HELP! Zama c3m flooding

[Shane¹]

I have multiple Zama c3m twin jets off dolmar 7900s and can't seem to get them to work no matter what I do they flood out. Have tried polishing needle seat put new kits in them Welch plugs seem good. Any suggestions?

 

[huskihl]

Polishing the seat with toothpaste or valve grinding compound on a Q-tip shank sharpened on an angle, and stretching out the spring has always worked for me

 

[Shane¹]

Polishing the seat with toothpaste or valve grinding compound on a Q-tip shank sharpened on an angle, and stretching out the spring has always worked for me

I tried toothpaste already but maybe I didn't get it clean enough I will give it another go

 

[Poleman]

Increase pop off pressure. As that’s an issue with those carbs.

 

[EFSM]

If you are hard up enough, you can press the seat out through the filter chamber and replace it with a known good seat from a functioning cheaper/spare carburetor. You need to remember to measure the placement of the seat from the pump surface because they don't "bottom out" very well.

 

[Shane¹]

I went through both again this morning and polished seat on one. Found one was leaking through impulse so cleaned that side and put different kit in will hopefully try again tonight

 

[Coupe]

Check your meter lever hight as well

 

[Shane¹]

Would a bad nozzle on these cause extreme flooding. Needles seems to be holding pressure. Anyone know where to get replacement nozzles?

 

[RCBS]

I been chasing this as well. Tried replacement spring ordered from Makita, no joy. Read up and found a walbro spring that was recommended to 'cure' the issue. Have not tried the Walbro spring as of yet. Will likely polish seat when I switch again.

I went through both again this morning and polished seat on one. Found one was leaking through impulse so cleaned that side and put different kit in will hopefully try again tonight

Dumping fuel via impulse line?

 

[Shane¹]

Both of them are just way over fueling needles seems to hold pressure as good as any other carb I have mess with but as soon as you start it it starts to over fuel and if you keep it revved it is better but eventually it just starts spraying fuel out of the intake. I have rebuilt quite a few carbs and never had this issue I am thinking the main nozzle is bad

 

[EFSM]

If the main nozzle check valve is bad, it will starve for fuel at idle, not overfuel.

 

[Shane¹]

If the main nozzle check valve is bad, it will starve for fuel at idle, not overfuel.

Good to know I will have to get back in to them when I have more time

 

[huskihl]

Would a bad nozzle on these cause extreme flooding. Needles seems to be holding pressure. Anyone know where to get replacement nozzles?

It looks like they hold, but they seep, which is why adding a little bit of spring pressure and polishing the seat can work. If you were to come back an hour later, you would have less pressure

 

[Shane¹]

It looks like they hold, but they seep, which is why adding a little bit of spring pressure and polishing the seat can work. If you were to come back an hour later, you would have less pressure

I am just glad it shouldn't be the nozzle I will keep messing with the needle I am determined to get it now lol

 

[Shane¹]

What should I try to get pop off pressure to on these carbs?

 

[Shane¹]

Had to improvise to get some pressure to these things. Messed with one for a long time tried valve grinding compound this time, stretched the spring even more etc etc. Couldn't get it to consistently hold pressure. Grabbed a spring for a tillotson hs put it in held pressure for 2 hours put it on a 6400 ran perfectly. Thanks for everyone for setting me straight with needle and spring pressure I will use my custom pressure tester to test carbs from now on. Lesson learned

 

[EFSM]

These are expensive but nice.

 

[Shane¹]

What do you guys normally go to psi for pressure testing carbs and how long do you let it hold for before you consider it ok?

 

[EFSM]

7-10 psi. Duckbill tank vents pressurize to about 7 before bleeding off. I don't like to see any leakage at all at that pressure, but sometimes you can get by with a little. It depends on the capacity of your tester and length of hose as to how soon leakage will register on your gauge, so I won't venture to guess what you could get by with on your setup.

 

[Shane¹]

I found a small gasket leak on another one with a different tester. It has been holding 10psi for a few hours now I would say it's probably ok now