billyt

Sam It has two base gaskets for a reason! That reason is taking one out to tune the engine. Of course it changes the squish BUT so does swapping for a modified higher compression cylinder head and people do that! If it were me! I would do the following in the order as I write. Take the cylinder/jug off Remove ONE BASE gasket Put the jug back on! THIS NEXT STEP VERY IMPORTANT! When putting the cylinder head back on and after torquing down cylinder head and jug/cylinder REMOVE SPARK PLUG AND TURN/PUSH START LEVER SLOWLY. This will verify that the piston is not hitting the lowered ( lower due to removing a base gasket) cylinder head! If it does NOT hit then proceed with re-assembly and then start bike as usual. You may have to increase the octane of the petrol If this first step works let us know and we can walk you through the next steps. Good luck! BillyT

yzeefoureight Firstly, I am not familiar with Gas Gas engines. BUT these principles work for all trials bikes. Okay Jay I will start. You pitch in at any time, or in fact anyone pitch in. If I wanted to increase a 125 cc trials bike for more bottom end, depending on the riders level of riding here is what I would do. An advanced rider: On a 125cc trials bike the bike is more than likely ridden with high RPM's most of the time. The bike in stock form is pretty close for high RPM riding. Leave the stock 26mm carb alone. I will explain why in the following changes to a 125cc if I was a average club rider. Change the head for a higher compression. Race fuel/ higher octane will be necessary now due to increased compression. Change timing. Open up the exhaust port to let the bike breath better. If I was average club rider and was NOT the greatest at revving the **** out of the bike to get up objects, hills rocks etc Here is what I would do to get more bottom end and snap with some torque. Change out the carb for a smaller one. Trials bikes usually come with a 26mm I would go with a 24mm. Why? The movement of the piston piston creates the vacuum on the carb. It will be the same level of vacuum regardless of what carb is on the bike. The smaller carb performs better on a smaller displacement bike for the following reasons. If the vacumm is the same regardless of carb size then a larger orifice carb such as a 28 mm will see higher air flow BUT lower velocity. This lower velocity (due to a larger throat on a 28 mm carb) will not aerate/atomize fuel at the venture as efficient as a 24 mm carb with a lower flow but higher velocity. The step from a 26 mm to 28 mm will gain flow but there was enough flow already with the 26 mm what we are looking for is mixing velocity at the needles/jets venture. A 24 mm carb has enough flow for an average club rider. In fact I always when possible switch out a the 26 mm for a 24 mm carb. This is carb basics. For the same amount of vacuum (air & fuel) to go through go though a smaller opening it has to speed up (velocity) making a better venture effect. The lower velocity from a 28 mm carb will feel funky at low rpm's and give the impression that one has lost bottom end due to running poorly/boggy lost snap due to funky fuel mixture. Granted the bigger carb will run better at higher RPM, and if you are a top flight rider on a 125cc you may want that? But I disgress, this segment is about an average club rider on a 125cc. I would also take off the jug/cylinder and either machine the base of the cylinder to lower the ports. Or if the jug has two gaskets remove one. Putting a thiner gasket is the cheapest and non destructive way of doing this. BUT not all manufacturers offer thinner base gaskets. If you do machine some of the base and you do not like the results or are now a top flight rider that needs to rev to the heavens then you can always put an extra base gasket back under the jug to take you back to where you started from. Lowering the ports by this method will also increase compresion and give some mid range power also. Obviously if money was no object then buy a spare jug and have the transfer ports lowered in the jug itself leaving the exhaust and intake ports alone. And for Jay. Wenn ich mich erh

Hey Paul It is not hanging anymore. I spilt some race fuel on it and it is driving me mad with power. It wants to go out and clean something. LOL How are things with you? So Jay. Lets try and help this guy as tag team to get more bottom end on his 125 si si senior! Okay? Please, no more silly magical horse power increase suggestion from puerly adding fuel. DEAL? Danka mein her.

Jay......... This is getting nuts. You must be a female as you will not admit that you are WRONG! LOL.... Lets do this.............. yzeefoureight go mix up some high octane race gas, put in the bike. do nothing else to the bike. And if you are still alive after all of that power increase let us know how marvelous the power increase was! LOl..... Over to you amigo! Das es das liebien. BillyT

Jay This is right from VP Fuels web site. Not one mention about extra power purely that race gas affords one the abilty to fine tune the engine heads, exhuast, carb etc without pre-detonation due to the charactistics of the fuel. It also affords a more consistant source of fuel affording leaner jetting etc. That is why you may see a slight cleaner (adding race fuel only) running of the bike due to fuel consistance and leaner jetting but more power hell no!. What does octane really measure and how important is it? One of the most frequently asked technical questions we get at VP involves the difference between Motor, Research and R+M/2 Octane Numbers. The next most frequently asked question is why some fuel companies represent their fuels with Motor Octane Numbers, while other companies use Research or R+M/2 Octane Numbers. 

Realize first that octane is a measurement of a fuel

Sherco Jay So we are both engineers (mine Mechanical & Electrical). So, one simple question one simple answer. If one does nothing to their bike (porting, exhaust, high comp head, timing etc) but add a higher race fuel will one see a noticeble higher output in power across all the power band on a trials bike? If so, tell me where this extra surface area of piston came from, how the stroke changed, how the timing changed, how the porting of the engine changed, all by mearly by adding a fuel source that had a higher flash point? Where did this HP come from? Over to you mon ami! BillyT

"Fifth gear did a test on the fuels about a year ago, yes I know its own cars and the engines aren

"Running higher octane does NOT give you more power!" "But it will up the overall bhp of the bike" Please tell me how it will possible do that? Purely adding a higher octane by itself will do nothing but burn more cleanly! When you add a higher comperession head you will need the higher octane to stop/prevent pre-ignition due to a higher compression and squish band. The flame or burn pattern will be more controlled with a higher octane, but adding a higher octane fuel to a stock bike thinking it adds more power is a placebo at best. In fact many studies have shown that you could in theory get less power by adding a higher octane to a factory stock bike. If you have or know something different please educate us! Respectfully BillyT

Hi Guys If I may offer my humble opinion on this subject. It is not mearly a question of bumping up power on a 125 cc but where you want the extra power in the power band? The suggestions offered so far will do the following: A larger carb, 26mm > 28mm will loose bottom end and gain top end. A higher compression head will boost power mainly in the mid range causing the bike to bind up in the higher RPM range. Running higher octane does NOT give you more power! I can go into details for each line if you wish? yzeefoureight Please tell us where you want the extra power? Cheers BillyT

Hey Dan I must commend you for your well written technical article. While I agree with what you wrote and the changes made there is MUCH more going on in the clutch that the lay person misses, and much more that can be done to smooth out the clutch and its pull, and releasing. We should talk as it is nice to have conversation with another tech head such as your self. If only I had the time, patience, and computer skills needed to post my thoughts. Cheers Dan. BillyT

Scotty Adjust the idle screw down (in) low to afford/allow slow idle speed AFTER CHAINGING TO A LARGER PILOT JET. The pilot jet should be a standard as a #30 I change mine to a number #35. Check the number stamped onto the side of the pilot jet and tell us what it is. Also disconnect the throttel cable from the throttle tube and see what this does? Cheers BillyT

Scotty If there is an air leak in the rubber boot the bike would be running lean/crazy at all RPM's not just coming down from idle. When you snap the throttle shut the pilot jet is the only jet supplying fuel at that point. If the bike was on a high rev before you shut it down the cylinder is looking for lots of fuel and air as it winds down and sucking air like crazy. It is not the mixture screw but rather the pilot jet it self. The idle air screw maybe out to far also. Been there down that........ BillyT

Hi Guys Pilot jet to lean.................... Simple. Cheers BillyT

Thanks for the help. I signed up and posted the picture. BillyT

I have the pictures ready to go on my Apple desktop. I posted a reply on the Honda forum and wanted to include a picture from my Apple desktop. BUT........... I do not see an area or button that says "upload picture" etc. I can find now were on the site that tells/gives instruction to uploading a picture or is it JUST silly old me? LOL..

Hey guys. For the life of me I cant seem to figure out were or how you post a picture. I am using an Apple. I wondering if the format of this site maybe different on an Apple compared to a inferior (oops LOL) regular computer? Any help welcome in how to post a picture. Thanks BillyT

Hey guys. For the life of me I cant seem to figure out were or how you post a picture. I am using an Apple. I wondering if the format of this site maybe different on an Apple compared to a inferior (oops LOL) regular computer? Any help welcome in how to post a picture. Thanks BillyT

Steve I am in a witness protection program. They allow me out now and then to check up on you guys. After all of the debacle over the Mikuni's leaking I had to hide Mikuni set me up in nice house, a regular paycheck, and a bike to ride. I can dream cant I? Contact me on face book William Traynor. Cheers mon ami.

Hey guys. It is an oil reservoir bottle. It is used to cool down the oil/nitrogen in the rear shock. They put it up front away from the engine heat, and also likely due to there being little room under the seat etc. There is probable another one on the other side of the down tube if it is a twin shock. This is me MANY years ago. Notice the bottle above the foot peg? Cheers BillyT MR4T

"Krylon Simi-Flat Black" Hey boy is that a Texas type of paint? I can only find "SEMI" flat black. Maybe Hank Hill can help me find it!

Mark You stated: "A slight pink when you chop the throttle does not bother me as you are cutting fuel off a that point. But only slight. Once again a tradeoff!" That alone tell me that the pilot is too lean, why. When the throttle is backed off, the engine is still turning at higher than idle requiring fuel. If the slide and needle is almost down or down, the only place it gets fuel from at that point is the idle and pilot circut passbye. The pilot is only designed to supply enough fuel for an engine running at low rpms. When one chops off the throttle at say 3/4 throttle the piston is still going up and down the plug is still firing. BUT it is sucking and starving for gas and gets from guess where THE PILOT circut. Ishy is eluding to a similiar thing in the other Sherco post about the pilot circut. My tuppence....

Mark Does the bike pink when you let go of the throttle. When I rode your bike at Austin I mentioned to you that your bike was too lean on the pilot jet. Remember the little test I showed you with the throttle position at varous openings??? Let me know. Cheers BillyT

Markus The jet itself may not be to small but rather the pilot circut blocked. Pulling in the choke an dthe bike starting helps determine if it is the pilot circut. If so then check jet size and/or pilot circut. Twit signing off for now

Mark.... Read: "then stopped for lunch and it wouldn't start at all until some guy helped me by turning the fuel off then kicked it few times then put fuel back on and gave it some choke and it started" The pilot jets are way too lean. Why do you think this is a twit answer? It has been proven on many occasions when a bike will not start when warm that the jet being lean messes it up. Pulling the choke in and the bike starting proves what I am saying.

Pilot jet WAY too lean. Next time it happens pull the choke in to start, it will start and run rich, turn choke off. Test over with...... BillyT