038 mag only starts on half choke **full choke floods it**

[Adam08ski]

I have adjusted the metering lever to spec, still no joy, still floods on full choke.

But it still starts fine if you miss the full choke procedure and works perfectly on all other accounts.

Any suggestions as this is starting to bug me, as it is just not right..

 

[HarleyT]

Have you put in a new needle and polished the seat?

 

[HarleyT]

By "adjusted", does that mean that now it is set correctly?

 

[Adam08ski]

Have you put in a new needle and polished the seat?

no, took it all apart, looks brand new, low hour bing carb

By "adjusted", does that mean that now it is set correctly?

according to the manual and set it with feeler guages and a straight edge

 

[HarleyT]

Does it leak? Have you inspected the needle?

 

[Adam08ski]

Does it leak? Have you inspected the needle?

no but seeing as you are pointing all issues towards the needle and lever I think I will take it apart and check it all thoroughly. I cannot find an OEM carb kit, so ideally wanna keep all the old parts, i am assuming i can clean it all up and polish the needle etc?

 

[HarleyT]

The needle looks to be the standard long needle, as Stihl shows it as #1110 121 5100,

 

[Adam08ski]

The needle looks to be the standard long needle, as Stihl shows it as #1110 121 5100,

I have a new spare needle from a Zama C3-S148, do you know if these are the same?

 

[alexcagle]

Have you put in a new needle and polished the seat?

*
I've never had any luck fixing a seat with a problem.
I've never ran across any old timey proceedure on "polishing" a seat, how do You do it?

 

[alexcagle]

I have a new spare needle from a Zama C3-S148, do you know if these are the same?

*
Are you pressure testing the carb to about 8 psi?
If it holds, bump it lightly on your work bench ans see if it leaks.
If it does, try lowering the needle fulcrum slightly.
Some diaphragms and springs can weaken or change slightly over time.
It could also just be that your diaphragm is getting "crinkley"- where it moves at an angle, or doesn't move in a linear motion.
If it passes that test, while it's still under pressure, try placing your palm flat on the back side of the carb, and pull light vacuum with your mouth on the other end. Under light draws of vacuum, try to make the needle drop 3psi and stop. If it bleeds on down, then adjust your needle fulcrum lower slightly, then try the test again.
This is not in any manual, and make sure there isn't any fuel still in the carb. lol

 

[Ozhoo]

I'll add to what alex said and to test it in a cup of water. You'll see the smallest of leaks.

 

[HarleyT]

I have used a q-tip and some fine abraisive. Probably has just removed some encrusted deposits..


An item search of the part number for the needle lists some Zamas too.

 

[alexcagle]

I've also seen needle fulcrum pins that can get slight rust pitting on them that can cause the fulcrum to stick or have a catch in it.

 

[alexcagle]

I have used a q-tip and some fine abraisive. Probably has just removed some encrusted deposits.

*
Ok.
What fine abrasive do you recommend?
This is interesting because I never had any luck fixing a seat in the past, and I tried many things.
Sure would be nice to save some of those $60-$120 carbs in my junk bad carb bin.

 

[HarleyT]

I have used baking soda and valve compound before.

 

[Adam08ski]

*
Are you pressure testing the carb to about 8 psi?
If it holds, bump it lightly on your work bench ans see if it leaks.
If it does, try lowering the needle fulcrum slightly.
Some diaphragms and springs can weaken or change slightly over time.
It could also just be that your diaphragm is getting "crinkley"- where it moves at an angle, or doesn't move in a linear motion.
If it passes that test, while it's still under pressure, try placing your palm flat on the back side of the carb, and pull light vacuum with your mouth on the other end. Under light draws of vacuum, try to make the needle drop 3psi and stop. If it bleeds on down, then adjust your needle fulcrum lower slightly, then try the test again.
This is not in any manual, and make sure there isn't any fuel still in the carb. lol

I am going to look at the diaphragm, I did notice a slight wavy effect on the diaphragm material. Think I will also find a decent carb kit for it in the long run.

 

[Adam08ski]

Have another thought, read a thread some time back that over tightening the air filer to carb nuts can crush the filter outta shape slightly. I mean ever so slightly but thus altering the way the filter choke flap works, I might remove the one half of the filter and see what happens then with the nuts tightened to just the one half..

 

[Chainsaw Jim]

A good method I've found of polishing metering seats is to use a round toothpick whittled down to match the pin and chuck it up in a dremel. Polish with wd-40.
I drill out metering seats all the time and bevel them perfectly. No leaking. They're even fixable if needed, but not easy.

The flooding problem is likely a low pop-off pressure which means the metering lever spring is too weak. When the choke primes it the weaker spring allows a gulp instead of a tiny sip. Slightly stretch it to make it about .025" longer, and be very careful or you'll ruin it.

 

[Adam08ski]

The flooding problem is likely a low pop-off pressure which means the metering lever spring is too weak. When the choke primes it the weaker spring allows a gulp instead of a tiny sip. Slightly stretch it and be very careful or you'll ruin it.

When I get my 362xp fixed up as a stop gap replacement I will start to disassemble this bing carb to get to the bottom of the problem. I have found an OEM carb kit. Hopefully it will fix all my problems. Until then it is usable just annoying as I know in cold weather it will probably give me problems starting it.

 

[a. palmer jr.]

We've gone through this before, the problem on most of the Magnums, including mine is the air filter. The choke in the air filter sticks shut unless it's set perfect. I have to seal mine against the carb and keep the mounting bolts slightly loose to prevent the filter from becoming deformed, making the choke stick. Loosen your mounting bolts on the choke and see if it improves.