CA erratic spark

Replaced the main idle jet in the tsx. Not significantly different running. It was really difficult to get out. The easy outs are too short for brass. Got most out then retapped the hole. Not going to try the main jet. Too hard to get to and these easy outs won't reach. Misses are back but runs all rpms fineish. So, probably going to send the tsx out for professional rebuild. I've replaced everything in it but the main jet. I also tweaked the float to shut off slightly sooner. No change.

I tried adjusting timing with the Zenith...could not resolve the problem.

In steps, I've increased the jet all the way .082...I no longer have to use the choke to get full throttle range, but any time the governor revs it it still dies unless I recover it by choking. And thats only with the adjusting screw all the way out. Screw it in, reduces the throttle running range.
Seems like a ridiculously large jet for a tiny engine...I may as well see where it goes with further increases. But then again, only a little larger than the tsx 486 new jet size of .780.

Hmmm, tsx 486 carb info says the economizer jet is .0775...the main is .0990...#39 drill

No, tweaking the budget chinese knockoff zenith...I went all out and bored the main jet out to .0990...it now runs almost normally. It does have a slight wavering behavior at max throttle, but it might actually be usable now. Unfortunately, there's not much meat left on the jet for more boring. But I also now have some control with the adjusting screw. The tsx probably won't be finished before this trip ends on Saturday. Next trip probably late Aug. This carb obviously should not have been marketed as a 486 replacement...should have been 12522...guessing somebody cut and pasted wrong...hey but I got it for less than 1/3 of a zenith...what's a little frustration and anger...

Edited by dfwallis - 30 Jul 2025 at 2:43pm

It seems odd that you would have to bore the main jet THAT FAR OVERSIZE... but you had the symptoms of "lack of gas".... so yes, what ever works is a great solution !!

Contacted the carb rebuilder today.  He has had considerable difficulty getting some of the mangled components out but now has everything apart.  Hopes to complete by next week.  He's trying to locate the specific replacement parts rather than a full kit since I already installed the full kit minus those mangled jets I couldn't easily remove.  If he can't find them, he'll go for the full kit and use what he needs.  

Inspected the rebuilt carburetor. My gosh, he does excellent work. It looks factory new, shiny even. I hope it works as good as it looks. I'll find out tomorrow.

Same symptoms with two different carbs says the problem isn’t with the carb.
This has been a long post so I don’t remember if you sprayed carb cleaner around the manifold to check for air leaks or not, but the problem doesn’t seem to be the carb.

After dismantling the "rebuilt" TSX 486, I've found incorrect jet size/placement, so I've shipped the carburetor to TX and will give it another look.  I've found better service documentation now which should make it easier and more thorough.  I also see what appears to be microcracks in the bottom of the float bowl, but haven't confirmed it yet.  I found that the "economizer" jet (the last non-removable/mangled one) was previously installed at the wrong location (according to it's size of 0.0775"), according to an AGCO drawing.  A smaller jet is now installed at the economizer location.  I'm not sure that matters at idle though.  I think it is more effective at high throttle settings.  There's no economizer jet (0.0775) at any jet position now.  Luckily, I have a brand new one and will correct that.

The carburetor is at least in the right city now...