btectonic wrote:Still workin' on it but the timing's not an issue anymore. Idle is surging, not an f.i.issue, not a vacuum leak issue, at least not on top of the engine. Maybe an air leak, could be a leaky jug or something, need a leak down test. The guy pulled the motor and went thru it again, AMC heads got new seats, new valves, new guides. Springs, rockers rocker shafts, all unknown to me. Stock length pushrods for sure, the machinist never did rocker geometry, just threw stock pushpods back in after taking 1.8 heads and dished pistons to 8.5:1. Shoemaker stuff.
The mechanic's such a dingaling a judge may need to help sort things out $$$ way, we'll see. New fellow will do the compression/leak down.
Yes...it is an airleak issue...but maybe not in the manner you think.
If you truely have found and fixed all vacuum leak sources...every tube, every hose, the gaskets between runners and heads and the runner boots, the TB o-ring, the proper closed position of the TB...meaning throttle cable adjustment, injector seals, valve cover gaskets, AAR, decel valve and its hoses if you have one, automatic tranny vacuum midulator and hoses, throttle dashpot, vacuum advance hoses and dashpot, MPS........everything verified....and you still get this problem then.....it is still an air leak. Or....more factually...and air to fuel imbalance.
When the idle is surging....check your fuel pressure with an accurate gauge. If all vacuum issues have been fixed, the problem is usually a gross excess of fuel. Occasionally it can be a gross lean situation but that is usually quick to see in poor drivability.
What many people do not get the feel for until they work on D-jet for a while is that it is really all vacuum based.
Here is the problem: since two injectors in this paired system fire way out of time....you tend to run with two ports wet at idle. If your fuel pressure is high or the adjustment is off on the MPS....the rich running always keeps an excess of fuel in the ports at idle and some very low rpm running like in bumper to bumper traffic.
Know this:....even small excesses or losses of fuel mixture at idle change the pumping efficiency of the engine as combustion efficiency rises and falls. That directly affect the vacuum signature......which directly and sometimes disproportionatly affects fuel mixture. If you are running say...10% to rich at the MPs.....the off an on surge of excess fuel being scavenged at the ports.....causes an overly rich situation from moment to moment. Idle falls. As the ports are scavenged clean idle rises again and spikes the MPS....which is adjusted to rich....and gives excess fuel mixture again....starting the process over.
In very excessively rich situations...usually an MPS maladjustment paired with variable or too high fuel mixture....a double whammy....the idle will submarine up and down for from 1-3 minutes before eventually stalling because it just cannot keep up with the excess scavenge fuel in the ports.
If all of your leaks are fixed, set fuel pressure to standard...and timing....and make a couple of tweeks to the MPS starting with the outer full load stop. Ray
