timing/idle

[1979C20]

Okay, I finally put a decent timing light on my truck and got my idle all dialed in. The timing is set at like 16-20 btdc. If i advance it much more it starts pinging like mad. My timing was WAY retarded and my idle screw was almost all the way out. So, I had to turn my idle screw in quite a bit. Now, I'm not getting as much acceleration as before, and it seems like I'm burning through a LOT of fuel now. Like, ridiculously. Is there 2 idle set screws on the stock rochester qjet? There is a screw on the left side of the carb underneath the chock and I'm not sure what that one is for, and there is the screw on the right side of the carb under the throttle linkage that I adjusted. Do you guys have any suggestions for getting my performance back and lowering my fuel consumption? It smelled like it ran REALLy rich before I adjusted it and it smells the same now. I'm not sure if its rich or lean or what.

[Grim 82]

The idle mixture screws (2) are in the front near the base of the carb, the screw on the pass side is for fast idle speed adjustment, and the one on the drivers side is your idle speed screw. Sounds like you need to set your idle mixture.

[1979C20]

the "fast idle" screw, would that be for the choke? And, how do you adjust the idle mixture? Is that the strangely shaped post at the bottom right corner of the carb?

[1979C20]

OOOOOOOOOkay. So, I did my timing and idle and it all sounded great and there was no pinging, 3 days ago. Last night, I popped my hood while my truck was running and it sounded like 2 or 3 of the pistons were pinging!  would a change in temperature make that happen? The distributor hold down was tight all the way, I even tried to turn the dist back a little bit to get rid of the pinging and I couldnt move it, with effort.

[1979C20]

Okay, I'm going to my buddy's dads' shop today to throw a timing light back on my truck. How should I time it and at what degree? I have the biggest cam you can put in a stock 350 with stock valve train. I dont remember the measurements of it, but I can try to find some documentation of it when I go home, I'm at work now.

[Grim 82]

That depends on alot of variables. I run 12 btdc initial, re-curved MSD, no EGR, and burn 89 octane. I can run alot more initial advance than that without pinging, but it runs better at 12 and doesn't kick back when you start it.

Plug the vacuum advance hose and put a vacuum gauge to manifold vacuum and advance it to the highest steady vacuum reading you can get and then see what the tab and balancer read. If it pings back off of it some.

the "fast idle" screw, would that be for the choke? And, how do you adjust the idle mixture?

Yes the fast idle screw sets the fast idle speed when the choke is engaged. The idle mixture screw (2) are in the front base of the carb. Most that I have seen have a rectangular shaped head on the screw that requires a special tool to adjust it easily.

[1979C20]

Okay, My engine is completely stock except for a bigger cam, headers, no AIR, no cats, no smog canisters. I just got back from the shop, I found out, the vacuum port my vac advance was hooked up to pulled ZERO vacuum. /: so, I switched some lines around. hooked it up to a manifold full vacuum, and now it seems to run better. I timed it by ear, and I do not have a vac gauge. I DESPERATELY need a new carb. Its been nothing but problems, it leaked fuel into one of the vac lines, had to plug it. and the one vac port doesnt pull vacuum. it runs terrible and back fires occasionally when i rev at a stop light, (have to clear it out everynow and again or it kind of loads up).

[Grim 82]

One port is not supposed to pull vacuum at idle.

It sounds like it's running pig rich and your timing is late. Clean your spark plugs, run your mixture screws all the way in and then back them out 1 turn. See if it runs. If it doesn't, turn them out another 1/2, and another, until it idles. Turn the distributor CCW until it pings and then back it off a little. Not saying that your carb doesn't need a rebuild, but a brand new one out of the box could behave the same way if not adjusted correctly...

[1979C20]

Okay, strange thing about what you said.... When I turn my dist counter clockwise, it just starts to stall, and when I turn it clockwise, it begins to ping.

[1979C20]

I'm looking at carbs on craigslist, because ANYTHING would be better than the one I have now. And, easier to adjust. Is there any other way to set the mixture screws without to special tool? Because I do not have one, or at least cant find it anywhere in the garage. I brought piston 1 to top dead center according to a bit of bailing wire in plug 1 whole and air coming out. The balancer mark was inside the circle on the timing marks, and a set my distributor with the point on the rotor pointing towards cylinder the driver headlight. Put the cap on, checked and rechecked my firing order, then adjusted the timing. The owner of the shop I took it to said the distributor could be wearing down, but it seemed normal and healthy. I think its just the carb. The plugs showed lean the last time I checked them, and the ends of my mufflers have white-ish soot in them.

[Grim 82]

Is there any other way to set the mixture screws without to special tool?

Take a piece of round stock and grind a slot out of it. Even a wooden dowel should work.

Okay, strange thing about what you said.... When I turn my dist counter clockwise, it just starts to stall, and when I turn it clockwise, it begins to ping.

 

[1979C20]

See what I mean about the CW and CCW? its WEIRDDDDD. I dont understand it even slightly. I know my distributor turns the correct direction. Maybe I'm just retarded?

[1979C20]

I am going to look at my distributor in a little bit and see, I may have moved the plug wires too far ahead of tdc, maybe? I dont know.

[1979C20]

My cap lines up appropriately, unless my distributor is in fact worn out. I'm not sure what to do, I can only assume its a carb problem. I'll see if I can find a way to adjust my mixture screws. You said, turn them all the way in then out a full turn, does that mean clockwise until it stops the counter clockwise a turn? Just making sure they arent reverse thread or anything.

[Grim 82]

I may have moved the plug wires too far ahead of tdc, maybe? I dont know.

What?
When you turned the distributor CCW what exactly did you do?

As far as the idle mixture, they are standard thread. Screw them in all the way clockwise to limit the fuel. Then back them out equal amounts each to allow more fuel until it runs. This should eliminate the rich condition unles there is some internal problem with the carb. Haven't messed with a q-jet in a while but if I remember correctly you should be able to make it go at about 1.5 to 2 turns out each.