Big Bore 250EX

[jay-r]

Does anyone have experience with the Powroll 2mm overbore kit for the 250ex? The kit includes 10.8:1 piston and high lift rocker arm. I was wondering how much of an increase in power this adds. I know that the reliability would probably suffer, but how much? My wife loves her 250 but would like more power. She does not want to move up to a manual clutch quad.:ermm:

[BaD_250ex]

Ask Brokitin. He has one, he said it helps alot.

[jay-r]

Thanks, I'll look him up.;)

[2qk4u]

let me know what he tells you

[GETSOME]

Originally posted by jay-r
Does anyone have experience with the Powroll 2mm overbore kit for the 250ex? The kit includes 10.8:1 piston and high lift rocker arm. I was wondering how much of an increase in power this adds. I know that the reliability would probably suffer, but how much? My wife loves her 250 but would like more power. She does not want to move up to a manual clutch quad.:ermm:

Dude! Are you like my twin or something? We did the Powroll kit for my wife's 250EX. Of course I dont have a dyno at my house but it feels like it gives it about 15 - 20% more power everywhere- top end, bottom end and even right off idle. We run straight race gas in it now and it smells good - 110 octane. No BS- you also gain some top speed because it will rev out more.

If your on a complete straight stretch and you hold it pinned - it will continue to accelerate until the it hits the rev limiter. I could never hit the rev limiter when it was stock.

Lets see what else, we gained a whole gear everywhere at the dunes - but its still a 250EX and will not climb steep dunes. It wheelies better. I took 2nd place in a wheelie contest with it at our local poker run. I would have taken 1st but I drank too much beer before the competition- I was not the only one drinking.

Here are the downsides: It now needs taller gearing and the only way to do that is with taller tires - gay:ermm:

The added power is slowly but surely destroying the stock clutch. EBC clutch is on the way.

$$ Spendy front suspension is another mod it needs to compliment the power, but for now we will just beat the hell out of the stockers.

I really hope this helps. It is not very often you get to chat about your big bore 250EX. No one on this forum except the loyal 250 owners care about discussing mods to 250EXs.

Here is one more important point: You cannot use an aftermarket cam with the high ratio intake rocker - thats what Powroll told me. The 250EX is still relitively new and eventually the big dogs like Curtis Sparks and White Bros. etc will develop larger bores and camshaft combos with different valves, springs, etc. Well be there.

I've seen it all before, I was there, yeah it was called the 80's!

I love that movie:p

[jay-r]

Thats some great info, just what I was wanting to know. But, do you have too much detonation on 92/93 octane pump gas? Also, what tire size are you running on the back?

We don't have dunes out here, but we do have wooded hill climbs, and the 250 just won't pull all of them in 2nd. I think that the powroll kit would give it the edge that it needs.

Of course my other option is to put an efm auto clutch in my Z400 and give it to her so that I can get a YFZ 450!!;)


Thanks for the information that sounds like a cool 250ex.

[GETSOME]

Have not ever tried running straight premium 92 octane. The closest we have come to that is half premium, half UNOCAL 110 octane. I'm just trying to protect my investment. Using race gas ensures that the top of the piston is properly cooled and it smells good.

We are running the stock tires on the back, I'd would like to get a slightly larger tire to get some more top speed.

Its a fun bike, it will destroy a stock 250 by quite a few bike lengths in a 100 yard drag

[mudderchic]

I am glad to hear that everyone likes their Powroll kit because I just ordered mine. However, I was just wondering if the Kit may come with jetting instructions or tips on how to jet it. I was just getting the hang of adjusting the jets on it with the White Brothers Exhaust and now i am worried that I'll have problems all over again. Any help would be great :)

[brokeitin3]

dont let just any jimmy joe bore the cylinder. and jetting will be a pain because you will have 20 different people tell you something different. Ive heard of some people running anywhere from a 98 to a 120 main jet. but if you need any help we will be here.

[jay-r]

Cool, let us know how you like it.

[GETSOME]

Originally posted by mudderchic
I am glad to hear that everyone likes their Powroll kit because I just ordered mine. However, I was just wondering if the Kit may come with jetting instructions or tips on how to jet it. I was just getting the hang of adjusting the jets on it with the White Brothers Exhaust and now i am worried that I'll have problems all over again. Any help would be great :)

No problem. I did the homework for you. Just to be safe we started out about six main jet sizes larger which equaled out to be a 130 main TO MAKE SURE IT WOULD BE RUNNING RICH. Then we went down one main jet size at a time until it quit blubbering on the top end.

We ended up with a 120 main being the jet size where it ran excellent.

We live at 600 feet elevation.

We use the dyno jet needle in the third clip position.

I see you have white bros. exhaust, but what other mods do you have?

Well at least you know you wont need any jets larger than a 120. But my wifes 250EX has a full exhaust system, and a three angle valve job which might require our 250 to need one jet size above yours.

Good luck, I hope I helped:p

[mudderchic]

Originally posted by brokeitin3
dont let just any jimmy joe bore the cylinder. and jetting will be a pain because you will have 20 different people tell you something different. Ive heard of some people running anywhere from a 98 to a 120 main jet. but if you need any help we will be here.

I am having it bored professionally by a Honda dealer. I already know that jetting will be a pain because it is without the kit. Do you have a 250? I was just wondering if you have had experience with it or if you are just guessing.

[2qk4u]

where do you order these powerroll kits from? also how much are they?

[jay-r]

Here is the website:

http://www.powroll.com/honda_trx250ex.htm

[RideRed400StYlE]

you are overdoing it with the 110 race fuel. it will run fine off of 93. I have a 13:1 comp piston in my 400, and all you need to safely run that is 108 octane. To tell you the truth your bike would probably run better on 93 octane than the 110. But whatever thats JMO and personally if I didnt have to run race fuel I wouldnt be spending near $5 a gallon for it

[mudderchic]

Actually, with the kit (I was told by Powroll) it is a lot better and safer to run race fuel with it because it runs a lot cooler. Plus it smells good too :)

[brokeitin3]

you cant listen to the goobs at powroll. they told me so much crap about mine it wasnt funny. the best one was they said the factory jet was fine not to even change it because the bike came from the factory way to rich. im not say for the application they did their test on it was wrong, but each engine will run differently a little. im running a 105 keihn in mine and another guy runs a 120 sometimes i run a 102 depending on temperature and if it get to about a 100degrees ill drop to a 100 main. and if you have the dj kit with the short really skinny needle then ill save you the trouble and tell you it wont work with this kit. no one i know has bee able to get it to work.

[brokeitin3]

first and second are easy to get the front end up. now all you need is the durablue axle, widen the front end, and some works shocks. all this really changes the handling of the bike. i may be selling some of my stuff in the near future so check with me before you buy.;)

[GETSOME]

Originally posted by mudderchic
Actually, with the kit (I was told by Powroll) it is a lot better and safer to run race fuel with it because it runs a lot cooler. Plus it smells good too :)

Correct. They recommend a minimum of 108 octane with the kit.

I have quite a bit of money into my wife's 250EX and I would like to protect my investment.

[GETSOME]

Originally posted by brokeitin3
you cant listen to the goobs at powroll. they told me so much crap about mine it wasnt funny. the best one was they said the factory jet was fine not to even change it because the bike came from the factory way to rich. im not say for the application they did their test on it was wrong, but each engine will run differently a little. im running a 105 keihn in mine and another guy runs a 120 sometimes i run a 102 depending on temperature and if it get to about a 100degrees ill drop to a 100 main. and if you have the dj kit with the short really skinny needle then ill save you the trouble and tell you it wont work with this kit. no one i know has bee able to get it to work.

Got the dyno jet kit and the powroll kit in our 250EX.

It works, no BS.

Clip is in the third position, 120 main, and it beats my cousin's stock 250EX in a 100 yard drag by (are you seated) 13 - 15 bike lengths.

It works

[Dusty]

I've posted this before, but i'll say it again for those who have a problem with the skinny needle that Brokeitin3 mentioned. Early DynoJet kits (and that includes the K&N kit), had a typo in the parts list, and the wrong needle was included. If you call DynoJet they will send a replacement. Although the replacement looks to be almost identical to the factory needle, with more circlip positions.

Brian

[brokeitin3]

Originally posted by GETSOME
Got the dyno jet kit and the powroll kit in our 250EX.

It works, no BS.

Clip is in the third position, 120 main, and it beats my cousin's stock 250EX in a 100 yard drag by (are you seated) 13 - 15 bike lengths.

It works im not trying to star an arguement but they told me 93octane was sufficent enough and the largest main that came with my kit from DJ was a 112

[GETSOME]

Originally posted by brokeitin3
im not trying to star an arguement but they told me 93octane was sufficent enough and the largest main that came with my kit from DJ was a 112

True! AFTER we bored our 250EX and had some valve grinding work done we had to order more jet sizes above the 112. Nothing above a 112 was in the kit.

The fuel thing, it all depends on how good you want it to smell while its running.

Sometimes we will run straight 110, other times we will mix it 50/50 with premium.

When the checkbook it tight we might even mix it 25/75

To put it another way;

What temperature would you like the top of your piston to be?

Higher octane - cooler running temp

Lower octane - hotter running temp

[mudderchic]

Those of you that have Powroll kits, did you resleeve the cylander head? Can this even be done on a 250ex? I took my quad apart today and the piston sleeve is VERY thin and will be even thinner when it is bored out. Will this hold up and be strong enough with a very thin sleeve? It looks like you can't resleeve it because you will have to do the whole engine. Any input?

[brokeitin3]

and no resleeving is necessary. but if you ever need to rebore the cylinder again thats when it will be necessary to resleeve it.