Overheating Problems!! Please Help, Any upgrades?

Posts: 4 · Newbie Joined: 02 Apr 2008 Posts: 4 Pictures: 0

I have a Roketa 250 that I have modified considerably. Ported head, shaved head (10:1), UNI Filter and have rejetted the carb to make it run great. The plug shows a nice tan/brown shade.

With these mods, the motor now spins up to what sounds like 7 to 8k RPM's. At the higher RPM's and 70 to 100% Throttle, the motor heats up from 190 to 230 in just 1 to 2 minutes. What Gives?

I have upgarded my radiator and fan and it doesnlt seem to make much of a difference. I seems as though the water pump may be cavitating under high RPM's.

Anyone have any ideas? Any

Any input would be greatly appreciated.

Doug Shackleford
DShackleford@Koning.us

Posts: 1612

Have you ever changed out the anti-freeze?" I think the stuff the Chinese use is really Windex!
You may have some "Crud" in there too.
Some of these 250's will run hot, it's why the new ones have a second cooler or an oil cooler.
Also, check the "Fins" if you have any, on the bottom of your kart.
These direct air up to the engine and help more than you might think.
Good luck!

Posts: 23

I took the bottom plastic fin off my HH-250 will it hurt anything, it was busted. or should i fabricate a new one.

Posts: 55

Is there a thermostat?

Takeit out and see if it overheats.

Posts: 2324

Temps up to 200 or so are ok if the read is coming from the sensor next to the Carb. The question is does it go higher after time or just sit at that temp? If your thermostat is gutted or stuck open, it can cause the temps to be a bit hi as well. The reason for this is the fact that the water is pullled through the radiator so fast that it cannot cool it. One ? I have is, is the temp really showing it run up to 200 within minutes? That is unlikely that it would be that fast, it typically takes an idiliing 250 5+ miutes to get up to around 160 or so.. Check the mix of your coolant also. I agree with Tom, if the coolant is the Chinese junk, flush it out and use a good 50/50 mix of a name brand.

Stu

Posts: 4 · Newbie Joined: 02 Apr 2008 Posts: 4 Pictures: 0

Yes, the coolant has been changed out. I initially ran 70/30 water/anti-freeze with water wetter. I then tried engine ice and it helped a bit more. It still it heats up quick. 30 degrees with in 2 to 3 minutes.

I run my buggy in deep sand and stay at WOT 80 to 90% of the time. This is running in the 6000 to 8000 rpm range wonder if the motor and the cooling system was designed to run this high.

My temps were read off a thermostat installed within 2 ft from exiting the motor. I removed the thermostat since the radiator doesn't seem to run at full capacity. The radiator stays cold on the top half all the time. This would suggest that the radiator will flow more "cool water" if the motor can draw it.

Thanks for the input.

Posts: 195

If I understand what you said that the thermostat is removed,the engine temps at 230 deg. and the radiator is cool up top, this would indicate one of two things. 1) you have a restriction somewhere possibly a hose,the hose is a 2ply hose and the inner ply could have collasped,or blockage in the radiator. 2) your waterpump is weak or not pumping at all.

Posts: 1612

Yep, sounds like there's not much movement with the water.
Sycarms has a good idea, check those hoses. Check the oil screen too. If it's clogged, there will be minimal oil flow and will heat up as well.

Posts: 554

Something is wrong with that picture
" The radiator stays cold on the top half all the time. This would suggest that the radiator will flow more "cool water" if the motor can draw it."

A radiator (most), the upper hose is the dump side FROM the engine and it should be as hot as the thermostate, also your reading from a gauge? what kind of gauge, factory installed, or is it calibrated to the sensor, I tryed puting an american made gauge on a china made sensor and it reads 265,pegs the needle, I used an infared hand held temp reader to verify the temps were ok, 180ish at the thermostate housing
Just thoughts
Tim