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I'm helping Chalemagne65 with his carb issues. Runs very rich at idle. When I got it I thought it was mostly the choke just set wrong. But it has no ifrs just .096" holes. I looked at a lot of complaints on these and they most always include too rich idle mixture. What I've come up with is they should have about .031" ifrs. Any input? John Z where are you?
I have not. I'm not a Corvette numbers expert. But I am persistent I like to say others have a different description. I'm gona get this right for him. Its a 4094.
The 4094 sounds right for a 2818 carburetor so the IFR should be down low, how far out were the emulsion screws because if someone drilled the brass idle feed restrictions the screws would be almost closed.
You can tap them 6-32 and install 1/8 or 3/16" brass set screws drilled .031. Just tap low enough so the set screw is flush with the hole from the main well. Chuck the set screw in a drill and hold the pin vice with the small drill bit so the drill turns and does all the work.
Check the power valve and the P/V gasket because that leak point will allow fuel to be sucked in the engine under the throttle plate so you will not see it.
He said one mixture screw had no effect. I didn't check them because something is a lot further off than mixture screws. The carb was set up with the secondaries closed and the primaries open so far almost the entire t slot was exposed. That combined with no ifrs may be why its so rich. I looked at a new 4094 plate and it had no ifrs either. So this leads me to believe they were never there. I'm hoping since this is the carb on C2s there are plenty here to help us out. I had him check the power valve early on. I checked it myself and it holds vacuum. I checked the pv gasket and it is good. IAB is .070". Jets are right. Everything is ok except the ifrs.
Well, if the transfer slot is exposed like you report that's why it's pig rich and a wonder the engine even ran. If you can't see a ifr low or high then I would remove the idle well brass plug and probe the idle well for the restriction. Does it look like the restriction has been drilled, if someone did this on the primary side you probably should check the secondary block as well.
While you work on the carburetor the owner may want to install some new #5 (AC 45) heat range spark plugs.
We will have to work through several issues as we go. The carb being first. Right now I'm assuming the carb is designed with no restrictor and uses the mixture screw as its only calibration. Here I'm waiting for a 2818 expert to chime in. I'm going to run the carb before I send it back so we know for sure its correct. I will check the secondaries for sure but if you look at the carb you can tell its way off, it's black and sooty all over the primaries. I was going to post a pic of the slots. After I cleaned the black off I could see they aren't as bad as I posted. They are a full rectangle instead of a square maybe .050-.060". My problem is I'm 5-600 miles from the car. Right now I'm looking at the choke being too rich, the primaries open too far, and the secondaries closed completely off.
I really thought I was the only one that said pig rich!
Look for the restriction, I have never heard of a Holley without a idle feed jet.
The purpose of the mixture screws has nothing to do with A/F ratio, they simply trim the emulsion from the curb idle ports for a clean idle. This emulsion along with the air passing around the almost closed blades sets the idle A/F ratio.
The idle restriction along with the air bleed set the A/F ratio for the transfer slot but also feed the curb idle ports (which the screws control). The goal is to have the slots just visible so the idle fuel is controlled by the curb idle discharge ports. Too much slot and you get your situation, but no IFR and I don't know how it even ran.
I think I put AC 43's in a while back. Think I should go to a hotter plug?
Originally Posted by tbarb
Well, if the transfer slot is exposed like you report that's why it's pig rich and a wonder the engine even ran. If you can't see a ifr low or high then I would remove the idle well brass plug and probe the idle well for the restriction. Does it look like the restriction has been drilled, if someone did this on the primary side you probably should check the secondary block as well.
While you work on the carburetor the owner may want to install some new #5 (AC 45) heat range spark plugs.
When we get that far let's try 44s. You already have detonation we've got to tune around. I worked a string through the idle circuit. Yes it was a pain in the ***, see persistent. I feel a restriction at the top of the idle well. I can't be sure if it's a sharp turn or an orifice. The string has 3 nots that I can pull all the way through. The larger not with the loop will not go through. The small knots are ~.026" the larger knot is a big.045". The only way can can measure for sure is remove the plugs. I was wanting to avoid that.
My suggestion is to go with the 45 plugs and if there is a ping pull some timing out. i would also remove the plug at the top of the idle well and find out for sure what you have there if anything.
If it were mine I would relocate the IFR on the bottom like a old school holley.
I don't like the location either. Maybe its because that's not where they belong. We certainly can use 45s but he has 11:1 and says pretty severe detonation. But as I mentioned we'll get to that next. But he has 87 octane in it also. Thats got to go. I just broke my string trying to pull a .035 knot through.
Chuck it's your carb so you make the decisions. What do you think about removable IAB, idle air bleeds. You would be able to see them if you looked down the choke horn. We would be able to fine tune much easier with these. I'm going to wait a day or so as its New Years and see what other responses we get, where are you John Z. But as of now I like moving the idle feed restrictions to where they should be and after that they will also be adjustable by changing them out. It's your decision. We probably can make it work as is with proper tuning and set up.
FWIW, if you carefully drill the IAB and tap for 8-32 x 3/16" deep brass set screws (Allen head) that will allow a hole size around .080 and I doubt you will go that big. These screws are hardly noticeable when installed, just tap deep enough so they are flush when snug.
To be honest I would have thought .070 was plenty. He does have a 30 30 cam. Which should pull10-11". He says its pulling 18.5. We haven't got that far yet but if its pulling 18.5 the valves have to be too loose. One thing at a time.
That's a good point but when someone tells me They have x cam I have to assume they know what they are talking about. We'll see after the car is fixed.
DUKE likes the LT-1 grind for this car, more than the 30-30. Think I could pull the cam without removing the engine? Has anyone been able to do this with the radiator removed?
DUKE likes the LT-1 grind for this car, more than the 30-30. Think I could pull the cam without removing the engine? Has anyone been able to do this with the radiator removed?
Those are the correct numbers for that cam, but having run that cam for many years with an onboard vacuum gauge, it won't get 18.5" Hg vacuum at idle. If you raised the idle rpm much higher like 1200+, maybe.
If the cam is indeed correct, it may have been installed too advanced - like one tooth off (an additional ~17 degrees of advance)?
Here's an easy way to check...
1. Remove the driver side valve cover.
2. Rotate the engine to 4 degrees prior to TDC-overlap on cylinder #1 (at this position, the exhaust and intake valves should be open an equal amount - each about .050, depending on the rocker arm ratio and the lash).
3. Place a short straight edge across both the intake and exhaust valve spring retainers - both should be the same height. If the intake is more open than the exhaust valve, the cam is advanced more than it should be, and vice-versa. Valve motion is about .003" per crankshaft degree at this point, so if the difference is .006", the cam is one degree off (no big deal), but if you find the difference is .025", it is off by about 4 degrees. If it is more than this - there could be several problems:
a. Wrong cam
b. TDC is incorrect; check for correct timing tag, correct balancer (early balancers were marked in a different location than later balancers ('69 and later?), balancer slip). In any event, measure to find the actual TDC.
c. Timing chain is installed incorrectly.
Yes, you can change the cam with the engine installed; personally, I like the 30-30 cam better than the LT-1 cam.
Let us know what you find. Good luck!
12-31-2017, 03:54 PM
2818 ifr ?
