thump chump

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Jun 20, 2001
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I have gone with the Big Gun pipe, and am now wondering what options are available for additional increases. My particular interest is in headwork. I am wondering about the amount of gain that is available by headwork. I am thinking that I would want to explore this option first to keep my bike within AMA limits. Ideally, I am looking for more mid to top without sacrificing any part of the existing powerband.

I did a quick search on the boards, but didn't see anything, maybe I missed this discussion?
 

thump chump

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Jun 20, 2001
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Mr. Farley-

My fear is that going with an overbore will make the bike ineligible for AMA 125cc competition. I must admit, I don't have my rule book handy, but can't imagine that doing an over-bore and/or increasing cc wouldn't make the bike illegal.
I guess my question is more focused towards does anyone have any knowledge/experience of the amount of benefits that may be gained by headwork.
 

Rich Rohrich

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I haven't gotten my 250F cylinder head yet so I haven't had the chance to do in-depth testing. If it's anything like the 400 & 426 heads I'd suggest you look elsewhere for horsepower increases. The heads can be cleaned up and made a bit better, but there is nothing major hiding in the stock 400 design. It's VERY GOOD. Chances are the 250F head is even BETTER out of the crate. At 13500 rpm you can't screw up the cylinder head and still make good broad range power like this engine does. Blueprinting the cylinder head and deck heights will certainly pay some dividends but tend to be a poor value in terms of HP/dollar. I realize this won't stop "tuners" from charging outrageous prices for porting. caveat imperative of cavere

High end fuels (oxygenated or high energy blends) will meet the power requirements you outlined and still be AMA legal, but it's still not cheap and it takes some tuning work to realize it's advantages. No free lunch when the engine starts out this good :)

The camshaft is the area where there is the most to gain, but I haven't seen anything (SO FAR) that meets your requirements.
 

thump chump

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Jun 20, 2001
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thanks again

That was the info I was looking for. BF said you were the techie in the group.

I believe that the design is extreemly good and thought that improvements would be very small. And also agree that there are numerous tuners that would disagree with me and be willing to charge a nice fee for a few angles on a valve edge.
I am curious regarding cam options, but then again have not found anything I feel comfortable with. Please post any results you come up with regarding cams.
I am a firm believer in stock for the most part. I ended up with the Big Gun pipe for it's nice mid range torque. I will have to say that it was a hard decision between Big Gun and Dubach's pipe.
 

Rich Rohrich

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It may be worth investing in a second pipe with a larger ID and shorter primary length for top end tracks . The stock pipe can be shortened to shift the torque a bit up in the rpm range, but the effect isn't as great as a new pipe with a larger ID. Running specific setups for specific tracks seems like the way to go for expert level riders running the 250F.

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

thump chump

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Jun 20, 2001
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pipe-

.. the good thing is that Mike @ Big Gun would probably make that for my to test. I'll call him up and pester him for it. Will keep you posted if I get one.
 

bashn

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Dec 6, 2000
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I just installed Gorr's 2mm overbore kit in my YZ. I think it's legal for the 125 modified class. It's less expensive than most pipes and adds about the same amount of power. I can feel it mostly in the low to mid RPM levels. Top end seems about the same to me. I can now pull 2nd gear off the starting line on a consistant basis. I can also ride the bike more effectively in a lower RPM range. Overall, I think this is the second best mod after a pipe.

'01 YZ267F
Yoshimura pipe
49T rear sprocket


Mark
Mark
 

vetwfo'er

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Try a good air filter, like White Bros or Uni. Then dial your jetting in. These are only small gains but, are also cheap mods. And they do add up to a larger gain overall.

vetwfo'er
 

Rich Rohrich

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Originally posted by vetwfo'er
Try a good air filter, like White Bros or Uni. Then dial your jetting in. These are only small gains but, are also cheap mods. And they do add up to a larger gain overall.

vetwfo'er

There is zero performance difference between the OEM and aftermarket air filters.
 

thump chump

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Jun 20, 2001
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another thought-

..and I know I've already spent a lot time on another thread regarding this particular subject, but in speaking with the R&D guy from Pro Circuit at the races yesterday, his comment was to put a high compression piston in the bike. I then suffled over to the other side of the pits and asked the Vertex piston importer if they had that type of piston available yet. (This is the REM race on Sat at Glen Helen- pretty much anyone in the industry who races races here evry weekend). He said the Weisco boght out Vertex. Unfortunately Jay from Weisco wasn't here this weekend. (Whew!)

So, In a long winded sorta way- Mr. Rohrich, your thoughts? Also, would you still run pump gas, or would you have to switch to a 99 octane leaded fuel? I have always understood that you don't run race gas in Yamaha's 4-strokes.
 

Okiewan

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Re: another thought-

Originally posted by thump chump
I have always understood that you don't run race gas in Yamaha's 4-strokes.
And toads cause warts.
 

thump chump

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Race Gas in Yamie 4-strokes-

Ahhh- but I have this info straight from the horse's mouth at Yamaha- Ed Scheidler. I was told that running race gas actually caused the valves to gum up and affect performance. One possible caveat though- this was on the YZ400. I have not heard this from Ed regarding the 250f. But I would presume the same holds true due to the similarity in head design.

But at the same time, does a high compression piston neccesitate the use of race gas as bumping up the compression in a 2-stroke does? I would believe so, but would like to hear from someone who has direct experience in this area.
 

holeshot

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Re: another thought-

Originally posted by thump chump
(This is the REM race on Sat at Glen Helen- pretty much anyone in the industry who races races here every weekend).

Yeah, I heard that one of Rich's idols (initials J.W.) races at that jumpless, featureless, mudhole, geriatric rider's track.:p
 

Rich Rohrich

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Re: Race Gas in Yamie 4-strokes-

Originally posted by thump chump
Ahhh- but I have this info straight from the horse's mouth at Yamaha- Ed Scheidler. I was told that running race gas actually caused the valves to gum up and affect performance. One possible caveat though- this was on the YZ400. I have not heard this from Ed regarding the 250f. But I would presume the same holds true due to the similarity in head design.

With all due respect to Mr. Scheidler assuming ALL race gas will have the same characteristics and cause the valves to (in his words) "gum up" while pump gas will magically escape this dire fate is ludicrous. Anyone who is attempting to extract real performace from these engines and thinks they will do it with the random supply of chemicals sold as "pump gas" is sorely mistaken. Pump gas is fine for the weekend warrior who rides for fun a couple of times a month and won't ever touch the jetting. Racers who use pump gas while bouncing the engine off of a 13.5K revlimiter are missing out on power and response. The 250F and 4xxF engines might not blow up on pump gas, but you can be sure they are far from optimized under these circumstances.

For your situation where you see a major swing in altitude density between your two riding areas, it would be very easy to jet the bike for the cooler high density area using a leaded race fuel like VP12, Phillips B32 or something similar, and use an oxygenated fuel like the VP MR series or Phillips B35 for the warmer lower density area. The change of fuel may be enough to balance the air denisty change once you get it dialed.
 

ACS

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One option not yet discussed is a new CDI. Wolf (FMF in USA) or Vortex add as much as a pipe. I have ridden a Wolf one on a 250F and it was otherwise stock and it had more in the mid and reved a touch higher according to the seat of my pants.:)
 

thump chump

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Jun 20, 2001
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Race gas and geriatric tracks

RE race gas: I will run some 108 this weekend and fiddle with the jetting some. I guess I will have to bite the bullet and start using race gas again. I hoping I could avert this additional expense switching back to a 4-stroke. Good thing it'a almost time to send out resumes for next year!

RE REM: Yes, Mr. Holeshot, it is Bon Jody's home track. However, the track in my opinion, is one of the most challenging in the So-Cal area. It is only jumpless if you are a riding very slowly.:p Unlike ALL the other stupid tracks in So-Cal, this one changes EVERY SINGLE WEEK due to direct input from the riders. And it is not filled with stupid, ludicrous, uneccessary doubles and triples. If you prefer a more crowded, supercross-oriented, hard pack track, then go elsewhere!:scream: Keep this in mind, REM should be more known for the fast locals who ride there. The entire KTM factory team showed up a few months ago and was SEVERLY spanked. Langston only beat one of the Vet riders by a last lap pass. This is also where you find many of the local national riders preparing for the nationals. But aside from that, Frank (the promoter) is the best promoter I have ever happened to come accross. The REM track seems to get slammed a lot just because Jody rides there. I presume you are complaining about the mud because you recently raced the Riverside OT race there. It was muddy, but I'de rather race a muddy track than a dusty one, and remeber this- everyone has to race the same track :D
 

Rich Rohrich

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Re: Race gas and geriatric tracks

Originally posted by thump chump
RE race gas: I will run some 108 this weekend and fiddle with the jetting some. I guess I will have to bite the bullet and start using race gas again.

Which fuel are you going to use?
 

thump chump

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Jun 20, 2001
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race gas

I have Philips 76 most easily available. Either 99 or 108 octane. I can get VP some of the time, but it is hard to get to the only place I know that carries it before they close. But I can get F&L the cheapest (my race buddy is sponsored by them).

Never an simple reply with me.:)
 

holeshot

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Re: Race gas and geriatric tracks

Originally posted by thump chump
RE REM: Yes, Mr. Holeshot, it is Bon Jody's home track. However, the track in my opinion, is one of the most challenging in the So-Cal area. It is only jumpless if you are a riding very slowly.:p Unlike ALL the other stupid tracks in So-Cal, this one changes EVERY SINGLE WEEK due to direct input from the riders. And it is not filled with stupid, ludicrous, uneccessary doubles and triples. If you prefer a more crowded, supercross-oriented, hard pack track, then go elsewhere!:scream:

I was there with the ROTMX two years ago and never returned, so I did go somewhere else. I may give the track one more shot (I'm getting geriatric, after all). This is one track where you can arrive with a '73 Maico and lay some whoopa$$ on someone riding a modern machine.

As for race gas, I've tried Unocal 76 (110 octane, I think, out of 50 gallon drums from Montclair Yamaha) and VP-12 in my 426, both straight and mixed with pump gas. There was some difference in how the bike responded, but I don't ride more than half throttle anyway.:silly: Your experience on the 250F may vary.

If I were motivated, I would run about 1/3 race gas to pump gas, just to hedge my bets against poor pump gas, and to allow the same jetting as straight pump gas. It was fun experimenting with different fuels and jetting, and it was interesting to see how quickly VP-12 evaporated when spilled on the garage floor, indicating a much different chemical makeup than pump gas (far more light ends content, or at least "lighter" light ends). Much of the neighborhood could smell the fuel, and were expecting a big explosion. :)
 
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thump chump

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Jun 20, 2001
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etc, etc, etc

Headwork for the 250f- I have a friend who had White Brothers do some work on his 250f head. I am going to ride it back to back with mine for comparison this weekend. I will also be trying some Phillips 76 110 octance this weekend.

Holeshot- Next time you come out to REM, look me up. #647. I'm in the raised yellow Dodge Dakota with black rims and yellow ez-up. Can't miss it. The track is actually pretty good right now, and this weekend is the last round (I think) of the No Fear summer series. They have been giving a lot of stuff away each week.
 

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After some meditation, and putting a 2mm os piston in my 426 I was thinking that if I had it all to do again on a smaller scale $$ wise, I would set up the deck height to get the right squish, run real gas, get a killer valve job from someone who understands and doesn't just pay magazine advertisements, and Laugh!
 

thump chump

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Jun 20, 2001
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proper set up

The bike is now garaged until I rebuild it. I was hoping to get one more race out of it, but now I don't want to push my luck, I can definately feel the decline in performance. So I'll just go ahead and rebuild it from the bottom end up.

On performance enhancements, I am hearing that Russ Fletcher has been working magic on a few of the top national rider's 250f's. Still unsure as to exactly which direction I'm going, but will soon find out, and hopefully soon be roosting on my 250f again. Untill then, it's back to the other side. Luckily I still have my 01' YZ 250 2-stroke..
 
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