Discontinued zama carburetor c1u-m35a mcculloch blower

Be careful doing that and make sure you get the right tube.
The pick up line is heavy walled and the return line is generally thin walled but that is not so important.
The tube must be a tight fit in the tank, if you can pull it through easily it is too thin.
Use the butt end of drill bits to measure the diameter, it steps up in 1/32" incriments.
And very important.
make sure you fit Tygon tubing ( or equivalent ) bought from a real reputable mower parts suppler.
I get emails daily from internet suppliers trying to sell me "PVC fuel line in popular see through yellow colour".
The genuine tube is very expensive and charged by the inch.
I pay around $ 10 to $ 20 a foot ( Aus) wholesale for genuine TYGON tubing
Stens have an equivalent but it is only 30% cheaper.

We have had a few people burned because the tubing on their cheap store branded trimmers leaked fuel all over it and in some cases the operator and then ignited.

bertsmobile1 said:

Also remember a hand held fuel tank runs under pressure.
The pump does not draw the fuel into the carb from the tank, the pressure from the returned fuel forces the fuel to the pump, much like the old outboards where you had to keep pumping air into the tank.
Now here is the rub.
the fuel cap usually has a one way valve ( air in ) and the tank usually has a vent to let excess pressure out.
If the tank vent is not working the tank will over pressurize and force too much fuel into the carb

Click to expand...

Not to be antagonistic, but there are several factors that prevent this theory of operation from being possible.

1. To begin with, it's not possible for most older fuel systems to operate on pressure from the return line, because the majority of older handhelds have no fuel return line.
2. On units that do have a return line, the return line is part of the air purge/primer bulb circuit, and is only used to return air and fuel to the tank when the engine is being primed.
3. There is no reason to have both an intake vent and a vent to release excess pressure. If the fuel tank runs under pressure, why does it need a one way valve to let air in?
4. The majority of handhelds have no pressure relief vent anyway. There's only one vent, and it's a one way vent that allows air in to take the place of the fuel used by the engine. The only way that the tank can over pressurize is if the fuel gets heated and expands, which will pop off the needle valve and over pressurize the carb.

Theory of operation, from Zama: https://www.zamacarb.com/page/carburetor-systems-operations

bertsmobile1 said:

Be careful doing that and make sure you get the right tube.
The pick up line is heavy walled and the return line is generally thin walled but that is not so important.
The tube must be a tight fit in the tank, if you can pull it through easily it is too thin.
Use the butt end of drill bits to measure the diameter, it steps up in 1/32" incriments.
And very important.
make sure you fit Tygon tubing ( or equivalent ) bought from a real reputable mower parts suppler.
I get emails daily from internet suppliers trying to sell me "PVC fuel line in popular see through yellow colour".
The genuine tube is very expensive and charged by the inch.
I pay around $ 10 to $ 20 a foot ( Aus) wholesale for genuine TYGON tubing
Stens have an equivalent but it is only 30% cheaper.

We have had a few people burned because the tubing on their cheap store branded trimmers leaked fuel all over it and in some cases the operator and then ignited.

Click to expand...

$10 per foot is outrageous. I use Oregon brand fuel line, and it costs me about $20 for a 50 foot roll...

primerbulb120 said:

$10 per foot is outrageous. I use Oregon brand fuel line, and it costs me about $20 for a 50 foot roll...

Click to expand...

St Germain, the makes do not sell Tygon in 50' rolls.
They market 5' rolls in plastic bag
10' rolls in dispenser carton
20' rolls in dispenser cartons
200' rolls on spindle

$ 20 for a 50' roll sounds more like standard 1/4" butyl lined, single cotton insertion neoprene tube as used on mowers , not hand helds.

Oregon sells Tygon fuel line. They have their own brand, and premium Tygon...

primerbulb120 said:

Not to be antagonistic, but there are several factors that prevent this theory of operation from being possible.

1. To begin with, it's not possible for most older fuel systems to operate on pressure from the return line, because the majority of older handhelds have no fuel return line.
2. On units that do have a return line, the return line is part of the air purge/primer bulb circuit, and is only used to return air and fuel to the tank when the engine is being primed.
3. There is no reason to have both an intake vent and a vent to release excess pressure. If the fuel tank runs under pressure, why does it need a one way valve to let air in?
4. The majority of handhelds have no pressure relief vent anyway. There's only one vent, and it's a one way vent that allows air in to take the place of the fuel used by the engine. The only way that the tank can over pressurize is if the fuel gets heated and expands, which will pop off the needle valve and over pressurize the carb.

Theory of operation, from Zama: https://www.zamacarb.com/page/carburetor-systems-operations

Click to expand...

Next time your get a MODERN hand held into your shop, and in preference one fitted with a CQ Zama, run it for 5 minutes then open the fuel cap.
You will find it is pressureised and should be in the order of 5 to 10 psi.
Old carbs had a bigger and stronger pump , a bigger metering chamber and 2 internal check valves which you used to access via the welch plugs that are no longer fitted.
If you go & check the 2 stroke diagnosis videos that Joe Pace has uploaded you will see that Husqvarna fuel tanks are tested under both pressure & vacuum .
A very large number of fuel caps used by Husqvarna have 2 valves in them, an inlet & an outlet.
The Echo fuel tank vent is an exhaust vent and nearly all Stihls have an inlet in the cap and an outlet from the tank.

If you are still in doubt, pull the return line out of a chain saw and run a long line down to a catch bottle, stick a plug in the return hole in the tank.
The saw will start & run, but it will be very sluggish under acceleration and most will not get to full speed.
Trimmers are not such a problem because they are generally used right way up but chain saws & blowers get used al all sorts of funny angles so really need the fuel pressure.

I have just done a pile of cheap imported chain saws that use PVC fuel tube.
Once they get a few ears old the fuel lines shrink & become loose in the tanks.
In that condition they will not even start.
If you want to check this search Ross brand chainsaws and read the customer comments.
I have fixed dozens of these cause the local hardwear chain flogged them off really cheap.
All that needs to be done is to fit new fuel lines that are airtight.

bertsmobile1 said:

Did you put a kit through the carb ?
Flooding can be caused by a perforated metering diaphragm. the metering diaphragm in the wrong place or upside down.
The metering diaphragm set to the wrong height, a loose or missing diaphragm spring a badly worn damaged or dirty needle or needle jet.

How much do you actually know about cube carbs ?

And yes you get a current carb and swap the throttle & choke .

Click to expand...

I am having the same problem as the original poster. I installed a new gasket kit and still having a flooding issue. What would be the correct current carb I can use to swap.

intimidator said:

I am having the same problem as the original poster. I installed a new gasket kit and still having a flooding issue. What would be the correct current carb I can use to swap.

Click to expand...

intimidator ... NOT trying to be rude, but you are HI-Jacking this fellas thread, it becomes chaos when folks do that, you have folks trying to help 2 different people on 1 thread you needed to start a new thread , nuff said on that !..
the information you seek is posted in post #5 & #6 of this thread posting, go to this page, (below) and click on the items listed under parts and service, then SCROLL DOWN on that page and there's the info, if you can't do a little research of your own, take the machine to a reputable dealer, I'm not going to hold your hand and walk you through it, I've already went beyond what most other folks would do, as it is .

https://www.zamacarb.com/page/products

We do everything POSSIBLE :
The IMPOSSIBLE, takes a little longer :
MIRACLES are by appointment only :

intimidator said:

I am having the same problem as the original poster. I installed a new gasket kit and still having a flooding issue. What would be the correct current carb I can use to swap.

Click to expand...

If you can find a parts book look at what carb is fitted to it and any others in the same series.
Often makers will use several different carbs according to what was available at the time.

Failing that ask Zama about what carb will replace yours .
Usually the difference within a series ( C1Q M35) will only be the throttle & choke shafts which have different ends
They are easy to replace, but the screw holding the butterflys in place must be loktited or soldered in place cause they have a habit of being ingested.

Having said that flooding in a cube carb is nearly always due to either a blocked fuel return or tank vent causing over pressurization
or
Incorrect needle height / worn needle or spring.

To test the operation you really need both a vacuum meter & a pressure meter.

Finally are you sure that the engine is flooding ?
A dirty spark plug , faulty ignition module ( including HT lead & cap) , blocked vent , shoring ground wire or cut out switch can all produce symptoms very similar to flooding.
Cube carbs rarely fail by flooding.

Check out the videos mentioned in a previous post to the original poster.
You can look at Taryl Fixes all , although he does not do much on cube carbs & Donny Boy.
Any video that mentions about "Pop off Pressure " should be ignored .