Before you touch the low end, replace the fuel lines. You may have a cut that is not visible.

Also, try a new glow plug and see if that helps.

Another possibility is with the type of fuel you are using. We had a lot of issues when using plain castor and no nitro on our engines at the field (random deadsticks similar to what you are having). Then someone tried a batch of Klotz 100 (I think). Its synthetic fuel with 8%-12% castor oil and synthetic lubricant in the Klotz lubricant (Total 20% lubricant) and we added in 5% nitro simply for some flexibility. That solved the problem so much so that when we had a shortage and tried plain castor again, we kept getting deadsticks.

With regards to the prop, you can try 12x6 or 13x4. The 12x6 is good for some hovering and the 13x4 for more 3D. I personally use 13x4 even on my sports airplanes as I like more acceleration than speed but that is your decision. I use MAS props only as the APC ones tend to break easily if you have a less than perfect landing. If you prefer APC, I suggest you use MAS till you sort your engine problems out

Ameyam