Jiffy Model 31 3.5HP won't run consistently

Older auger, that ran well for a number of years, but now I’m having trouble.
It has the 3.5 HP techumseh and 10 inch chipper.
I’ve had SEVERAL people work on it, with new carb kits, gas lines, fuel cap, over the last 3 years…even a new carb, which didn’t work….put the original carb back on.
On several occasions, I paid and walked away with an auger that seemed to run. Then after a few more tanks of fuel, it always acts the same–it will idle, but will stall out after a few revolutions when the throttle is engaged.
If I hit the primer bulb, and the throttle, it will spin 4-5 turns and bog down again.
Latest small engine shop advised me to have them check for bad rings, scored piston, etc…where do I stop.
Anybody had the same issues with the same auger–anything come to mind?
THX.

Was the fuel pump diaphragm replaced?

it sounds to me that the carb idle screws may be vibrating out of adjustment. I have worked on a couple of that model and know they are very touchy when it comes to the carb adjustments.

Time to go electric.

Does it run not under load?

Possibly a bad reed valve,Ive ran across a couple over the years but not many,looks like everything else has been covered.

I had mine rebuilt two years ago, mine acted similar, if I run it on half choke it doesn’t miss a beat. Don’t have the heart to retire the old girl.

Replace the diaphragm if you already tried fresh gas.

If all those previous mechanics didn’t change the diaphragm you went to some real airheads. They had to I would think but you should ask.

Time to let here go, she gave you many great days cutting ice but the old lady needs to go to motor heaven. So many better choices today to replace her, like the 24 and 40 v strikemaster.

I assume like my old model 31 you have two adjustment screws on the carb? If so, have you played with the high speed adjustment? Mine ran great when not drilling a hole, but as soon as I started cutting ice it would bog down and even die sometimes. Playing with the high speed adjustment completely fixed mine, and that was after doing everything you’ve done already.

My older jiffy had a plastic diaphragm cover that was warped. Had to keep priming it to drill a hole. Replaced with metal one ran fine.

IF the carb and fuel lines have been done correctly and no lines are pinched or a filter in the tank plugged,you may want to check out the kill switch and its wiring.
corrosion in the switch or chaffed wires shorting out can cause this.

Another thing that may be going on is the module in the ignition coil or the coil itself is breaking down and shorting out internally causing a very poor spark issue under load,this is a fairly common problem in these small engines,dont over look it.
It will show up about the time the coil starts to get some heat in it which doesnt take long, eventually it will quit making spark all together.

H&L supply or pats small engines,Jacks small engines etc should have them on hand.

Fantastic comments (ideas)–THANKS.
Follow-up;
-fuel pump diaphram has been changed several times–altho I have learned it has a seal with it that goes above/or below, depending on motor serial number..
-both carb jet screws are staying put–marked them–but will try some smaller HIGH SPEED adjustments per advice here. Does the low speed jet have any effect on faster run performance?
-haven’t been inside to reed valve–how to tell if its defective?
-using fresh 90 “NO” fuel and Jiffy oil mixed 40/1
-no filter in tank that I can see
-Iowaboy1…have not checked either of these items.
THANKS ALL…
Have considered electric–the 10″ chipper blade just fits my use…

OK Guys–I may have found the culprit—only fair to pass this along…
There are two springs on the top of the carb–one of those is about 1.25 inch long, and when the throttle is opened, that spring pulls on the metal piece that sits verticle and pulls over when acceleration starts…there are two holes where that end of the spring can be attached . I remember somewhere I read to use the hole setting closest to the engine block….and that is where the spring has been for some time.
By using the other hole, the linkage doesn’t pull open as far….and the auger cuts holes much better…make any sense to you guys?
Next, I’ll fine tune the high speed jet…but so far I’m much happier.
Thanks for everyones help…

Mike; Hi, I have the 3.5 hp jiffy auger also not many at all around anymore! Rare to see one on the ice anymore. The biggest engine Jiffy ever used! Kinda like me at 71 years. I also have had problems with mine. Engine is just fine and I think it will last forever. I’ve had it many years bought it new. I took it in to a (Jiffy guru). I Use non-oxy with a 50/1 mix. I’m sure 40/1 is o.k. also.
The (carb jet settings were my problem). The one on the left is suppose to be out 1 1/8 turns. The one on the right is from 3/4 to 1 turn open. After that it has run really great! I remember adjusting them long ago when I should have (not done). It just needs to be always warmed up good before punching holes. My spring is in the hole farthest from the block, fyi. I love starting it and showing the kids how real men used to punch holes!! Tom Edberg

Post deleted, I just noticed problems were fixed