Will this piston still work ? ( husqvarna 445 x-torq chainsaw )

[naimc]

I had another go at it today with fresh VP 40:1 pre-mix 2 cycle gas and same thing over all situation.

Saw starts on high idle it run's way to fast then on 1st trigger pull to dis-engage the high idle is stalls.
I am now thinking fuel delivery as after 5 min of this cranking it would not start at all, I opened the fuel cap and felt of pop of air, the repair manual list a process to test the 2 way fuel tank purge vale.

I will give that a try. and I will have a look at the carb the repair manual also has leak down test that seems simple enough.

carb pressure test :

Fuel tank test :

 

[naimc]

I did not have the proper small size hose to connect my MiVac vacuum / pressure tester so I took the carburetor apart.

A part for some dirt on the bottom pump side everything was in good shape, Pick-up screen clean, gasket's all appear to be in great

shape. Watching

After watching a youtube video (by The Greasy Shop Rag) on this subject , I now think I was sloppy on the 1st assembly.

I did not know about the impulse signal connector on the bottom of carb, very possible I did not have this in the proper position.

Also probable that I did not have proper 4 carb bolts in the proper position, 2 short on top 2 long on bottom, might have reversed them causing air leakage.

All carb parts appeared in good shape.

All reassembled now , but it's 11 pm to late in suburbia to fire-up chainsaw.

 

[Fordiesel69]

That was a clean carb for sure. Whatever fuel you had been using, keep using it!

 

[naimc]

Put the fuel back in the saw, expecting nothing but success !

No go same issue, chains just run on bulb squirt , then bogs down on the trigger. there are few YouTube video's for this chainsaw and its always are carburetor issues.

took the carb apart again, I did find some fuel under cab so there must a small leak.

Found there was no filter in the fuel tank I blew out both lines.

Tested the gas tank vent and it lets pressure both ways. ( so it's fine although when I opened the gas cap today again I did feel a small pop of air going it. guess this normal positive pressure in tank ?)

Next carburater pressure test on the intake, staying steady at the 5 psi,

Next the submersion test under pressure , still at 5 psi but I can tell its slowly leaking, the screw is as tight as it will go so I have ordered a carburetor gasket kit.

I still think I am missing something, I don't see how a tiny leak could have such a bit impact on the saw not running. I also have to do a lead down test on all lines to make sure they are not leaking.

 

[Fordiesel69]

Yes that is the fuel pump side that is leaking. It will not run this way. The plate that says "China Zama" with the single screw in the center will have a male pathway or edge on it that indents the gasket. The carburetor surface is the female or flat side. When you scrape the gasket off the plate, make certain not to mar it up. Make sure it is spotless.

Consider soaking the black gasket in 2 cycle oil for a bit before you assemble.

Do not soak the actual fuel pump with the two flaps.

Also take a pick, and poke and clean the holes that alignment pins go into. I have seen debris go inside these holes, and when you tighten the plate, the holes are packed full and cause it to warp, therefore preventing a good seal.

 

[naimc]

Update, I let the gasket soak as suggested , all the parts are super clean.

Re-assembled and it's still leaking, not by much. I am waiting for new gaskets, while I wait I think I will try just a tiny line of gasket seal.

I am now very familiar with this saw and can break it down and re-assemble it in record time ! enjoying myself very much in the troubleshooting process.

 

[Fordiesel69]

That is a shame. Hopefully the new gaskets correct the issue.

As another home DIY test you can place the piston at bottom dead center, plug the carb with a wet blue shop towel, and then cover the muffler discharge, and blow gun shop air about 30 psi into the cylinder with a rag wrapped around the blow gun, and than soap up the cylinder to plastic case seam and see if there is an air leak. Also the crank seals.

30 psi wont hurt anything as there will be so much escaping thru what you can perfectly plug up.

If you had professional blocking plates like the guy in the video 30 psi would be very bad, you'd want 5 or so psi.

This is a 450 but the same saw as your minus 5 cc's. I stumbled across a video on youtube here:

 

[naimc]

@Fordiesel69 , Yes I saw that video an others showing the importance of the leak down tests, I made gasket out of rubber for the exhaust port and found some silicon plugs.

I did the leak down test with soapy water No leaks on pressure and vacuum test.

Undid the carburetor again and watch a few more videos just on the topic.

I tightening the carb screws a bit tighter than previous attempts, pressure held.

That's when I realized that on re-assembly I had the L and H screw reversed because darn the illustration in the repair guide I have been following was wrong !

After re-assembly and some more adjustments, fiddling around with the L and T screws I got a results I am happy with. Final adjustment to be done when I get the oiler plate and saw fully assembled. thanks for your help !

 

[Fordiesel69]

Oh wow, that is a relief. I was fairly certain you would have gotten a good seal on the cylinder using black as I did as well. I did not with Grey moto seal. Didn't know at the time it was only for metal to metal. Any who, glad the issue was just the carb. Tinman on YouTube had the best audio for carb tuning. On this saw, slight richer is better, it will last a lifetime that way.

 

[Fordiesel69]

Also the internet finally was good enough to listen. Without load it sound like you have the high needle rich enough for testing. Excellent you nailed the tuning for no load. One you get it buttoned up and start cutting I'm confident you'll get it right.

 

[Zaedock]

Awesome! Snappy too!