Saw kills as throttle is applied

[sonnyboy53]

I am out of ideas and need some help.  Poulan 4218AVX starts & idles fine but as the throttle is applied and before it revs enough to engage the clutch, it kills with a little pop back through the carb.  I have tried the following:  new fuel lines & filter, carb kit installed & double checked, compression at 130psi, vacuum & pressure tested the crankcase-no leaks, piston & cylinder smooth, muffler & spark screen clear, flywheel removed to make sure the key is intact-no change when flywheel reinstalled.  Any suggestions or thoughts about what I should try next would be appreciated.

[dougand3]

Looks like you covered all the bases. I'd try another carb. New AM ones are ~$18. Or try a diagnostic carb that you may have handy. Forget the strato part - any 50cc or smaller carb would work if impulse hole is in center. If diagnostic carb throttles up fine, you can buy a strato carb.

[Bill Saf]

Did you check and see if the garb tube is good at the mount and did you take the mount off and look a the o-ring or gasket? Primer bulb?

[DelawhereJoe]

Did you check to see if the choke is completely connected, the old wild thing I was given has a problem keeping the choke hooked up, it likes to pop out of its catch. Sometimes you hit the throttle and it sucks the choke closed and kills it.

[joe_indi]

This could happen if there is some fault in the ignition module (coil). A bad circuit like a faulty speed limiter circuit.
If you could lay your hands on another coil for a test, you could verify this possibility.
Joe

[ZeroJunk]

I'm not familiar with that saw, but some of these newer carbs with no needle adjustment on the high speed side are hard to get clean if you get a bugger in the circuit somewhere. Or, at least I haven't been able to do it on a few.

[sonnyboy53]

Thanks for your ideas everyone.  However I've tried most of them already.  I neglected to add that I've tried a different ignition module and a 2nd carb (also cleaned & swapped out the new pump & reed diaphrams from the 1st carb).  This Zama carb has removable screws for both L & H jets.  So keep the ideas coming. 
I'm glad this is a backup for my backup saw but at this point, it's more of a challenge to find out what the heck the solution is rather than something I really need to use.

[dougand3]

Bill alluded to this: Are you sure the impulse tube through the big black strato intake is clear? You should be able to run a phone wire all the way thru intake and cyl base to the con rod. If no good pulse gets to the fuel pump diaphragm, it won't supply fuel.
I have a PP4218AVX in a box of parts. Here are pics of impulse with a green wire thru it.


https://forestryforum.com/gallery/albums/userpics/36829/IMG_20160810_174212.jpg

https://forestryforum.com/gallery/albums/userpics/36829/IMG_20160810_174128.jpg

[John Mc]

Have you played much with the low-speed mixture setting? I haven't heard one "pop" as you describe, but being too lean on the low speed mixture can cause it to die when you try to accelerate. It's a quick and cheap thing to try, anyway.