Edelbrock Air Gap on Magnum 318 Problems

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kennygene

kennygene

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I have been running an edlebrock air gap intake on my magnum 318 and can't get the hesitation worked out of idle. I have been told the intake has too much plenum for 318 cubic inches and this combination will never work. Can anybody give me some advice?

Engine details...
1994 318 Magnum stock crank, pistons, bore all rebuilt
Comp Cams 264/270 adv dur with .512 final lift intake and exhaust advertised
Harland Sharp 1.6 ratio roller rockers
Heads are stock magnum milled .010 with hughes springs to match the cam.
Heads have had some home porting and have been gasket matched to the intake. Intake was gasket matched as well.
Heads were treated to a valve job recently and checked for cracks-all is good.
Ignition is stock Mopar electronic tuned to run 16 degrees initial timing and then 31 degrees at idle with vacuum hooked duirectly to the intake manifold. Timing past 3k rpm is set to max out at 34 degrees using a timing plate from FBO.
Compression is 9.27
Carburetor is a Holley HP 650 installed new. I am running 71 jets on the primary and 75 on the secondary. Holley tech had me up the primary jets. They told me it would help the issue. I later found out they were wrong.

Can anybody offer any help here? I have been fighting this problem for almost a year and just can't win.
 
2 inch spacer plate may help if nothing else is wrong it helped mine bigtime
 
what type of hesitation do you have? Is it a part-throttle hesitation (like accelerating up a hill with half throttle) or a Full-open throttle hesitation?

I noticed you say you have the vacuum hooked up directly to the intake. This is not advised on a street driven car. (where it hardly ever runs wide open throttle) You want to run the vacuum line to the ported side of the carb. That way you wont have a bog at part throttle.
 
Have you tried more accelerator pump shot or a larger discharge nozzle? Adjustment and nozzle change are easy to to do.
 
What is the vacuum level at idle, in gear? Have you done a basic compression test? Also if you can be much more specific on the circumstances of the studder... Like was asked - accelerating lightly? aggressively? Does it get worse with light/part/full throttle?
 
Wow, quick responses - awesome. The hesitation is off idle. I forgot to mention the transmission is a manual 5 speed so no torque converter worries.

The hesitation is off idle and even in neutral with no load. It hesitates and then picks up. WOT is fine.
Also, low speed cruising is horrid. I can be running 1400 rpms and when I press the throttle, it is really bad and then jerks taking off.
 
H'm off idle bog...
Could be a bunch of things.. vacuum leak, carb floats out of adjustment, not enough carb pump shot, stuck choke, fuel pressure issue, timing issue etc...

Do you know what manifold vacuum reading you are getting at idle and at idle in gear (like asked above)?

First lets look at the timing:

If you disconnect the distributor vacuum advance (that you have currently plugged into the manifold source) what is your timing at idle? Now with the advance still disconnected, what is the timing at 3000rpm?
 
67cuda360 said:
H'm off idle bog...
Could be a bunch of things.. vacuum leak, carb floats out of adjustment, not enough carb pump shot, stuck choke, fuel pressure issue, timing issue etc...

Do you know what manifold vacuum reading you are getting at idle and at idle in gear (like asked above)?

First lets look at the timing:

If you disconnect the distributor vacuum advance (that you have currently plugged into the manifold source) what is your timing at idle? Now with the advance still disconnected, what is the timing at 3000rpm?
Click to expand...

Floats are correct, no vacuum leaks, Holley HP doesn't have a choke or choke tower. Transmission is manual so no in gear test to perform.
Timing is 34 degrees at 3000 rpms. Fuel pressure is 7 at the carb.
I have the pink pump cams and a 28 squirter on the primary side.
 
kennygene said:
Floats are correct, no vacuum leaks, Holley HP doesn't have a choke or choke tower. Transmission is manual so no in gear test to perform.
Timing is 34 degrees at 3000 rpms. Fuel pressure is 7 at the carb.
I have the pink pump cams and a 28 squirter on the primary side.
Click to expand...

The manifold vacuum is around 16 at idle.
 
What is the part number for the carb you're using?
Since you don't have a choke, does it have the same bog with a cold engine and when it is fully warmed up?

Is the initial timing (at idle) 16 degrees BTDC?
is there any difference if you have the vacuum advance totally disconnected and the port blocked off (on the manifold)?
 
To answer your original question, I doubt the intake has anything to do with it, especially the volume of the intake. If you had an intake leak, that would affect the idle, but not cause a bog.

As others suggest, the carb is probably the culprit. Since upping the primary jets made it worse, you may be running rich at idle. If your accelerator pump is working, it may be going too rich when you accelerate. Down the road, think of installing an O2 sensor, otherwise you are flying blind.
 
I don't think the intake manifold is your problem. A wideband would go a long way towards helping this.

Sounds like you either need more pump shot, a different style of squirter, or perhaps the idle mix is too lean. Have you messed with the squirters at all?

I am guessing the HP doesn't have a timed vacuum port? I'd remove and cap that vacuum line until you get the problem figured out.

HP 650 is a lot of carb for that motor. It could maybe might be air bleeds. Maybe.
 
I have changed the squirters but I think I went too big since I only had one bigger in my cabinet. I may order a squirter tuning kit and see if I can get it to work better. I tried a 1 inch four hole spacer which was supposed to help with my problem - (velocity) but it didn't seem to help which points me back to the squirters or/and pump cam.
 
LXguy said:
I don't think the intake manifold is your problem. A wideband would go a long way towards helping this.

Sounds like you either need more pump shot, a different style of squirter, or perhaps the idle mix is too lean. Have you messed with the squirters at all?

I am guessing the HP doesn't have a timed vacuum port? I'd remove and cap that vacuum line until you get the problem figured out.

HP 650 is a lot of carb for that motor. It could maybe might be air bleeds. Maybe.
Click to expand...

I thought about a wideband and I've thought about just adding fuel injection since but I'd like to get it worked out without going that far.

From what I've read, the airbleeds are fine as long as you have enough adjustment on the air screws -which I do.
 
I do not think that intake manifold vacuum is the right source for the distributor advance pot, that alone might be causing the stumble. If you check out page 6 here, you'll see Holley indicates that the port at 2 o'clock from the choke is the correct source for advance vacuum.

If that's not the problem -- I am not a carb expert, but everything I have read about off-idle bogging basically points to accelerator pump being the wrong size, either its too big and it's making the motor run rich until you stop moving the pedal down, or it's too small and making the motor go lean until the power valves come in from the increased airflow. You can either fiddle around with those in a hunt-and-peck way or you could beg/borrow/steal an oxygen sensor (bungs are pretty cheap and I _hear_ you can just jbgoober em in, but my muffler shop welded one in for me for $15) to help you figure out which direction it's going.
 
A few things to try:

1. Make sure squirter lever is adjusted right (the screw with a spring that rides the lever on the other side of the pump cam).

2. Get a pump cam assortment and try a few different ones. If its a lean stumble, it should get fixed by getting more pump shot early. Also, make sure your squirters are delivering a nice hard stream of fuel. If they are just letting fuel dribble out, its time for a rebuild (the diaphrams are cheap and easy to replace).

3. Lastly....Another thing to try would be locking your timing out @ 32 (I think that was what you said your max was). This helped my street/strip car years ago with a off idle stumble that I could not get rid of...but if you are mostly street you might not want to go this route.
 
Thanks fellas, it looks like the one item nobody argues is the intake. I was told by a pro the intake plenum was too big for a 318 and I would need at least 380 ci to make it work correctly. Today, I'm gonna order the Holley pump tuning kit and see if I can get it worked out.
This is the kit I'm gonna get...

http://www.streetsideauto.com/p/holley-36-184/

Is there a vendor on here for Holley parts? Streetside has fast shipping and a great pricing.
 
I doubt the intake is an issue. Unless everything else was fine and all you did was change the intake and it started to happen. Hard to imagine.

I bet it's in the tuning of the carb....let us know how you fair w/ the kit
 
Beatnik said:
I doubt the intake is an issue. Unless everything else was fine and all you did was change the intake and it started to happen. Hard to imagine.

I bet it's in the tuning of the carb....let us know how you fair w/ the kit
Click to expand...

I have a Magnum M1 single plane and the air gap but I chose to use the air gap since it's dual plane and this is a street driven car. I had the M1 on the car for a while but the engine had other issues (blown head gaskets) so I really haven't ran it with everything working properly.
 
Like mentioned before, I doubt the intake has anything to do with the stumble, If it did, then throwing on the single plane would only increase the issue. It sure sounds like a carb issue. Do you know anyone with a good working carb that you could throw on? That HP 650 that you have there is pretty beefy for a 318 (depending on internals). Do you know how much horsepower and torque you are putting out?
 
67cuda360 said:
Like mentioned before, I doubt the intake has anything to do with the stumble, If it did, then throwing on the single plane would only increase the issue. It sure sounds like a carb issue. Do you know anyone with a good working carb that you could throw on? That HP 650 that you have there is pretty beefy for a 318 (depending on internals). Do you know how much horsepower and torque you are putting out?
Click to expand...
i think 67 cuda has a good point. over carbing a motor can have anyone scratching their head, even though he didn't say that. swap it out to a smaller one and see what happens. sounds to me like you have too much fuel . fuel \air mixture is the secret to performance. a smaller carb may be the ticket. try it you have nothing to lose ,wont take long and then you can go to plan b if that doesn't help. good luck.
 
MY engine is putting out around 290 hp at the tires with somewhere in the neighborhood of 350ish torque.
I ordered the holley tuning kit and a new 4 hole 1 inch spacer just now. I'll update later after i receive the parts and get a minute to work on it.
 
kennygene said:
Thanks fellas, it looks like the one item nobody argues is the intake. I was told by a pro the intake plenum was too big for a 318 and I would need at least 380 ci to make it work correctly. Today, I'm gonna order the Holley pump tuning kit and see if I can get it worked out.
This is the kit I'm gonna get...

http://www.streetsideauto.com/p/holley-36-184/

Is there a vendor on here for Holley parts? Streetside has fast shipping and a great pricing.
Click to expand...


I agree with the others, I doubt there is a problem with your intake. The pro you talked to must not have much experience with small block Mopar. If the Air Gap is only good for 380 ci strokers then about half the 340's at the Mopar Nats must be using the wrong intake. They work really well. I am trying to rebuild a 340 now and trying to find a used Eddie Air Gap is thin pickings. People really like them and never take them off their car.
 
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