Tecumseh won't run past half throttle

[Arkie]

I've never seen the points lobe marked like that.
I think maybe I seen mention somewhere in the manual that the lobe has a in and out and maybe some mark like a dot indicating that end to be out, but I'm not sure.

Appears some engineer with Tecumseh woke up and tried to help the mechanic's.

Sure is a clean engine.
Drag a dollar bill or non fuzzy white piece of paper through the closed points contacts before installing the flywheel.

[bgsengine]

Yep, have seen those before, I never really paid that much attention to the fact they pretty much line up - you can line those marks up several positions and still be off on timing, though I suspect that was added just as a "guide" during assembly (they could care less for the mechanics after the fact, but it likely aided in a few seconds time shaved off assembly line during production) - making sure their workers put the stator and cam lobe on in the correct orientation, etc..

And that's the cleanest Tecumseh I have ever seen outside of a brand new one that I tore down and rebuilt during "school" (Foley-Belsaw small engine repair course back in 1983)

[Roadrunner123]

UPDATE:
Ok I know it's been a while but I'm also building a model railroad at the same time so I'm dividing my time. Ok so I broke the engine down and removed the head. Cleaned the piston, head and valves. Reset the points and timing. Have to say everything was almost perfect before I started but was perfect after, as far as timing and point gap are concerned.
Cleaned the carb for the fourth time before reinstalling. So the next part has me scratching my head because in all the years I've played around with small engines this one is acting like nothing I've seen before. Starts right up and will run to about 1500 rpms no problem. If I gradually move the throttle toward fast I can get it to accelerate but only slightly at first. The more it warms the more I can increase the throttle. Eventually I can get it to run at full throttle, 3600 rpms. Now this is when it gets really crazy as I can turn the high speed jet in all the way and it still runs at 3600 rpms. Never seen anything like this. This diaphragm carb. really has me baffled. I did see a new video on line concerning these carbs and the guy said there is a check ball under the welsh plug in the hole where the high speed needle measures the amount of gas going to carb.
I warmed up the engine and removed the high speed jet and saturated inside the jet orifice with carb cleaner because I figured it would clean this ball but nothing changed.
I searched on line for hours trying to find a replaced carb but with not luck.
I'm open to any suggestions cause at this point the only thing I can think of doing is to get more welsh plugs and see if I can see this so called ball and see if it may be stuck or something.
Thanks to everyone that has contributed so far.

[bgsengine]

I do not believe the fully adjustable diaphragm carburetors are available any more, HOWEVER, it being a snow blower, and I assume a 4-stroke, you can actually replace the diaphragm carburetor with a regular float carburetor (assuming the engine doesn't operate at any weird angles, but tends to operate on a relatively level angle of operation) you can pick up a couple (or three) cheapo chinese clone carbs for H35 Tecumseh for fairly cheap on Amazon (I'd buy more than one, since if one does not work right, the other might) You may have to modify or alter the fuel inlet fitting and fuel hose routing, may need to alter (or fabricate) throttle linkage (and if that is the case, reset the governor static adjustment, or maybe should reset it anyways if changing carb) But an H35 float carb can easily replace the diaphragm carb as long as the engine does not need to set in an extreme angle of operation (but then if it did, it'd starve for oil) In fact you might even be able to locate a fully adjustable chinese clone carb for H35 (or H40)

I have seen these engines with diaphragm carb do that before, and good luck getting any check ball loose.. However your acceleration problem may be the low speed adjustment is too lean - Bear in mind that when the engine is not under load, most of the fuel the engine uses is coming through the Low speed ("Idle") adjustment , also, so adjusting high speed when it is at "fast idle" (top no load AKA 3600 RPM but no load) may not necessarily do much for it, since the throttle plate is mostly closed and most fuel would feed through the idle metering and transition ports.

[Arkie]

I went over to that m&d link I posted and seen the H35 and it shows both a float or a diaphragm carb for the H35's. (no part number for the float type though but such can be found)
I'm not sure I've ever seen a diaphragm type carb used on a H35 or H50. Most were float carbs
If you can turn the H jet all the way in a get a still get a run is a hint of probably some dried hard crud or the check ball stuck.
Guy gave me a H50 engine not too long ago with no carb/manifold or gas tank. Engine checked good with a leak down and looked engine was clean.
I installed a float clone carb as bsengine suggested to you and used survey flag wire making up the governor and throttle linkages and all came out great. I used a more user friendly softer type wire at first until I got the patterns correct. I happened to have the Tecumseh drop type intake manifold so as to keep the carb low for gravity feed. I seem to remember that maybe the clone carb had idle and h jets as adjustable. The carb was like $12 from flea bay. I used a plastic gas tank from a Briggs engine that bolted on using the head bolts and the bracket. I installed the engine on a rototiller with good results.

If your carb looks like the Tecumseh 631400 diaphragm carb shown in the link I posted at m&d
You can go to a clone float without too much problem since you already have the drop manifold and gas tank maybe.
If getting a clone carb or any float replacement be sure and measure/match the center to center mounting hole dimensions of the intake manifold mounting holes. (Replacement carbs are not all the same here)

You can fool around on-line and come up with a Tecumseh float carb part number and then go looking. One with adjustable jets will work on both the 3.5 to 6hp's
Here is a link to how to's for several cabs including some Tecumsehs. Just scroll down and select Tecumseh. Also be aware that some of the Tecumsehs have a intake drop type manifold that the carb bolts to that turns 90 degrees and keeps the carb closer to the engine.
You can see a pic of such at this link also when looking at the Tecumseh carb choices.
http://outdoorpowerinfo.com/repairs/

As a last ditch effort on you might consider trying:
If you do not have a HEATED Ultra sonic you might conside doing a 50/50 mix of water and white vinegar and heat to about 140-150F and keeps soaking the carb and using low pressure air. Soak for about 1 hour, neutralize and test if no go back to the HEATED solution If you have a heated Usonic just keep doing heated runs. The USonic has tendency to break-up hard crud and rust internally in a carb. Use little bit of baking soda in water to neutralize the vinegar water mix when removing the carb for a test. The vinegar will keep acting on aluminum and magnesium and make it turn black and feel gummy/greasy if not neutralized.

Does you carb look similar to this piece of trash over on flea bay?

Tecumseh 3.5HP H35 OEM Carburetor NLA (PARTS OR REBUILD) 631400 | eBay

Some float type on flea bay
https://www.ebay.com/b/Tecumseh-H35-Car ... 7023422684

[Roadrunner123]

Thank you bgsengine and Arkie for your quick response. I have searched previously for a bowl carb and tried again today but have not found one that looks similar that has both jets adj. I did however find another welsh plug and I'm going to remove the carb. today and see if I can see this ball. I do have a heated Ultra sonic cleaner and will try that again. Thanks for the tips about what to use as a cleaning solution.
I actually found someone on line that has my carb but he's selling it as parts only cause it looks in rough shape. Asking $50. It may have the same issues if you saw what I saw. I will update everyone when I find anything suspect.
I haven't had a challenge like this in a long time. It would be very satisfying if I could resolve this. I love fixing things!!

[Roadrunner123]

Update: Tuesday 22nd. I removed the carb again and to my disappointment the nylon ball was free. I included a link from my Tecumseh that shows the breakdown of my carb and also shows that ball. After reading this If the ball was stuck shut then I can see how I would have high speed issues but it's not. I'm now wondering if the welsh plug is not preventing gas from leaking around it? I'm wondering if I need to compress it more with my punch. I understand what bsgengine said about the gas going through the idle jet even at high speed because the throttle shutter is closed but I manually opened the throttle shutter during high speed and it still ran.
https://photos.app.goo.gl/qZv6nWa1LRSZvoBu6
Maybe this photo of my carb might give someone an idea.
Thanks

[Arkie]

You need to make sure them 3 orifices in the carb throat by the throttle plate are not restricted.

I've sealed those welch plugs using a slow set liquid epoxy when I have to drill a small hole for removal and then re-use the same welch plug. The slow set epoxy will do a really good long term job. I do not like JB weld epoxies, but you can use such for a temp test. Nail polish or other quick dry sealants will usually be eventually broken down if exposed to ethanol fuel.

That diagram shows the check ball as captured, should not have been loose per the diagram.
If it's of a type that was loose in that chamber check it's sealing seat for back checking but it appears must allow fuel to go up through at higher rpms. Keep in mind that someone may have been into that carb before, make sure that the H and L jets adjusters are not reversed.
Some Small diaphragm carbs use a orifice check and if not back checking causes idle issues but that chamber must be open for H speed. Some of the idle check valves were designed to be not serviceable. (located below a non or hard to remove orifice plug)
You are correct that if the welch plug was not sealed good it would upset the High jet apple cart.

I use a magnifying glass and these type cleaners to see if the orifices are open.
Carburetor Carb Cleaning Jet Cleaner Kit Tool Set For Motorcycle ATV Lawn Mower
Item number on flea bay 233704985416

You can sometimes use a tag wire but if it breaks off you will be SOL.

[Arkie]

You also need to make sure that the breather assembly on the engine is back checking normally or not blocked. It will upset the pump pulses to a diaphragm type carb.

[bgsengine]

You also need to make sure that the breather assembly on the engine is back checking normally or not blocked. It will upset the pump pulses to a diaphragm type carb.

Huh? these tecumseh diaphragm carbs don't have fuel pumps integrated - they're gravity fed. But for a fuel pump (separate from the carburetor), good point.