chevy 350 questions?

[ERIC87442]

I have a 74 chevy 350 in my 87 442, no matter what ive been trying it just seems like it doesnt run right. So im searching for ideas: the engine is; a supposably rebuilt 74 chevy 350 with about 60,000 on it, vortec heads, gm performance intake, 224/234 duration cam with .465/.488" lift, holley street avenger vaccum secondaries 570cfm carb, 160 thermostat, 17 inch plastic flex fan, a slightly larger 3 core radiator, accel plugs, wires, distributer, headman headers, and march serpentine converstion. My issues are: heats up to about 250 or slightly higher if i leave it idle for a while and the idle gets higher with the heat. I can feel the secondaries open and it pops throught the exhaust when they open. I cant get it to run worth a sh*t when its cold, and it sometimes randomly will miss and another question is, what should my idle in gear, and timing should be? right now i got it at 650 in gear when the cars running about 180ish degrees and the timing is 8 degrees advanced at 650 and im running some where around 10" of vaccum in gear idling. Any suggestions for improvment?

 

[monte olrac]

first of i would bump that timing up to about 10 or 12, then i would put a 160 degree thermostat in it, use a stant (NO MR. GASKET), then put the silver or brown spring on your secondaries and make sure your timing is about 36 degrees at 3000 rpm, while you're at it you may need a distributor tune up.

in gear your idle should be around 5-600 rpm

 

[megaladon6]

that and i think you're running lean. though i don't recommend a 160 t-stat unless you're in a very hot climate or have to compensate for a bad cooling system. engines generally run best at 180-210*F.
i'd also start looking for a bigger carb, at least a 650cfm but preferably a q-jet.
anyhow, first thing to do when diagnosing a running condition is to pull the plugs. if possible, post pics of them on this thread. with some practice you can tell alot from plugs.
also, what plugs do you have? and what are they intended for? i had weird issues with my engine because i wasn't thinking and got ones for an 87 monte. when i got ones for a 97 suburban (to match the vortec heads and i got NGK's) things went much, much better!

 

[ERIC87442]

I do have a brand new distributer in it so i think thats fine. I had a 670 holley street avenger carb on it when i got it that seemed like it was too big, maybe i was wrong, it took a sh*t anyways so i got the 570 and i think it may be runing lean alos like you said. I got accel header plugs (the little short ones) for a 74 chevy, and i have no clue the year or what the vortec heads came from. I do have a mr gasket 160 thermostat in it, i will probably go back to a 180.

 

[megaladon6]

the plugs are probably the wrong heat range. IIRC the old engines used a "cold" plug and the newer ones use a much "hotter" one. but i might have that backwards. i'd get ones for a 97 suburban 2500 with a 5.7l. (vortech were used from 96 to about 2003 i think, and they are all the same for a given engine) but before doing that, see what the ones in the engine look like.
also, hook up a vacuum gauge to manifold vac and tune the carb for the highest vac signal at idle. with that cam (i'm assuming the lift numbers are at .050 lift) you might want to bump the idle to 750+-50. as you adjust the carb, adjust the timing but a basic area for it is 10-15*btdc.
do you know what cam it is? you can usually look up the expected idle vac for a given RPM from the manufacturer. i'm thinking you should be higher. i have a bigger cam and run about 12-14in of vac at 750, but it's a hard comparison since i have a different and larger build.
as to the carb size, the formula for a 350 returns a 600-650cfm but people usually get better results with a 750 after mods, especially with cam and heads. that's why i like the q-jet. it has a 750-800cfm total capability, but due to it's design it only uses what is needed and is much more adjustable. you can run one on anything from a 250ci 6cyl to a 500ci v8 (with tuning of course!)

 

[ERIC87442]

it is .050 lift, now should i set my timing at 650? or 750ish like you were saying? its at 8 degrees btdc at 650

 

[megaladon6]

i'd try and find the spec card for the cam and try and tune to their specs for rpm and idle vac. but if you don't have the card, first try 12* at 650rpm and see what happens (since you're already there and the increased timing might raise the idle), then bump it to 750 if you still have problems and/or low vac--after tuning the carb too.
unfortunately there's no simple way to tune, it's one big adventure in chasing your tail. every adjustment you make affects everything else.
just a thought, where are you located? maybe there's a member near you if you need some help.

 

[ERIC87442]

yeah, i have the spec card but there didnt seem to be anything about idle and vac. on it, the spot on the cards there but no information, im located in southern wisconsin

 

[megaladon6]

what cam number/company is it? maybe i can find it online

 

[ERIC87442]

ok well i messed with it i set the timing at 12 degrees at 650, bumped the idle to 750ish in gear and its at 14 inches of vaccum and it idles about 980-1000ish out of gear how does that sound?