3120 carb settings

[kinderscout]

After running the 3120 today with new engine I found it to be running lean on top end.

which carb scew needs to be opened up?

[Will Heal]

The H screw

[Darrin Turnbull]

[ame]

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[adw]

The 3120 does not have a H screw, it has a fixed main jet, the no. will be on it, there are some bigger jets to go in it, there is a L screw and idle screw.

[spudulike]

If it is over revving I would suggest that you have an air leak, the "New Engine" suggests a new top end and would assume the old one seized or was damaged.

 

The machine should really be pressure and vacuum checked then have a tach put on it but they rev pretty low so it is usually pretty obvious if it is running fast.

 

ADW is correct about the carb having a fixed high speed jet and be aware that the crank has an Internal hole and valve that lets a little air out to the needle bearing to lubricate it and has a one way valve in it so if you do pressure check it, make sure it holds vacuum and you need to plug it on the pressure test.

 

If it has a bad air leak, you will find your L screw setting will have to be set more than one turn out and the saw will hang on to revs when the throttle is released also in bad cases, you may find the idle screw cant bring down the idle speed.

[kinderscout]

The old engine had always run quite hot for my liking it eventually gave up two weeks ago.

After three years of milling, its performance had gradually got poorer and poorer.

So complete top end replacement fitted,head,piston exhaust.

the new set up I can't start with the decompression valve in starts ok and runs lovely,But still gets to hot running full out.

So had a look at the carb settings and found the L screw to be only a quarter of a turn open from new.

Now I have reset it to 3/4 of Turn open.

which going by my model engines would be more realistic ?

[Sawchip]

The old engine had always run quite hot for my liking it eventually gave up two weeks ago.

After three years of milling, its performance had gradually got poorer and poorer.

So complete top end replacement fitted,head,piston exhaust.

the new set up I can't start with the decompression valve in starts ok and runs lovely,But still gets to hot running full out.

So had a look at the carb settings and found the L screw to be only a quarter of a turn open from new.

Now I have reset it to 3/4 of Turn open.

which going by my model engines would be more realistic ?

In case you have not got the manual ..

[woody paul]

Did you get the carb cleaned will you rebuilt it .

[kinderscout]

Thank you spud,saw chip, sorted and running seems so far to be OK not as warm on the hand.

[spudulike]

Thank you spud,saw chip, sorted and running seems so far to be OK not as warm on the hand.

 

One turn out is normal, you can use a laser thermal gun on the top end which will give you a good indication of how hot the saw is running. I have no data to help you on this though.