Decompression valve problems

Michael Vogt /

The decompression valve on my Vespa Bravo is not working I tried tightening the decompression valve cables but that does not work and I tried pushing the valve all the way in with a screwdriver and that does not work either any ideas?

Re: Decompression valve problems

Michael Vogt /

Also what is the right fuel/oil mix for my Bravo?

Re: Decompression valve problems

maybe some grime or something stuck inside the valve, take the cylinder head off and get an air gun and blow that shit out.

Re: Decompression valve problems

Micheal is your decompressor valve in ANY away affected by your clutch? if so you must readjust both so that the decompressor valve is depressed just as the starter clutch is activated. check your service manual to obtain the precise clearance between the cylinder head and circlip. DO NOT push it in with a screwdriver man but _do_ blow the grime and grease out with an airgun.

Re: Decompression valve problems

Mix should be 2% or 2.5 ounces of a good 2 stroke oil to 1 gal of regular gas. Best to mix it in a gas container and them pour it into your tank as needed.

Re: Decompression valve problems

Not sure I understand what you mean that the decompression valve is not working. You only pull on the decompression lever when you are trying to start your Bravo.

When you squeeze the decompression lever on the handle bar it should depress a spring on the cylinder head that causes a decompression valve in the cylinder head to open. As soon as the moped starts you release the decompression lever so the valve can close.

Don't use the decompression lever to kill the engine. Some people do this and it can it build up an oil and carbon residue outside the decompression valve and cause it to remain open.

You can remove the cylinder head to check the valve.

1 Remove the spark plug

2 Disconnect the decompression cable from the cylinder head.

3 Remove the three nuts and washers and slide the cylinder head off.

4. put the cylinder head on the bench or work area and clean off all the carbon build up from the cylinder dome using WD40 and 0000 Steel wool.

5. once you have cleaned the cylinder dome and can see the decompression valve and with the cylinder head dome up so you are looking at the inside of the head, squirt some WD40 in decompression valve area. It should form a pool. If it doesn't pool up or leaks out, then the valve is not closing properly. If it is leaking try cleaning the underside of the valve and where it seats of any oil and gunk build up.

6. If you can't get it to work properly you need to replace the valve or replace the head with a head that has a working valve.

You don't have to remove the cylinder to perfom this operation.

When you reinstall the cylinder head torque nuts to 7 ft lbs. Don't over tighten or you could snap a head bolt.

Re: Decompression valve problems

Michael Vogt /

I only ues the decompression valve when I am starting the engine what it seems to be doing is that the valve is not opening even when the spring is all the way down.BTW. 2.5 ounces of a good 2 stroke oil to 1 gal of regular gas. I think is 50:1 I think that 50:1 would be to lean a mix for a 1977 Bravo are you sure that this is right? Also what would be a good 2 stroke oil?

Re: Decompression valve problems

Michael Vogt /

Also my Bravo does not have a manual clutch it uses 2 centrifugal force clutchs.(not sure if I spelled centrifugal right)

Re: Decompression valve problems

The Vespa Bravo and Service manual specify 50:1 mix for your Bravo.

See Attached Pic

Do you have the spring (part # 73) and is the barrel cable end hooked into part #69 and the cable sheath into part # 68?

1115268805_ciao_bravo_decompression_assembly.jpg

Re: Decompression valve problems

Michael Vogt /

I have all of the above part and the cable and they are install properly.It worked up until the time that I took the engine out to set the points could this have something to do with it?

Re: Decompression valve problems

you don't need to take out the engine to set the points, hell you don't even have to remove the flywheel cover... i don't know if it had something to do with your decompressor (highly unlikely) but it was certainly unnecessary. if you were fooling around the with points and now your engine won't start it's more likely that you misadjusted the timing.

Re: Decompression valve problems

Michael Vogt /

I did not know that you could set the point without takeing the engine out. The points needed to be gaped after I gaped them the engine now runs great.BTW I was reading the Ciao,Bravo&Si service manual and under maintenance it says to change the rearhub oil do I have to do this on my Bravo if I do where do I do it at?

Re: Decompression valve problems

Probably a good idea to change it if it has any oil in it.

A lot of new Vespa moped owners don't know about the oil in the rear hub so after sitting for 20 years it probaly needs oil.

You can buy 80-90 wt gear oil in a plastic nose cone squeeze container at most auto parts stores.

To change it remove the left side cover (belt side).

Look on the left rear hub near the Free Wheeling Button (black button thingy) for a screw or hex head bolt (if it is a bolt, don't confuse it with the two Top and bottom wheel mount bolts).

Anyway remove the screw or bolt. If oil runs out of the hole it is full. If you wish to change the oil, tilt the moped to the left and let it drain into a pan or wide mouth conatiner.

Refill with the new clean 80-90 weight gear oil until it runs out the hole (I think it take about 3-4ozs). Then replace the screw.

Check the old oil to see it there were any metal pieces in the oil.

Re: Decompression valve problems

Do you have an assembled, (real world photo of the decompression valve setup.) It's my first rebuild of a bike with a decomp valve, and the genius that I am, i did not make note properly of how the spring was attached.

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