861 tsx-662 carb tuning questions

RB981

New User
I rebuilt the TSX-662 over the winter along with a lot of other repairs at the same time. New manifold, elbow, exhaust, fuel line, repaired fuel tank and more.

The carb was rebuilt with a new float, which I set as the instructions said. New throttle shaft, seals, and everything else that came in the kit.

First question I have is, should the tractor start and idle with the power jet closed completely? If I close it, it stalls every time. I have the idle jet set so it idles smooth with no black smoke.

Second, While trying to get the power jet tuned (I can't tune it 100% until I can move it out and put a real load on the engine) I'm having lots of issues with it stumbling and backfiring. I can rev and hold it and it runs fine, no overheating, etc. However, opening the throttle quickly almost every time it will pop through the exhaust and carb.

I put my dwell/tach meter on it and idle seems to be around 475-500, a little high, but not too bad. The timing was advanced a good bit, so I backed that off to 5 degrees BTC at idle.

I also noticed fuel leaking from the power jet adjuster/needle. This wasn't replaced in the rebuild, so I am ordering a new one.

There is still fuel leaking from the carb inlet when it sits with the fuel on and not running. I'm guessing that maybe I have the float adjusted a little high, but I'm open to other thoughts there.
 
First off fix the leaks they can cause odd problems and the main jet leak can cause it to suck air in which will make it run odd. As for fast opening of the throttle that is pretty much normal since these carbs do not have an accelerator pump which in a car give a shot of gas to make things work. As for it idling with the main jet closed all the way well that shuts off gas to the carb so yes it will not run. When you cleaned the carb did you poke out all the passage ways with a piece of wire or as I use a torch tip cleaner tool
 

Thanks. I've ordered a new adjusting needle set, so that should fix that leak. I ended up using a piece of wire to clean the passages along with some compressed air.

It had been run for years with no filter or sediment bowl before I bought it, so it was pretty full of dirt and such.

I'll get this little stuff fixed and continue trying to get it running properly. I still need to get the correct solenoid on it, sheet metal back in place and change all of the fluids.
 
I have found when rebuilding a carb it is a good idea to soak it in carb cleaner over night or longer then use air and spray carb cleaner and a piece of wire etc to clean out passage ways. I use all 4 or I do not even bother messing with them
 
"should the tractor start and idle with the power jet closed completely?"

No. Closed completely should equal no fuel.

"I have the idle jet set so it idles smooth with no black smoke."

That's a good indicator as long as it is down around 450 RPM
[b:c61291d8e8]after[/b:c61291d8e8] you have the top end performance adjusted right. You
may have to adjust top speed and then low speed several
times before you get it dialed in exactly right.

"I'm having lots of issues with it stumbling and backfiring."
"opening the throttle quickly almost every time it will pop"

While this isn't a race car engine, there is no reason moving
the throttle from low speed to full speed should stumble or pop.
This could be a carb problem or a timing problem.

"I also noticed fuel leaking from the power jet adjuster/needle."

Liquid gas should never be high enough in the carb to leak here, so this one raises other questions for me.

"There is still fuel leaking from the carb inlet when it sits with the fuel on and not running."

That's why we always turn the fuel off when not in use.
Even when everything works right, it will eventually fail.
Then the cylinders and possibly the oil get filled with gas. Once
you get the leaks fixed, adjust the carb according to the manual.

I start with the main adjustment out 1 1/2 turns and the air
mixture screw out about 1/2 turn. Let it warm up fully.
Then, adjust the main adjustment so that you can achieve full RPM.
Turn the main in until you hear a change at full speed, then
turn it out until it is smooth. Idle it down, then rev it up.
Stumble? Turn the main out a quarter turn and try again.
Once it will achieve full speed and accelerate normally, you can
move on to adjusting idle. If it won't do that, there's still a
problem to address. No need to proceed further.

Once it will achieve full RPM and not stumble, idle it down and
adjust the idle speed to ~450 RPM and adjust the idle air screw.
Here I'm looking for the fastest, smoothest, relaxed, idle.
May require re-adjusting the idle stop screw.

Once done with that, let it idle a bit and test the throttle response.
If it loads at idle you will need to readjust.
You may have to repeat this process 3 or 4 times to get it dialed in.[b:c61291d8e8][/b:c61291d8e8]
 

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