It seems odd that the day before you rode the bike a great deal with no issues but now won't start. It would seem a cold/lean condition exists, but this usually causes no issue with the pumper carb. You have a pumper. Even if the bike is jetted lean at idle and/or in the starter circuit, you can get a bike to start with a pumper carb because you can introduce fuel regardless. It may still be hard to warm up, but you can usually get it to fire. Do you think you might have even flooded it with the pumper?

Usually in cold weather the hard starting complaints are usually reserved for the stock carb because of a lean starter jet and no way to introduce the extra needed fuel at startup. Also the pumper has a really reliable choke, so I wouldn't think that was the cause. You should have enough fuel to start the bike where it will at least fire up even if you're overall jetting is off, so I wouldn't waste time tinkering with the other jetting you mention at this point. You didn't mention it, but I assume you are using the choke, correct?

Here's another method that I'd suggest that will usually always work with a pumper. Turn the choke off. Given the throttle two or three good wide open whacks. Hold the throttle open on the last whack. Crank the engine over with the throttle held wide open. If the bike won't fire after just a few seconds, you've got another issue usually...as long as your spark plug isn't already fouled or such.

I hate you're having this much trouble, because the TM36-68 is fairly trouble-free carb when your jetting is at least in the ballpark. I've been surprised to find that I don't even rejet anymore for higher elevation with my home settings like I used to have do with the OEM vacuum carb.

 

It is hard to get the right mix, if you use the pumper to charge the engine it is easy to flood it. Seen it so many times on cars.
Trust the choke first. If it doesn't fire, give it one twist & try it again with the choke. Next time 2 twists and try. If it don't fire, it is probably flooded and just choke off & full throttle till it starts.

 

Update
Thanks guys for the input, I have learned so much from this forum...
So last weekend tried the starting methods mentioned. No luck.
Kept trying for about 20 minutes with the battery charging from my vehicle, hoping I wouldnt burn out the starter, but finally got it running.
Shut it off, fired right up multiple times.

Took it out for a ride, seemed fine, but if I left it shut off for more than 5 minutes, it was back to cranking and more cranking.
Actually had to jump start it one time as my new battery was getting tired. Back home I went

So I'm thinking as things cool down and contract, I must have a compression problem. Made sense why so long to get started.
Bought a tester today.
Got a total of 35 PSI, Its not the carb!!!

Now Im thinking the worst....checked the valve clearances. Intakes are as tight as a drum, couldnt get the smallest feeler in. Exhaust at min limits
I shimmed the intakes about 8000 kms ago
So I'm hoping to buy some new shims and problems solved

Does this sound normal that the valves would go this far out after 8000 kms ?? Can you think of any other issues other than rings?
Hoping thats all it is, or it may be time for a 351........stay tuned

 

I am not surprised at your compression readings if you still have an active automatic compression release.

Realize when you're doing your compression test the automatic compression release is active - reducing compression for starting. Disable the compression release, it is unnecessary for the 250. Take off the spring and it will be disabled. (If you don't like the idea of the CR shoes flopping around PM me for the method to lock them in the released position.) The engine will spin over just fine and likely start easier.

As for the valves, if you are at 8000 Km, it is entirely possible the valves can seat in that much. From past experience with my 650 I would check valves right about the point you are at. They can also cause starting problems if not opening at proper timing, but with tight valves that is the least of the concerns. Burned valves are a greater concern if they get too tight - been there done that.

 

Is there any way to increase the amount of fuel the tm36-68's accelerator pump expelles? I have the slight bog when I crack the throttle from idle and my jetting is perfect. I have the bike set up as a snow bike in the winter and with the colder temps the bog is worst. When I follow the accelerator pump with my finger and force it to squirt more fuel the big is gone.

 

Is there any way to increase the amount of fuel the tm36-68's accelerator pump expelles? I have the slight bog when I crack the throttle from idle and my jetting is perfect. I have the bike set up as a snow bike in the winter and with the colder temps the bog is worst. When I follow the accelerator pump with my finger and force it to squirt more fuel the bog is gone.

 

Yeah, I'd suspect the valve adjustment first at this point based on your observations. A lot of bikes will run fine but have really hard starting issues with tight valves. On that 35 pounds of measured compression, it's a fact that you won't get a true reading with the KACR in place. However, the compression is usually at least within the 60's pound range even with the KACR operating.

 

Finally found the time to get at the valve adjustment.
On the intakes - right side went down 3 sizes of shims to get within middle of spec
- left side took 4 sizes to get to .13 mm
Does this seem like a lot? I suspect a valve job in my future.

Anyway, put it back together, pulled the choke.......started right up!! idling fine. Hard rain is preventing me from a ride

The carb is no longer my enemy, we are getting along fine now, and hoping for a lasting relationship.....
Thanks for everyones help and input as I continue to learn from my experiences

 

 

Running what is shown in previous threads i think
mods are in my sig.
cheers