Fuel system problem

[fstephens]

I have a couple of old Homelites a 14" XL and a 16".
I'm working on the XL now and it runs OK for a minute or so but then seems to starve out and quit. I took the carb off and cleaned it w/gas, blew it out with air. Seems OK, diaphram & gaskets look good. I am not sure of why there are 2 small hoses going to the gas tank (and oil tank too). Does one pressurize the tank and one feed fuel? Or is it done by suction? What setting should I start with on the 2 mixture screws, 1 turn out?
Also cleaned the air filter and checked the muffler/spark arrestor screen, spark plug too.
Any ideas appreciated!
Thanks.

 

[retoocs555]

Set the carb jets to one turn out from lightly seated for both H and L. That will give you a good starting point.

Replace your fuel filter. Also replace the gaskets and diaphram in the carb. A diaphram can look fine but in reality be slightly hardened.

Two holes in the fuel tank. One is for the tank vent which should have a little red, rubber thingy in it called a duckbill which acts as a one way valve to relieve tank pressure. The other is for your fuel line, while you have everything apart I would replace the fuel line as well.

Oh, and before you go to all this trouble you should check your compression to make sure you aren't working on a lost cause.

 

[RED-85-Z51]

If it starts good, and only runs for a little bit then it probably isnt a carb problem, but it could be an adjustment problem.

Now, my carb on my XL only has 1 adjusting needle, on mine, I would try turning it 1/4 turn OUT.

If I had 2 needles, I would turn the HIGH (H) needle out 1/4 Turn, and the L needle out 1/8 turn, and see how that goes.

If the fuel line is stiff, and looks dark and nasty, Id go ahead and replace it.

 

[retoocs555]

If I had 2 needles, I would turn the HIGH (H) needle out 1/4 Turn, and the L needle out 1/8 turn, and see how that goes.

Do you have saws that run set like that? 1/4 turn from lightly seated is way lean. Factory pre-set is standard 1 turn out on 99.5% of chainsaw carbs, usually you have to adjust it some but that's a good starting point. I could copy pages out of my Tillotson, Walbro, or ZAMA binders that would all say start at one turn out, sometimes they even say 1-1/4 on the low speed jet. Where have you read 1/4 to 1/8 turn?

The described symptoms could be any number of carb/fuel related problems: plugged filter, plugged inlet screen, leaky fuel line, gummed up fuel line, stiff diaphram, mal-adjusted metering, carb re-assembled with the gaskets in the wrong places.

I assumed that since it was mentioned that he had two mixture screws he must have an XL with both adjustable jets. If it is set up with adjustable H and L there should be 3 screws on the carb. The H and L next to eachother and a little over to the side will be the idle speed screw.

 

[fstephens]

Yes, it has 2 metering screw and one idle speed screw. It says it's an XL, but I don't know how old it is. A friend gave it to me. There is no inlet screen, other than the plastic holder for the foam air filter. Where is the fuel filter located? In the tank at the end of the hose? If so how do I get it out? As I mentioned this has 2 lines going to the tank- I don't see the "duckbill". There was a crack in the end of one of the line, so I cut off the end and reattached it. I think the other one is starting to crack too, in a place where I can't do that, but I didn't have any fuel lines this small. Are they widely available? I'll also check if they are plugged.

How can I tell if the diaphram is too stiff? Seemed OK to me. I tried adjusting the metering screw from about 1 turn out (good guess huh?), but I don't think that is the whole problem. It runs good while it runs, and cuts good too. I think RED-85-Z51 meant to change the adjustments by that amount, not use that as a starting point. I am pretty sure I put the gaskets in the right place. I have rebuilt lots of carbs, a hell of allot more complicated than this one. I don't have a shop manual or diagram though. Admittedly, I don't have too much experience with chain saws, despite having my picture in a dealer magazine holding one about 50 years ago

Thanks for the tips guys.