I, for the first time in the 8 years and 50K miles I've owned this truck, finally have dry, light brown spark plugs in my old F. It ran terribly rich when I bought it all stock, replaced it with 2 rebuilt carbs from SOR which both ran worse than the original and leaked gas from the lower part onto the intake. Then put on a weber 38 with headers and a jacobs. It ran great for about a week. All the time I had mounds of powder black on everything from the plugs back. I now have a weber 32/36 with an HEI dist and it runs better than it has in the entire time I've owned it. I now have a new issue. It idles nice when cold and when it is warm, for about 30 min. After about 30 min of arond town driving it will no longer idle. It also likes to stall no mater what temp if under hard breaking. The other thing I've noticed is that when coasting downhill in gear it pops out the exhaust. I once was told what causes that, but my fading memory can't pull it back. Can anyone help me out with this stuff?

tom

p.s. It is a 70' F with a rebuilt head, 145-150 psi in each cylinder and close to 180,000 miles.
thanks

do you still have the old webber?...fo sale???:rasta:

I know this doesn't help much but either your carb isn't adjusted correctly or your timings off. If I remember correctly its your timing. But I still think it could be either. The weber's are pretty idiot proof so muck with your timing. remember with hei you can gap the heck out of your plugs. My thoughts here are to fix your puttering down hill problem. Not sure about the stops on hard braking.



arndog

I might be seeling the 38, but I have a couple of project trucks and one might end up with a 2F with the weber. I'll post if I decide to sell it.

Any good advice on mucking with the timing? I set it at 7degrees btdc. The dist has the vacuum advance, but when it was hooked up it ran great at low rpm but would knock and rattle like crazy in the mid range. Any good timing how-to would be greatly appreciated.

thanks
tom

If you have vacuum boosted brakes, this could cause your motor to die under heavy breaking...however, I don't think it's the booster's fault...it sounds like the carb has issues and it's not running well enough for the motor to not stall when the booster takes all the vacuum from the motor.

I don't have a booster, just manual brakes. Have a new manifold and all new lines so there shouldn't be a vacuum leak.

Originally posted by trw


Any good advice on mucking with the timing? I set it at 7degrees btdc. The dist has the vacuum advance, but when it was hooked up it ran great at low rpm but would knock and rattle like crazy in the mid range. Any good timing how-to would be greatly appreciated.

thanks
tom

If its pinging & knocking w/ the vacuum advance there is something wrong. sounds like youve got way more advance than 7d BTDC. double check w/ an advanceable timing light (7d BTDC is the round hole or BB & TDC is the line) are you running high commpression? if so you need to try higher ocatane fuel. to check for vacuum leaks run water over the manifolds while the truck is running if there is leaks it will kill the engine.

for timing what I use as a starting point on a sbc is to unhook the vacuum advance and plug it up with your thumb then set to 8 degrees btdc. hook vacuum advance back up. should be somewhere around 14 at that point. Not sure if that is the same starting point on a six though but timings is easy to play with so might as well

also make suer you are doing this at the correct idle

arndog

also make sure you vacuum line is on the correct port. pretty sure there should be zero vacuum at idle for an HEI

arndog

I by no means a pro, but why would you risk introducing water into your engine? i have always used something like wd40 or such....as the engine is running spray it around and if there is a vaccum leak the engine will speed up.

Originally posted by buford
I by no means a pro, but why would you risk introducing water into your engine? i have always used something like wd40 or such....as the engine is running spray it around and if there is a vaccum leak the engine will speed up.

I've always liked the water method b/c I'm not too fond of spraying flamables next to my header. water has an oposite & more dramtic effect on an intake leak. the water should not cause any problems to your engine as long as it does not sit in the cylinder for awhile. (its only minute amounts anyways). one other plus is it will also clean carbon deposits in the combustion chamber :D

Get the little things sorted out:

Check that ignition timing! Typically at idle you disconnect the vacuum advance. Cruisers always set idle to 7 BTDC, but with the HEI not sure what the initial setting should be (basically you want the same amount of advance at high rpm as the stock distributor, and adjust for the amount advance curve back to idle).

Vacuum advance - ported source (i.e. hooked up the carb base, NO -or little- vacuum at idle, LOTS of vacuum under partial cruising, NO -or little- vacuum at Wide Open Throttle).

Back firing in the exhaust on a downhill section is common on "desmogged" motors, as you'll be dumping a rich mixture into the exhaust manifold.

Once you have the ignition timing, and vacuum advance sorted out, you should be able to readjust the idle speed to prevent stalling under heavy braking.

Tom :usa: