[Hpi savage 21bb]

Put a drop of loctite in the screw/bolt hole on the backplate, as well as the screw/bolt threads. The threads should be free from oil/dirt and let the loctite cure overnight. 

[Hsp N3 Glow Plug in a traxxas tmaxx]

Dont see why not.

[Nitro carb spitting]

Are you using electric starts on the others?  

[Nitro carb spitting]

If the exhaust is blocked then some of the atomised air/fuel mixture will be forced out the carb due to the crank creating positive pressure as the exhaust port is blocked.  

[Nitro carb spitting]

What is hold down the exhaust mean?  Is this brand new?

[Thunder tiger ts4n starts then stalls after about 2-4 seconds]

Welcome to the world of buying used, inheriting someone elses problems. Have you tried a new glow plug? Is the fuel tank lid seal good? Pressure pipe connected to tank from exhaust? Has the fuel line got bubbles in near the carb when it cuts out?  Just lean the LSN 1/2 turn with 1mm idle gap. Maybe air leak around carb or backplate, or just a knackered piston/sleeve. How much pinch does the piston sleeve when turning over with glow plug out?

[Glow plug colour]

If the car ran well with no obvious signs or sounds of running lean then I wouldnt worry. Always best to know what too lean and rich sound like and wont hurt if you just see with a couple of wide open throttle passes after adjusting. The image is a guide as nitro fuels dont all use the same additives but is a general indication, so yes 1 is the closest to your plug.

[Glow plug colour]

[Glow plug colour]

Looks ok, no significant coil deformation, they can fail relatively quickly just down to the variable quality of the plug, another one may last much longer. I had a number of the HSP N4 plugs fail in quick order, the next few lasted.

[Best budget battery for tamiya lunchbox]

Try the 4000Kv motor,  looks like it will work according to this video, how long the drivetrain will last will depend on your trigger finger. You could reduce the throttle power if your transmitter has adjustable end points. The program card will help to control punch and brakes.

[Thunder tiger ts4n starts then stalls after about 2-4 seconds]

Are needle settings close to factory? Always best to know where you are starting to tune from. Could be too rich or dodgy glow plug or carb idle gao too small. Rule of thumb is to be able to get it idling then tune HSN first, then adjust LSN and idle. You can always adjust the throttle trim to increase idle rpm.

[Servo arm/horn setup - so many washers?]

You may see a solution here...https://www.arrmaforum.com/threads/servo-horn-issue.35909/

[Servo arm/horn setup - so many washers?]

Is the servo horn stock or aftermarket, as the latter maybe the issue?

[RC Helicopter pilots. What was your line of progression via models and would you change the line up?]

Recently addes a K110S, great deal on Banggood and enjoying it, flying outdoors where crash landings are kinder. Find that main gear comes loose or twists out of position after some crash landings. Even dusted off Phoenix RC sim for more practice and muscle memory for inverted flying. Not had any rc cars out yet, but hopefully soon, after rebuilding a few nitro engines.

[Any idea what chassis this is?]

My money is on a Yokomo, https://rcworld.us/rc-1-10-drift-mazda-rx7-toyo-tires-yokomo-awd-chassis-w-gyro-led-rtr/

[Any idea what chassis this is?]

Have you tried google image search? Sometimes you can be lucky. 

[Exhaust gasket]

You should feel the manifold touching the gasket as you push it in, so an interference fit. Otherwise your just relying on the  faceplate seal. Sometimes you can cut one gasket down and double up, one on top the other, on the engine, but depends on thickness.  A spring that looks stretched or is very easy to put could also be part of the problem. Unfortunately exhaust manifolds and engines vary in their sizes.

[Exhaust gasket]

I've always found the HPI gaskets to be thicker, https://wheelspinmodels.co.uk/i/109078/

[Servo issues]

If the servo isnt rated for 7.4v then your 2s li rx battery is probably the reason why the servos have died, but you also need to set the servo end points, Setting end points means setting the points where the servo stops moving left or right. If the servo moves more then your steering/throttle can turn, then the servo components will be under stress causing electronics to over heat and potentially stripping gears. Your receiver also needs to be rated for 7.4v.

[Battery conversion lead.]

1 hour ago, Redback said:

Got a pick locky of your adaptor and the esc connectors?

Cant tonight.  The TRX esc has the new ID connectoer and the adpater has the old TRX connector with XT90 on the other end.  Plenty of info out there such as this.

[Battery conversion lead.]

10 minutes ago, Mr Johnty said:

Thanks for that locky i saw that it not right Traxxas end im affraid but thanks for the info.

I'm using an adapter for my TRX4 esc which has same TRX  connector and fits on the TRX4 esc TRX connector. The old TRX connectors fit the new TRX connectors.

[Battery conversion lead.]

traxxas esc to nimh tamiya? https://www.modelsport.co.uk/product/412931

[RC Car Batteries for the Traxxas XRT Ultimate]

Not sure but if you press  plus or minus whilst charging then the display should show the voltage for each cell, which will reach 4.2v when fully charged. The charge rate will significantly decrease the closer it gets to full charge as the charger will use it's balance lead to ensure each cell reaches 4.2v. you can get cheap battery voltage tester which plugs into balance lead for testing lipo pack condition.

[Traxxas Maxx Slash]

USA/GBP exchange rate isnt what it used to be and  UK 20% VAT, US has on average 5-7%  sales tax and this is added at checkout so not added to the display price,  it is what it is. 

[GT3B flashing]

Improvemnet depends if you want to use the additionals features such as extra channels, extra model memories, alarm if left on, key mapping, 4WS, etc.