new motor

[mcguire22]

well, I got my motor in(283 out of a 65 impala). First, let me tell you what it has. Lunati cam, weiland intake, edelbrock carb, and headers. The thing idles great but as soon as I give it gas it backfires. Then it started backfiring when at idle. So i got it home from the shop and its overheating( brand new waterpump). Any pointers with the backfire? It still has the 6 cylinder radiator but it started overheating pretty quick after I started it up and timed it. By the way, I set the timing a 4 degrees. Does that sound right with the mods. Thanks for your imput, I know it will be great

[markeb01]

It would be easier to diagnose if you knew more about the engine details - how rough are the cam specs, was it installed straight up, retarded or advanced, compression ratio, condition of plug wires, and the condition of the plugs themselves. If it still has points, those are the first thing I'd look at. It's easiest to set them with a feeler gauge, but a dwell meter should be used to double check the gap is set correctly. Dwell specifications always show a range, and the points should be set to the lower dwell number, as it will increase as the rubbing block wears. Points should always be set before the timing, as big swings in the dwell will change the timing. If it has solid lifters they may be out of adjustment enough to cause problems.

If everything in the ignition looks okay you might check to see if the accelerator pump in the carb is working. With the engine off, pull the air cleaner and cycle the carb linkage. If it's working you should see gas squirting into the throats. A dead accelerator pump will cause an immediate lean condition when the throttle is opened. Depending on how much you know about the history of the engine, the primary jets may be set too lean, or something as simple as a plugged fuel filter could be causing problems. If you have access to a vacuum gauge, that may also show something obvious.

[mcguire22]

new plugs, new wires, Didnt check the gaps (stupid), carb is working good, Just have long tube headers right now with no mufflers yet(might be the problem, no back pressure), Cam I think is 480 lift but that is all I know, I have no idea about the compression ratio( should be stock). See if this helps. thanks

[ob1monkey]

are the valves adjusted right? did you install new valve spring to accommodate for the lift of the cam? If not or they are adjusted to tight? that would cause exactly what your describing . start from cold idles good until the lifters pump up then back fires at idle.

[Wrenchbender Ret]

Try giving it more timing. With a performance cam you need more timing. If your cooling system is still full, you may have gotten a bad thermostat. About 1 out of3 new thems. are defective anymore.

[mcguire22]

ok, Ill check the thermostat. About how much timing? 5 degrees or like 8 degrees?

[mcguire22]

not too worried about the valve springs since the engine ran great before I bought it. I road in the car just for my own satisfaction

[mcguire22]

any suggestions for the timing?

[ob1monkey]

I've got a 477/488 lift and mine is set to 8 degrees.

[mcguire22]

thanks monkey. Looks like i might be going a little conservative. I think thats where I will start.

[Bugeyev8]

sounds like an arc in the ignition system, or firing order wrong, 18436572, is the dist cap got any carbon tracking ?

[mcguire22]

not sure. Ill check for carbon sometime tomorrow. The firing order is correct though

[tapeworm]

I'd almost say the springs on the metering rods would have to be changed with the reduced vacum, but if it ran OK before, then I'd guess we could rule that one out.

For timing, you will need alot of timing with that cam, especially on a smaller motor like a 283. Don't be afraid to go high; you can always retard it if starts pinging or hard to start.

Also, did the cam get properly broken in? Cams going flat has been a problem lately, especially with the newer oils. Most newer oils do not have the zinc necessary for cams on these motors. If you are running the high $$ synthetic, I think you might be OK then.

Also, is it possible the motor sat awhile, and has some junk in the carb?

[mcguire22]

the motor was pulled the day before I got it. I put the carb on, Although, it had sat for a while. When we first fired up the motor, it idled and rev'd good. Then when I started it back up about 30 minutes later it was hard to start and started backfiring. Im running 10w-30 castrol. Not synthetic(i figured with an older motor, it wouldnt like it too much)

[bullington]

Running lean?

[Steve Van Gent]

Timing chain hopped a tooth or two...