Helping my buddy build his 2.3 turbo and I am wondering where I should start on his PCVR's...should I stick to the same 5/64 as a base? I'm going to be putting vent tube extensions on his car as well.
2.3 with T3/T4 hybrid Stinger header and 3" turboback
P&P Eslinger head with 2.02 1.89 valves and some frumpety Eslinger cam
Large NPR with 3" cold side and homebrew 650 with EV o-ringed hat
Stock 5/16" feed line and 255 in-tank into Mallory reg and -8 return
MSD 6AL, TFI coil, and stock TFI dis to fire it.....STILL TRYING TO HOOK THAT UP!!!! (different thread, different head-banging issue...)
Snow kit to be installed after we get the base tune nailed.
All of this looking for 30# and 450 rwhp on pump gas.

I've built my sc carb, but I know the turbo carbs are different i.e. vent tube extensions and boost referencing the bowls and pv's from under the carb etc. Can y'all think of anything I am missing, need a heads-up on, or need to do to make this b/t work for him?

OK, here's the problem...Got it running at 24* locked 64/78 jets and it won't idle, it keeps wanting to backfire through the carb. If I let it idle and I manually pump the accel. pump arm to give it fuel, it will run but will puff everytime I do it. The idle screws are turned out 2.5 turns and the throttle blades were open a good bit just so it will get into the transition slot and give it some more fuel. If I mashit and hold part-throttle, it will burn off the accel. pump gas and then puff through the carb (lean backfire). Vac leak you think? I disconnected the tree and plugged all lines...no avail.
Here's what I'm thinking, weak booster signal to jets, need bigger main jets (much like changing from 650 to 750 on 302, I had to go up in jets), but still won't explain why it seems it is getting crazy extra airflow at idle.
HELP!
Jesse
Thanks,
Jesse

 

ttt

 

ttt

 

Hi
Asuming there are no engine mechanical problems...
Have you checked your base fuel press?
Where is the fuel press regulator referenced to?
Have you checked if the timing mark is correct?
Have you assembled the carb correctly?
Vac leaks? Recheck every connection to and from the intake manifold
Keep us posted
Peace

 

Mechanical timing is set
Base fuel pressure is 6
Fuel pressure reg is referenced to the bonnet
Will recheck the carb and more importantly the throttle and base plate gaskets
If nothing else, will have to take the intake off of the head and check to make sure that gasket is sealing properly...
Jesse

 

Well turned out one of the problems was that the carb gasket wasn't sealing right so replaced that and it still seems to be getting too much air... on to trying other things.
To be continued...

 

I think I may have put the wrong baseplate gasket on...the one between the throttle plates and the main body. I made sure that every hole going into the main body had a hole through the gasket...I'm at my wits end now.
Jesse

 

IAB's or IFR's?

 

Stock Holley 650
Jesse

 

As long as the holes all match up on the main body, the gaskets are pretty much one size fits all? I've never had this problem before.
Jesse

 

Have you tried the wire trick in the IAB's? Those are the bleeds on top and furthest outside. That would richen up the idle circuit like you are explaining is too lean. Let us know.

Kirk

 

Here's what I don't understand. I am running the exact same carb on my car in the sig and I didn't need to modify anything. His motor is flowing less air, if anything I would think he needs bigger IAB's to compensate for low signal. Is there anything else that I could be missing? Let me know if I am thinking about this incorrectly.
Jesse

 

If I am hearing you right, and tell me if I am not, yours is a SC motor and his is a blow-thru. That would explain why the symptons you are having with the same carb, but on different motors, right? You are sucking thru (no pressure) the carb and he is blowing thru (pressurising) the carb. Anyways, his motor flowing less air, and using that carb with those same BIGGER venturi's, sure, he is not going to have the same signal strength and pull enough fuel at idle. That's why the 500cfm 2-barrel is pretty popular. If going the full race scenario, yeah, then a 4-barrel works great uptop, but lacks the idle quality you are looking for. With that 650cfm on there, that why you have to set the idle so high just to get it to run, to get enough air across the venturi's to pull fuel out.

Try the wire trick in the IAB's, it can't hurt it. Simply bend the wire so one side goes down in the bleed and the other end hangs over the edge of the carb so the bonnet can hold it in place. That ought to get you headed in the right direction. You could also open up the IFR's in the metering block, but that is only if you want to take the carb apart. Keep us updated.

Kirk

 

Mine is a SC'd blow-thru motor. At idle, his motor is acting as an NA motor because the turbo is not creating any boost. Furthermore, we are doing all of this with the carb hat off. We have the idle screws turned out 2.5 turns. Should we go ahead and keep the blades in the transition slot for the additional fuel or keep trying to tune it where it is?
Another issue that may be related and made me think it was getting extra air is that I would rev it up and then let off and the RPM's would hang, at one point I actually had to turn the car off to get it to come back down. Throttle blades are clean, return spring was functioning correctly (I saw it close) but it still was rev'd up.
Dunno...
Jesse

 

That is happening because you have too much of the t-slots exposed at idle and it is allowing the extra fuel. You only want to see maybe @ 0.020" of the t-slot showing with the blades fully closed at your desired idle speed setting. Like I said making the IAB's smaller (wire trick) or enlarging the IFR's will bring in more fuel at idle (only do one at a time, though). This is so you don't have to be into the t-slots at idle, try it, you might like it.

Kirk

 

And I did read it wrong, yours is not a draw-thru. Still the larger venturi's with a smaller motor, you loose your signal strength to pull fuel thru. Now if you want to spend the $$, they can insert liners to make the venturi's smaller. I have seen it somewhere on here.

 

Update: Pulled the main body off to double check gasket, everything is good. Screwed out idle screws three turns (I know...) and set the throttle plates where they need to be and fired it up. I have to keep on the accel pump to keep it going, but it keeps wanting to lean backfire. It did rev up one time and clear out nicely but after that if I open the front throttle plates all the way and keep the rear ones closed it would hold about 2k rpm's and wouldn't go any higher. While it attempted to idle it pulled barely any vacuum, the only vacuum I saw was when I rev it up and saw 10 inches on the way back down. I take it tuning this carb is going to be similar to tuning a big-inch big-cam car...?
Since we are doing all this testing on an open carb with no hat to hold on the wire (with no way to measure the wire either), I reckon I can try to drill the IFR's. What's a recommended starting point? Where are the IFR's? This is moving into the voodoo side of carb's to me
Jesse

 

Drilled the IFR's to .0625 and it will now idle with the screws 1 turn out, but it seems to still only have ~4" vac. Going to hook up the wideband and see what the verdict is.
Jesse

 

Have you checked the cam timing? Maybe the rubber band slipped when it backfired?

 

Try it with the hat on. My blow-through won't run without it. Check the rear and under the manifold, there are some plugs that need to be in place and sealed on some of the 2.3 intakes. Just a few simple things to try.