GlowingBulb

When you state it wont run without the starter on it, do you mean that it cuts out when you remove the glow starter? Sorry for the obvious question but have you tried to replace the glow plug?

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I'm not familiar with your engine so I cant say for certain but 107degC seems very low as a max temp, I aim for 120degC above ambient temperature (so if air temp is 20deg I avoid going over 140degC measured at the glow plug). Edit: I've checked CML's website & these temps are correct, it runs cooler than mine. Performance will take a hit running 20% Optimax but temps will drop due to a smaller detonation within the engine. It does sound like there's something off if you're struggling to hit a decent tune; the adjustment windows seem very small, you should be there or there-about & have a tolerance of a couple of hours turn either way without too much difference in performance. You've done all of the basics - factory default settings, lean off small turns on HSN until improvements are seen then adjust LSN the same. It might be time to look at other variables rather than just your needles - is the glow plug correct type, functioning at peak, correct grade (temp), do you have a new 1 to replace it with to try & eliminate this? Is the exhaust gasket seated correctly / not damaged? Is the pressure return tube from exhaust to tank in good condition without kinks or holes? Is your fuel filter clean & passing fuel correctly? Is your air filter clean? Is the fill lid on your tank seating correctly?

Just took my sons buggy out this evening, had what sounds like exactly the same problem as you're having, bogging after idle. Didn't matter what I did with the needles couldn't get it right. I managed to find the issue because the idle was all over the place - I found a slight airleak in the fuel filter, you could see fine bubbles entering the fuel messing up the mixture, not bad when blasting about but the bubbles got bigger when idling. Could be worth a look for you also?

Today I learned a valuable lesson whilst tuning my sons MP9 - we ran a tank of fuel & left to cool for a few minutes, unknown to me my son had decided to switch off the receiver & knocked the throttle wide open in the process. I fitted the glow starter, grabbed a handful of pull start & gave it a yank. Trying to stop a buggy shooting off at WOT using just the glow starter initially isn't fun, grabbing hold of the hot exhaust with your other hand is definitely not fun, sticking your thumb on the exhaust to kill the engine hurts like hell. Lessons learned today: Wear gloves Check TX is connected to RX KE21SP engine at full whack is quite loud & scary when you're not expecting it Heat blisters hurt more than I remember

Best of luck mate! You cant beat FLIR for accuracy, they've been around for years, I used to nick 1 from work to check temps when I started to my buggy but I found that I'd get variable readings depending where I pointed the gauge (obvs). With a pen type that has a bung to push into your heatsink you can be sire that its always pointing in the same position & is the same distance away from the glow plug. https://wheelspinmodels.co.uk/i/252617/ That looks exactly the same as my Fastrax just a different colour, you can see the bung installed on the photo which helps consistency. I'm sure its not as accurate as the FLIR but I'm really interested in the same reading every time as reference not a reading accurate to 0.5deg 😉

Its a minefield mate, you can be too rich LSN & too lean HSN at the same time. I do think you're too lean HSN now I've heard that overrun. I think you're bogging with too much fuel after extended idle also. 2 problems caused by separate needles. If it was my buggy I'd richen off the HSN, that's an easy fix, you're just slightly over lean IMO. Once that's done you can forget about it (until it gets much hotter / colder than the day you did your tune, or you change fuel brand, or glow plug etc etc). Personally I think you're over rich on your LSN & it needs to clear its throat on WOT after a while so you need to reduce the fuel being presented to the throttle after idle. Tuning is really subjective, there must be science behind it all but your ears, eyes & a screwdriver seem to be all that's available to us mortals

I genuinely wouldn't worry too much about the pinch test, it's very subjective & variable based on how far away from the carb you pinch, how firm you pinch, etc etc. I believe that if the engine is performing correctly & isnt overheating then you're pretty well tuned. What fuel are you using, I know that Optifuel fuel, especially the 25% RTR mix is very smoky, you can be too lean using that & still get good smoke, When checking the tune of my engine I use a Fastrax IR Temp gauge to be sure I'm not cooking it, if I see the cylinder head temp (top of glowplug) higher than 130degC then I richen the mixture by 1/8 turn https://www.modelsport.co.uk/fastrax-temperature-tuning-temp-gun-and-screwdriver/rc-car-products/374120 - its out of stock at the moment everywhere I've looked but there are similar available, I like the rubbe bung on this type that makes sure you're locating it correctly in the heatsink at a repeatable distance each time.

Also after watching your last video a few times I think I've heard the engine over-running a fraction when you come off the throttle at 1:39, if you listen underneath your talking you'll hear the engine flutter before the revs drop, I'd richen your HSN by 1/8 turn min, maybe 1/4 & see if there is any major change in top end performance. Again, its an observation based on a video & it was WOT for a long time, probably more than you would usually do if not doing a demo.

When everything is in the right area then you shouldn't have to adjust any needles between cold start & warm running. If this problem was on my buggy I'd try a drastic change on the LSN by leaning it 1/2 turn & see if the problem gets worse or better. If worse / no change then you know that its not too rich, try 1/2 turn richer from its current position if leaner doesn't work. When making big changes to any needle always watch for smoke & check temperatures to be certain you're not damaging internals - this is usually most important when leaning out the mixture. Just a thought - when you let the buggy idle to a point you know it will bog down when you open the throttle take a look at the fuel tube, is there any tiny bubbles in there? I'm taking a wild guess but you could potentially have a very slight air leak which is being pushed through to your carb when its been idling for a while - probably not though, just trying to think bout what would cause an issue of any description with your fueling after extended idle.

Very interesting, I'd look at leaning the LSN a little, it sounds like its trying to clear its throat after idling for a while.

I've re-watched your video & from what I can see / hear it seems good. It revs out well enough (it'll get more snappy the more tanks you run), idle settles down after 10secs or so & there seems to be a slight hesitation at WOT after its been sat for a short while. The hesitation / bogging might be more noticeable when you're physically squeezing the throttle vs. what I can see from your vid but if you can give it a few more tanks I think you'll see performance gains right through the rev range as it get more loose. Quick question: are you using after run oil when you finish each day? FYI - I've got an SMD box, it's great!

Looks & sounds like you've got the tune somewhere very close & for the time being I wouldn't adjust either the HSN or LSN any further. You'll find the engine will loosen up some more once you get more runs in. After a few more tanks perhaps 1/8 turn leaner on the LSN but not a lot - take your time, you wouldn't rag the nuts off your brand new car straight out of the showroom would you? Besides looking for a nice trail of blue smoke you should be listening to how the engine sounds (plus check the temps to be sure you're not cooking it!) There are lots of tuning vids on YouTube, some with conflicting information, the best I've found for an explanation is this by Mike Craddock, skip to 8mins for the tuning description. A starter box is definitely the way forwards, I skinned my knuckles 1 too many times before I bit the bullet & bought 1, makes life so much easier - I've left the pull start in place so when I'm out bashing I don't need to carry the box around with me I just get it started off the box in the boot of my car then the engine is nice & warm for the next time I need to start the engine again.

Or you could blow down the fuel tube going from the exhaust to the tank to pressurize the fuel line

You should find that most engines are interchangeable with others e.g. Kyosho .21 engine can be changed with an HPI .21 engine or any aftermarket engine of the same displacement. Upgrade parts in other areas might be available such as shocks, springs, clutch etc. but anything designed for a particular make / model will probably be specific e.g. lower suspension arms etc.