How big a deal is the compression release

Bought a 77 Piaggio Bravo yesterday and the PO had replaced the head due to a broken CR spring. Now I am a complete virgin when it comes to mopeds and the CR deal is new to me.

Will the moped only start with the CR lever in (valve open)? Will it not start or just be difficult to start with the CR lever out (valve closed)?

How much throw or lift is there to the CR valve? The cable and linkage is kinda sloppy and the lift looks just minimal.

I ask because I have a no start problem and I'm looking at service history and operating theory for all possibilities.

Re: How big a deal is the compression release

Re: How big a deal is the compression release

How 'bout this then.

Will a faulty CR valve keep it from starting?

Re: How big a deal is the compression release

Downhill Harvey (OFMC) /

If the compression release is releasing compression, then yes, it will keep it from starting.

Re: How big a deal is the compression release

Given that the PO had CR problems when he got it, put a used head on it, was starting and running great when I bought it and all of a sudden its not, I think I will look here next. Doesn't have an obvious or any noticable difference in sound or feel between CR open or closed when pedaling to start.

Perhaps I can 'lap' the valve and check the actuator mechanism?

If I pull the head to inspect, can I reuse the head gasket? What is a general retorque spec? (edited)

Re: How big a deal is the compression release

Downhill Harvey (OFMC) /

The decomp (that's what we call it) has a spring to keep the valve closed. It will stay closed even without a cable attached. You should be able to push the spring, and see it return. If there's no spring, or clip, the valve will/might be hitting the piston (maybe, I forget my Vespas decomp config). Pull the cylinder head off, and check the valves actuation. Reattach with 7lbs of torque (yes, I said 7, no more). A new gasket is always preferable.

Re: How big a deal is the compression release

Decomp just helps starting, as long as it is staying closed it should run. On my Honda I have never used it and it is not hard to start at all, on Motobecane it is a BITCH to try and start without using it. Seems to depend on the bike. Never had a Vespa, but if it is closed it should run and start without using it, just may be much harder. As mentioned above a new gasket is always the way to go. It can work re-using the old one, but new is the correct way.

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