another problem quadrajet

Buick has never had real super power. Timing was off. Then installed electric choke. Works good but now the motor at idle seems like its running out of gas after letting off pedal. The vac advance has been disconnected.
When it does idle and tickle the throttle there is a slight hesitation, then it revs up ok. Rev it up to 1500 let off it slows to idle then eventually losses rpm and quits. Please help. Thanks Frank

 

first check the plug wires. I had a vexing problem and it turned out a wire was bad. Hard to time it on 7.

 

I am not the expert here by any means but it sounds like you need to tweak the fast idle and the mixture screws.

 

thanks Gary checked them and points and cap and plugs. Frank

 

I can't seem to find the fast idle screw. Manual transmission car.

 

I also checked the front vacuum pot and its good. I have to get a pump to check the back one. Car has low vacuum. Frank

 

Maybe this will help.

 

Not enough information to help out.

Would need a carburetor part number, and all of the engine/drivetrain/vehicle specs.

NEVER run w/o the vacuum advance on anything driven on the street, unless perhaps it's a "full race" car with mufflers.......Cliff

 

Cliff why is the v/a needed? How will motor react without it. Frank

 

The vacuum advance is a "load sensing" device and will add timing at very light load (high engine vacuum) only. This allows for a much leaner mixture to be effectively burned, improved throttle response, less throttle angle at any vehicle speed, and improved combustion efficiency/fuel economy.

Even with all that said and the great information available on the subject, we continue to see folks install those POS aftermarket spring/weight kits into their distributors and unplug the vacuum advance and not use it. Even IF you get all the mechanical timing in earlier (which actually is NOT beneficial for most well thought out engine builds) at cruise/light load you are still missing quite a bit of timing and loosing out and quite a few benefits that it will provide.

There are no negatives anyplace from using a Vacuum Advance, even on pretty high HP set-ups, provided they are street driven, so we ALWAYS tune using them here, and recommend that our customers do the same thing. Even with all that said a very well thought out engine build, with very tight squish and higher compression for pump fuel, plus a very well chosen cam will NOT require a lot of timing or fuel anyplace right to start with. With this in mind we often reduce the amount of timing added by the mechanical curve and the Vacuum Advance unit, but we still use them.

My own engine, for example is 11 to 1 compression, exactly 455 cid and right at .035" quench distance. It has a custom ground roller cam, 289/308 @ .006, 236/245 @ .050 on a 112LSA with .639" lift at the valves. Initial timing is 10 degrees, 10 more degrees from the mechanical advance (20 at the crank for a total of 30) and another 14 degrees from the vacuum advance (ported vacuum so only added at light load). The distributor is a stock HEI with a positive stop welded in to limit total timing and how much, and a custom vacuum unit which starts at 9" and all in by about 12" vacuum. I use stock HEI weights, springs and center cam, timing is "all in" right at 2800rpm's. The engine will make at least 560hp and around 600ft lbs torque if not tad more. It pushes my daily driven car to 7 teens in the 1/8th mile around 95-97mph and nearly into the 10's in the 1/4 mile over 120mph. Runs fine on any grade of pump gas I feel like putting in it, but for a "warm and fuzzy" it get at least half a tank of 92-93 octane on race days.

My distributor set-up is pretty close to what most of them are that we do here, lower compression engines and those with more squish or a bit too much cam may get a bit more timing, especially from the vacuum unit, and we may move it to manifold vacuum if the cam is big enough to have engine vacuum below about 10' with "normal" initial timing.

Anyhow, we always use the vacuum advance, even if it is employed differently and adding custom amounts of timing at light load.

Even with all this said, we see scores of folks not using them, even on pretty "mild" street engines. To this day I don't know why, but even some pretty big names in the engine building industry don't use them either. Not sure why, accept that some folks are still follow "old school" tuning tricks, which were probably OK when gas was .29 cents a gallon and no one minded horrible fuel economy and burning everyone's eyes when you stood behind their cars in the High School parking lot!.......FWIW.....Cliff

 

Thank you Cliff

 

You are most welcome.

I'd like to add here that believe it or not we see more complaints from folks that have installed those POS weight and spring kits into their distributors than any other. They ALWAYS blame their idle tuning issues on the carburetor, big drops in RPM's when placed in gear, etc when it is actually the mechanical timing curve at fault.

It's difficult if not near impossible to tune with a timing curve that is allowing any advance at idle speed. The weight kits and springs are designed to improve leverage and get the timing in much quicker and all in sooner than stock parts. The problem is that nearly 100 percent of the time some of the curve is in below 1000rpm's and the engine will have trouble "settling down" to a steady idle speed after tapping the gas or coming to a stop.

The springs used in those kits also go "soft" as they are very poor quality these days.

What is needed with these engines is a smooth timing curve that starts right off idle and reaches total mechanical advance relatively early, but not clear down at 1500-2000rpms. Doing this on a very well thought out engine build does NOTHING to improve performance anyplace.

We use and prefer a mechanical timing curve that is starts around 900-1000rpms and all in by 2800-3200rpm's. We bring in more timing in the "normal" driving range for improved efficiency via the vacuum advance. Most factory units will add too much timing as they were used on lower compression engines trying to get them to be more efficient and thru emissions, so we modify them if/as needed for the application.

Another BIG problem with GM HEI units is that if and when you install light springs on them, they can and will add a BUTT LOAD more timing at high rpm's as the weights will roll out past the "flats" on the center cam. There is no positive stop in an HEI like their is in a GM points distributor, so one needs to be added to it or you're likely going to put some rod bearing in the oil pan using an HEI that is not set-up correctly.......FWIW.......Cliff

 

After playing with spark plug wires, car now won't start. Sneezes thru carb and sounds like fireworks in oil pan. Is there two marks on damper? Went to TDC with piston stop, and redid wire order. #1 is about 10 o'clock, and damper line is about 1/8 inch off. When trying to start the fireworks start. Could the choke be too tight? After trying to start, i'm getting heavy gas smell. PLEASE HELP. Frank

 

Larry I did the plug wires one by one. Tomorrow I will get under it and look real good at the damper