300ex motor in 250x

[zell250x]

will a 300ex motor bolt right in 250x. i would like to have a electric start and a little more power. thanks

[Trevor]

It should but I don't know if there is any more power though.

[Ryanwolfe911]

Of course there's more power. It's more displacement isn't it?

You will have to have the 300ex wiring harness to make it work.
It's kinda not worth it though. Youd be better off putting a350X motor in. You can bore it to over 400cc's without even stroking it and beat the pants off a 400ex.

[riley1374]

I just did the motor switch. I took an 87 X frame and put in a 300ex motor. If you are gonna do the switch do yourself a favor and buy a 300ex frame off of ebay. Comes in handy with the mounts for the battery box and gives you the bracket for the voltage regulator and some other electrical items.

As far as more power, the 300ex is almost the same as the 250x so if its not a worked motor dont even bother. I had a rolling chassis 250x, and a 300ex worked motor, that was the reason for my switch. Whatever you decide, good luck. PS Also you will need all the 300ex wiring as someone else suggested.

[zell250x]

i was planning on rebuilding the 300ex motor first, but how did yuo put the battery box and all that electrical stuff on?

[riley1374]

I bought a battery box off of ebay, and had my buddy weld up tabs so that i could bolt the battery box to the tabs. As for the electrical, i had my buddy weld up one long bracket next to the battery box and bolted the majority of my electrical stuff back there. After doing all this, it would have been much easier to just spend the money for a new frame off of ebay, but if your good with a welder, go for it.

[Ryanwolfe911]

Like I said, big giant waste of time. 350x enginescan be had for less than a 300ex engine, and will plug right into your 250x harness. I've ridden one with a stock 350x motor.(still had the factory pipe) and it was twice a fast as when it had the 250x motor still in it.

[bwamos]

Agree. If your looking for a motor swap.. get a 350x motor. A 300ex motor has more low end torque than the 250x, but revs out slower. I actually prefer a 250x motor over the 300ex motor.

[zell250x]

i got the 300ex motor for almost nothing and i think i might bore the cylinder and get a new piston and ring set and put it in my 250x. and the clutch too. but still looking for a cheap 350x engine if you now ehere any are. thanks guys

[fasterblaster09]

I rem. a while back when I was thinkin about the swap, someone told me Lerch had a 350x motor,not sure if he still does or not though..

[bwamos]

Originally posted by zell250x
i got the 300ex motor for almost nothing and i think i might bore the cylinder and get a new piston and ring set and put it in my 250x. and the clutch too. but still looking for a cheap 350x engine if you now ehere any are. thanks guys

Ahh.. I gotcha.
As stated before, you'll need a wire harness for the 300ex. A CR style kill switch will work good for a starter button, and you could custom mount your battery on the lower frame rails in front of the motor, as the 300ex has a light front end anyway. ;)

Not sure if the CDI is transferable or not. I'm thinking it wasn't but I'm not sure.

[nossquirrel]

Just a follow up of the above, a 300ex cdi is different than a 250x cdi. And as everyone else posted, you get a 350x and it is a plug and go with the wiring. Just need some minor modifications to get the motor lined up correctly.

I personally am building a 250x and the reason for this is to get away from the battery b.s. You take the 250x bottom end and put it with the 300ex top end, and you got yourself a honey pie!

[zell250x]

i got that 300 motor and the gut i got it from said it ran . but i started to take it apar tcuz im going to put the head and cylinder on my 250x and the cam was broke and the cam sproket was off and broke inhalf. that pissed me off cuz the guy told me it ran but o well i got the top end to put in my 250. im still looking for 350x motor if anyone has one forsale.