OK I am stumped on Husqvarna 450

[rupedoggy]

Customer came to me with a 450. Claimed it was running good last fall. Now won't start. New fresh fuel, clean exhaust screen. New plug (several), Air filter spotless. Well just a clogged carb, right? Sonic cleaned the carb with new diaphragms. Hit the primer button and get one hit, then to off choke and one more but no run. Fuel squirt into carb, no help.
OK I got this. Have another perfectly running 450. Swap the coils. Good saw now runs crappy so I figure I got it. Customer saw now tries to idle to no acceleration. Gives it the huh,huh huh only. Check magnets on flywheel, check timing on both saw, same timing. Ok Chinese carb so probably messed up. Swap carbs and the customer saw is still doing same, other running perfect (with coil from inventory).
White flag, anybody?

 

[Jacob J.]

Do these have a fuel tank vent? I've never seen a 450 but some of the newer Huskies have been having tank vent problems.

Compression, fuel, and spark - do you have good compression?

 

[RED-85-Z51]

Fuel line not pinched where it passes into the tank?

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[rupedoggy]

Good thoughts. New fuel line not kinked. It goes into the side of a tank shelf. Great compression. Tank vent hold pressure but anyway should work a little even if plugged. Great compression still has machine marks on piston.
Going to start tearing it down just to find out. Parts swap until fixed and will let you all know. Mike

 

[OM617YOTA]

Long shot, but.......kill switch wire, contacts, etc?

 

[PV Hiker]

Yea I was going to say a short in a wire somewhere causing a resistance as another option along with bad or dirty ground.

 

[OM617YOTA]

Feels silly to even offer a suggestion to the guy who only took a few minutes to figure out a saw I got sick of and moved on.

 

[axeandwedge]

Blocked muffler?

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[Bob Hedgecutter]

Blocked muffler?

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Read the initial post again- screen clean........ was my first thought as well.

 

[rupedoggy]

Thanks, nice of you to say. Does it with the wires disconnected also. Tried with the muffler off and same result.
Anyway just when you think you can fix any saw, along comes one to humble you. I have it completely torn down and am going over ever piece with my magnifiers to see if a crack, hole, gasket or seal is bad. This is a really low hour saw by the looks of things.

 

[Bob Hedgecutter]

Only thing I can offer and still only a guess- saw is not impulsing through to the carb pump.

 

[stihl86]

Any chance at all the ring (s) are stuck. Had a similar PITA repair on a blower. Red Max EBZ8500
Felt like it had good compression. Looking in the muffler the rings moved.
Finally, was at the point you are and torn it apart. Both rings were stuck
to the locator pins. (Maybe that husky only has 1 ring IDK.)
The engine moved a gauge when I tested the impulse.
I guess a leak down test might have caught that but the repair would be the same.
A total loss.
Primary compression is as important as secondary is the lesson I relearned (Again)

 

[Jasonrkba]

Something clogged the impulse?

 

[Jasonrkba]

Also sometimes people over tighten the carb and crack the adapter behind it. Noticed that one has a pipe assembly.

https://www.ereplacementparts.com/inlet-pipe-assy-p-616382.html

 

[Bob Hedgecutter]

If you are satisfied fuel is getting in and air getting out- then I would be checking to see the flywheel has not moved out of sync, air gap of coil, clean unbroken magnets on the flywheel and swapping out the coil for a known good one again.
Are there not two different 450's with different flywheels and possibly different coils?
Again, I know next to nothing about the 450's and I am only guessing. Probably guessing at areas you have already covered!

 

[Jasonrkba]

Sometimes it just takes a different set of eyes.

 

[rupedoggy]

Yes there are definitely two types. One is the rancher and that is the problem child. The other is just a 450 I guess and has a compression release. I have just taken it down to every last nut and bolt. The seals were perfect the piston and ring perfect. The cylinder perfect. The side transfers were new looking and I even took them apart to check. resealed the crankcase and re-assembled. Took the flywheel off and it was not missing the key.
When I tried again it has the same problem. Wants to idle a little but not very well I am going to try Ignition again in case there are two different. BTW when it was down the intakes and pulse line were checked and also perfect. I take the plug out and not wet but not dry just looks like it is getting what it needs for mix.

 

[Bob Hedgecutter]

100% sure there is good contact between plug and high tension lead?
Sillier things have happened and I assume it has a spring coil under the rubber cap?

 

[Jasonrkba]

Does sound like coil.

 

[rupedoggy]

I now have two different numbers for the ignitions 573935701 and 579638803 so maybe getting close. Mike