkage, shorten the pump plunger, open the idle screw ports and adjust the secondary hanger height. That should get the full benefit of the mods you have made to your engine.

God bless, Sensei
 

LannyL81

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Oro Valley, AZ USA
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81 White/Cinnabar, 96 CE LT4 sil/blk
Since I have a varying dwell I would say that it is in closed loop.

Sensei going to need more instructions with regards to those carb mods.

Modify the air valve
Tune the linkage
Shorten the pump plunger
Open the idle screw ports - if you are referring to the idle air screws at the base of the carb, this was done by the previous owner. I can take one of them all the way out before there is a change in engine idle...as it dies.
Secondary hanger height - I doubt that the secondaries even open up.

Tell me more...

LannyL81
 

Sensei

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These are covered in detail by Doug Roe in "Rochester Carburetors, but here is the idea:

Modify the air valve

The butterfly over the secondaries has a small metal tang on the end of the shaft that keeps it from fully opening. You do not need the full 800 CFM capability of the carb, but if you cut/ grind off part of this tang, it will allow more airflow through the secondaries as engine demands it. (For full 800 CFM, cut the tang to allow the air valve to go 90 degrees.)

Tune the linkage

With the engine warm but NOT running, have someone sit in the car and press the accelerator to the floor as you look down through the primary and secondary bores. The throttle plates should simultaneously go perfectly vertical when the pedal is on the floor. If not (and this is common), the linkage needs to be adjusted.

Shorten the pump plunger

The accelerator pump can give a stronger/ longer pump shot if its shaft is shortened about 3/32".

Open the idle screw ports - if you are referring to the idle air screws at the base of the carb,
Yes I am
I can take one of them all the way out before there is a change in engine idle...as it dies.

You need idle control. Carefully drill these ports out to 3/32" so you can negatively affect idle by both screwing in and out (before the screws fall out) so you can find the sweet spot.

Secondary hanger height

Lars Grimsrud has a good paper on bending any secondary hanger for best performance (google), or you can buy one from Edelbrock

I doubt that the secondaries even open up.

This would be a problem in itself. If they open when you check the linkage, they should work fine. If not, let me know and I'll tell you what to do.

God bless, Sensei
 

LannyL81

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Oro Valley, AZ USA
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81 White/Cinnabar, 96 CE LT4 sil/blk
Weekend update:
Okay, I set the idle air blled valve using the J gauge. Mixture solenoid travel is right at 4/32"...slightly less.

I then turned the idle mixture needles to 3 1/2 turns, started engine and let it warm-up...had varying dwell. Turned the idle mixture needles the same amount until I had an average of 30...range was 27 to 33. Connected vacuum gauge to manifold vacuum port for the headlights....had 11" to 12". Adjusted timing just a bit to give me 12" to 13" and had to readjust the idle mixture needles to the final setting of 4 1/4 turns.

Went for a drive and the main difference now is that idle hangs at about 1000 now (this is a 4 sp) but then slowly drops to around 800 during a stop light duration. Still smells rich at start-up and no real difference in performance which feels sluggish.

Oh and the secondaries do open-up.
 

Tim81

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North Canton, Ohio
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81 Black on Black Corvette
First off I'm no expert when it comes to carb adjustments. 41/2 turns on the mixture screws seems a bit must and might be why its running rich. I set mine to 31/2 turns and adj. the Air bleed valve until I average a good 30 degrees of dwell. Also it might be because of your cam, I read 18 to 21 hgs of vacume at idle with a completely stock engine, if you're only reading 11 or 12 then maybe the computer does think you need more fuel and is riching the mixture. Just a thought...Tim
 

Sensei

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'81 dark blue
I use vacuum reading to adjust idle mixture: adjust idle mixture screws, keeping the idle speed constant, until you find the setting that gives highest vacuum, then make final idle air valve adjustment.

I have a comp 262 cam and get about 15"-16" vacuum. I'm not sure your 268 should be that much different. I would also be sure you don't have any vacuum leaks.

Gerry has a comp 268 in Gail, maybe he'll chime in here with what kind of vacuum he gets.

God bless, Sensei
 

LannyL81

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81 White/Cinnabar, 96 CE LT4 sil/blk
I did find the source of my oil leak, it is the rear of the intake manifold. Could this also be a vacuum leak?
 

Peer81

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The back of the intake manifold has only oil passing by it there is no vacuum inside the space above the camshaft and underneath the intake manifold.

What I would do is disconnect and plug all vacuumlines you can find (also from the carb and to the brake booster) then see how much the vacuum is then. After that with the engine running try to spray some WD40 underneath the carb to intake thick gasket and between the space from the intake to the heads. See if the engine reacts to that and you'll know if you have a problem there.

Greetings Peter
 

Peer81

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I had a similar problem and turned the carb bolts a little extra and problem fixed :) (that was after I disconnected everything of course)

Greetings Peter
 

LannyL81

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I did not think the oil leak could also be a vacuum leak...but thought I would ask just to be sure. I will still be checking for vacuum leaks this weekend.

Otherwise I think I need to decide to either just leave everything alone, accept that this is all this engine combination is going to give in power or spend some serious money and time and get the power I think I want.

I think the main problem are the 882 heads I put on, just not enough flow there, even with 2.02/1.60 valves and shaving them down a couple of cc's. I could get a set of Sportman II heads or just get some Performer 70cc aluminum heads. I would like to go Vortec, but only come in 64cc and that would require me to change pistons which would require balancing, which would require pulling the engine once again. I sold off my hoist and stand as I did not have space to store them any longer. The Performer heads would cost me $1300 with gaskets and new bolts....not cheap by any means.

Anyone have other ideas??
 

LannyL81

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81 White/Cinnabar, 96 CE LT4 sil/blk
UPDATE on this thread:

Oil leak is not intake manifold or rear main seal. Possibly the dip stick tube or somewhere above the starter. Still looking.

After getting two lower compression readings I decided to take the valve covers off and check / re-do the lash setting. Took the dist cap off so I could watch the rotor position and be on #1 TDC and not #6. That is when I noticed the rotor position with respect to #1 cap terminal and balancer tab was not all lined-up. It looked like I was off a tooth on the distributor as the balancer and rocker arms seemed correct.

With the balancer tab aligned to #1TDC I pulled the dist out, turned the oil pump slot to point to #1 terminal, dropped the dist back-in and then checked all the valve lash. I also had pulled all the plugs out and checked the gap. I had set the gap to the original 0.045 gap instead of the wider 0.055 gap that my higher HEI dist called for. Corrected that.

Put everything back together, hit the starter and engine fired up really nice. Set base timing to about 10 BTDC. Shut engine off, reconnected computer, restarted. Timing was at about 18, rev'ed engine and watched timing advance to 32-34. Went about setting the M/C dwell (again) and still had to turn the mixture screws out 4 to 5 turns to get an average of 30. But engine was sure running nicely....had a completely different tone....really good. Took out for a long drive and engine ran very smooth....was very pleased, all problems solved......except still have oil leak.

But the 4 to 5 turns on the mixture screws bothers me. So after checking my dwell meter at work, making sure it was accurate....I discovered that for the three years I have been using the wrong dwell scale!! Really need to put my glasses on and READ the fine print. So last night, hooked dwell meter up....warmed engine...turned mixture screws in, then out 3 1/2 turns....and what do you know.....average of 30 on the 6 cyl scale....:boogie.

Only thing left now is the oil leak.
 

Peer81

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Great to hear Lanny!

Lets hope your oil leak is as simple to solve as this problem :)

Greetings Peter
 

LannyL81

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Oro Valley, AZ USA
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81 White/Cinnabar, 96 CE LT4 sil/blk
Oil leak fixed. It was a combination of loose oil pan bolts and the engine oil dipstick.

Have tightened and replaced....all is really good now.

Would like a better off idle response than I have, so some additional fine tuning of the carb is likely needed.
 

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