If it isn't one thing its 10 others.

Hopefully someone might be able to help me out on this one- I've got a 74 454 in my 69SS. 10.8:1 compression, cam has .527/.553 int/exh lift and adv duration of 232/235 and 114 degrees of seperation. Running HEI dist, 750cfm carb.

Problem is, when its cold- as in only ran for less than a half hour or so it runs good and strong. If I drive it for more than 20-30 miles or an hour or so when its up to full operating temp and has sat in traffic for awhile it starts to run poor. It idles down slightly, when I'm going about 25-30MPH and try to accelerate slightly hard it acts like it's bogging, then will pick up and pull okay, but not as strong as it does when its colder.

If I jump on the gas while going this speed it'll rev up real quick, but won't catch and take off also. Basically acting like the tranny is slipping.

My timing at idle (900 RPM) is around 20-28 degrees. Max timing at 2500-3000 is 36. When I had my timing backed off to around 12-16 it did the same thing, and I'd have to up the carb idle high enough that it caused it to diesel half the time.

My temp is staying at a nice 180-190, and creeps up to around 200 when I sit in traffic. It hasn't backfired when open the throttle fast either. I was originally chasing this problem thinking it was running too lean, increasing the fuel helped a bit but has not solved this problem. This has been going on since before when I was running my old setup (10:1 compression, everything else the same). I don't get any knocking or pinging either.

Would bringing my timing down be a step to try? I've always been under the assumption that you should run as much timing as possible before the motor starts to give you problems. Maybe I'm just losing power before I run into detonation?

Also, my carb is currently as rich as it can get. Its 12% rich in power and cruise (edelbrock performer carb). This did help, before when it would get hot I'd have no power at all, and if I opened the throttle quickly it would backfire.


Thanks for any info you can throw my way.
Wes.

Wes, I have a lot the same problem. Mine I roll it out and let it warm up a little 140-160 and pull it out it runs fine but I just get out of the neighborhood and it starts to run bad. What kind of carb are you running?

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JT
71 SS Vortec 355
www.angelfire.com/co/KellyMotorsports (http://www.angelfire.com/co/KellyMotorsports)

The carb I'm running is an Edelbrock Performer 750CFM (#1407).

I'm going to change my timing around in hopes that it will solve this problem. I gotta make a 80 mile trip today in this thing and I don't want to limp it along.

Wes

I have the same carb (Carter 750) and I did the same this of richening it trying to get rid of the problems. I have had the timing all over the place trying to figure it out. A friend of mine thinks the bowls can't keep up with the demand so I may try his Holley just to give it a shot.

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JT
71 SS Vortec 355
www.angelfire.com/co/KellyMotorsports (http://www.angelfire.com/co/KellyMotorsports)

Hi Wes,
Could it be that you have vapor lock ?
What happens is that the gas actually
"boils" in your line or bowls. Your pump, line and carb are all built to handle liquid in a stable state.
Check that your fuel line is not touching or in close contact with any hot engine or exhaust parts , headers in particular. If you just have a really hot
engine compartment then an auxilliary
electric pump (near the tank) will increase
fuel pressure and make fuel less likely to
vaporize.
Don't know if this is your problem but it may be worth checking out.

I don't think it could be my fuel supply. I was running the same carb setup on my previous 427 and had this problem once, but solved it all by running my fuel lines away from the motor, and installing a head shield under the carb.

I checked my total timing again today, and at 3000RPM I was only pulling 30 degrees of timing, and even past 3K it wouldn't go over 30 degrees. I upped it to 36, but now my initial timing is clear up at 22 degrees. It cranks fine, but isn't 22 degrees of initial timing a bit hardcore? Will it hurt anything if I run it longterm?

I drove it about 130 miles today on the freeway and had no problems and the problem so far has appeared to go away. Hopefully I've actually fixed it this time.

Thanks for the help.
Wes

Hey Wes, what kind of distributor are you using?

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Wally
Gold #67
67 malibu

I'm learning about coils now since I had the same problem with my new 427 on Saturday. Ran mint in the garage, idled nice. Started her back up and drove her out to fill her up and after about 3 minutes, a real bucking bronco, especially at cruise ( low throttle opening and high mani vaccum). I suspected we wrenched a wire, but my ignition man says it might be the coil. ( Mine is not HEi). Says that bad coils generally malfuntion when hot causing an open curcuit or ground. I don't know exactly what sort of resistance readings you should get, but I'm guessing throught the primary winding something between 1 and 5 ohms, and more resisitance through the secondary. If its closed ( o ohms), it's a bummer.

[This message has been edited by Gene Chas (edited 08-30-99).]

Wally- I'm using a GM HEI with light springs, full advance is supposed to kick in by 2500. Its being fed by a holley annhilator and lasershot coil.

Another day of driving around and it hasn't done it yet. I'm guessing I just didn't have enough advance. I'm gonna check my spark plugs tomorrow to see if I'm frying 'em.

Wes.