Keep your new top end from taking a dump, here’s how.
1. Get a temperature gauge. Spend the lousy $40 and consider it a $40 insurance policy. If you are running an eBay 60cc kit, SHUT DOWN YOUR BIKE if you get to 380F. Maybe a little sooner if you are worried. Then figure out why it is so hot. If you are running the Malossi kit, shut it down at 400F.
2. Install your kit right. Check the link but the must-do’s are as follows:
– Check and adjust ring gap as necessary;
– Install ring or rings correctly;
– Chamfer the ports with small file or 400 grit sandpaper;
– Use new base, head and exhaust gaskets;
– Use new circlips;
– Get an inch/pound torque wrench and torque your cylinder head nuts properly;
– Break in your kit – don’t just slap it on and blast.
I go in to more detail here. Read it or suffer the consequences.
3. Replace the crank shaft bearing seals or DIE! Number 1 cause of seizures in qt50s.
4. Run a cooler plug. The higher the number, the cooler the plug. Start with an NGK B8HS and work your way up or down by looking at your temp gauge.
5. Run Premix and forget about the oil pump.
6. Run 32:1 of a decent quality oil. Don’t listen to the fools who claim Amsoil Saber at 80:1 or 100:1 is fine. Ask them a few questions like (1) what is the flashpoint of your magical Amsoil Saber?; (2) What is the viscosity at 100C; (3) What is the viscosity index? Chances are you will get a blank stare. Here are the answers that they don’t know – (1) 180C or 356F; (2) 14 and (3) 132. Read more here.
What does this mean? Well, your eBay kit will get up to 380F but the magical Amsoil Saber burns at 356F. If you are going to run Saber then you will need more oil to replenish the oil that is burning up at 356F or beyond. But if you listened to the Amsoil Fanboys, you only mixed at 100:1. 100:1 is less oil than 32:1 (3 times less). Better hope that it doesn’t burn up faster than it is replenished because that means one thing – seizure. Anyhow, if your oil rich then who cares. You might foul a spark plug. If you are oil starved, you will seize a kit. You pick the lesser evil.
Get an oil with a high flashpoint and high viscosity index and mix at 32:1. Ideally, get an oil with a higher flashpoint then you will ever reach with your kit.
7. Get a more restrictive air filter. This will change your jetting to a smaller main jet. But less air = less heat = no seizure.
8. Standard main jet in a qt50 is 70 if you are using stock carb. Get a range of main jets from mid 70s to mid 80s. Start high and work your way down. Find the right jet through temperature monitoring and four stroking.
9. Get a bigger carburetor and jet it right. Bigger carb = better cooling.
9a. Run a better/bigger cylinder head that will cool it down. That crappy/tiny cylinder head that came with your 60cc ebay kit won’t do the job. The cylinder head linked to above also has a squish band so you will run cooler.
9b. Install an offset timing key to retard timing. In this case, you would be retarding timing 3.6 degrees. When you do so, you will blow more heat out the exhaust.
10. Tighten all your bolts and nuts related to cylinder head and exhaust on regular basis WITH A TORQUE WRENCH TO THE PROPER TORQUE. Loose stuff means air coming in means more heat.
10a. Sand down the mating surfaces of your cylinder head and cylinder to ensure a better fit and no leaks. Tape some sandpaper over a piece of glass and sand in figure eight pattern. You’ll figure it out.
11. Check and replace gaskets as needed.
12. Run a thicker cylinder head gasket.
13. Run thicker base gasket or two base gaskets.
14. Try a higher octane gas to prevent detonation.
14a. Go to 1/4″ fuel line to get more gas to your carburetor.
14b. Use your oil tank as a 2nd gas tank and use a Y or T splitter to connect fuel lines from both tanks together. Have those lines lead into the carburetor. Have fuel flowing from both tanks simultaneously. I’ve had to do this with a really big carburetor to keep it fed.
15. Be careful going up hills. Hills means engine get hot real quick.
16. Don’t use the stock 49cc head on bigger kits.
17. I don’t care how hot it is outside, let your qt50 warm up for a few minutes at idle and then ride easy for another few minutes before you blast. Don’t just start it up and blast it at full throttle right away. And don’t full throttle rev it on the stand either. That’s just not smart, bro.
18. Don’t go full throttle down bigger hills and especially don’t do it after riding up a big hill. Keep giving it gas downhill but don’t over-rev the thing.