Primer bulb wont prime!

[Rich2484]

So is there a blockage in the pipe from tank to bulb??

 

Other than that blockage in carb.

[18 stoner]

So is there a blockage in the pipe from tank to bulb??

 

Other than that blockage in carb.

 

As I say Rich, the pipes are clear.

 

I think you are possibly confusing the way this carb works. The fuel is drawn from the tank by the bulb, but it passes through the carb before reaching the bulb. There is a return pipe from bulb back to tank with a breather off it.

 

There is pipework at either side of the carb, all these are clear. They were all fitted new by the workshop, I just checked over them all again.

 

As said earlier, the carb is removed and has an inlet and outlet fuel point. Vacuum or pressure will not free these and suspect this is where the blockage is.

[WorcsWuss]

Presumably you've tried aerosol carb cleaner and lots of compressed air through a completely dismantled carb...?

Is it a Zama or Walbro carb on the 192 Pete...?

[18 stoner]

Not got that far yet Simon. I have some cleaner, but think a total carb strip will be tomorrows job.

 

I was hoping the 2 days on the sonic cleaner and fitting the kit at the workshop sahould have cured any need for carb cleaner, but its looking more like I need to follow their footsteps to find out.

 

Oh, and it is a Zama s103

[WorcsWuss]

I don't know the Zama carb, but when I fitted the metering diaphragm & gasket back to front in a Walbro recently the whole thing was dry, there was no evidence of any fuel getting into the carb.... If the primer can't pull ANYTHING through at all, could it be something as simple as one side of the carb in back to front...?

[18 stoner]

Now that is a thought

 

Cheers bud, will give me something else to look out for. I'll report back later

[GardenKit]

The primer bulb, when pressed, pushes fuel past a one way valve through the return pipe to the tank. The bulb then reforms, causing a vacuum which pulls fuel from the metering chamber and at the same time pulling the metering diaphragm down allowing more fuel to enter the chamber. This fuel is pushed from the tank by atmospheric pressure, via the pump diaphragm (impulse, not primer) and the inlet valve.

 

For the primer not to work, one or more of several reasons may exist.

1 the inlet valve is not opening. could be due to incorrectly assembled (or set) metering diaphragm and needle

 

2 vacuum is being lost between inlet valve and tank. this could be due to a leaking pump membrane and gasket. This in turn could be due to damaged membranes, or damage to those little ridges on the back of the pump cover plate (the one with one hole) A blocked gauze filter could also be responsible.

 

Its been to a dealer, so everything should be clean and assembled properly, so my money is on the damaged ridges. If this is the case a new carb may be needed, but a new (or good ) plate would be a better bet.

 

Edit, oh, there is also a check valve in the metering chamber, this would prevent vacuum build up if it is stuck open allowing air in rather than fuel.

Edited November 23, 2012 by GardenKit

[18 stoner]

Many thanks for that mate, I've been having a strip down yesterday.

 

What I have found is, the pipe that comes from the carb to the bulb seems to be blocked.(the brass coloured one in the carb)

 

The carb has spent a very long time in the sonic cleaner already and seems to not have cleared it, so I'd assume we're looking at a new carb?

 

If it does come to a new carb, is there any way of finding another alternative to the one fitted? Perhaps on another machine with the same carb, etc, etc? Reason I wonder is, the £100 +vat I've been quoted is hardly a viable option as the dealer says the "correct" carb would need to come from the US

Edited November 25, 2012 by 18 stoner

[GardenKit]

Many thanks for that mate, I've been having a strip down yesterday.

 

What I have found is, the pipe that comes from the carb to the bulb seems to be blocked.(the brass coloured one in the carb)

 

The carb has spent a very long time in the sonic cleaner already and seems to not have cleared it, so I'd assume we're looking at a new carb?

 

If it does come to a new carb, is there any way of finding another alternative to the one fitted? Perhaps on another machine with the same carb, etc, etc? Reason I wonder is, the £100 +vat I've been quoted is hardly a viable option as the dealer says the "correct" carb would need to come from the US

To be honest, the saw should run without the primer, that just makes it easier to start.

Without it you need to pull it over a few more times so that the impulse operated pump can pump some fuel up.

Some carbs I buy have a little cap to block the brass pipe when fitted to a machine without a primer, which is what yours is now.

I will check tomorrow to see if there is an alternative and let you know.

[Eddy_t]

Could you not try to break up the blockage with a needle or fine pointed tool?