Build up - Stage 1 something for nothing Mojo GT 50 When you only have 50cc's you need all of them working Brendon Watson Mojo's GT50 is a budget scooter, budget scooters generally have budget conscious owners. I'm not out to insult anyone but more than one owner did say the only reason they put air in the tyres is that it's free.
With this in mind we've developed a few kits for the Mojo GT50 in various stages of tune, Stage 1 is "Something for Nothing" basically for those who are confident & able to do a top end rebuild on a 2 stroke engine. Lets be 100% clear this is going to void your warranty, we (or any mechanic) will easily be able to tell so don't even try for warranty if you stuff something. All mechanics will treat you with more respect if you have the guts to say "I think I stuffed...."
All the work you see here has been performed by a "non mechanic", we wanted to be sure. You really should be governed by the disclaimer - "if you don't know what you are doing don't do it"
Step 1 - You will need to remove the head & barrel. We aren't going to go through this process step by step for two reasons, our website limits us to one photo per article & if you don't know you shouldn't do it. Scooters are mass produced on a production line, not hand built with love. What we are doing here is adding a bit of love to the engine.
The top shot in the photo shows the bottom of the barrel, notice the black gasket which due to the mass production aspect isn't exactly a perfect fit. If you look at the image showing the barrel without the gasket its obvious that the top port the gasket blocks about 30% of this port which is going to reduce flow & power. Eliminating this blockage by matching the gasket to the port is free power.
The correct way to go is to buy a new set of gaskets, in this instance we used Vmoto (QJ) gaskets which offered a better match. You have the choice of fitting the new gasket as is or trimming it so there is absolutely no gasket hanging into the ports restricting flow. The bottom image shows the trimmed gasket against the original gasket. If you are going to trim make sure you have a ruler, suitable sharp blade & a few gaskets for when you slice through on your first attempt which is what our non mechanic did.
The gaskets aren't the only offenders, a quick look at the ports shows there are some casting dags around these ports also. You have three options here
- Leave it alone - highly recommended
- Using a metal file clean up the dags, by this we mean just removing the obvious casting irregularities. We definately don't want any shaping or enlarging of ports. Remember to err on the side of caution here, its easy to take metal out but bloody hard to put it back in. Stuff this up you will need a new barrell, go too far & it will need other work to get it right.
- Take it to a Scooter shop or mechanic who is into two strokes & ask them to spend up to 1 hour cleaning it up.
The bleedingly obvious thing we haven't touched on is the size of the exhaust port, I know many of you will be sitting there with file/drill in hand ready to rip into this port. If you do have a go at enlarging this you will need to remove any shavings/ debris when finished, more than likely it will need the ports chamfered & the bore honed. Best bet is to have this done by a shop or buy a spare barrel just in case. We have seen many a port job that doesn't work, in this instance less is more. This is only Stage 1 of the Mojo GT50 build up, we will cover more aggressive tuning in later instalments. To generalise very simplistically big ports = high power at high revs, small ports = bottom end grunt. We strongly suggest leaving it alone at the moment.
Being budget conscious some will reuse the original gaskets which isn't the best but something you can get away with if its in good condition. Now it's time to put it all back together, make sure everything is clean & a light coating of 2T oil on components going back in.
What difference did it make? Accelleration & ability to hold revs and speed, this simple mod allowed the Mojo GT 50 to hold a good 10km/h over a normal one up a decent hill. It is also able to gap & pull away from an untouched Mojo, reusing the old gasket meant this cost absolutely nothing.
As you have found some free power & if the barrel has been ported you really should spend a couple of dollars in tuning the transmission, in particular the engagement of the rear clutch & pulley. We recommend a yellow Contra Spring $22 & set of clutch springs $44.00 (contains three spring sets) this will allow the engine to build up revs before engaging the transmission, which set you use depends on your weight & how you want it to launch.
This is our first in the series, if you have any feedback or input we'd love to hear it drop us a line at info@scooterHQ.com.au.
published 26/10/2009 |