250 vacum source

[NicoSlam]

So I finally replaced the dampner on my 250 over the weekend so I attempted to timing it using the light. I disconnected the vacum line from the distributor and plugged it. I set the timing accordingly (0TDC with standard). When I reconnected the vacum line I noticed there was no change in timing at idle. I disconnected the line again and tried to feel for vacum (using tongue) from the carb but I couldn't. The carb is an original monjet. Is the vacum that suttle? what should be the vacuum at idle (950rpm)? Honestly, I was expecting a hissing sound and a very obvious shift in timing with and without the line connected to the distributor.

Thanks for your help.

[Wrenchbender Ret]

Most of those were hooked to ported vacuum. It will only have vacuum when you open the throttle a little & will increase as you raise the RPM. If it still has emission controls on it the advance may be blocked untill the engine warms up or the trans. is in high gear. Make sure the chamber on the vacuum advance unit on the dist is not ruptured.

[68gmsee]

Yeah, that 250 Rochester should have two vacuum sources -ported and non ported. The higher one above the butterfly valve is ported, the lower one below the valve is engine or non ported. If you are connected to the top one, nothing will change until you are at a certain rpm.

I've tried both on mine but prefer non ported.