50cc 2 stroke minarelli impossible that it won't start. By nobodyspecial (Read 6,006 times)

[nobodyspecial]

I have a 2 stroke 50cc VMoto Monza (same engine as the TNG Venice and Keeway Fact I believe) For a while now I have had a faulty vacuum hose / fuel tap which intermittently cut the supply to the carburettor and caused the bike to stop. I had replaced the carby at one stage and have now noticed the metal nozzle part of the carb that the vacuum hose connects to is blanked off. It is not possible for an air vacuum to be created. I suspect I may have a wrong carb now (it has Mikuni written on it) and came off another Monza, does someone know about this?  Should there be a hole from the vacuum hose through the body to the inside of the carb?

Now the impossible part. After the last stoppage the bike refuses to start, pop, ignite, show any sign of life at all. I am getting a very good spark from two different plugs I have tried and have sprayed ether "Start ya bastard" down the plug hole and there is no sign of this igniting. That is the impossible bit I can't work out, big spark from the plug, Start ya *** in the compression chamber, no go, not a whimper, plug is dry when I remove it also so even with fuel in the carb nothing is happening. Any ideas? Please help, this is doing my head in!!!

Surely spark plus ether equals some sort of bang.

[trashtruck12172]

are you testing for spark on the motor or the frame? testing for spark on the frame isn't good enough as there may a ground issue between the frame and motor so you get spark while at the frame but not in the motor. now for the basics, is the kill switch on?

[nobodyspecial]

Kill switch was on, spark was tested against the exhaust near the barrel.

[Alleyoop]

You said the plug is dry which means one of two things NO FUEL is being drawn into the motor or no spark. And yes if your using a PETCOCK it needs vacuum and it gets it from the motor on every down stroke of the piston.
So I would check your VACUUM.
Take the fuel hose off the carb and stick it in a cup and crank the motor over and fuel should stream into the cup.
Alleyoop

[nobodyspecial]

I fitted a new fuel tap and by sucking and blowing on the vacuum tube I can hear the diaphragm opening and closing. I have sucked on the vacuum tube and fuel flows from the fuel line into the carb and tried to start it at the same time. I don't know why it won't even fire when I have sprayed the ether down the plug hole.

[Alleyoop]

I do not want you to create the suction I WANT THE MOTOR to create the suction. So take the fuel hose off the carb and stick it in a cup and just crank the motor over and then see if fuel flows.

[trashtruck12172]

their should be a vacuum line connected to the carb or the intake. without vacuum, the fuel diaphragm doesn't operate and the carb doesn't get fuel.

[nobodyspecial]

Mar 13, 2016 19:19:23 GMT -6 Alleyoop said:

I do not want you to create the suction I WANT THE MOTOR to create the suction. So take the fuel hose off the carb and stick it in a cup and just crank the motor over and then see if fuel flows.

Fuel does not flow from the fuel line when I try and crank it over. (see first post re vacuum line on carb blocked off)

[nobodyspecial]

Mar 13, 2016 19:26:21 GMT -6 trashtruck12172 said:

their should be a vacuum line connected to the carb or the intake. without vacuum, the fuel diaphragm doesn't operate and the carb doesn't get fuel.

There is one connected to the carb but there is no hole in the carb for a vacuum for the line to suck (see first post)

[nobodyspecial]

see pic

My finger is on where the vacuum hose connects.  This is blanked off. You cannot say poke a piece of wire through it to the inside of the carb. It is just a post that the hose fits on with no hole in it.

[Alleyoop]

Well that is your problem on the INTAKE MANIFOLD and OR ON THE CARB(depending on what type of carb is on there) there should be a connector for a VACUUM HOSE to go on to OPERATE vacuum needed parts like the PETCOCK.

So take pictures of the carb area and hoses and the INTAKE MANIFOLD(that is the part that connects to the head of the motor then the carb connects to it).

Is there a connector on the INTAKE MANIFOLD?

If that carb has the vacuum port blocked then you must have bought the wrong carb.

[Alleyoop]

Now IF YOUR FUEL TANK is above the carb you can just go from the tank to the fuel filter to the carb(NO PETCOCK).
But make sure the fuel hose from the tank all the way to the carb is downhill NO UPS AND DOWNs in the line and not lower than the carb.
Alleyoop

[nobodyspecial]

I will do that (pics) but in its present form, with that carb, I have been able to start it previously and ride for 15 minutes or so. Now it won't fire, even artificially (ether)...

[Alleyoop]

I can see it maybe started once when the carb bowl had fuel, but with no vacuum to operate the petcock once the carb bowl was empty then no more fuel no more fire.

You have to understand the petcock needs VACUUM so if no VACUUM no fuel period.

[nobodyspecial]