Mac 10-10 spark “fuel” and compression but won’t start.

[MelonBoi1]

You could try this to help with diagnosis.  Get a clear bottle Put 2 stroke fuel in it about half full.  Mark fuel level with a sharpie.  Use a clear hose from the bottle to the carb inlet fitting.  Remove the spark plug.  Have ignition shut off so there is no spark.  Pull the engine over a few times and see if it pulls fuel through the clear hose.  This would determine if the saw is capable of pumping fuel.

I would do that but the fuel line is molded and I cannot put clear line on it.

[MelonBoi1]

Didn't see any mention of pressure and vac testing the crankcase after the rebuild, I read the seals were changed but that doesn't mean they're not leaking. Obviously a leak would cause a very weak or non excitant pulse to the fuel pump. 

Also if you used sealant on any of the gaskets make sure it hasn't plugged the pulse channel.  And as mentioned many times, the inlet gaskets and insulator need to be the correct ones and fitted correctly. 

Yes but the problem is I don't have a pressure test thing for that and I don't really have a way to cover up the cylinder ports with anything. I think I should focus on that right now, because I thing one of the seals I might have installed wrong.

[beenthere]

Melonboi
You have your work cut out for you, and we wish you the best finding where that problem lies. Good luck, and hope you take us along on the hunt. We are interested.

[doc henderson]

Maybe you understood this, but I think DHanson was suggesting a dry clear water bottle of fuel with some clear tube the same size as the fuel barb on the carb.  with switch off and plug removed so it is easy to crank but will not fire, see if the carb is working to pull fuel.  this is a test that you can do with simple materials.

[Al_Smith]

Al you weren't paying attention, we covered that. 

Well for Pete's sakes we've collectively covered just about anything that could be wrong with the danged thing .Of course there's the "new" carb which doesn't say it's a good one .I give up it's just got saw gremlins uncurable evidently .Maybe I'm just lucky,i have several 10 series Mccullochs from early right hand start 10-10's up to nearly the last model ever made plus including an 805 .They all run and quite well considering how old they are .Like I've touted --'tain't rocket science .

[MelonBoi1]

Maybe you understood this, but I think DHanson was suggesting a dry clear water bottle of fuel with some clear tube the same size as the fuel barb on the carb.  with switch off and plug removed so it is easy to crank but will not fire, see if the carb is working to pull fuel.  this is a test that you can do with simple materials.

I don't think it will help because we already went over the fact that when I took the carb apart after it wouldn't start, it was bone dry.

[doc henderson]

Okeedoke!

[DHansen]

Yes, your carb as stated was bone dry.  So now we try and figure out why.  Its a simple fuel system.  By doing the test I suggested you eliminate part of the fuel system and you determine if the pump is capable of pumping fuel.   If it is not pumping, either the carb is put together incorrectly, or the pulse line is obstructed.    I can link to a vacuum pressure test I did a while back.  Not hard to do.  

[chet]

Have you pulled the carb and double checked that the gasket isn't flipped yet? I would not proceed any further until you verify that!

[MelonBoi1]

I pulled it apart so yeah.

[doc henderson]

guys if the carb is off can you/should you hear or feel pressure/air from the port to the impulse channel with the carb off and pulling it over?  I have never tried it.  Melonboi, you did not want a video and asked for help.  It may just be your communication style, but all the suggestions seem to be dismissed.  It sounds like the saw has a minor hard to figure problem that can be fixed.  we are trying to isolate and diagnose the problem.  It has a fuel problem.  we are trying to narrow that down, so you are not shooting in the dark, and only have to check a few things.  We are happy to try and help you get that thing running.  

[Al_Smith]

In general conversation concerning carbs if you place the spacer gasket for the main disphragm out of order in assembly it will not pump .Carb out it's spacer then diaphragm then cover .I once had a brain fart and assembled one out of order but it was a Stihl not a McCulloch .That one about drove me bonkers .Got mad and punished the saw by parking  it on the shelf for a couple of months .After which with cooler heads prevailing the answer was as obvious as the south end of a north bound goat .Humbled by a carb ,things happen  

[chet]

I pulled it apart so yeah

So the rather more than obvious question is, what did you find? 

[MelonBoi1]

guys if the carb is off can you/should you hear or feel pressure/air from the port to the impulse channel with the carb off and pulling it over?  I have never tried it.  Melonboi, you did not want a video and asked for help.  It may just be your communication style, but all the suggestions seem to be dismissed.  It sounds like the saw has a minor hard to figure problem that can be fixed.  we are trying to isolate and diagnose the problem.  It has a fuel problem.  we are trying to narrow that down, so you are not shooting in the dark, and only have to check a few things.  We are happy to try and help you get that thing running. 

I am not dismissing anything 

[MelonBoi1]

I pulled it apart so yeah

So the rather more than obvious question is, what did you find?

Nothing worth noting besides the fact that it was bone dry, I can always use the other carb that I rebuilt but I don't think it will make a difference.

[MelonBoi1]

And people keep mentioning this but I know you can put the gasket on the wrong way and stuff. Every time I put it back together I always put it on the right way You can't mess it up because of the way it is designed.

[beenthere]

As "jack of all trades", you will find the problem and have it up and running in no time. Let us know when you find it. 

[Hilltop366]

So if the carb is assembled correctly and everything in there moves freely, the needle valve leaver is set right, the diaphragm is installed correctly on the leaver and the flaps on the pump side are not stuck to the carb, the fuel line and filter are good and the carb is still dry it only leaves the crankcase pulse to be faulty for the carb to be dry so with the carb gasket on correctly it leaves:

1) the pulse hole is blocked in the top piece or crank case, with carb removed put some heavy oil in it to see if the oil moves when pulling saw over. 

2) a leak in the crankcase or seals or in between the crankcase and the rear handle/ fuel tank assembly.

A pressure/vac tester tool will answer that, could improvise with a bicycle pump with a gauge so not to over pressurize it and a spark plug with centre removed and solder a metal tire valve to it.

[MelonBoi1]

As "jack of all trades", you will find the problem and have it up and running in no time. Let us know when you find it. 

Yeah well the reason I want help is because the Mac 10-10 is in my opinion a poorly designed saw and I wouldn't just make a thread like this just to document what is going on. The point is for me to ask for help.

[MelonBoi1]

So if the carb is assembled correctly and everything in there moves freely, the needle valve leaver is set right, the diaphragm is installed correctly on the leaver and the flaps on the pump side are not stuck to the carb, the fuel line and filter are good and the carb is still dry it only leaves the crankcase pulse to be faulty for the carb to be dry so with the carb gasket on correctly it leaves:

1) the pulse hole is blocked in the top piece or crank case, with carb removed put some heavy oil in it to see if the oil moves when pulling saw over.

2) a leak in the crankcase or seals or in between the crankcase and the rear handle/ fuel tank assembly.

A pressure/vac tester tool will answer that, could improvise with a bicycle pump with a gauge so not to over pressurize it and a spark plug with centre removed and solder a metal tire valve to it.

Yeah probably not. Too much DIY. I will look for a pressure test kit but I need to know how to use it on this.

[MelonBoi1]

Is there any part number or plate thing that I can use to cover up the ports for the pressure test? And I am not going to cut up a piece of metal I don't have the tools fot that.

[Hilltop366]

No metal needed, it is common to use a solid rubber gasket in-between the muffler/ carb and the saw body. Even a piece of inner tube (or doubled over) would do as you don't need much pressure, 7 or 8 psi would be enough.

Check out a couple of youtube vids for ideas.

Check the pulse hole to see if it plugged first, no special tools required.

[DHansen]

Just some added information about vacuum and pressure testing.  I would get a Mighty Vac gauge set up.  They work great for this test.  An old compression gauge fitting to screw into the spark plug hole works great.  An old inner tube cut to fit and block the exhaust port on the cylinder between the muffler and the block will seal the exhaust side.  You can put the rubber in and bolt the muffler back down.  On the intake, rubber from an inner tube will also work, but a small plastic block, metal or work to seal the rubber to the intake works better than bolting the carb back on.  But whatever works best for you or what you have around to seal it with. 

ADDED:  I found information saying not to apply too much pressure.  Seems that 5-7 PSI is the recommended pressure for pressure testing.    Also seems that most are also using 5-7" Hg vacuum for vacuum testing.

ADDED:  No more than 1" HG loss per minute and no more than 1 PSI loss per minute.  But I have seen several comments that a good saw will hold 7 Hg vacuum for 5 minutes and not lose any. 

[DHansen]

Photo of Mighty Vac gauge.  Compression fitting with core removed and vacuum hose connected to compression gauge fitting.  It sounds like you already have a compression tester, so use that fitting, but remove the valve core.  I bought my Mighty Vac used for $30.00 US.

[doc henderson]

great information gents!