250f mod options

[thump chump]

jumping off into the void-

the engine is out and is being shipped to Nor-Cal this weekend. The whole thing is being rebuilt from the crank up. From what I understand, it will receive some blueprinting, larger ti vavlves, flowbenching, new cams, and a new carb intake.

will post results of how this sucker runs in about a month. Until then it's back to the 2-stroke side of the world.

 

[jimt_yz400]

Who is doing the work on you motor in NorCal?
Just wondering since I know a few engine builders and how much is it going to set you back? By the way why do you need the bottome end done? I would expect that a bike that young would not need any crank work.

 

[thump chump]

Nor-Cal

Russ Fletcher. It's being all done through Big Gun. I figure there's about 30 or so hours on the engine. Since it will be almost all apart anyway, I going to have the crank rebuilt and the timing chain replaced. Don't care if the are worn out or not. Call it preventative maint. by a guy who is very hard on his engines. I rebuild the bottom ends in my 2-strokes every 8 weeks. If I don't I am gauranteed problems.
Big Gun sponsors me, so I am not sure how much the cost is. I do know that they are coming out with different stages of the same engine. It the same one that Brandes runs in the nationals. As for reliablity, I know for a fact that he ran 4 nationals, including the practice sessions, without even re-ringing his bike.
I am also told that the full mod gives the bike approx 12hp over stock when combined with the Big Gun pipe. Given, the pipe accounts for 3 to 4 hp, but that's still a healthy gain. I was told that these figures are dyno figures, but do not know the type of dyno- I'll try to find out.
If you want more information on the different stages- give Big Gun a call, and tell them Paul Kellen sent you.

 

[jimt_yz400]

Thump,
I actually just bought the Big Gun Quiet series exhaust for the 250F. It's not bad, in other words it's not as strong as some of the others of of the bottom but it is noce and quiet. I want something strong down low with lots of smooth
torque ans a decent over rev. I'm using this bike for Enduros and other
off-road stuff. I have another 250f that I use just for track time to stay aggresive. I was really interested in why you chose to re-bulid your bike so soon. It's making me wonder if I should reing mine real soon bu if I do it would be nice to do something else to get more hp's out of it. It would probably cost me a *mint* to do what you're doing , though, so that's out of the question~~
I've heard of Russ , but I've never met him.

 

[thump chump]

rebuild time

I ride the Pro class, four 20 min motos a week, plus 3 practices. The bike has about 30+ hours on it to my estimate (i bought it used). I have been recommended to re-ring the bike after only 5 hrs. If you don't beat on the bike as hard as I do, I wouldn't worry so much. But I have noticed a significant decline in performance since I began riding it. I have a 2-stroke YZ250 as well. I have to re-ring that once every three weeks, and put a new piston in it every 6 weeks. I do it mostly for preventative maint.

I know people that haven't touched their 250f since the bought it. And they haven't needed to. But I have seen pros in So-Cal blowing them up with an increasing regularity as the seasonhas progressed.....

 

[thump chump]

more info-

I have heard that MXA did a rider impression on the Big Gun modified 250f in this month's issue. I haven't seen it yet, but am hearing some really good things about it. This bike in this case uses a different piston that what they are putting in mine, but I am unsure what the difference is. I believe that the piston they are using in my bike is a higher compression piston.

I can't wait to get it back now:)

 

[roosteater]

Originally posted by Rich Rohrich


We'll be cracking open Okie's 250 to do a 267 kit soon, so I'll have more info at that point.

Okay.....that's it....I've decided that Okie has a sickness. He absolutely cannot leave his bikes alone, can he? We first see this in the 99 KX 250, which he promptly converts into a monster 310. Shortly thereafter, we see him fall prey to the wiley charms of the Service Honda CR500AF. Finally, he puts a leg over his old man's bike and we see Okie's fickleness yet again! Boom.....a brand new YZ250F sitting in the driveway in fairly short order. Now we find out he's tearing that open to overbore it to a YZ267F. Man....I don't know how much more I can stand. (Color me green!) Sorry Okie....but, I think you're insanely compulsive. Time to seek professional help?

;)

 

[jimt_yz400]

Regarding rebuilding the 250F:
I spoke with a friend of a friend who road races single thumpers and is very
experienced in modifying thumpers (not to say that the folks out here are not
expereinced) and recommended not to go to a high compression piston. He
said that you would get better gains from an exhaust, porting and new cams.
He also mentioned that in his experience you might want to replace the valve
springs when doing the top end. He has seen springs in Yamahas go soft after long hard use.
So, I'm wondering if I shoudl replace the springs since I have the top end
apart.
Thump, are they replacing the springs in your bike?
Any comments?