Gv125 2007 won’t get past 45mph or 7.5k revs

[Joshua O’Shaughnessy]

Hi guys I need advice. My gv125 2007 won’t go over 45 mph. It hits 45 and 7.5k revs in top gear and literally won’t go any higher. It has upgraded reg/rec it has upgraded coils and plugs. I’m stuck on what to do to get more speed from it.

[♠️ MARCEL]

Hey Joshua,

It sounds stupid and probably a chore but this is the “guaranteed” way to be sure it isn’t the engine itself.  Can you go to a nearby garage and ask them to do this:
– Let engine warm up for 15mins max  (unless you ride there hot)
– Lift Tank (remove rear spark plugs)
– Drop the 2 screws holding the front oil cooler  and let it hang down  (don’t disconnect pipes)
– Remove front spark plugs

Take pictures and send us (we gotta see the sides  (burnt threads? and the middle of the plugs  (rich vs lean))   Be sure to note which is front or rear.

Then before he puts everything back inside ===> Tell him to get a compression tester with a METAL pipe  (flexi hoses are crap)

Put the Tester inside the front engine plug hole => Crank your bike at full throttle for 5 seconds ===> Tell us the PSi

Do the same for rear ==> Tell us the PSI

Come back to us and I will advise further…..

In the meantime ,

• Have you considered adjusting your clutch incase its slipping ? (click here)
• Have you ever changed the clutch plates ?
  (Remember the engine makes the power first, then sends it to the clutch to convert power to your wheels)
  So old plates may need attention  (click here and read where it says “symptons / how to measure” )  (Yes that includes heat fatigued springs.
  Have a vernier caliper to measure things for accuracy  (our eyes are deceptive, so using a measuring tool is best)
• Do you have a 520 kit from us ?  = If yes, ignore this sentence
  Or else , if you have stock chain (factory 428 , then count the teeth on both sprockets and tell us)

Lets look at the air system

• When it is running => Spray the intake pipes and airbox areas = If revs change, you have a leak which affects power.  Then click here for the “O-Rings” first

  Also here is a tutorial on how to remove the airbox   (click here)  and (click here too)  , use these guides because the 125GV intake pipes are rare as hell. So you don’t want to damage them.

• Sounds silly, if the air filter is more than least 5,000 miles old , open it and look at it, if its dirty , then it is probably time to replace then  (yes you will need new plugs again)   (Air vs Spark vs Fuel , which fuel we will get to in a moment)  = A cloggy air filter will make the bike feel like its on a leash at higher speeds.

Let’s go to the exhaust system.

I do custom GV builds for customers and trust me when i say this …. the  OEM system makes the best power.    If the bike has “Short Shorts”  , “Slash Cuts” , “Shorties” , any kind of custom exhaust whatsoever, you will have a a lot hell as I don’t know why yet but there is something about the OEM GV exhaust system making the most power out of any custom exhaust combination i have tried.  Believe me , I have tried!

250cc can get away with some custom pipes if done right, but the 125 simply wants its factory.   The  GT125R / GT125 will be fine with straight pipes and a big scorpion can, but a GV125 ? Nope!  –

Try an OEM exhaust if you can ?   (here is a stock one we have from a 250cc which will probably help?)   and if you need the mount  (here it is too)

If you have a standard exhaust system already, then that’s good, check it for any blows!

Something about the GV125 specifically needing as much backpressure as possible to maintain the torque, so it has momentum to build speeds up as revs go up.

Even if its not the exhaust system in the end, it still helps the bike overall in the long run.

LEO VINCE exhausts for GV125 are very expensive but they do lose a little bit of power to be fair but they sound nice and they supply the baffles for it.

Well, i saved fuel for last , it’s a bit of a chore this one but if you get it right, you won’t go here ever again.

• Carbs – Find out what size Pilot Jets you have and i will advise if it helps to downsize or stay at the stock size.
• Carbs = Find out what size MAIN JETS you have and tell us.   Clean both pilot jets and the main jets.
• Carbs = Try and get 3x cans of carb cleaner at halfords , and use all 3 cans to blow every single hole you can find inside the carb , believe me , finish all 3 cans, she will THANK YOU!
• Carbs = If the slide Needles are stock or lean , then click here for a tutorial on how to adjust the slide needles to enrich the “mid-range to full-range”
  If the slides look bad or badly scored ,  replace them! – Stickyness during rides will give the symptons of a bike stuck at certain revs and throws off the whole mixture.
• Carbs = Check the “Choke Rail” moves back and forth free , a sticky rail isn’t good for anything.  So use a recommended grease such as “PUTOLINE RACE GREASE” and use it to grease the outside of the carb for any moving parts  (good for winter!) and also the “idle adjust likes to seize hard, so grease it up.
• Float height = Important,  so make sure it is 7mm (dead on) , if unsure , please check this topic here and look for the picture of float height,.
  If in doubt , replace floats & get a proper carb rebuild kit too.  (includes new float needles and float seats to match) 
• Since the floats will be out anyway, clean the “mesh cone” that sits under the gold float seat, as this will make sure fuel flows in to the carb nicely with no obstructions or debris coming from the tank or clogged fuel filter.

Fuel system part 2 = Yes, its going no where faster without adequate fuel (more power = more fuel)

• Tap – Get a bucket , open the tap in to a bucket , if fuel comes out fast. The tap is OK.
  Tap – If on the “OFF” position = fuel still leaks out, replace tap!  (hydrolocking can damage crank)
• Fuel Tank CAP = yes , where your key goes to open the tank cap. It can fail to vent, sometimes the bike rides for so long, the tank literally fails to vent, and the bikes forced to die down in speed, due to venting issues from the tank.

  It is NOT wise to do this but , but on private land away from civilization , ride with the tank cap open, if its better = replace the cap! Check fuel tank for WATER also, if the cap doesn’t seal properly , you will find your E5 fuel is now pretty much like trying to burn water which isnt good for the cylinder walls at all and you will end up replacing engine pistons.

• Speaking of E5 = Make sure you use just that. There is no advise out there to use e10, it’s a juice from hell.   E5 forever.
• We have approached the fuel filter = If it faces the wrong way ,  it will cause issues. If it “looks” dirty inside , just replace it here. 
• Strange enough but kinks can stop the bike reaching its full potential, so make sure fuel lines are routed properly with minimal kinks but here is a tutorial to double check and compare.

 

But all in all,  start with engine compression first , it is that crucial, do what i said bit by bit, you will have your bike back to its glory

Sometimes it might end up being something small and stupid that was overlooked   (welcome to bike life!)

// Meditation doesn't mean you have to sit still....

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