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So I bought a used 2018 CRF 250l with about 4500mi last week, private sale. I have always owned 4 cylinder street bikes for the most part, although I did have an 84 XT 600 enduro. I knew this bike was going to be quite low powered compared to any bike I had before, though I am still very impressed with how refined it is compared to older models I’ve owned. I do wish it had just a bit more punch if possible, Now, the bike came with all the recommended upgrades I’ve read about here as far as all the rock guards and lighting mods etc. He also gave me, still in the box, a complete 305 big bore kit, with the pre-programmed EJK for it also. I am wondering if, since I already have them, I should put these in right now. The bike has 13t and 45t sprockets, and I don’t like the fact that I can’t even drive down route 1 at 60mph without being at almost 9000rpm, but worry that going back to stock gearing will make the bike far more anemic. Basically if installing the big bore kit and buying a full exhaust will really make a noticeable difference, I am willing to do it, and at that point bring up the question between the Yoshi complete kit, and the two FMF options, the “power bomb” and the “mega bomb”. I am curious about what the differences are between those products, also there appears to be two different FMF slip ones for my year, both at the same exact price.

Welcome to the site !!

I personally do not think the big bore kit alone will give you what you are looking for , what I would do is experiment with the gearing till the bike pulls the way you want , but yet still will go over 40mph

Here is a gear chart to help you decipher where to go , compare your current setup with the stock gearing , and maybe go somewhere in between if stock is too boggy and what you have is all bottom end , like keep the 45 and go to a 14 front , or something along those lines , this will give you the best (or at least as good as it is going to be) between freeway riding , and not needing someone to push you to get thru a intersection after stopping ....

1 tooth on the front will equal around 3 on the rear , so keep that in mind , larger changes can be made easier by swapping the front sprocket , and fine tuning done with the rear , and also going larger on the front will lessen the torque , where smaller will give more , then compensate with the rear for top speed , in the chart you will see that different combo's give close results , so a front or rear can make the difference , so with a 45 , for example , you could go with a 12 ,13 , or 14 sprocket to maybe get what you want , and same goes for the rear ................. for example ............. , my 2020 450R pulls like a monster , so to mellow it out , I went with a 14/52 , instead of the stock 13/49 , I have about the same speed everywhere , it still pulls hard , but it does not rip my arms off now
, all I changed was the power delivery with the change in gearing , I did not lose power , nor did I lose torque , I just changed how it is delivered and put to the ground .... that is what you will need to do to get what you want

Of course depending on how far from your current setup you go , you will need to either add or lessen the chain links , so get a 120 link chain and a couple of master links , this way you can swap around and add or subtract links till you get what you like ( buy the cheapest chain you can find) when trying different sprockets , then once you add/subtract links and sprockets and find the sweet spot , then you can order a good chain in that length or close and cut a link or 2 , and you are good to go , as there really is not set gear ratio for your or any bike to do this to get this , its unfortunately a bit of experimenting till you get what you want , or as close as you can ....

Thanks for the info. I am aware that this is never going to be a fast snappy bike, so I really never would have gone out and spent $900 on the 305 kit and EJK, but since they came in a box with the bike, I am certainly going to install it since my labor doesn't cost me a dime. I wonder if the header pipes, either regular type or the FMF chamber type are worth getting, or just the slip-on makes much of a difference on this bike. Fortunately I'm not much more than 145lbs fully dressed, so I've got that going for me at least!

What you need to do is contact whomever you are planning on getting the pipe fro, whether it is FMF or another company , and go over what pipes they offer for your bike , then go over the HP and Torque gains/losses that each has , then weigh the options , usually aftermarket is less restrictive than stock , so usually they produce better numbers , but that is not always the case ...... For example , the 2020 450R I have , the Factory Edition comes with a Titanium Full Yoshimura system .... but .... it actually puts out less power than the stock muffler system ,,, what it does is deliver the power differently , but as far as power , you gain nothing ,,, that system to buy is over $1300 , and it creates less power .... so again , you have to weigh the options , and go over the specs of each system you are interested in , including Slip Ons .....