I have a 75 Valiant more door with a 225 that I recently put back on the road after about 25 years of sitting. Everything on the motor is stock.
I am having an inconsistent issue to where sometimes the car runs and accelerates great. Other times it has noting off of idle and blogs like it is lean. It only does this while under the load of driving. It will rev clean and sounds great in park or neutral. Once I get over 1/2-2/3 throttle it clears up and runs strong. This seems to be an on or off issue, there is no in between. One thing I notice is that the idle rpm changes about 150-200 rpms when this happens. When it runs bad the idle will drop that amount. If I try to re-tune everything and reset the idle to 750 it will jump to about 900-950 once it starts running well again.
I'm thinking that the only two things that would change the idle rpm would be a vacuum leak or the timing changing. I have checked for vacuum leaks around the carb and intake with none found. I also tried to run it without the vacuum canister on the distributor hooked up with no luck. I'm still in the process of removing and plugging the remaining vacuum circuits one at a time while it's running bad to test each. I'm also going to start carrying the timing light in the car with me as well so if it does change to the bad I will check to see if the timing has changed.
I have not been able to pin point when this change happens consistently yet. It will normally do it in the mornings after getting down the road 2-3 miles. It seems to sometimes come and go when the engine is shut off, like it resets. It was running bad once and I gave it a couple of good stabs at the throttle in neutral and it cleared up and started running well again and continued to for the remainder of the drive.
I have the 1945 Holley. It has been rebuilt and back apart many times. Had issues originally that have all been worked through. (Accelerator check ball missing, accelerator pump passage blocked, power valve vacuum piston stuck in bore in extended position, missing fast idle cam). There is a new fuel filter, gas tank, sending unit, and all lines(hard and soft). I thoroughly tested the accelerator pump circuit and check ball system. Everything there is good.
Plugs, wires, dist. cap and rotor were all replaced. All vacuum lines have been replaced. EGR valve, OSAC valve, vacuum solenoid, and vacuum amplifier/canister have been removed.
Timing is set at 1° BTDC at 750 rpm's (17° total). The motor pulls 19.5-20" of vacuum. I have not had a chance to adjust the valves yet.
Am I on the right track with the timing or is something else going on? The only other thing that I could think of would be a sticking valve but I wouldn't think that it would clear up in the upper rpms. Thanks ahead of time for your help.
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