Hot Rod Forum banner

350 small block vortec problems, stalls out

8K views 22 replies 7 participants last post by  cobalt327 
#1 ·
Hello thanks for looking, I recently just built a 82 Chevy small block 350 with 98 vortec heads. The motor fires and runs but think we have a vacuum leak because it won't stay idling long! It fires runs for about 5 sec then putters out! Will continue running if you keep on Throttle. We have installed a mother thumper cam and roller rockers. It has a quadrajet carb and lots of vacuum ports on it. Could someone please send me a diagram or something to tell me what I need for this motor to run reliabley without during out? It's not a street truck its 4x4 strictly toy off road. We have the vacuum advanced hooked up to what we think is the right vacuum to the carb. And the break booster as well. Any help or hints tips would be great thanks! If you need more info I'll do my best to answer them thanks
 
#2 ·
Plug all the line(temporarily)set timing for 35 total at 3k.turn idle screw up to 1400 rpm( w/e it takes to keep running. adjust carb,turn down idle . check all tune up specs and continue down until it idles at 850 ish.
test for vacuum leaks with carb cleaner or other aerosol spray.
 
#4 ·
Help on 350 small block vortec head build! Please!

If you think you have a vacuum leak, here's how to check. Using a can of starting fluid spray sparingly along the intake where the gaskets are. Spray around base of the carburetor too. If you have a leak the idle will increase. What type of intake do you have? When you installed the intake did you use any sealer on threads? Here is a link to an article to read about setting your timing. http://www.crankshaftcoalition.com/wiki/Hot_rodding_the_HEI_distributor
 
#5 ·
I don't thinks it's quiet a leak but I think more I'm either pulling to much vacuum or not enough we aren't sure what goes where off the carb. Vacuume wise. And the intake is an off brand that is made for the 350 with the newer vortec heads and yes we sealed everything with gasket sealer thanks for the thread/ web site
 
#9 ·
What about re tuning carb to have no choke I mean we can get it to stay running to warm it up. I can hold the pedal at let's say two grand and it will run there constant! But when you let off it will idle for about 5 seconds and it tries to stay idling but eventually dies out. So still leaning towards choke?
 
#10 ·
Its not going to be a choke issue, I rarely have a choke on any of my junk, get it started, get it to 1500ish for a minute or 2, should idle down and stay running...and that's in chilly Canada climate and with the heat risers blocked. The mother thmpr is a pain in the ***, ask me how I know....get all the vacuum ports plugged, get your base timing to 24°, adjust idle down to 800, and see what it does....but yes, this is after you have plugged everything and confirmed no vacuum leaks....if it runs decent, and stays running, then we can worry about where all your vacuum should be routed. That cam is going to want alot alot of initial...
 
#15 ·
I forgot about your vacuum lines. If I remember correctly, the Q-jet has a threaded fitting on the backside of the carburetor. This is where the vacuum line from the brake booster goes. The brake booster should have its own vacuum port, do not tee anything else to it. There should be a 3/8 port on the front of the carburetor for the PCV valve. You should have a vacuum port fitting that screws into the manifold behind the carburetor for your vacuum to modulator valve on the transmission. There will be other vacuum ports on the front for the distributor vacuum advance. Just remember the ports that have vacuum at idle are manifold vacuum and the ports that don't are ported vacuum. I have a picture from a website that might help you. Look at post #7. Good luck. PALEEZE help me hook up my QuadraJET and vaccuum stuff. - THE H.A.M.B.
 
#17 ·
Ok man, got the truck running and idling ok..... Now we have another issue that's kinda stopping us. I tuned the carb I set the timming good it will run and stay running fine but now when I put it in gear it dies out.... I can keep it running in gear with the idle turnt up or foot on gas and keeping it running! As soon as I let off it kills. I have a correction it is a comp thumper cam NOT a mother thumper. We were told we shouldn't have to have a stall with this cam. Are there any tricks am I missing something? There are no vacuum lines to the trans nor cables atached to the motor/carb from the 350 turbo trans. Thanks for any input!
 
#22 ·
Look at the transmission pan on your car. A 350 turbo has a square pan with the right rear corner cut off. The turbo 400 has a odd looking oil pan with two or three dimples on the bottom of the pan. check yours to see which one it matches. Do you have the part# for your camshaft?
 
#23 ·
It's very possible the modulator just isn't hooked up. There's not many GM automatic transmissions w/o a modulator (overdrives like TH700R4/2004R). I would run a vacuum line to the modualtor after it's been checked for being bad/leaking vacuum. The detent (kickdown) cable can be left disconnected if you want to shift manually. If the whole cable's missing you'll definitely want to plug the hole in the case where it enters to keep dirt and water out.

Anyway, here's info on ID'ing your transmission.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top