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dfwallis 
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 Posted: 30 Jul 2025 at 12:21pm |
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.089, best behavior so far...starting to have some adjusting screw effect. Super snappy governor as long as it doesn't rev too much...seems far fetched...
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1952 CA13092
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dfwallis
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Posted: 30 Jul 2025 at 11:38am |
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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.
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1952 CA13092
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dfwallis
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Posted: 24 Jul 2025 at 8:07pm |
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Place i sent the carburetor to has been repairing all types of carbs for 80 years...and can actually test them...that part wasn't clear at nearly all the other places I looked at...fingers crossed...
Edited by dfwallis - 24 Jul 2025 at 8:08pm
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1952 CA13092
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Les Kerf
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Posted: 24 Jul 2025 at 6:48pm |
 dfwallis wrote:
Brother brought a better quality vac meter. Engine reads 22 in hg, steady. Agrees with my cheap farmer calibrated meter... |
Excellent!  That means you do not have sticky valves and your rings are sealing properly.
Once you get the correct carburetor on there with the proper jetting your troubles should be over. Hang in there 
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dfwallis
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Posted: 24 Jul 2025 at 3:14pm |
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Brother brought a better quality vac meter. Engine reads 22 in hg, steady. Agrees with my cheap farmer calibrated meter...
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1952 CA13092
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dfwallis
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Posted: 20 Jul 2025 at 3:52pm |
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I tried adjusting timing with the Zenith...could not resolve the problem.
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1952 CA13092
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dfwallis
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Posted: 20 Jul 2025 at 3:48pm |
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I think the low vacuum reading was due to cheap uncalibrated meter. But I'll verify when my brother brings a higher quality one.
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1952 CA13092
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dfwallis
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Posted: 20 Jul 2025 at 3:45pm |
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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.
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1952 CA13092
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steve(ill)
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Posted: 20 Jul 2025 at 3:23pm |
when you choke it, it will REV UP right ? ... Not something like a timing issue way advanced at high RPM ? .... Sure it is CARB related ?
What if the Intake manifold or gasket had a leak and was sucking air ? ..... Restricting the air ( choke) makes the engine SUCK harder and more monifold vacuum ? Les thought your vacuum was on the low side ?
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Like them all, but love the "B"s.
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dfwallis
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Posted: 20 Jul 2025 at 3:17pm |
  it's brand new...shouldn't have that sort of problem
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1952 CA13092
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steve(ill)
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Posted: 20 Jul 2025 at 3:13pm |
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if the choke keeps it running... that means your running out of gas.. Could be the main jet or could be the venturi in the throat ?
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Like them all, but love the "B"s.
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dfwallis
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Posted: 20 Jul 2025 at 2:12pm |
No difference...idles perfectly, any attempt to go beyond mid throttle dies without choke regardless of adjustment
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1952 CA13092
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dfwallis
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Posted: 20 Jul 2025 at 1:21pm |
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By accident I found a drill bit .0630, about to try it
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1952 CA13092
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steve(ill)
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Posted: 20 Jul 2025 at 1:03pm |
I bought a tsx428 and it was .041 inch... and i made it .043 .... ......... the 428 was used on a 120 CID FORD tractor..
remember on the jet size your interested in the AREA of the hole... The DIAMETER might change .002-3 for a 5% difference, but the AREA gets 10% bigger since you Square the RADIUS when you figure the AREA..... dont go too large, to fast.
Edited by steve(ill) - 20 Jul 2025 at 1:14pm
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Like them all, but love the "B"s.
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dfwallis
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Posted: 20 Jul 2025 at 12:12pm |
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Zenith: .0640 > .0600
TSX new main: .0775
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1952 CA13092
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dfwallis
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Posted: 20 Jul 2025 at 11:47am |
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Much smaller than the tsx486 main jet also, all the way through...not that they're necessarily comparable
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1952 CA13092
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dfwallis
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Posted: 20 Jul 2025 at 11:42am |
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Question...the Zenith main jet is not the same size all the way through...the very tip is much smaller. Either it is stepped or they didn't bore all the way through...docs online seems to suggest Zenith does not use stepped or tapered jets ?? 12566
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1952 CA13092
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dfwallis
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Posted: 20 Jul 2025 at 10:40am |
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My brother will bring his high $ gauge out and recheck it
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1952 CA13092
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dfwallis
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Posted: 20 Jul 2025 at 10:28am |
And in another laughable (or angering) episode...my cheap Chinese vac gauge was not calibrated. I had to open it up and manually adjust it to zero. Now the vac pressure reads in the normal range at about 45 in hg. 
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1952 CA13092
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dfwallis
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Posted: 20 Jul 2025 at 9:43am |
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I updated the gtc505 firmware...surprise surprise...the electrical misfires are gone. They've updated the cycle menu with a distributor specific selection and algorithm...if you have one, you'll probably want the 211c or later update. It could be costly otherwise:(
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1952 CA13092
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dfwallis
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Posted: 19 Jul 2025 at 9:42pm |
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Yes, the meter itself shows a green good range as you suggest. I agree it is starving for fuel. I will consider a tweak to the jet.
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1952 CA13092
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Les Kerf
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Posted: 19 Jul 2025 at 8:48pm |
dfwallis wrote:
All rpms, changes very little |
Hmmm... assuming your elevation is under 1000 feet above sea level, that engine should pull 40-50 cm hg (18-20 inches) at low idle, you are at about 11 in hg, not enough to run a milking machine (usually about 14-15 inches hg).
If the throttle butterfly is open too far then the idle circuit is ineffective and you are then trying to run it on the main circuit, which also appears to be wacky
Steve's suggestion makes good sense.
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steve(ill)
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Posted: 19 Jul 2025 at 8:21pm |
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I bought an "aftermarket" carb for a B that did the same think... FInally decided is was missing a little FUEL at high RPM... i had about 10% choke, so i pulled the carb, pulled the main jet and made the main jet .003 inch bigger diameter and that FIXED the lack of fuel problem.
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Like them all, but love the "B"s.
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dfwallis
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Posted: 19 Jul 2025 at 8:16pm |
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All rpms, changes very little
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1952 CA13092
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Les Kerf
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Posted: 19 Jul 2025 at 8:06pm |
dfwallis wrote:
... Vacuum shows steady 28 cm hg vac |
At what RPM? That's pretty low if it's at idle.
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dfwallis
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Posted: 19 Jul 2025 at 7:48pm |
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Does not seem to be any carb setting that allows it to run at high rpm without very slight choke. Has both adj screws. Vacuum shows steady 28 cm hg vac
Edited by dfwallis - 19 Jul 2025 at 7:51pm
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1952 CA13092
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dfwallis
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Posted: 19 Jul 2025 at 6:46pm |
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New Zenith carburetor...no more misfires...not adjusted right yet, dies at high throttle...these Zeniths based on 12566 and 12522 are not acceptable substitutes for a tsx486...many mods needed. Throttle link rubs the block unless you saw off the throttle flap through bolt. Would be better if I took off some of the lock nut holding the lever arm. Had to borrow some parts from the tsx to make it fit correctly. Boy, that's a load off.
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1952 CA13092
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dfwallis
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Posted: 15 Jul 2025 at 5:50pm |
Les Kerf wrote:
Hope it helps
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Hope I can figure out how to install the update 
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1952 CA13092
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Les Kerf
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Posted: 15 Jul 2025 at 4:59pm |
Hope it helps
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dfwallis
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Posted: 15 Jul 2025 at 11:26am |
The GTC-505 vendor has agreed there could be a trigger level issue and has provided a firmware update that adjusts the algorithm for distributor systems. If the voltage is held high too long (e.g. coil hysteresis), the trigger may not reset properly ready for the next cycle.
They are also working on an update to facilitate trigger level adjustment and will provide that update when ready. It isn't clear whether that will allow manual adjustment or whether it's just an update to the automatic internal adjustment process.
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1952 CA13092
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