Hi everyone

I have had several 300EX's over the years, but have never had any mods done to the engine. A few weeks ago I bought a new 2005 300EX from the dealer.

Well...I'm considering doing a big bore on it.

My question is this.

First off, the bikes electric start only. Why they made these electric start only has went through my head for years. The more compression the motor has, the more it needs a compression release to crank/kick it over. I know that doing a big bore kit of 330cc to 350cc will increase the compression so much that the starter and battery will then be christmas ornaments.

Powroll makes these kits and mentions the starters won't do anything after the modifications.

How the heck do I get it started????

 

I have seen the 352cc powroll stoker/bigbore, fire right up with the stock starter. I know the 250x engine has a compression release, and that rocker assembaly works on a 300ex. You would have to rig up a cable to bars, but I have seen it.

 

Floorit, I have the Powroll 329cc 80mm 10.5 to 1 kit with the billet midrange cam and it starts fine and runs great.

I'm still running my old big gun pipe which is fine but I have been actually wondering if there was a pipe that was better enough to justify spending the extra money to upgrade it?

The only negative was the edelbrock carb I put on during this build. The carb performs great but is continually lets the float bowl dry up. I have 10 other quads in my garage and this carb is the only one that gives me a fit.

I've thought very seriously about putting the 400ex carb on it.

In fact the starter/battery still work well enough to let me keep starting it to get gas flowing to the carb.

Hope this helps.

CRR

 

TractorPacker & CRR,....Thanks for the replies

TP - The compression release did come to mind, but the top of the heads are different [I think]. Maybe only a slight difference. I'll check out the jug to see if the compression release can be adapted.

CRR - That's good to hear. How's the heat....any problems there? Have you added an oil cooler to it ?
I've heard that adding the 400EX carb is one of the best things there are to do..considering the added area for fuel/air volume, ie - bigger valves, mild/high lift cam when the heads been punched.

LOL.....this thread brings a mod to mind that I did with my 88 250X. I was wanting more power. Well, a buddy of mine had a 86 350X that I bought from him. I stripped my 250X to the rolling chassis and pulled the motor and the swing arm off [I guess it wasn't rolling then..lol] Anyway, I pulled the motor and swing arm off the 350 and put it in the 250X frame. The swingarm bolted right in without any mods needed. The 350 motor went in fairly easy too without having to do any cutting. I did have to add a brace for the top of the 350 jug to mount solid due to the frame from the 350X being part of the motor.

It was a powerhouse and had plenty of torque. I rode it like this for about 6 months and then got tired of not having reverse. Where I live I do a LOT of trail riding and cross country making my own paths where no quads gone before. But having to manhandle the damn thing got old fast. I eventually reverted back to the way things were just to have reverse again.

Thanks Again Guys. I'll look into this further.

Floorit