Yamaha Jog R - New Chinese carb (Dell' Orto PHVA 12 ZS1 has been replaced)

[cabrinha]

Hello 2strokers.

For some time now my Jog was running rich. Had difficulty to turn the engine on if the scooter sat for three or more days, the exhaust tip had oil residues (besides normal) and was smoking a lot, the spark plug was full of petrol etc.

I decided today to check what is going on. So I removed the carburetor, the reed valve and the fuel cock.

The reed valve was not sealing properly (fixed) and the fuel cock was leaking as well as the neck (which joins the carburetor with the reed valve) was cut. I am going to buy new parts to replace them tomorrow.

At first I thought that the problem was the faulty fuel cock. However, the fact that the fuel cock is leaking does not mean that the fuel can enter the float bowl. Except for the fuel needle valve could not seal properly.

So I opened the carburetor in order to inspect it. I measured the float height and it was outside the limits set by the manufacturer. The problem is that my float has no metal tang which I could bend in order to achieve the correct float height. Instead there is a plastic tab which, of course, can’ t be changed.

Then I thought that the correct height is set by the float needle and the needle seat. I removed then the float needle but I do not know how I can remove the seat. It looks like it is press fitted.
I do not think that if I change only the float needle I will be able to achieve a correct float height. So how can I manage to remove it?

And…some more questions:
What gasket maker should I use if I don’t find a new oring for the float bow?
If I fix the float needle problem is it necessary to buy a new fuel cock?

In accordance with the above mentioned is it normal that all this time I had my mixture adjustment screw fully screwed in in order for the scooter to run without bogging?

Thanks in advance and sorry for grammar mistakes.

[aeroxbud]

Is the head of the needle worn? The coating on the top should make it seal.
The float bowl gaskets are readily available from most scooter parts stockists. Not sure where you are based. www.scootertuning.ca/en/carburettors-accessories/5174-gasket-kit-dellorto-phva-phbn.html or www.scooter-attack.com/carburetor-gasket-kit-phva-cgn176357-39.html

[cabrinha]

Here is the float needle.

[aeroxbud]

It's hard to see from the pictures, but there is definitely a line round the sealing face. Is it worn?

[cabrinha]

Went shopping today. Bought a new fuel cock and a reed valve manifold . No oring available, no float needle, no reed valve gasket (made a new one myself).

I adjusted the carb and everything seems to work fine (big improvement in low end). Except for full throtle. The engine refuses to rev up and in some cases it almost stall.

Any suggestions? Main jet is the stock one and clean.

[geoffh]

Cabrinha,I run a stock 50cc jog r ,check the accelerator cable is adjusted so the slide is opening fully,make sure the air box is sealed and clean,use duct tape to help this.post a picture of your exhaust and the air box,if money is not to tight consider a cheap £20 carb

Geoff

[oldgeek]

You can also adjust the float by CAREFULLY heating the plastic tab on the float and bend it just a tad.

I can't tell from the pictures for sure, but you should also use a pencil to push the needle jet tube out of the carb for cleaning.

[cabrinha]

Dec 2, 2018 9:53:43 GMT -5 geoffh said:

Cabrinha,I run a stock 50cc jog r ,check the accelerator cable is adjusted so the slide is opening fully,make sure the air box is sealed and clean,use duct tape to help this.post a picture of your exhaust and the air box,if money is not to tight consider a cheap £20 carb

Geoff

Cable slack is ok. The airbox is clean and taped.
I use a generic exhaust like this one www.scooter-works.co.uk/chinese-2t-50cc-exhaust-cpi-keeway-generic-1e40qmb-a-50cc.html

There is a restrictor cone in the exhaust downpipe which I did not grind off.

Dec 2, 2018 10:17:40 GMT -5 oldgeek said:

You can also adjust the float by CAREFULLY heating the plastic tab on the float and bend it just a tad.

I can't tell from the pictures for sure, but you should also use a pencil to push the needle jet tube out of the carb for cleaning.

Too dangerous for me. I am not tha patient.
After carburetor cleaning and fuel cock replacement the overflow problem seems to have been solved.


Should I lift the needle one place up?
I read that mixture screw and pilot jet set the mixture for idle untill 1/4, needle is for 1/4 to 3/4 throttle and main jet for 3/4 to wot. When I richen the mixture via the screw the engine works fine in hole throttle range. If I set correctly the idle mixture (I find the where highest rpms are achieved) and then screw 1/8 more towards rich I have very good acceleration but then the engine cant rev up. When the engine gets warm I can open fully the throttle withoutbl having the engine to stall but rpms refuse to go up.

[oldgeek]

I wonder if your electric choke is warming up and closing properly.

I would also consider removing the restrictor in the exhaust.

[cabrinha]

Dec 2, 2018 20:53:06 GMT -5 oldgeek said:

I wonder if your electric choke is warming up and closing properly.

I would also consider removing the restrictor in the exhaust.

From the little I know removing the restrictor will make things worse unless I upjet. But I think it is better to solve the current issues and then proceed.

The choke is controlling fuel or air? When the engine is warm the problems with partial and full throttle are diminished. Next Saturday I will remove again the carb and I will also check the auto choke.

My observations so far:

1) Perfect idle.

2) Partial and full throttle hesitation and engine is bogging down. If I keep on throttle the engine revs down till it reaches idle. Does not stall. Some times bogs down and suddenly starts revving up again (steady throttle position).

3) If I turn the mixture screw in (clockwise) the scooters works almost ok, perfect idle and partial throttle, acceptable full throttle. Engine works pretty rich.

Any opinion about cheap chinese carburetors (eg. this one)? Apart from the carb and a new intake manifold is there something else I must buy? 17,5 or 19?

[geoffh]

You don't,t need a larger carb,I'll post a picture of a Chinese one later,meanwhile get the exhaust ring removed your engine can,t function properly with it in,take the exhaust to a garage or local handyman all the advice given hinges on the ring being gone.set the mixture screw to 2 1/2 turns out.no need to upjet.

Geoff

[cabrinha]

Ok. Saturday morning I will dremel it.
As far as the carburetor I think that maybe it is time for a new one. It has never been serviced, parts (seals and orings) are not available here anymore and maybe, after about 50000km, it has been worn. But I see that in these chinese carbs there is no vacuum line (for the fuel cock) and no oil line.

[aeroxbud]

Scooter attack do a MotoForce one for €45 www.scooter-attack.com/motoforce-carburetor-phva-17-5mm-carburateur-motoforce-phva-175-39.html
Not the best quality, but way better than a cheap eBay carb

[cabrinha]

Removed the exhaust restrictor today.

Also I removed the spark plug after about 50km of normal use.

Dec 5, 2018 20:31:54 GMT -5 aeroxbud said:

Scooter attack do a MotoForce one for €45 www.scooter-attack.com/motoforce-carburetor-phva-17-5mm-carburateur-motoforce-phva-175-39.html
Not the best quality, but way better than a cheap eBay carb

I will search for a 17.5 carb with auto choke and also oil and vacuum port.

[cabrinha]

I bought a new carb. It is a 17mm one (thats what the box says).

Jog is now running better than ever before
BUT
Mixture screw does not make any difference. The same thing happens even if I screw it all the way in or all the way out.


After some kms the plug looks like this.