What I have done so I don't have to change all my older rolling stock over . I took one car and have an older coupler on one end and a new knuckle coupler on the other. I use it as an adaptor car for the newer engine I get with knuckle couplers.

I have been running trains and RC boats, cars, trucks, aeroplanes, and helicopters for 40 years. Adding weight causes the motor to run hotter and wear out sooner. It can also cause gears to strip out under load. Everything has it's limit, so why always run at that limit when you don't need to. Would you add weight in the trunk of your car for winter and drive around with it all year long?
Send an engine in for repair under warranty with weight added and see if it is covered.
It's my railroad and all I know is what has worked best for me.

More than 20 years ago I purchased an MRC 20 (known then as a hogger). It has a walk around control also.
It was listed for N scale, HO scale, and G scale. I have had as many as 6 Athearn HO C44-9w's running on it at one time. It is still running strong today and has served me well. I have also run as many as 4 Broadway Limited sound units together.

I have over 80 English engines in both HO and N scale from Ebay UK. Never had a problem running on my US layout. I only run DC. Can't vouch for DCC. Couplers are different.
Never had a problem with sellers in the UK and everything was delivered thru Royal Mail with no problems.

No trick. Try, try and try again. Takes a lot of patients. You can put a small amount of grease on the end of the shaft.

Adding weight to the engine can be done, but why add extra strain on the engine , power pack and motor if you don't need to. It will also add strain to the running gear (side rods and internal gears).
If you can reduce weight in the cars  and have no problems operating why not? You can always put it back in.
On some older engines when they added rubber tires they did not do it very well. The engines would wobble down the track. Some say the track gets dirty faster from the rubber also. On engines with few wheels the rubber tires took away from the wheels to pick-up current.
If you add bullfrog snot or rubber tires to your engine you may have to add extra electrical pick-up to your tender for better running.
For over 30 years almost all European engines (Hornby, Roco, Liliput, Rivarossi) have had rubber tires.
Broadway Limited USA uses traction tires as well as Bachmann on N scale steam and Proto (Walthers) steam. They are some of the best running engines still today and well worth buying.

When they were $75.00 at Trainworld you should have purchased a bunch. The HO crowd is having the same problem.  No availability. When the HO was selling for $65.00 I got 4 of them. Only managed to get one of the N scale for $75.00.
I waited almost 3 years to get a 2-10-2  in scale. Great engine but a bit high price. If they ever go below $100.00 I think I will get 3.
Would like to see Bachmann do a re-run with more roads.

You need to get a bigger engine or you can try this.
WARNING   WARNING Only do one of these things at a time then run the train for a test. If it works OK then go to the next step. If it developes a problem put it back to the way it was.

See if the connection bar between the engine and tender is lifting any weight off the rear of the engine. If it is you will have to adjust it so it does not take any weight off to engine wheels.

With the engine on the track lift just the 2-XX-2 wheels to see how much weight is on them. They are not providing any traction If you can adjust for less weight it will add more weight to the drive wheels. Make sure they are also turning free.

If you don't have any switches used in your track and it is level and smooth you can take 1/2 the weight out of the inside of each car and the coal tender. Most cars and tenders are overweight.

I have an 0-6-0 Casey Jones that will pull 11 passenger cars all day long.

Make sure the track is clean and has no oil on it.
If the engine has rubber traction tires make sure they are ok, clean and are not loose on the wheels.
Check each car to be sure they roll free. No drag. If you have to oil the ends of the axels with very little oil. You may have to spread the frame of the trucks so the axels roll free. Don't break them.
If it is a steam engine see if the drawbar between engine and coal tender is lifting the rear of the engine off the track. Adjust so it doesn't.
I don't use or have a lot of switches on my railroad so I have removed about 1/2 the metal weight inside each car so I can pull twice as many without over taxing the engines. On level track I can pull 25+ cars with one engine.
Get another engine and run two together.
Bachmann (4-6 axel drive) engines are good  stay away form anything with only 2 drive axels. Athearn, Kato, Atlas, Life Like Proto are all good brands.

If this is HO Gp40. The coupling the drive shaft rides in on the front tuck is probably pressed on to far. It is just a press fit. After putting the  shaft back in try to slide it closer to the front of the motor. Also check the front truck. It may be loose from the screw in the top. This will let it move to far when lifted off the TRACK and let the shaft pop out. Just tighten it a little don't over due it.

First make sure track is clean. It might be new but could have oxidation on it. Then run it for at least 15-20min in each direction to break it in. If this does not help then separate the engine from the tender and put the drive shaft aside. Remove the tender trucks (center screw on each) Don't loose the springs. Clean the springs top and bottom. Clean the area where the springs contact the brass strips and where they contact the truck frames. I have never removed the tender shell to clean the brushes. I have 4 of these engines. Put a small drop of oil on the motor drive shaft behind the shaft coupler and the motor frame. Then put the trucks back on making sure the springs are where they should be. You can also stretch the springs just a little to give more pressure. Just a LITTLE.
For he main engine remove the one screw in the center and the shell should lift off. Use light oil or light grease to lube the worn gear and the shaft. When you but the screw back in before  you tighten all the way turn the shaft to make sure all wheels spin free. Reconnect the engine to tender and you should be good to go.
These engine always seem to run a little rough after sitting for awhile but get better after a few laps.

WHAT system are you using? Sounds like you have a short circuit. Might be one of the tender truck got turned around 180 deg. That will cause a short The same thing can happen if the front truck is turned around.

The engine out  of the box new should run on DCC or DC without the jumpers installed. It has a duel mode decoder. It will just take more power to get going. Put it back to the way it was and try it. If it works then the decoder is ok and it is the way you are installing the jumpers that is not working.

You are correct. I thank the lord for a good day.
It was like being on an episode of Gray,s Anatomy. Also what a birthday party it was , there were a bunch of nurses ripping my clothes off.
I guess the important thing was to get to the ER before any real damage was done to the brain also. If you have chest pain and your arms hurt get to an ER fast. Glad I only live 8 blocks away.

Lets see. On Sat the 21st it was my birthday. GOT up in the morning and had a breakfast sandwich. Walked the dog and thought I had indigestion. Came home and both my arms were hurting like they were hit by a base ball bat. Went to the emergency room and found out I was having a heart attack. One artery 100% blocked and 2 more partial. Within 1 hour both were fixed with stints and I get to stay around for another birthday and Christmass. They went thru my wrist with the wire in a hole no bigger then a mosquito bite. Can't say enough about how great they were at to hospital. Was home on Monday afternoon.
THURSDAY afternoon bought a new lap top and took delivery of a N scale 2-10-2 I ordered. One great week.