Well looks like I'm gonna be on my 4th engine. While doing all these rebuilds I have some advice to give to anybody that is considering going to a big bore kit on their X or EX.

1. Big bore is cheap horsepower
2. If you have to resleve the cylinder BORE THE CASES!! I don't care if you're told you don't need the cases bored do it!
3. Old timing chains and big bore kits don't mix, replace your timing chain
4. Port your head.
5. Beef up your clutch
6. Get a 350X air intake boot
7. On a 250X go no higher then 11:1 compression if you want to be able to kick it over. You're in for a workout if your engine doesn't want to start when it's warm.

These are just a few things. All my big bore stuff came from FST. No it's not FST's fault I'm on my 4th engine. It's been my own stupidity well some of it and just abuse. On the 250X and 300EX FST doesn't tell you to bore the cases but do it anyway. On some models the sleve will expand and hit the cases and then when your piston expands it will have nowhere to go and crack both your sleve and the piston. BORE YOUR CASES!! But I do have to say Dunlap is second to none when it comes to customer service and he knows his stuff. All my problems would have happened if I would have used anybody elses big bore kits. No hard feelings here. I've had a lot of questions from a lot of different people lately about my ride and I'd rather make one post then pm them all.

 

Very good advise indeed.

 

<< But I do have to say Dunlap is second to none when it comes to customer service and he knows his stuff. >>



Sorry, but I have to disagree with you there. Any business that only answers their phone one day a week has pretty poor costomer service and any motor builder that doesn't check out why a motor went bad (oil pump) and fix it doesn't 'know his stuff'!

 

I think for all the money and time you spent you should have just bought a 400ex. As for workmanship, I don't know but 4 engines? I would try a different builder and see what happens.

 

Don't want a 400EX. Everybody has one, I don't want to be like everybody else. As for workmanship the parts that he supplies are good parts. It's just that he never reccomended to bore out the cases on the 250X's. I had to find out for myself because I keep cracking pistons.

 

i thankyou for the info i plan to do either the 350cc big bore by profab or powroll or the 395cc by fst. let me ask you this do you recommend to have your crank stroke ?

 

I don't reccomend FST's 390 kit, Dunlap said they had problems with oil pumps failing. I think the Powroll 350 kit is a good kit but I reccomend buying their crank and DO NOT use your stock one.

 

i remember seeing a 390EX once at the local play track. it seemed like it ran pretty good. the only problem with it was this: IT WAS PURPLE! other than that, it looked like a beast.

 

Reliability is pretty good on these engines up to the 352 kit. Any bore/stroke larger than that is hard to keep together. They shorten the rod so much that it puts a major load on the cylinder walls and lower bearings. I had powroll do the crank work and have had great luck. I will definetly go back to them when I freshen the 410 up (and up it to a 426-the largest possible). I am tossing around the idea of building the 350x motor laying in my shop floor to a 454. Also, I have heard of using the 350x top end on the 250x bottom. But why do this when the 350x bottom has six gears?

You think 11.0 is hard to kick. Try kicking over my 410 with between 14.5 and 15.0! Basically, you can't. I am looking for a 300ex clutch cover so I can take out the kick start and shave weight (I weigh 270 and can't lose any so I will take it off the bike[img]i/expressions/face-icon-small-smile.gif[/img]).

 

thanks for making up my mind for me !powroll it is!