I have an issue with a csu carb. I got a 355 chev 8.5:1 twin turbo sbc with a 850 csu carb on top. i have 6 psi f/p at idle when it first satarts a/f is sitting at 14.7 (GREAT!) THEN AFTER about 30 seconds it goes from 14.7-10.5. I have tried dropping from a 89 to a 72 prim but it didnt change a thing same thing happens so, instead of chasing my damn tail all day tomorrow like I have for 2 days now wondering, reading, trying, kicking, screaming, and thrwing wrenches at the fence I would ask here and see what the hell I am missing. any help would be awesome. thanks

 

I have been reading thru some tech posts. I didnt know about the entire combo affecting everything else and the info if needed it here:
Sbc .030 over 350= 355 cid, 8.5:1 comp. twin turbo with 63 AR, T3/T4's (cheapo ebay turbos) World sportsman 2 heads (not ported) 64cc. torker 2 intake (not ported), 1.6 roller rockers. summit 1104 hyd ft cam @ zero, CSU 850 blow thru carb, Aeromotive A1000 pump with Aeromotive F/P reg (boost referenced) The pump is under the bed of the truck and the cell is in the bed. -10 feed lines and -8 return, timing is at 34* locked out with a msd crank trigger, vacuum block getting its vacuum from the large vacuum port on the back of the carb, MSD 85551 distributor, the plugs are 2 colder, and am running it on 112 race fuel. for the down pipes I have 3" pipes right off the turbos about 36" long dumping right behind the front tires. i have a air to air cooler. if there is anything I have missed please ask. thank you for reading. Also, I am absolutely new to turbos. I seen them run, tried to do my research and build what I thought would catch my BBC nitrous friends and maybe beat em in the burnout contest coming up on the 4th of July party i go to every year and its about time I bring a car instead of watching lol. thanks again. I will try whatever it takes to drive this damn year as I have been building, saving, and punishing myself with the torment of the new car gremlins thus far but, I am sooo close to the dream I can taste it........ well, almost tase it.

 

How do the PV's work in this thing? Sounds like they open after a time.
Make sure the pressure does not rise after this time for some reason
I assume no water meth, nitrous or other shenanigans?
When this happens, look down the throat of the thing and see if the boosters are dripping. Or the accell squirters for that matter. Nor reason to, but screw it look anyway.
Is this only at idle? Or is it a global thing?

 

no no meth or any nos. it happens when it is at idle. I tried to give it a little gas and it is responsive but just blips of the throttle. af goes right to the 14's then when the rpm's drop again it goes right to 10.5 or so right away. How do I check for pressure drop? that i dont follow. I will check on the squirters and boosters in the morning maybe they are too tight? I will throw a feeler gauge under them too. I sure hope it is something simple enough. I just dont know where to begin to look but for sure, i will start there . I want to thank you for shooting me in some direction. You have no idea how appreciative i am for your help.

 

Call Kevin at CSU- he’s always been very responsive to questions. Also do you know if if your afr meter is accurate?

 

where is your boost ref line on your fp reg. connected on the motor?

Does it start running badly when it goes in the 10s or stay the same?

 

My f/p reg line is hooked up to the carb hat. Although I dont have a gasket under the hat anymore (rubber bonnet/hat ring) would that make a difference? as far as it starting to run bad when it goes into the 10's.........not sure. You are giving me the info to look at. Again, Thank you! I am going to go out in a min or two and run some tests and get that information

 

Yeh dont worry about the gasket on the hat. It wont effect anything.

 

Today I had it running and as usual it was PIG rich and burning your eyes (even outside good Lord!) I looked at my vac gauge and it was in the 15's. I took out the front bowl and after rearing and reading I realized I had a adjustable valves. After I went and bought a mighty vac pump I think thats what it is called (vac hand pump) I tried every which way to check when the things were opening and at what press. I even tried using positive pressure off of a compressor slowly turning up the flow but again couldnt get any reading due to my work regulator being a real pos and wouldnt stay steady at that low of a setting and kept turning off air flow so, after I blew another $50 on the hand vac pump for no apparent reason. I decided to change back to the original jets and clean the power valve with some carb spray and see if something was stuck in it. there was a little crud and got it out and then when there was really no change. I tried to tighten up the flat head screw setting on the adjustable brpv 1 turn at a time and after about 2-2 1/2 turns in.... It made it better for sure. It wasn't burning your eyes anymore and it went from a vac reading from 15 to 10 and the a/f went from 10.0 -10.5 up to 11.3-11.7 so it is going in the right direction but, I ran out of sunlight today as I work in a parking lot in front of my house.... ok its a trailer but looks like a houst in the inside (kinda lol). I am running 3" down pipes about 3' long off each turbo and no mufflers yet. I am still trying to get the electric cut outs i need so it is a little loud to say it lightly and I have neighbors and I dont want eggs thrown at my truck lol. I have a 2 stage turbo smart boost controller and screwed the settings all the way in for no boost (if that maters at all?) I'll be back out there tomorrow again as soon as I get this damn fence fixed by a customers house in the morning. Now knowing what i did does that help at all? and what is hurting me perhaps?

 

Today is hopefully the day to give it a little drive. Not get into the throttle a whole lot but just a cruise and see it it somehow balances out a little. My thinking is, because it is a fresh build and new everything it needs a little run time putting around the neighborhood for about 3-5 miles. Not to mention, I can get it away from my house and try to tune it while running before my neighbors come out bitching/asking me to turn it off and then give me the old "evil eye" for gassing them out of their houses with exhaust and loud noise when I say no, I have to do this. but it is what it is I guess. if it were easy....everyone would be doing it and everyone would have a fast car lol. I'll lyk what happens or what the conclusion is with the numbers so to speak. I am also going to try to back off the timing a little from 34* to like 28-30* and see if that helps a little as the 34* was just where I set it at on the crank trigger install and never changed it. CHEERS! wish me good fortune on the tune.

 

It"s possible the return line could be causing some back pressure, Is it returning to the tank sump or top of tank?
-8 feed -10 return would be the better option.
Check float level also.
Good luck...