Homelite chainsaw woes

[Matt1995]

Hi everyone,
I've been working on a Homelite 150 chainsaw for the last week and I've all but given up on it. I fixed a few issues with it and now I have good spark, good compression, and fuel in the carburetor. I cleaned the carburetor and have fuel on both ends which means fuel is pumping. Replaced the fuel line and filter. I can get the saw to start on starting fluid but it will not run on its own. If I prime the saw with fuel it'll run but won't stay running. Every time I've taken the carburetor off I have fuel in it. Can someone please give me some guidance on this issue? What am I missing here?

 

[Okie]

From your description we know that the engine is not sucking fuel from the carb.

Have you pressure tested the carb?
What is the compression on the engine?
Have you installed another correct type spark plug?

 

[Matt1995]

From your description we know that the engine is not sucking fuel from the carb.

Have you pressure tested the carb?
What is the compression on the engine?
Have you installed another correct type spark plug?

I have not pressure tested the carb. Is there a way to do this without a vacuum gage?

Compression is at 135 psi

New spark plug and boot

 

[buzz sawyer]

You need something to apply pressure to the fuel inlet. Some vac testers have this function. You can make your own with a bulb from a blood pressure tester, some vac hose and a low-pressure gauge. Since you are getting fuel into the carb and it is not flooding, I don't think that is your problem. Could be an internal passage clogged.

What are the H and L screw settings? Can you remove the two screws and shoot carb cleaner into them - and see it come out into the carb throat?

Please don't use starting fluid - it has no lube and can damage the saw.

 

[heimannm]

I don't know where the carburetor gets it impulse signal to drive the fuel pump on that model but I suspect it is through the carburetor mounting flange. Make sure your gasket(s) have holes in the proper location and are correctly lined up so the impulse signal can get to the fuel pump section.

Also, recheck the height of your metering needle and make sure fuel can pass when the lever is depressed. It could be a simple as a sticking metering needle.

Mark

 

[Old2stroke]

Since it runs when fuel is squirted in, compression and spark timing must be OK and it sounds like it's just a problem with fuel delivery and you need a better diagnostic approach to find the fault. Start with a dry sparkplug, pull the engine over 6 times with the choke open and the throttle set to fast idle then pull the plug and check that is still dry and you will know you don't have a flooded engine. Next, close the choke and verify that it is completely closed, set the throttle to fast idle and pull it over a number of times again. If it doesn't fire at all, pull the plug again and see if it's still dry. If it is dry, there is something wrong with the carb, faulty fuel line connection, sticking inlet valve, stiff main diaphragm, faulty pump diaphragm, nozzle check valve stuck closed, blocked idle and transfer ports. For starting it's all about the choke being closed and engine vacuum pulling fuel into the carb. If it starts and runs briefly and stops, it's because the fuel pump is not working, missing or weak impulse from the crankcase, faulty pump diaphragm or gasket on the wrong side. If the plug comes out wet and it never fired we have other problems. Are you sure the throttle is being held partly open when set to fast idle? Most saws will not start cold with the throttle closed. Are both mixture screws set to 11/2 turns out?
No idea what you mean when you say the carb is working when you have fuel at "both" ends.

 

[Matt1995]

Since it runs when fuel is squirted in, compression and spark timing must be OK and it sounds like it's just a problem with fuel delivery and you need a better diagnostic approach to find the fault. Start with a dry sparkplug, pull the engine over 6 times with the choke open and the throttle set to fast idle then pull the plug and check that is still dry and you will know you don't have a flooded engine. Next, close the choke and verify that it is completely closed, set the throttle to fast idle and pull it over a number of times again. If it doesn't fire at all, pull the plug again and see if it's still dry. If it is dry, there is something wrong with the carb, faulty fuel line connection, sticking inlet valve, stiff main diaphragm, faulty pump diaphragm, nozzle check valve stuck closed, blocked idle and transfer ports. For starting it's all about the choke being closed and engine vacuum pulling fuel into the carb. If it starts and runs briefly and stops, it's because the fuel pump is not working, missing or weak impulse from the crankcase, faulty pump diaphragm or gasket on the wrong side. If the plug comes out wet and it never fired we have other problems. Are you sure the throttle is being held partly open when set to fast idle? Most saws will not start cold with the throttle closed. Are both mixture screws set to 11/2 turns out?
No idea what you mean when you say the carb is working when you have fuel at "both" ends.

So the carburetor has fuel on "both ends" because the fuel comes in one side and passes through the round screen which on the opposite side is the needle. Both ends have plenty of fuel in them. I checked the height of the metering valve with the walbro tool and it's set perfect. I know the carb is getting vacuum because it's allowing the needle to open and close properly, it's not flooding the engine. Both screws are turned out 1 1/4 - 1 1/2 turns each time I put it back together. I can pull on the cord forever with no fire but with a shot of fluid it fires up and dies. I just pulled both screws out and spayed wd40 in them and watched fuel come out inside the carburetor like it should, so I am stumped on this issue. I have the throttle lock on which holds the butterfly open slightly but even holding the throttle wide open when trying to start it makes no difference. It's like the fuel isn't getting from the carburetor into the cylinder, but from what I can see, the carb is clear.

I will begin testing as you described.

 

[Okie]

Look around for another carb.
I did not say your carb is bad, I'm saying add another carb as a test.
Leon or you tube has several videos of how to test a carb using a blood pressure bulb.

 

[OnlyHomelites]

I've run into several of these saws with this type of problem and found that the distortion on the intake manifold creates a vacuum leak. Over decades, the pressure of the carburetor compresses and alters the shape of the intake manifold where the carb should be sealing. I've been able to trim some of the excess uncompressed material and then use 400 grit wet/dry sandpaper to smooth the sealing surface. I've never tried it, but as a backup plan I've thought about using motoseal to create a new sealing surface...obvious risk there is plugging up the impulse hole in the carb.