Long time owner Yoder YS640S, and 1500 at one time.

[SammyJ]

Been cooking on my YS640S from late 2012. Yes, upgraded to S, I have rehabbed my 640 twice. Be glad to answer questions

[DogFaced PonySoldier]

My question - do you have major temp differences in your 640?

I have a 480 and usually run 50-75º temp difference from left rear to front right. Not a ton of temp swings, it's fairly consistent and made with great heavy-gauge steel - but the temp difference drives me batty.

[SammyJ]

Been so very long since I've check checked. I did a biscuit test years ago, all pretty close. Most times the meat will tell me its done, just let the cooker run.

[DogFaced PonySoldier]

Can't be done on mine. If I put racks of ribs, the temp difference is so extreme they're burnt before the other end gets done. I've resealed mine thinking the brittle sealant on the firebox was the culprit, but even with new red sealant, it hasn't changed much.

Love the build quality, but the uneven cook has me questioning if I should look at another brand.

[600hpcummins]

May I suggest that you check the bracket the the diffuser plate hangs from, remove the diffuser plate and put a straight edge on top and see where it is in relation to the body. My 640 was way off and I believe it was the cause of the the diffuser plate warping, mine was warped diagonally causing high temps in opposite corners of the cooker.
If you don’t have the 2 piece diffuser, I would highly recommend it as the bracing for the door helps to keep the plate flat.

[DogFaced PonySoldier]

My diffuser plate is pretty flat, there's no warping I can see - it's just the one-piece plate. I have a little bit of adjustability on the diffuser plate, I can shift it more toward the front or back, probably 3/4" or so total, but I've tried with it in various orientations over the last several years. I know I don't like it with it shifted more toward that back, as that really exacerbates the high temps in the front and right.

[SammyJ]

My question - do you have major temp differences in your 640?

I have a 480 and usually run 50-75º temp difference from left rear to front right. Not a ton of temp swings, it's fairly consistent and made with great heavy-gauge steel - but the temp difference drives me batty.

Check also, the stack needs to be flush on the inside. If not air flow is disrupted.

Also Yoder has top notch support.

[DogFaced PonySoldier]

The stack? What do you mean?

I followed their forums, but YoderHerb is gone and every post I saw on there about temp differences got blown off.

[SammyJ]

The stack? What do you mean?

I followed their forums, but YoderHerb is gone and every post I saw on there about temp differences got blown off.

The exhaust stack, comes down, makes a 90, and into side of cooker.

[DogFaced PonySoldier]

Oh, yeah I am sure mine is flush.

[600hpcummins]

Even heat requires even air flow in the cooker, if you look at the underside of your diffuser and the ash in the bottom, you’ll see the telltale signs of uneven airflow. My YS640 diffuser would warp more as it heated up, maybe have a look without the grate installed.