O-320-E2D head scratcher

[lr172]

The OP indicated that leaning has no effect on the problem. The carb's mixture valve is the very first item after the bowl. Fuel cannot get to the venturi without passing this valve (accel pump well has two check valves that require force to get the fuel into the metering passages-it is not common for these to fail). Therefore, if one leans agressively without improvement, the problem cannot be a rich mixture. At least not being fed from the carb. Further, he states that it takes 10 seconds for RPM drop to occur. This is not typical of a rich carb. It will immediately bog, stumble or lose power; There is no delay (unless rich condition is due to boiling fuel, which is often not immediate). Notice when you shove the throttle in. The engine immediately speeds up. The accelerator pump shot is gone in less than a second. Carbs adapt to changing airflow and vacuum in milliseconds, not seconds.

Keep focused on the ignition. The RPM drop in your problem is the same value as your mag drop RPM loss. That is just too much correlation to ignore.

Larry

[RV Jerry]

The post on the primer was not to mean accelerator pump in carb, but a remote primer, quite often people only put primers lines on a couple of cylinders , when the primer leaks the mixture on those cylinders are all over the place ,the engine runs rough and mixture control has no effect

[lr172]

Originally Posted by RV Jerry

The post on the primer was not to mean accelerator pump in carb, but a remote primer, quite often people only put primers lines on a couple of cylinders , when the primer leaks the mixture on those cylinders are all over the place ,the engine runs rough and mixture control has no effect

I understand, but I discounted a primer leak and was addressing the other post about accel pump leakage. If the primer was leaking enough to run overly rich at 1700 it would be too rich to even run at idle or would be VERY rough. The fact that it runs fine at idle and takes several seconds to run poorly at 1700 led me to exclude a leaking primer as a possible source.

Larry

[RV Jerry]

I agree that there is a strong poosblity that is is an ignition issue, just suggesting to eliminate the simple easy to check items first.