Proper Transfer Slot Position
- Thread starter jmanhoff
- Start date
-
Post #119. The idle jet, often called the IFR [ idle feed restriction ], supplies fuel to the transfer slot [ TS ]; it is sized for the TS, not for the idle mixture. There is always enough range on the mixture screws to get the idle correct.
The TS controls off idle. I would enlarge the IFR 2-3 thou. Leave the PV alone.
The TS controls off idle. I would enlarge the IFR 2-3 thou. Leave the PV alone.
Pardon me for forgetting, but I did actually slightly change my IFR when I had the carb apart. When I was driving on the highway and noticed the exact problem I’m noticing now, I figured I would put in a 0.031 IFR going up from a 0.028, and it made everything really rich at idle and transition.
While it was idling, I had to have all 4 screws at a little over half a turn out, and it was eye watering rich. While I was driving, my AFR would read 13.8-14.2 while cruising on the transfer slot, with 20 inches of vacuum.
I did then change the IFR again when I had the carb apart the other day to a 0.0292 (that was the drill bit I had), and went up from a .070 IAB to a .073, I know you’re only supposed to change one thing at a time, but I’m experimenting and also wanted to see if I could bring my mixture screws out more.
I’m assuming I should go back to a 0.031/0.070 combo for the IFR/IAB and continue to idle off of the primary side only?
This is what you get when you change too many things at once. Just idle off the primaries. Other brands of 4bbl carbs only have idle screws on the primaries.....& they idle & cruise just fine. I doubt that the 4 corner idle carbs were EVER designed to be used with an engine that has such high idle/cruise vacuum...& hence the richness.
Yeah I did some more research about it and it makes sense. It seems like everything I’m reading, the 4 corner idle is for engines that need the secondary blades open to idle, so they need extra fuel from that side. Obviously in my case I have them fully shut, so no point in feeding fuel. Plus I’d imagine using just the primary side gives the transfer slot more cushion as well
This might be a stupid question but, are the weights that come in spring kits the same as the ones that are already in the distributor? I’m going to try to map out my timing curve tomorrow while I’m at work, but I don’t know if the weights that are in the kit would give me the same curve as the ones that are currently in the distributor from the factory
Sorry if you have already covered this but, have you verified that the tdc mark is correct?
To my best ability yes, I don’t have a piston stop but when the heads were off and the crank was installed I looked at the marks while it was turned by hand and it starts the power stroke right after 0 on the balancer. Low mileage engine with a brand new at the time balancer, so I’m sure it’s still the same now
Probably close then. I would give yourself plus or minus a few degrees when considering actual timing numbers read from the engine.
What the 4 corner idle gives you is better distribution especially in engines with lower vacuum levels at idle.
But in the case of my engine with high vacuum, it’s essentially just pulling way too much fuel as opposed to having just 1 side open more?
Very possible. You can try going smaller on the IFR and IAB. When you get it right it should whistle as the air goes sonic.
When would it be whistling? While it’s idling or when the t slot starts pulling?
When its idling.
With the 31ifr/70iab combo I do hear a whistle with the hood open, I either never heard it previously or never paid attention to it but I’m pretty sure it’s new with this combo of bleeds
After driving around for awhile with the .031 IFR and .070 IAB, and a .070TSR, I still have a lean spot while accelerating at low rpm, even during the point where the power valve opens. I can see it in my gauge but I can also feel it in the seat. It richens out at about 2500 or so, which is when I’m assuming the mains start to flow. Is this a transition slot timing issue or do I need the mains to come in sooner? I have 65 jets in the front with 0.028 MABs
I also have been getting occasional dieseling on shut down, only like a puff though. Not sure if that’s related but isn’t that usually either too much timing or throttle open to far? My floats are set right so it’s not fuel dripping through the boosters
I also have been getting occasional dieseling on shut down, only like a puff though. Not sure if that’s related but isn’t that usually either too much timing or throttle open to far? My floats are set right so it’s not fuel dripping through the boosters
Last edited:
-
Similar threads
