85rotarypower

I have a little problem. So far the tuning on my Edelbrock carb has been pretty good, but I've been having problems with the idle. The idle speed is fine, but for some reason the idle mixture fluctuates a lot. Today when I started the car up, the idle mixture was so lean it wouldn't quite run. When I last left the car it was just perfect, right around 13:1 air fuel. So I adjusted the mixture to about 12.5:1 and left it like that for a while. I ran around the block a couple times and when I got back and parked the car, it was fine. I let the car idle for a while but I noticed that it had started to lean out. It got so lean it stalled within about 1 minute. I didn't change anything. What could cause this?

diabolical1

iTrader: (3)

where is your pressure? is it stable?

85rotarypower

Pressure is stable at 6 psi. I can try turning it up to 7 but I don't think that will change anything.

84stock

iTrader: (5)

Check for vaccuum leaks and then check the float level. The Edelbrock is by far the smoothest running carb out of my collection, idle is never an issue for me.

85rotarypower

I've adjusted the floats already and as far as I know there aren't any vacuum leaks. I'll have a look though.

85rotarypower

Anyone else have any ideas? I should have mentioned this before, but when i try to use the choke to start the car, it starts up and then stalls. I have to get on the gas pedal to help it start and get the RPM's up, then it will just run ultra rich (10:1 or lower). This happens even if I have it leaned out to 14:1 or higher without the choke. I'm wondering if the porting the past owner of this intake manifold did has anything to do with this. There might be uneven vacuum on the idle circuit because of the way they ported the top of the intake. My guess is that full choke evens out the vacuum. I'll try to get a pic tomorrow. But there is definitely no vacuum leaks. Also I'm going to get a vacuum gauge and check that out.

84stock

iTrader: (5)

Try a 1" open spacer between the carb and intake.

85rotarypower

I would try this, but its quite impossible to keep that on there. As it is even with the low profile air cleaner I have on the carb its nearly hitting the hood. The Jay-Tech intake is much taller than a RB intake. I was worried at first I wouldn't be able to fit it under the stock hood. My guess is that the intake was originally used with a 1" open spacer, hence the reason its ported the way it is. I could buy a cheap 1" spacer and see what happens, and if that solves my problems then I'll take the intake mani off and take the die grinder to it to make an open plenum 1" down.

sgieldon

Hey 84stock;
Nice Crab Setup!
Never seen this style before.
You should get some Spec's on this and Post It.
If you've posted it before, bring it back to life just to update some other aftermarket Carb Ideas besides Holley and Weber or off the Shelf setups that I've seen lately on this Forum.
sgieldon
steve

85rotarypower

My setup is unique. Ive got an edelbrock performer carb with a Jay-Tech intake, one of the best intakes made so I hear. The past owner of the intake ported it and designed it to be used with a 1" open plenum spacer under the carb. Due to the height of the intake, its nearly impossible to put a spacer under the carb as it would drive the air cleaner into the hood. As it is I have to use solid motor mounts to keep the engine from torquing over and smashing the air cleaner into the hood. The problem is that the upper portion of the intake was made smooth and the runners blended together, leaving a nice sharp edge between all the runners. Because of this there is a peak in the center, and it mearly dips down between the runners. Im wondering if these dips are what are causing the idle mixture to fluctuate so much. The vacuum around the idle circuit ports might be compromised by this, but I dont know enough about air flow to know if this is the problem.

85rotarypower

Well, I went out and bought a vacuum gauge. I had the car idling at about 900rpm and it registered at 15 in hg. I raised the idle to a little over 1000 rpm and it registered at about 16 in hg. I don't know whats normal for a rotary, but it doesn't seem too bad. In both cases the vacuum didn't fluctuate much at all. Now I know my timing is off a little bit, advanced by probably 5-7*. This might be affecting the idle, but its strange how this has changed since I first got it running. I had the timing set as close to 0* as possible, but the leading was way advanced when I checked it today. Any thoughts?

trochoid

iTrader: (6)

Sure, you raised the idle and around 1k rpm, the mechanical advance begins to kick in. Drop your idle down. I have a Jay-Tech intake that I bought off eBay, ported the same as your's, except the idiot seller never said it was for an REW.

85rotarypower

Here are pics of the intake. I'm about 75% sure its the intake manifold now. Because I have a true dual exhaust like RB sells for the FC, I can see what each rotor is doing independantly just by feeling and looking at the tailpipes. Because its quite cool here, the difference between rotors is easy to see. Cooler exhaust gas doesn't condense right away. Anyway, watching the exhaust for about 5 min I was able to see that when the engine idled fine, there was equal amounts of steam from the two tail pipes. When it started running rough, sounding like it had some major porting, the steam would switch to 1 of the 2 rotors, the other showing little or no steam. This was erratic as well. It seemed to oscillate between the 2 rotors, and when this was happening the A/F ratios would go up and down by up to .8 at times. The wideband only monitors the rear rotor. Anyway, here are the pics.

trochoid

iTrader: (6)

I went and looked at mine. It must be one of the spare RB intakes that's ported like that. My Jay-Tech is knife edged and not cut down.

I doubt that the intake itself is changing the afr's between the rotors, if anything, it should blend them more.

85rotarypower

I would think it would blend them, but something is making this car run strangely. I've got the intake off the car and I'm going to try making it more of an open plenum. Those dips only go down a half inch, I'm going to make a 1" deep open plenum. Shouldn't be too hard on a milling machine.

Sanspistons

85rotarypower I have run an Edelbrock 600/RB intake on my street ported motor successfully for about 4 years now and have had a problem like that before.

Try loosening and pivoting the needle tops/caps/holddowns whatever they call those things and push the needles up and down a few times. Sometimes they tend to stick especially on used carbs. I found this out when my car ran really rough and one of the headers started glowing orange at idle!!! At night, of course.

Am curious about your vacuum advance arrangement: are you running straight vacuum or timed? I found straight to be much superior in response, low-end torque and mileage. If you are running timed raising the idle will tend to kick in some vac advance on this carb.

I am/have run different spacers but have only joined primary to primary and secondary to secondary as I have been afraid of the effect of the intake pulses on the vacuum needle system. Glad to know the carb will run with all connected.

Good luck and let us know!

Sanspistons: Edlebrocks rule over Holley fuel leaks anytime!

85rotarypower

The carb is brand new, but I'll take out the metering rod pistons and clean them up. I've got the intake off the car right now as I'm having the top machined out to accept an insert to go back to separated runners. I'll probably end up with better power that way anyway.

What engine do you have the carb on Sanspistons? Just wondering about what jets and metering rods/step up springs you are using. I've got the original step up springs in there still, but it was running WAY too lean on stock jets. I've went up to 104 primaries and 101 secondaries. Can't remember what metering rods I got in it right now. I just wanna know if I'm on track with my tuning.

Oh yeah, I'm running timmed vacuum on the dizzy. Figured I'd keep that stock.

85rotarypower

bump so I don't lose track of where this thread is.

trochoid

iTrader: (6)

You can subscribe to it also.

85rotarypower

Ok, just about got the manifold converted back to separated runners. Here are a few pics. Even if this doesn't solve my problems I think I'll still end up with more power from it.

trochoid

iTrader: (6)

Nicely made piece. Once you get it back running, you may find it needs a bridge between the primaries. If you had a 2nd one made, you could compare them.

85rotarypower

What do you mean by a bridge?

trochoid

iTrader: (6)

If you look at the oem phenolic spacer or intake manifolds, there is a gap cut to bridge the primarys on almost all of the oem carb setups.

84stock

iTrader: (5)

That should work very well indeed.

84stock

iTrader: (5)

For the gap he is talking about, just get a 1/4 " pheonlic 4 hole gasket/spacer and remove some of the gasket between the 2 primary ports. Do not connect the primaries to the secondaries. http://www.jegs.com/webapp/wcs/store...64166_-1_11747