Idle Drop

[jrcotner]

I am having similar problems as the gentleman with the fuel injected Pinz, but I have carbs. I set the idle to 950 rpm and balanced the carbs, reattached the rods, and took it for a test run. Shortly thereafter the idle dropped to around 350rpm and the voltage light on the dash was flickering. I checked the vacuum lines and there didn't appear to be any leaks. So I removed the air cleaner cover again and installed the balancers, and proceeded to adjust bots carbs to get the revs to 950 rpm. Trouble was, once I got to around 700 rpm, the vacuum on the front carb shot doubled, and the revs shot up to around 1200. I tried to dial it back down but the slightest touch of the front carb idle adjust screw caused it to either drop to below 600 rpm or shoot up to 1200 rpm, and wild changes in the vacuum of the front carb. I finally got the carbs balanced and the rpm set to 1200. Reinstalled the air cleaner cover, and just for fun kept the timing light attached while I engaged gear and applied some load to the engine. Revs dropped to 1000 rpm and after a few moments went back up to 1200 rpm. In every other respect the truck runs great.

Here's the laundry list of recent repairs and additions:
- carbs rebuilt in November 2011, with the exception of the accelerator pumps, which the rebuilder said were fine;
- replaced the rear solenoid on the rear carb last week. After listening to the new one engage, all of the others sound quite weak, but still make a faint "click";
- new fuel filter in November;
- mixture screws set at 2 3/4 turns out from seated;
- fuel pump rebuilt in June 2011;
- fuel lines replaced from fuel tank to carbs June 2011;
- tank relined June 2011;
- plugs replaced July 2011, still look good;
- timing set at 8 degrees BTDC (Petronix ignition);

Any advice is much appreciated.

[audiocontr]

I would initially say the idle adjustment screws are too far out. Now im absolutely not an expert but in my own experiences, i've found somewhere between 1.5 and 2 to be the sweet spot on my carbs. My second instinct is a worn butterfly shaft . Does the shaft move if you wiggle it from the outside? Did the rebuilder check the shaft?

[jrcotner]

I'll ask the mechanic and check the shafts. I have the carb with the large idle screws and it seems to run well at this setting. I've adjusted everywhere from 1 1/2 turns out to three, and this seems to be the sweet spot.

[Jim LaGuardia]

Have you checked the vacuum equalizer hose under the tin?

[Roverchef]

What about the brake booster hose since it hooks right into the side of the front carb...? Just throw'n it out there!

[jrcotner]

I checked the exposed vacuum hose and connections on the carb and didn't identify any suck in of the WD-40. However, I did not check the vacuum equalizer under the tin. I'll do some exploring this weekend and check it out. Other than normal vacuum checks, is there something else to look for with the equalizer?

[edzz]

Is the mechanical advance mechanism in the distributer lubricated and functioning properly?

[jrcotner]

I put a few drops of oil on the shaft every few months. I have not disassembled it to give it a full cleaning, though.

[jrcotner]

More strangeness. I started to make a detailed check of the vacuum lines and found an obstruction in the vacuum line near the elbow at the distributor. Specifically, a small screw was stuck in the elbow. I replaced the lines and elbows and vacuum lines and the idle smoothed out. But it still won't hold idle at 900 rpm. Vacuum at the engine side of the line rapidly varies between 15 and 20 pounds. Should it be steady? Does this indicate a problem with the vacuum modulator?

[Jim LaGuardia]

If the needle is dancing try adjusting the valves first. If that fails to steady the needle then do a leakdown test to find the bad valve(s).

[og]

I am having problems with idle RPM adjustments since I first got my Pinz. I have replaced worn out shafts in the carb bases, replaced plungers in carbs, and replaced and adjusted valves in carbs. linkages work fine, no freeplay, carbs balance fine. I can adjust the idle to 900 RPM and after test drive it will jump to 1300 RPM. Sometimes it will come down to 900 RPM. Similarly I sometimes adjust it to 900 RPM and it drops to ~550 RPM. After some thinking and reading posts, I figured, I may check the distributor which has Pertronix conversion installed. I also checked the vacuum hose, everything seems to be fine with it. To be honest, I never opened the distributor since I got the truck (5000 miles ago). Since there are no points, there is nothing to adjust, but I forgot that it still makes sense to add few drops of oil onto the felt. I opened the distributor, the felt was still oily. If I twist the rotor clockwise, it moves smoothly until hard stop and then moves back smoothly. I can either let it slowly return or let it go to return under the force of return spring. However, I have noticed that the stop it makes is really a fake stop, since I can nudge the rotor further anti-clockwise with a very little effort. It appears to
me that this possibly can be the root of my problem. Depending on where is rotor position (true or fake stop) when I am adjusting my timing, idle speed can wander in
either direction. Has anyone experienced this before? Can distributor be disassembled? Looks like new distributors are not to be found, and even used ones are quite
expensive.

OG

[edzz]

http://goatwerks.com/distributorgallery.htm

Thank Jim