Previous owner does not remember what engine he put into the car, but he remembers that he swapped engine about 10 years ago.

Please see attached photos.

I suspect this is Chevy 350HO/330HP with Vortec heads. Here is what makes me think so:
- It is Chevy 350 with chrome valve covers with red chevy logos.
- Zigzag pattern on front and back.
- There is "880" casted on the block.
- Intake manifold has 8 bolts (2 on every corner).
- Intake part number is GM12486570.

I could not find engine casting number. There is no part number on front or on the back of the engine. Is there supposed to be casting number under passenger side valve cover?

I could not find any visual difference (except rust) from this one:
http://www.jegs.com/i/GM-Performance...ductId=1231165

If this is actually a Vortec engine, what kind of spark plugs should I install? Do all Vortec heads use 0.708" reach spark plugs?

When I bought the car it had Autolite 26 plugs (0.46" reach), I swapped them for ACDelco R45TS (also 0.46" reach), but according to engine technical description for the engine by the link above it needs 0.708" or 0.715" reach plugs (ideally R44LTS). How bad is it to run engine on short plugs? What can happen if I put 0.708" plugs into engine that is designed for 0.46" plugs?

Currently the engine idles a bit rough, hesitates before hard acceleration and backfires&afterfires when decelerating from 80 to 50 MPH. I have adjusted the carburetor to optimal settings (choke spring, TPS, mixture, idle, fast idle) and eliminated all vacuum leaks, that had almost no effect on these problems. Vacuum is not completely steady, vacuum pump arrow jumps between 19 and 21 inches very fast. Idle timing is set to 12, vacuum advance works. Spark wires are in good condition, they are plugged correctly, they do not crossfire. Could short plugs cause such problems?

 

The block casting number will be on the flange the trans bolts to- look down under the cruise servo. If you can see the block the number will be looking up at you.

 

All I see there is "Manufacturado en Mexico". There is supposed to be the number right under that, but there is nothing else there.

 

My 69 had a nearly-new Vortec crate engine in it when I bought it. The thing was always fouling out plugs. I kept replacing the AC R45T plugs (at least a couple of sets plus individuals). The car always had a rich gas smell. And when a plug would foul, I'd get raw gas explosions in the exhaust system! So, I finally asked the question - does this thing have the proper plugs? After a little research, I found that the correct plugs were AC R44LTS. No more fouled plugs. Gas mileage much better and better performance.

I did have to buy a spark plug thread chaser to clean all the holes. The R45T's were so short that the final threads in the spark plug holes were carboned up. I was unwilling to attempt to force the R44LTS's all the way in. The chaser was $9 at Advance. I set gap at .045".

 

I just took off valve covers and found 12558062 part number on heads! These are Vortec heads that need R44LTS plugs. Going to buy new plugs right now. Will report on how new plugs will affect engine.

 

Installed R44LTS plugs and tuned the carburetor a bit (choke was not completely opening). Now engine works great, idles nicely.
Plugs installation was not easy, at first new sparks did not want to screw deeper than old sparks, but some brute force solved that problem.
Autolite 26 plugs that were originally installed are completely black, so they are definitely not a good match for this engine.

Did not have much time to test it today, but it seems like all problems related to spark plugs are gone.

Hesitation before acceleration is probably caused by combination of old accelerator pump, malfunctioning TPS and loose secondary flaps spring. Ordered a new flaps spring, accelerator pump and TPS, will probably spend next weekend partially rebuilding my Quadrajet.

 

according to your info it says you have a 1980. from the looks of it, it appears your car originally came with a California only 305 from the factory. I'm wondering if you will need to rejet the carb for the extra cubic inches. the experts will know better than me.

it also looks like none of you sensors are hooked up to the carb so I'm guessing your distributor was replaced with a vacuum advance style. You might want to find a new carb altogether

 

What makes you think you need a new flaps spring? Is it missing? And what is TPS? Throttle Position Sensor?

Scott

 

the TPS doesn't look plugged in and there doesn't seem to be any wiring near it.

 

qwank, the TPS is not connected on the photo because I took of the carb and photo was made in the process of unplugging everything. Fuel line and some of vacuum connection are also unplugged on that photo. Everything was connected before I took off the carb and I connected everything back after putting carb back in place. Otherwise I would be getting check engine error about missing TPS, right?

I think the distributor is exactly the same was originally installed on 305 engine, the original one had vacuum advance too.

Yes, this car originally had 305 engine and it still has it's original computer controlled Quadrajet. According to multiple sources on the internet, Quadrajet should do just fine on this new engine. I'll do some more research on this, thanks!

Throttle Position Sensor sends random signal time to time and that makes check engine light turn on. Even after adjusting it to 0.7 volts on closed throttle I am sometimes getting "TPS voltage to low" error code after car warms up and idles. TPS signal voltage starts to drop after I start the engine and it settles to 0.35 after about 5 minutes, then after I press and completely release the accelerator pedal TPS voltage resets to 0.7 and starts smoothly dropping again. Check Engine Light turns on when TPS signal voltage is below ~0.5 volts.

Scott, I think that secondary flaps spring is bad because flaps sometimes they do not close completely and it is too easy to open them. I don't have any experience with other carburetors of this type and I don't know how hard this spring should be, but I am pretty sure that it should be able to always close flaps when engine is not running. I know that it is possible to adjust the sprint, but to do that I'll need to take off airhorn anyway, so I'll just replace the spring (it costs about $3).

 

It is not necessary to take the air horn off to adjust the spring tension, but doing that makes it easier for a novice. I would not replace the spring, just adjust it to the proper tension. Make sure the shaft is clean (spray carb cleaner). Then adjust spring so it just closes the flaps, tighten another 3/4 turn, and tighten the set screw. Mark the air horn with a very fine file so if you need to adjust on the car you have a reference point (I set mine a little looser so the secondaries open a bit quicker). Don't loosen more than a tad or you will get the infamous "quadrabog". While you have the A/H off, I would go up 2 jet sizes on the primaries to account for the 350. my 2c.

 

Rich's'78, thank you! I did not know that it is possible to adjust that spring without taking off airhorn. I just googled for it, seems easy to do, will try tonight.