Manifold intake and air chamber of Yamaha RXZ

[snookie51]

I used to get a mileage of over 340 km per tank when my RXZ was new. But now, it can only achieve 260 km at the most. Have tried the usual possible things - changed spark plug, replaced piston, clean and retuned carburetor - but to little avail. I now suspect it might be due to the ignition coil, or CDI, or the Control Unit. However, if any of these is the culprit, then I would have starting problem in the first place, which is not the case now.

 

From the parts catalog, I see there is a manifold intake connected between the engine and the carburetor. (See diagram).

 

http://fcvxxg.bay.livefilestore.com/y1p3KZi9P3pjceXJ3xhDpcfzVvlm7VUYLIVnmFdZFfjQ5HIsLlDSbUp2-ZmWICdAJhvvdeoPBsoF58rCCKiVuuaFaXbMsqvArkO/air%20chamber.bmp

 

In the manifold are valves which I believe help to regulate the flow of air into the piston chamber during combustion. I am curious to know to what extent the failure of these valves in regulating air flow properly can affect fuel efficiency. What kind of symptoms will we get when they fail?

 

Can member who have the answer or knowledge please respond. Thanks.

[ben1112]

It's called a reed valve. They prevent gases from reverse flowing back to the carb during combustion and pass in back again thru the carb again during intake which can cause doubly rich mixture.

 

First check your plug readings to see if the engine is running rich. If not then check if reed valve seats flat against the reed cage.

 

All okay then only proper procedure i can think of is to use a compression tester and check cylinder pressure.

 

The things u mentioned rarely fail. If u have the bike from new and havent replaced the piston/overhaul, it might be time.

[snookie51]

It's called a reed valve. They prevent gases from reverse flowing back to the carb during combustion and pass in back again thru the carb again during intake which can cause doubly rich mixture.......

 

Thanks ben for your input.

 

I guess you meant 'gases' as mixture. I can't see how the mixture can get doubly rich due to the reverse flow. But I can see that this will lead to reduced compression thereby causing less than complete combustion. This will make the mixture to appear rich because of the presence of remnant fuel.

 

I think this is what you meant right?

[Syaitan]

What are the things that u have changed since the time ur RXZ hit 340km per full tank? Sprocket size? Rim size? Exhaust pipe? Because all these affect fuel consumption.

[sleazsith]

used to have 220km only but my mech checked my pin jet and changed it. now reaching 300++km.