Venom powered Terse Racing built.

Thanks to Correy at Advantage Tuning for the tuning!

2008 YFZ
WR crank
Venom 14.1 piston
Venom ported OEM Valves/ Springs
42mm Sredrum bored carb with Venom Rat Stack
Stock cams... cam modded
FCI intake
HMF exhaust
Dyna ignition stock and curve 1 were the best.
15/38
Hoosier 59/10/10



Here it is with the GP small cone pipe and my Ron Woods pug (both drag pipes)

Green HMF

Red is Gigot OOF small cone drag pipe

Blue is Ron Woods Pug drag pipe.



And before I bent the holy hell out of his axle! :icon_eek: :mhihi: Sorry again about that!




We also learned that if Justin advances his ignition at the dip/ flat spot in the power curve @ 8600rpm the dip will go away.

Wow, seems like great torque for a stock bore YFZ! Nice job tersejr.

How'd you bend the axle?

Do you have any graphs without the dip?

I had a similar dip on my '05 TRX...it couldn't be cured by ignition timing, it was a severe crank case pressure problem.

Nice work bro.

How did you determined it was bottom end crankcase pressure?

Thanks every one, and yes this is the second YFZ to make this kind of tq on this dyno with the simple parts mentioned. Not my stock bore yfz though

Well we played with the curves on his Dyna ignition (stock curves that came with it) and one of the curves that retarded the timing made that dip in that exact rpm range worse, so we figured he could advance it more in that rpm range and that dip would disappear. This customer, Justin is a car tuner for like EVO's and Subie's and such and he has seen the same thing with adjusting the timing in one sport in the rpm range and the curve smooths out.

As far as crank case pressure that has crossed my mind when I was building my 534cc. I made a seperate line for each the head and the cases, and used very larger tubing, so more pressure could flow.... and I do not have any dips (per say) with the 534cc and it has the stock cdi on it.

I made a thread about this a long while ago actually....

The first indication of a problem was, of course, the dip in the upper RPM...and the bike didn't sound too good. Later, it was put on a superflow loaded dyno...and when loaded, the bike sounded like it wanted to die in the upper RPM's.

There was also always an oily film in the exhaust port...like oil was being pushed up from the bottom end into the combustion chamber and out the exhaust port...

After everything in the top end was checked meaning...

Swapped millions of jets, the airbox, intakes, air filters, exhaust pipes, cams, heads, pistons, carbs, clutches and springs, and ignitions...

After exhausting all those possibilites, we went to the bottom end to look for the problem and found it.

The first picture is of the relief valve in the oiling system. If the oil cooler gets some blockage, it forces the relief valve open and returns the oil directly back to the crankcase. You can see the black piece of material to the left of the spring in the first picture...this piece was in the relief valve holding it open, bypassing the oil cooler and dumping the oil directly back into the crankcase. The piece of material looked to be a plastic piece off of the timing chain guide....possibly an imperfect chain guide mold...a piece that chipped off and eventually found its way into the relief valve.

When the relief valve was unplugged...the oil level went down a 1/2 quart lol (had to add that much back)...and she ran RIGHT...no more sick sounding, no more dip...dynojet verified.

WPP Racing and Wicked Motors helped me through all of this and actually found the problem...cause I couldn't find it haha.

Sorry for the hi-jack...tersejr, if you like, I can delete this info and send Chad a PM.

Just thought it'd be cool to have this info in another public spot so that if anyone else experienced a similar problem...this might be something worth looking for to attempt a diagnosis.

No worries! I am glad you posted it here too, as I must have missed your other post on it. Thanks. What you describe makes a lot of sense and I will hold it in my brain under Honda stuff :) The yfz is a little bit simple then that though and aside from making the crank case vent line and the valve cover vent line diameters larger.... and ditching the black box on the sub frame there is nothing else to be blocked. Aside from a blocked passage in the side cover to the crank case vent line. This was tuned on a super flow, and I don't post the DJWP corruption numbers (as I have found them to be higher then an actual dyno jet), and this motor revved clean. We could tune some of the dip out with more fuel as this motor made more power Not at a 13.5-14.1 range but closer in the 13.1-13.5 range as well. If we gave it any larger main jet the low to mid rpm power would go to rich and start to loose power. Also I have seen it over and over again, richer jetting has seen to produce more tq in the yfz.... with not as much "peak" hp.

Thanks for Sharing it gives some of these Yamagay guys hope. (aka turd427)

Excellent job tracking down the problem...........Ive seen similar problems like this. Another way to track something like this is use a manometer to measure crankcase pressure, then varify what caused it. At anyrate you tracked it down until you found it.......most people dont take the time to really see what can cause this.
This should be pinned somewhere. Ill see what I can about pinning this in the engine tech section.

Thanks Zips!

I can do a much better/more formal write-up if you like.

I really need to give credit where credit is due tho...WPP/Wicked are the guys who found the problem. I, myself; switched jets, intakes, cams, filters, pipes, and ignitions...but when things started getting into the cylinder head and below, they took over and found the problem.

Brian @ WPP even sent me his Dyna Programmable overnight so I could see if that helped anything!

I have used two separate breathers like a dirtbike for years and have never experienced the common dips....maybe terse is onto something

Ghott if you start another thread writing your findings and situation up I will pin it in the Tech section.

Will get this done when I have a little extra time and I'll send you a PM, Thanks!

looks impressive! now you're making me really scratch my head on my rebuild. all that torque. long rod crank! safer, smoother, nice setup for sure. what kind of toque you think you could get with the venom pipe?

IMO the peaks won't change with the Venom pipe just a different curve. Yes with the Dyna programmable ignition. His was stock shelf curves. None worked better then stock, but one worked worse then stock. So custom curves are going to help, but IMO they won't make more peak power, just smooth out the curve.

what are the advantages of the wr crank/rod?
is this literally the dirt bike crank- no mods? other than the obvious 103.5mm rod.
is the rod stronger with the smaller wrist pin hole? or is it lighter?

I'll list them as differences... not necessarily advantages as it may not be an advantage to every one for every style of riding.

18mm wrist pin hole in piston = more piston material around the wrist pin. Most all of the failures I've seen the wrist pin is ripped out of the piston, not the wrist pin breaking.

WR oem crank... not mods straight up from Yamaha, is 1lb lighter then the OEM 06 crank.

103.5mm rod vs. 06 101.5mm rod (same stroke)

thanks for the insight. lot of great power on your build! plenty at 7500 rpms. should pull nice.